- Email: [email protected]
Injury, condition, and mortality of Pacific halibut bycatch following careful release by Pacific cod and sablefish longline fisheries
Fisheries Research 38 (1998) 131±144
Injury, condition, and mortality of Paci®c halibut bycatch following careful release by Paci®c cod and sable®sh longline ®sheries Stephen M. Kaimmer*, Robert J. Trumble International Paci®c Halibut Commission, PO Box 95009, Seattle, WA 98145, USA Received 11 November 1997; accepted 26 May 1998
Abstract Paci®c halibut caught as bycatch or intended for discard by longline vessels in US and Canadian waters of the north Paci®c must be removed from the hook using careful release techniques required by regulation. In many ®sheries, trained observers subsample the released halibut for ®sh condition. These condition codes are used to track cumulative bycatch mortality in these ®sheries. Tag return rates of halibut released from longline gear near Kodiak Island, Alaska, are used to estimate relative and absolute mortalities of ®sh by release method, hook removal injury, and condition code. Generally, the proper application of the careful release techniques results in only minor hook removal injuries. Survival rates of moderately and severely injured halibut are 1.5±2 times higher than previously assumed. One result of our study is the ®nding that not all ®sh judged at tagging as likely to die actually die. We recommend a reworking of the condition code methodology. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Paci®c halibut; Bycatch; Condition code; Mortality; Survival; Hook injury; Careful release; Growth
1. Introduction Paci®c halibut, Hippoglossus stenolepis, is caught in the northeast Paci®c and eastern Bering Sea by directed hook and line ®sheries and as an incidental catch in other trawl and longline ®sheries. Paci®c halibut larger than the minimum size (81 cm) may be retained only with hook and line gear during open ®shing periods. In Alaska and Canada retention is restricted to vessels or individuals which possess individual quotas for longline harvest. All other Paci®c halibut must be released. Both US and Canadian ®shery regulations require that halibut bycatch must *Corresponding author. Tel.: +1 206 634 1838; fax: +1 206 632 2983; e-mail: [email protected]
be returned to the sea in as good a condition as possible. The mortality associated with this incidental catch is substantial, ranging from 8 to 10 thousand metric tons round weight per year since 1990. About 80% is due to trawl bycatch and about 20% longline (Williams and Wilderbuer, 1995). Halibut is a very hardy ®sh, and survives capture and discard to the sea if treated moderately well. In the case of hook and line ®sheries for ground®sh, potential survival of discarded halibut is very high. Circle hooks and semi-circle hooks used by the majority of hook and line ®shermen usually catch halibut in the mouth, the hooking process itself causing little damage. However, inappropriate release methods cause severe wounds that lead to higher probability of death (Kaimmer, 1994). Careful release of halibut bycatch from
0165-7836/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0165-7836(98)00153-2
132
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
hook and line ground®sh and halibut ®sheries in Alaska is required by regulation. These ®sh may not be landed onto the vessel, but must be released outboard of the roller. Methods currently allowed are hook straightening, cutting the gangion near the hook, or carefully removing the hook by twisting it from the halibut with a gaff (careful shaking). Comparison of careful shaking and automatic hook stripping (Kaimmer, 1994) led to a ban on hook stripping during halibut ®shing in 1987. This ban was dropped in 1995 because hook strippers are considered to be essential for some multi-species ®sheries, although hook strippers may not be used for the release of halibut bycatch. For many longline and trawl ®sheries in Alaska, and for some ®sheries in Paci®c Canada, onboard observers monitor both the amount and viability (condition code) of the Paci®c halibut released. The observers closely examine a subsample of the halibut bycatch and assign each examined ®sh one of the three IPHC condition codes: excellent, poor, or dead (Williams and Wilderbuer, 1995). Mortalities associated with longline condition codes are estimated indirectly from earlier survival or holding studies. These studies suggest that the handling mortality of hook and line caught ®sh in excellent condition ranges from 2% to 5% (Peltonen, 1969), that survival of poor condition ®sh is approximately half that of ®sh in an excellent condition (Myhre, 1974), and that all ®sh judged as dead actually die (Williams and Wilderbuer, 1995). From these relationships, mortality rates associated with the three condition codes are: 3.5% for excellent condition ®sh (midpoint of the 2±5% range), 52% for poor condition ®sh (half the survival of excellent condition ®sh), and 100% for dead or likely-to-die ®sh. The assumption that survival of ®sh in excellent condition is almost 100% is more recently supported by our own observations in collecting halibut and holding them for long periods in tanks or net pens (authors, unpublished) and by a study on the longline survival of the closely related Atlantic halibut Hippoglossus hippoglossus (Nielson et al., 1989). The International Paci®c Halibut Commission (IPHC) manages Paci®c halibut and uses the observer data to determine a discard mortality rate, the proportion of halibut that die, which is then applied to each longline ®shery that causes bycatch. Many ®sheries operate under an annual limit of allowed halibut
mortality and ®sheries have been closed with quota left un®shed when these limits have been exceeded (Wilson and Weeks, 1996; Sadorus and Williams, 1996). The IPHC estimates bycatch mortality prior to each year's directed ®shing, and subtracts the estimated halibut mortality from the yield available to the directed halibut ®shing ¯eet in the coming year. The halibut mortality thus subtracted in the years 1990±1996 has ranged from 8 to 10 thousand metric tons, with 19±31% coming from longline ®sheries. Almost all of the ground®sh longline mortality of halibut results from the ®sheries for sable®sh (Anaplopoma ®mbria) and Paci®c cod (Gadus macrocephalus). Annually since 1990, the allowed removals in the directed halibut ®shery have been reduced by 4±9% to compensate for longline discard mortality, representing annual losses to halibut ®shermen of about 10 million dollars US. In 1993 and 1994, the IPHC conducted a tagging study to evaluate the condition code methodology and for the ®rst time used relative tag return rates to directly estimate halibut bycatch mortality rates by condition code for the longline ®sheries. Over 13 000 Paci®c halibut were examined, tagged, and released in the vicinity of Kodiak Island, Alaska (Fig. 1). Halibut were examined for hook injuries and assigned a condition code. Each halibut was removed from its hook by one of the three careful release methods or by hook stripping. Halibut were caught using circle and autoline hooks typical in size and style of those commonly used in the ground®sh longline ®sheries in the north Paci®c. 2. Materials and methods The 23.5 m US ®shing vessel Rebecca B was chartered from 27 April 1993 to 8 May 1993 and from 4 July 1994 to 28 July 1994. Fishing during both years took place in the vicinity of Kodiak Island off Alaska (Fig. 1). The vessel's captain was experienced in the longline ®sheries for Paci®c cod and sable®sh and was tasked to keep his vessel operations as close as possible to those which might be experienced during commercial ®shing trips. Halibut were caught using the two styles of hook and were removed from the hook by one of the three careful release methods (careful shaking, hook straightening, and gangion
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
133
Fig. 1. Location of tag releases during 1993 and 1994 longline bycatch mortality study.
cutting), and by an automated hook stripper (Table 1). The ®sh in this study were necessarily landed on the deck of the vessel for observation and tagging, whereas the application of careful release techniques by a commercial ®sher would result in the ®sh falling into the sea. Care was taken to minimize any injury associated with bringing the ®sh aboard the vessel. The resultant hook removal injuries and ®sh conditions were noted and ®sh were tagged and released. The time period from hook removal to ®nal release was always 3 min or less. Tag recovery rates are used to determine relative mortalities associated with hook removal injury and halibut condition code resulting from each of the four release methods from the two hook styles.
2.1. Fish capture and tagging The ®shing location was chosen to provide both a good probability of tagging large numbers of ®sh, and an area that would be heavily ®shed by the commercial longline ¯eet, facilitating recovery of tagged ®sh. During both the years, halibut were caught with autoline and circle hooks ®xed to the groundline at 1.07 m intervals. The only change in ®shing gear between 1993 and 1994 was in the method used to ®sh the autoline gear. The chartered vessel used a Mustad autoline system (`automatic' baiting during setting, and racking during hauling) during 1993. The autoline system was removed after the 1993 charter, and in 1994 this gear was ®sh `conventionally' (hand coiled
134
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 1 Hook removal methods and numbers of fish tagged by year, hook style, and method Method
Description
Careful shaking
The fish are removed by catching and twisting the hook with the gaff; the hook is held upside down against the tension of the gangion, which allows the fish to fall from the hook. Sometimes a careful `shake' is needed to drop the fish from the hook The gaff holds the bend of the hook against the roller until it is straightened, pulling out of the fish The gangion is cut between the hook and the groundline, resulting in release with the hook still embedded in the fish Automated removal by allowing the fish to be held on the horns of the hook stripper while the hook is torn from the fish as the groundline comes aboard
Hook straightening Gangion cutting Automated hook stripping Year
Hook style
Careful shaking
Hook straightening
1993
Circle Autoline Circle Autoline
277 381 1065 939
0 435 1095 608
109 545 864 790
1358 680 2326 1379
1744 2041 5350 3716
2662
2138
2308
5743
12 851
1994 Total
and baited). The circle hooks were a full circle style (Mustad 39965 13/0). The autoline hooks were an `easy-baiter' style (Mustad 39975 13/0) which was required by the racking and baiting system. All hooks were baited with thawed Loligo sp. squid. Gear was set as early as practical each ®shing day and retrieval was started after a 5±7 h soaking time. If time is allowed, additional gear was set in the afternoon. All gears were usually retrieved before midnight of the day of setting, although on three instances hauling continued two or more hours after midnight. Baiting, setting, and hauling procedures and times were typical of those experienced by commercial ®shers. While the setting and hauling procedures did not control for capture time of day or soak time, gear type and release method were alternated between sets in order to distribute the gear and release treatments as evenly as possible over the course of the experiment. The experiment could not control the area of ®shing for tag recovery. Treatments were distributed evenly among release areas so that uneven distribution of ®shing effort during tag recovery would not bias results. 2.2. Hook removal methods Careful shaking entails sliding the bend of the gaff down the gangion to engage the bend of the hook on the bend of the gaff. Keeping the gangion taut while
Gangion cutting
Automated hook stripping
Total
lifting and twisting the gaff rolls the hook out of the mouth of the ®sh. As the gaff is twisted, it is often given a gentle `shake', thus the term `shaking'. Automated removal of ®sh from the hook is a `hands-off' process. The ®sh is pulled aboard the vessel by the incoming gear and led by the gangion to the hook stripper. As the groundline and gangion are drawn through a constriction, the ®sh is drawn up and held as the hook is torn from the mouth (Kaimmer, 1994). Hook straightening is similar to shaking, in that the gaff is slid down the gangion to engage the bend of the hook, but in this case the gaff is then held against the outer edge of one of the side guide rollers mounted on the vessel's rail. As the gangion draws tight the bend of the hook straightens, and the hook is pulled backwards out of the ®sh's mouth. Gangion cutting involves cutting the gangion close to the hook, allowing the ®sh to fall free with the hook still embedded in the mouth, often with a short piece of the gangion attached to the hook. 2.3. Live holding experiment During both 1993 and 1994, halibut were held in aluminum tanks to assess short-term mortality from hook removal injuries. The tanks were approximately 1 m1.5 m in width and 1.2 m in depth with a grated
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
outlet near the top of the tank. A hose fastened near the bottom of the tank supplied fresh seawater, and a loose cover was ®xed over the top. Fish were observed daily for signs of stress or mortality. Halibut ranged in size from 56 to 90 cm, and were selected to cover the extremes of hook removal injuries observed during the charters, with about equal numbers of minor injuries and more severe injuries put into each tank. Eight halibut were held for four days in one tank in 1993. All eight were robust after four days, and on release swam directly into deep water. Two of the four ®sh tanked with autoline hooks in their mouths shed their hooks during the holding. During 1994, 35 halibut were held in four tanks, 8±9 to a tank, for 10 days. Fifteen of them had torn face wounds, and were coded as likely to die. Seven ®sh caught on autoline hooks, and eight ®sh caught on circle hooks, had hooks in their mouths resulting from the hook release method. Three of the autoline hooks had been shed during handling and tagging. Two more of the autoline hooks and four of the circle hooks were shed during the tank holding. All ®sh were very robust at the time of release. We observed no short-term mortality during either year, nor any apparent difference in either vitality or behavior among ®sh with different injuries. 2.4. Data analysis Observed frequencies of hooking and hook removal injuries, tag recovery rates, and mean growth in length of recovered ®sh were compared among treatment groups and across sizes of halibut to determine signi®cant differences between the groups. Differences in the distribution of injuries and tag recovery rates were examined using the 2 test. Expected values were calculated assuming that if the null hypothesis were true, then the distribution of tags across the groups would be the same for both the releases and the recoveries. In some groupings by injury classes, release numbers were so small that the expected returns were less than 5. These classes were either pooled with similar injury classes, or in some cases not included in the analyses. To determine differences in growth rates, the t-test was used. For both tests, the level of signi®cance was set at 0.05. Relative survival was determined by comparing the ratio of tag recovery rates between the groups. Absolute survival was estimated by taking a ratio of the recovery rate of a group
135
to the recovery rate of excellent condition ®sh, and multiplying by the estimated 96.5 survival assumed for excellent condition ®sh. 3. Results In all, 12 851 halibut (8879 sublegal-sized and 3972 legal-sized ®sh) were examined, tagged and released from both years (Table 1). The fork length of tagged ®sh ranged from 34 to 191 cm, with an average length of 77 cm (9.4 cm SD). Fishing depths ranged from 46 to 290 m with an average depth over both years of 116 m. In 1993, hook straightening was used with the autoline hooks only. About half as many ®sh were tagged during 1993 as during 1994. During both the years, approximately equal numbers of ®sh were removed by each of the careful release methods being used, and about twice the number were released using the hook stripper. The 1993 capture and release area was relatively large, extending 240 nm along the top and the edge of the coastal shelf. The weather during 1993 was extremely poor, and the ®shing area was forced each day to move away from an approaching storm. The 1994 releases were from a much smaller geographic area, extending 50 nm along the coastal edge and the shelf (Fig. 1). To avoid biases that may arise from possible different recapture probabilities from the two release years, these release years are treated as separate experiments. Within either year, all releases were in areas of subsequent commercial removals. The commercial catch in these areas was similar for the recovery years over the areas of recovery, and there should be no signi®cant variation in recovery probability for the treatments. 3.1. Hooking location Combining information from both years, 98% of the halibut caught on circle hooks and 94% of the halibut caught on autoline hooks were hooked in either the left or the right jaw (Table 2), with the point of the hook encircling the jawbone. A further 1% of the ®sh caught on circle hooks and 4% of the ®sh caught on autoline hooks were caught with the hook protruding through the eye (an extreme form of a right jaw hooking). While small differences in hooking location between the size of the ®sh or hook styles are statistically
136
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 2 Hooking locations in numbers and percent observed for autoline and conventional gears and size of fish (1993 and 1994 observations combined) Code
Description
Number (and percentage) by length category and hook style Circle hooks
LJ RJ EYE RM PP TO JB JH NO
Left (blind side) jaw or cheek Right (eyed side) jaw or cheek Eye Roof of mouth Pharyngeal pad Tongue Jig or snag body Jig or snag head No injury apparent
Total
Autoline hooks
<82 cm
82 cm
Total
<82 cm
82 cm
Total
4165 (79.3) 980 (18.6) 66 (1.3) 11 (0.2) 0 (0.0) 20 (0.4) 6 (0.1) 4 (0.1) 3 (0.1)
1471 (80.0) 351 (19.1) 8 (0.4) 4 (0.2) 0 (0.0) 2 (0.1) 0 (0.0) 0 (0.0) 3 (0.2)
5636 (79.4) 1254 (18.8) 151 (1.0) 15 (0.2) 0 (0.0) 22 (0.3) 6 (0.1) 4 (0.1) 6 (0.1)
2932 (80.9) 489 (13.5) 153 (4.2) 11 (0.3) 0 (0.0) 10 (0.3) 8 (0.2) 8 (0.2) 13 (0.4)
1678 (78.7) 323 (15.1) 96 (4.5) 9 (0.4) 1 (0.0) 6 (0.3) 4 (0.2) 7 (0.3) 9 (0.4)
4610 (80.1) 730 (14.1) 331 (4.3) 20 (0.3) 1 (0.0) 16 (0.3) 12 (0.2) 15 (0.3) 22 (0.4)
5255
1839
7094
3624
2133
5757
signi®cant, the only difference of biological signi®cance to this study is the increased incidence of eye hooking from the autoline hooks, which is identi®ed as a more severe wound after the hook is removed. 3.2. Hook removal injury Hook removal injuries were classi®ed into one of the 14 categories (Table 3), ranging from minor injuries NI, CO, JO, TL, TC, through the moderate TJ, CJ,
and EYE, and to the severe TF, SJ and TS, and jig injuries. The minor wounds NI±TC are generally only the hooking injury, with no further injury caused during hook removal. During both the years, just over half of the ®sh exhibited these less severe removal injuries. More severe wounds are the result of the hook being torn from the ®sh during removal, or the hook puncturing the eye. Forty-three percent of the ®sh examined had the moderate TJ, CJ, or EYE injuries, while just over 4% had more severe injuries.
Table 3 Hook removal injuries and codes in increasing order of apparent severity and frequency of occurrence (1993 and 1994 observations combined) Severity
Code
Description
Overall percent frequency
Minor
NI CO JO TL TC
No apparent injury Cheek only; point of hook partially penetrates the cheek Jaw only; point of hook partially penetrates the jaw Torn lip Torn cheek; small hole through cheek only
0.7 5.3 1.4 0.4 44.5
Moderate
TJ CJ EYE
Torn jaw; jaw is torn on one side or the other, little or no tearing in cheek area Cheek and jaw; tear in cheek extending through jaw Hook penetrates eye
16.6 26.4 0.3
Severe
TF SJ JB JH TS
Torn face; torn through cheek and jaw as above but large flap of side of head is ripped or missing Split jaw: lower jaw is split laterally Jig body; fish was snagged by hook somewhere on body other than head Jig head; as above but snagged in head area Torn snout; upper jaw is split laterally, usually tearing through snout as well
3.8 0.3 0.1 0.0 0.1
UN
Unknown or unrecorded
0.1
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
137
Table 4 Most common hook removal injury or class of hook removal injuries by hook removal method and hook style (1993 and 1994 observations combined) Removal method
Hook style
Hook removal injury TC or less
TJ
CJ
TF
Others
Total observed
Careful shaking
Circle Autoline
1188 (88.5) 1043 (79.0)
88 (6.6) 80 (6.1)
56 (4.2) 169 (12.8)
1 (0.1) 2 (0.2)
9 (0.7) 26 (2.0)
1342 1320
Hook straightening
Circle Autoline
667 (60.9) 644 (61.7)
62 (5.7) 186 (17.8)
346 (31.6) 202 (19.4)
11 (1.0) 6 (0.6)
9 (0.8) 5 (0.5)
1095 1043
Gangion cutting
Circle Autoline
918 (94.3) 1227 (91.9)
20 (2.1) 67 (5.0)
24 (2.5) 34 (2.5)
1 (0.1) 0 (0.0)
10 (1.0) 7 (0.5)
973 1335
Automated hook stripping
Circle Autoline
494 (13.4) 543 (26.4)
1112 (30.2) 522 (25.4)
1722 (46.7) 836 (40.6)
325 (8.8) 140 (6.8)
31 (0.8) 18 (0.9)
3684 2059
Hook removal injuries by hook style and hook removal method show differences between the careful release methods and the automated hook stripper (Table 4). The smallest proportion of severe injuries was observed in ®sh that were released by gangion cutting. Gangion cutting leaves the hook embedded in the jaw or the mouth. It is likely that most of these hooks either quickly fall out or erode away after a period of time. In the few minutes between gangion cutting and our inspection and tagging, almost 15% (355 out of 2380) of the then unattached hooks had fallen from the ®sh' mouths. This percentage was similar for both circle and autoline hooks (16.5% and 13.9%, respectively). During the 1994 holding experiment, half of the 12 ®sh put into the holding tanks with hooks embedded in their mouths shed their hooks during the 10 days of the experiment. Careful shaking and hook straightening had higher proportions of ®sh with more severe injuries. To some extent, we think that this was due to our application of the techniques. Shaken ®sh were guided over the vessel's rail before hook removal, and hook straightening was performed on an inboard roller, both of which allowed ®sh to fall to the deck rather than into the sea. Our requirement to have the ®sh fall into the boat made the techniques more dif®cult and in all likelihood contributed to more severe injuries. Under normal commercial application the releases would occur while the ®sh hung vertically, outboard of the rail, resulting in a more direct removal process. Injuries were far more severe with ®sh removed by the hook stripper, less than 25% exhibited minor hook
removal injuries (Table 4). In only a few instances with each hook style (33 circle, 14 autoline), the gangion broke during the removal process, leaving the hook embedded in the mouth. Small but signi®cant differences were found between the severity of injuries resulting from all of the release methods from the two hook styles (Table 5). When the removal technique involved stressing (hook stripping) or deforming (hook straightening) the hook, injuries were more severe for removal from the stronger circle hooks compared to removal from the weaker autoline hooks. Construction from a lighter, smaller size wire makes autoline hooks easier to bend or straighten than similar sized full circle hooks (A. Forsberg, personal communication, O. Mustad&Son (USA), NY). 3.3. Condition codes Condition codes were assigned based on a close inspection of hook removal injuries, bleeding and gill color, evidence of predation, and muscle tone (Table 6). Condition codes assigned closely followed the hook removal injury (Table 7), with very few ®sh receiving codes more severe than those suggested by the hook injury. Generally, ®sh with minor injuries were coded as excellent; moderate injuries were coded as poor; and severe injuries were coded as dead. Jig injuries were coded as either poor or dead depending on hook location and penetration. Codes more severe than those suggested by the hooking injury were given most often as the result of bleeding associated with the
138
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 5 Results of 2- and t-tests (pooled data are indicated by square brackets) Groups
Treatments
Test value
df
p
Comments
2
Hook removal injuries by release method and hook style ± -test [TC], TJ, CJ for careful shaking Hook style [TC], TJ, CJ, TF for hook straightening Hook style [TC], TJ, CJ for gangion cutting Hook style [TC], TJ, CJ, TF for hook stripper Hook style
66.0 69.1 13.5 140.5
2 3 2 3
<0.00025 <0.00025 <0.0025 <0.00025
More More More More
Hook removal injuries by hook style and release method ± 2-test [TC], [TJ] for circle hooks Release method 3565.3
3
<0.00025
[TC], [TJ] for autoline hooks
3
<0.00025
More severe with hook stripper More severe with hook stripper
Release method
1737
Tag recovery rates by year and injury class, release method, or condition code ± 2-test 1993 releases Injury classa 15.1 2 1994 releases Injury classa 6.4 2 1993 circles Release method 10.2 2
<0.0005 <0.05 <0.005
1993 1994 1993 1994
<0.00025 <0.0025 <0.0025 <0.0025
releases releases releases releases
Condition Condition Condition Condition
(E, P, D) (E, P, D) (E, P) (P, D)
Growth in length by condition code ± t-test Annual growth for all releases Condition (P, D) a
18.9 13.7 13.8 10.9 3.483
2 2 2 2 145
<0.001
severe severe severe severe
with with with with
autoline circles circles circles
Minor>moderate>severe Minor>moderate>severe Shaking>gangion cutting> hook stripper E>P>D E>P>D E>P P>D Greater growth for better condition
Minor, moderate and severe.
Table 6 Halibut condition codes and criteria for assignment (adapted from Williams and Wilderbuer (1995)) Code
Description
Criteria
E
Excellent, no sign of stress
(1) Hook injuries are minor (limited to hook entrance/exit hole, torn lip) and located in jaw or cheek (2) Bleeding, if present, is minor and limited to jaw area (3) No penetration of the body by sand fleas (check eyes, fins, anus) (4) Muscle tone or physical activity is strong (5) Gills are deep red
P
Poor, alive but showing signs of stress
(1) Hook injuries may be severe: broken jaw; punctured eye (2) Vital organs are not injured (3) Bleeding may be moderate but not from gills (4) No penetration of the body by sand fleas (check eyes, fins, anus) (5) Muscle tone or physical movement may be weak or intermittent; little, if any, response to stimuli (6) Gills are red
D
Dead, no sign of life or, if alive, likely to die from severe injuries or suffocation
(1) Vital organs may be damaged: torn gills; gaff wound to head or body; jig injury to viscera; side of face torn loose or missing jaw (2) Sand fleas have penetrated the body (they usually attack the eyes first, but also fins and anus) (3) Severe bleeding may occur, especially from the gills (4) No sign of muscle tone; physical activity absent or limited to fin ripples or twitches (5) Gills may be red, pink, or white
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144 Table 7 Number of observations by condition codes and hook removal injury (1993 and 1994 observations combined) Hook removal injury
Number (and percentage) by condition code E
P
D
NI CO JO TL TC TJ CJ EYE TF SJ JB or JH TS
87 (93.5) 665 (98.2) 174 (95.1) 48 (98.0) 5516 (96.4) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0)
5 (5.4) 10 (1.5) 8 (4.4) 1 (2.0) 93 (1.6) 2104 (98.5) 3296 (97.3) 38 (100.0) 0 (0.0) 34 (97.1) 7 (43.8) 8 (100.0)
1 (1.1) 2 (0.3) 1 (0.5) 0 (0.0) 113 (2.0) 33 (1.5) 93 (2.7) 0 (0.0) 486 (100.0) 1 (2.9) 9 (56.3) 0 (0.0)
Total
6506 (50.6)
5604 (43.6)
741 (5.8)
139
3.4. Tag returns A total of 631 tags were recovered by the end of the 1996 ®shing season for an overall tag recovery rate of 5% (4.5% for 1993 releases and 5.2% for 1994 releases). Most of the tags were recovered in the area of tag release by commercial longline ®sheries (of 602 tags returned with recovery location, 505 were recovered less than 35 km from their release locations). 3.4.1. Tag return rate by hook removal injury Least severe injury classes showed higher recovery rates than the more severe injury classes (Table 9). While the overall recovery rate for the 1994 releases is higher than that for the 1993 releases, a signi®cant trend towards higher recovery rate for less severely injured ®sh holds for both the years. There is no signi®cant trend of declining recovery numbers for the more severe injuries in subsequent years, suggesting that injury-induced mortality does not increase over time. However, the small number of releases in these categories could mask this effect.
hooking and hook removal process (46 cases) and occasionally as the result of amphipod (sand ¯ea) predation (17 cases). Condition codes by hook removal method and hook style (Table 8) were consistent with the trend for hook removal injuries by these criteria. Generally, ®sh released by one of the three careful release methods were coded as excellent, with the particular exception of those ®sh which received poor codes as the result of our hook straightening technique. Depending on the hook style, about 66±76% of the ®sh removed by the hook stripper were coded as poor, with an additional 9±10% coded as dead.
3.4.2. Tag return rate by hook removal method Generally, the return rate for any of the three careful release methods is higher than that for ®sh removed using the hook stripper (Table 10). However, the return rates for all methods are very close, and signi®cant differences in return rate by removal method are seen only in one of the four possible hook style and release year combinations: 1993 releases from circle hooks.
Table 8 Number of observations and percent by condition codes, hook removal method, and hook style (1993 and 1994 observations combined) Hook removal method
Hook style
Number (and percentage) by condition code E
P
D
Careful shaking
Circle Autoline
1170 (87.2) 1010 (76.5)
158 (11.8) 267 (20.2)
14 (1.0) 43 (3.3)
Hook straightening
Circle Autoline
653 (59.6) 631 (60.5)
412 (37.6) 396 (38.0)
30 (2.7) 16 (1.5)
Gangion cutting
Circle Autoline
891 (91.6) 1159 (86.8)
55 (5.7) 142 (10.6)
27 (2.8) 34 (2.5)
Automated hook stripping
Circle Autoline
489 (13.3) 503 (24.4)
2804 (76.1) 1370 (66.5)
391 (10.6) 186 (9.0)
140
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 9 Tag recoveries by year of release and hook removal injury (number and percent) Hook removal injury
Year of release 1993
1994
Releases
Returns
%
Releases
Returns
%
Minor NI CO JO TL TC Total minor
51 283 109 35 1371 1849
7 14 5 4 72 102
(13.7) (4.9) (4.6) (11.4) (5.3) (5.5)
42 394 74 14 4351 4875
0 25 7 0 243 275
(0.0) (6.3) (9.5) (0.0) (5.6) (5.6)
Moderate TJ CJ EYE Total moderate
1229 599 1 1829
36 20 0 56
(2.9) (3.3) (0.0) (3.1)
908 2790 37 3735
40 140 2 184
(4.6) (5.0) (5.4) (4.9)
85 12 0 5 3 105
1 1 0 0 0 2
(1.2) (8.3) (±) (0.0) (0.0) (1.9)
401 23 8 5 3 440
13 0 1 0 0 14
(3.2) (0.0) (12.5) (0.0) (0.0) (3.2)
3783
160
(4.2)
9050
471
(5.2)
Severe TF SJ TS JB JH Total severe Total all injuries
3.4.3. Tag return rate by condition code The difference in return rates by condition code was signi®cant for both of the release years. Trends were similar between years (Table 11) and also similar to those seen by injury class. A notable difference between rates by injury class and rates by condition code are the return rates for dead ®sh `D'. In Table 9, rates for ®sh with more severe injuries were 1.9% and 3.2% in 1993 and 1994, respectively, while rates for
®sh coded dead in those years are 0.8% and 2.1%. While all ®sh with most severe injuries were coded as dead, the return rate of code `dead' ®sh is lower by about 50% when compared to the ®sh grouped by hook removal injury only. The difference arises from the additional dead codings as the result of bleeding or sand ¯ea infestation. There were 46 and 17 releases of ®sh with these conditions overall, with no subsequent recoveries.
Table 10 Tag recoveries by year of release, hook style, and hook removal method (number and percent) Release year
Hook style
Hook removal method Careful shaking
Hook straightening
Gangion cutting
Automated hook stripping
Total
1993
Circle Autoline
16 (5.8) 27 (7.1)
0 (±) 19 (4.4)
4 (3.7) 26 (4.8)
31 (2.3) 37 (5.4)
51 (2.9) 109 (5.3)
1994
Circle Autoline
56 (5.3) 57 (6.1)
45 (4.1) 38 (6.3)
52 (6.0) 44 (5.6)
116 (5.0) 64 (4.6)
269 (5.0) 203 (5.5)
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
141
Table 11 Tag recoveries by year of release and recovery, and condition code (number and tag recovery rate) Release year
Recovery year
Condition code E
P
D
1993
1993 1994 1995 1996 1993±1996 Total
29 29 18 23 99
(1.7) (1.7) (1.0) (1.3) (5.7)
12 20 9 19 60
(0.6) (1.0) (0.5) (1.0) (3.1)
0 0 0 1 1
(0.0) (0.0) (0.0) (0.8) (0.8)
1994
1994 1995 1996 1994±1996 Total
27 129 112 268
(0.6) (2.7) (2.4) (5.6)
16 99 76 191
(0.4) (2.7) (2.1) (5.2)
0 6 7 13
(0.0) (1.0) (1.1) (2.1)
3.5. Growth in length
3.6. Relative and absolute survival
Recovery fork lengths were recorded for 331 of the tag recoveries where the time at liberty ranged from 90 to 1263 days. The increase in the overall length ranged from 0 to 31 cm. Growth in centimeters was divided by the fractions of years at liberty to determine an annual growth rate (cm yearÿ1). The trends in growth by either hook removal injury or condition code are similar to those seen in recovery rate by both the criteria (Table 12). Fish with more severe injuries, or in poorer condition, appeared to grow in length more slowly than those ®sh in either better condition or with less severe injuries. The difference in growth rate was signi®cant between ®sh in poor and dead condition.
Survival rates for injury classes or conditions were estimated by using the proportion of ®sh recovered in each class, and applying that proportion to the estimated survival of ®sh in excellent condition (Table 13). Sixty-nine percent of halibut with moderate injuries are expected to survive, while about 2/3 as many, or 43%, of ®sh with severe injuries survive. While the 73% survival estimate of poor condition ®sh is similar to that for ®sh with moderate injuries, the survival of ®sh judged to be in dead condition is only 26%, just over half the survival rate of ®sh with severe hook removal injuries. While the dead condition ®sh have the worst
Table 12 Annual growth in length by hook removal injury and condition code (includes recoveries from both 1993 and 1994 releases) Number of observations
Annual growth (cm)
Std. dev.
Hook removal injury NI CO JO TL TC TJ CJ TF TS
2 22 9 2 183 45 87 6 1
6.10 4.09 2.36 3.03 3.46 3.19 2.90 2.53 0.00
3.18 2.59 1.69 ± 2.58 2.68 2.55 2.00 ±
Condition code E P D
210 141 6
3.51 2.99 2.53
2.56 2.56 2.00
142
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 13 Relative survival by injury class and condition code as inferred by tag recovery rates (includes recoveries from both 1993 and 1994 releases) Survival by injury class Injury Class
Injuries in class
Tag recovery rate*
Survival
Minor Moderate Severe
NI, CO, JO, TL, TC TJ, CJ, EYE TF, SJ, TS, JB, JH
5.5% 4.3% 2.6%
97% 76% 46%
Condition code
Description
Tag recovery rate*
Survival
E P D
Excellent Poor Dead
5.6% 4.4% 1.5%
97% 76% 26%
Survival by condition code
a
Determined as average of recovery rates from 1993 and 1994 releases
survival, clearly the term `dead' is a misnomer for this group. 4. Discussion Hooking locations are consistent with our earlier study of hook removal injuries (Kaimmer, 1994); the great majority of halibut, over 95% overall, are captured on either hook style with the hook encircling the jaw bone, usually with the point of the hook penetrating the tissue of the cheek muscle. This hooking location is characteristic of the circle or modi®ed circle hook for many species (Johannes, 1981; Bjordahl and Lokkeborg, 1996; Kaimmer and Trumble, 1997). Proper execution of any of the three careful release techniques either leave the hook in place, which may eventually fall out (gangion cutting), or result in the hook being removed back out the same way as it entered (careful shaking and hook straightening). They leave no additional injury beyond that caused by the hooking itself. No short-term mortality was observed over periods of 4 or 10 days, even for ®sh with severe injuries. This observation is conservative, since small tank sizes and rough weather during the tank holding could be expected to increase stress conditions during holding. Tag recovery rates, by either class of hook removal injury or condition code, showed signi®cant differences. From these tag returns, the survival of poor condition halibut is estimated at 73%, while the survival of dead halibut is estimated as 26%. From
the perspective of mortality, the mortality of poor ®sh is almost eight times as great (27% compared to 3.5%), while the mortality of dead ®sh is over 21 times greater than that of excellent ®sh (74% compared to 3.5%). These numbers agree with those currently used for the management in direction, but not in magnitude, and suggest that poor and dead condition ®sh survive at higher rates than currently assumed. While more severe hook injuries appear to associate with reduced growth rates in ®sh which are subsequently recaptured, even these are shown only as trends in the data, the differences not being large enough to be statistically signi®cant. These differences were signi®cant in an earlier study with heavier gear (Kaimmer, 1994), and, if present, reduced growth of survivors could represent an additional component of loss to the ®shery. 5. Conclusion All three of the careful release methods used in this study are approved methods to remove halibut from longline gear. However, differences in hook strength or operator skill can alter the success of any of these techniques. Since hook strength and operator skill appear to be important variables, removal method alone is not suf®cient to estimate survival rates. We achieved fairly consistent, and signi®cantly different, estimates of survival based on the condition factors developed by IPHC for use by ®shery observers.
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
While the nomenclature and mortalities associated with the condition codes may need to be changed or realigned, the applications of the codes themselves seem to function well as a predictor of individual halibut survival. Currently, setline bycatch mortality is assessed at 3.5% for ®sh in an excellent condition, 52% for ®sh in poor condition, and 100% for ®sh in dead condition. Although not designed to assess mortalities associated with condition, the results of Kaimmer (1994) suggest that less than about 50% of poor condition ®sh actually die while only about 75% of dead condition ®sh die. Our study is the ®rst designed speci®cally to determine longline bycatch mortality rates associated with hook removal method, hook removal injury, or condition code, and suggests that even lower mortality rates should be used, 27% and 74% for poor and dead condition ®sh. It will be necessary to reassess both the nomenclatures used for condition codes and the parameters used in bycatch calculations for the light gear longline ¯eets in the north Paci®c. The need for a change in nomenclature is obvious. The use of `dead' as a description of a category where all ®sh do not die is clearly inappropriate. The implementation of these changes requires further study. One complicating factor lies in the application of the condition code criteria. In our study, most ®sh in dead condition were so coded as the result of hook removal injuries (criteria 1, 3, or 5 in Table 6), with only a small proportion of the dead codings resulting from predation by sand ¯eas (criterion 2). A survey of observers at the end of the 1996 ®shing season gave sand ¯ea predation as the most common reason for coding halibut as dead (Sadorus, 1996). Although less than 10% of the halibut bycatch in the sable®sh and Paci®c cod longline ®sheries are coded as dead (Williams, 1996), it is very likely that our releases of ®sh in this condition do not adequately represent those observed in the ®shery. None of the ®sh released in our study in which sand ¯eas had penetrated the body were subsequently recovered, for an implied survival of these ®sh of 0%. A survival of 0% for the dead condition ®sh in the commercial ®shery might be very appropriate. The most common reason given for coding ®sh as poor condition was the injuries sustained while being released from the hook, suggesting that the mortality estimated for poor condition ®sh from this study should be representative of
143
that experienced by ®sh coded as poor condition in the commercial ®shery. Acknowledgements We are grateful to J. Nielson, B. Leaman, and an anonymous reviewer for their comments on an earlier draft. Thanks are also due to Ron Hegge, skipper of the Rebecca B, and his crew for their co-operation and assistance during the experiments.
References Bjordahl, A., Lokkeborg, S., 1996. Longlining. Fishing News Books, Oxford, UK. Johannes, R.E., 1981. Words of the Lagoon ± Fishing and Marine Lore in the District of Micronesia. University of California Press, CA. Kaimmer, S.M., 1994. Halibut injury and mortality associated with manual and automated removal from setline hooks. Fisheries Res. 20, 165±179. Kaimmer, S.M., Trumble, R.J., 1997. Survival of Pacific halibut released from longlines: hooking location and release methods. In: Fisheries Bycatch: Consequences and Management. Alaska Sea Grant College Program Report No. 97 (2), University of Alaska Fairbanks, pp. 101±105. Myhre, R.J., 1974. Minimum size and optimum age of entry for Pacific halibut. Int. Pac. Halibut Comm. Rep. 55, IPHC, Seattle, WA. Nielson, J.D., Waiwood, K.G., Smith, S.J., 1989. Survival of Atlantic halibut (Hippoglossus hippoglossus) caught by longline and otter trawl gear. Can. J. Fish. Aquat. Sci. 46(5), 887± 897. Peltonen, G.J., 1969. Viability of tagged Pacific halibut. Int. Pac. Halibut Comm. Rep. 52, IPHC, Seattle, WA. Sadorus, L.L., 1996. Results from 1996 NMFS observer questionnaires. Int. Pac. Halibut Comm. Report of Assessment and Research Activities (unpublished), IPHC, Seattle, WA, pp. 235±248. Sadorus, L.L., Williams, G.H., 1996. The 1996 groundfish fishery off Alaska: Groundfish catches, halibut bycatches, and bycatch rates. Int. Pac. Halibut Comm. Report of Assessment and Research Activities (unpublished), IPHC, Seattle, WA, pp. 169±188. Williams, G.H., 1996. Pacific halibut discard mortality rates in the 1990±1995 Alaskan groundfish fisheries, with recommendations for monitoring in 1997. Int. Pac. Halibut Comm. Report of Assessment and Research Activities (unpublished), IPHC, Seattle, WA, pp. 211±228. Williams, G.H., Wilderbuer, T.K., 1995. Discard mortality rates of Pacific halibut bycatch: Fishery differences and trends during 1990±1993. In: Proceedings of the International Symposium on
144
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
North Pacific flatfish. Alaska Sea Grant College Program Report No. 95 (4), University of Alaska Fairbanks, pp. 611± 622. Wilson, W.J., Weeks, H.J., 1996. Policy and regulatory measures to control incidental mortality of Pacific halibut in groundfish
fisheries of the North Pacific ocean. In: Meyer, R.M., Zhang, C., Windsor, M.L., McCay, B.J., Hushak, L.J., Muth, R.M. (Eds.), Fisheries Resource Utilization and Policy, Proceedings of the World Fisheries Congress, Theme 2. Oxford and IBH Publishing, New Delhi, pp. 219±239.
Injury, condition, and mortality of Paci®c halibut bycatch following careful release by Paci®c cod and sable®sh longline ®sheries Stephen M. Kaimmer*, Robert J. Trumble International Paci®c Halibut Commission, PO Box 95009, Seattle, WA 98145, USA Received 11 November 1997; accepted 26 May 1998
Abstract Paci®c halibut caught as bycatch or intended for discard by longline vessels in US and Canadian waters of the north Paci®c must be removed from the hook using careful release techniques required by regulation. In many ®sheries, trained observers subsample the released halibut for ®sh condition. These condition codes are used to track cumulative bycatch mortality in these ®sheries. Tag return rates of halibut released from longline gear near Kodiak Island, Alaska, are used to estimate relative and absolute mortalities of ®sh by release method, hook removal injury, and condition code. Generally, the proper application of the careful release techniques results in only minor hook removal injuries. Survival rates of moderately and severely injured halibut are 1.5±2 times higher than previously assumed. One result of our study is the ®nding that not all ®sh judged at tagging as likely to die actually die. We recommend a reworking of the condition code methodology. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Paci®c halibut; Bycatch; Condition code; Mortality; Survival; Hook injury; Careful release; Growth
1. Introduction Paci®c halibut, Hippoglossus stenolepis, is caught in the northeast Paci®c and eastern Bering Sea by directed hook and line ®sheries and as an incidental catch in other trawl and longline ®sheries. Paci®c halibut larger than the minimum size (81 cm) may be retained only with hook and line gear during open ®shing periods. In Alaska and Canada retention is restricted to vessels or individuals which possess individual quotas for longline harvest. All other Paci®c halibut must be released. Both US and Canadian ®shery regulations require that halibut bycatch must *Corresponding author. Tel.: +1 206 634 1838; fax: +1 206 632 2983; e-mail: [email protected]
be returned to the sea in as good a condition as possible. The mortality associated with this incidental catch is substantial, ranging from 8 to 10 thousand metric tons round weight per year since 1990. About 80% is due to trawl bycatch and about 20% longline (Williams and Wilderbuer, 1995). Halibut is a very hardy ®sh, and survives capture and discard to the sea if treated moderately well. In the case of hook and line ®sheries for ground®sh, potential survival of discarded halibut is very high. Circle hooks and semi-circle hooks used by the majority of hook and line ®shermen usually catch halibut in the mouth, the hooking process itself causing little damage. However, inappropriate release methods cause severe wounds that lead to higher probability of death (Kaimmer, 1994). Careful release of halibut bycatch from
0165-7836/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0165-7836(98)00153-2
132
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
hook and line ground®sh and halibut ®sheries in Alaska is required by regulation. These ®sh may not be landed onto the vessel, but must be released outboard of the roller. Methods currently allowed are hook straightening, cutting the gangion near the hook, or carefully removing the hook by twisting it from the halibut with a gaff (careful shaking). Comparison of careful shaking and automatic hook stripping (Kaimmer, 1994) led to a ban on hook stripping during halibut ®shing in 1987. This ban was dropped in 1995 because hook strippers are considered to be essential for some multi-species ®sheries, although hook strippers may not be used for the release of halibut bycatch. For many longline and trawl ®sheries in Alaska, and for some ®sheries in Paci®c Canada, onboard observers monitor both the amount and viability (condition code) of the Paci®c halibut released. The observers closely examine a subsample of the halibut bycatch and assign each examined ®sh one of the three IPHC condition codes: excellent, poor, or dead (Williams and Wilderbuer, 1995). Mortalities associated with longline condition codes are estimated indirectly from earlier survival or holding studies. These studies suggest that the handling mortality of hook and line caught ®sh in excellent condition ranges from 2% to 5% (Peltonen, 1969), that survival of poor condition ®sh is approximately half that of ®sh in an excellent condition (Myhre, 1974), and that all ®sh judged as dead actually die (Williams and Wilderbuer, 1995). From these relationships, mortality rates associated with the three condition codes are: 3.5% for excellent condition ®sh (midpoint of the 2±5% range), 52% for poor condition ®sh (half the survival of excellent condition ®sh), and 100% for dead or likely-to-die ®sh. The assumption that survival of ®sh in excellent condition is almost 100% is more recently supported by our own observations in collecting halibut and holding them for long periods in tanks or net pens (authors, unpublished) and by a study on the longline survival of the closely related Atlantic halibut Hippoglossus hippoglossus (Nielson et al., 1989). The International Paci®c Halibut Commission (IPHC) manages Paci®c halibut and uses the observer data to determine a discard mortality rate, the proportion of halibut that die, which is then applied to each longline ®shery that causes bycatch. Many ®sheries operate under an annual limit of allowed halibut
mortality and ®sheries have been closed with quota left un®shed when these limits have been exceeded (Wilson and Weeks, 1996; Sadorus and Williams, 1996). The IPHC estimates bycatch mortality prior to each year's directed ®shing, and subtracts the estimated halibut mortality from the yield available to the directed halibut ®shing ¯eet in the coming year. The halibut mortality thus subtracted in the years 1990±1996 has ranged from 8 to 10 thousand metric tons, with 19±31% coming from longline ®sheries. Almost all of the ground®sh longline mortality of halibut results from the ®sheries for sable®sh (Anaplopoma ®mbria) and Paci®c cod (Gadus macrocephalus). Annually since 1990, the allowed removals in the directed halibut ®shery have been reduced by 4±9% to compensate for longline discard mortality, representing annual losses to halibut ®shermen of about 10 million dollars US. In 1993 and 1994, the IPHC conducted a tagging study to evaluate the condition code methodology and for the ®rst time used relative tag return rates to directly estimate halibut bycatch mortality rates by condition code for the longline ®sheries. Over 13 000 Paci®c halibut were examined, tagged, and released in the vicinity of Kodiak Island, Alaska (Fig. 1). Halibut were examined for hook injuries and assigned a condition code. Each halibut was removed from its hook by one of the three careful release methods or by hook stripping. Halibut were caught using circle and autoline hooks typical in size and style of those commonly used in the ground®sh longline ®sheries in the north Paci®c. 2. Materials and methods The 23.5 m US ®shing vessel Rebecca B was chartered from 27 April 1993 to 8 May 1993 and from 4 July 1994 to 28 July 1994. Fishing during both years took place in the vicinity of Kodiak Island off Alaska (Fig. 1). The vessel's captain was experienced in the longline ®sheries for Paci®c cod and sable®sh and was tasked to keep his vessel operations as close as possible to those which might be experienced during commercial ®shing trips. Halibut were caught using the two styles of hook and were removed from the hook by one of the three careful release methods (careful shaking, hook straightening, and gangion
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
133
Fig. 1. Location of tag releases during 1993 and 1994 longline bycatch mortality study.
cutting), and by an automated hook stripper (Table 1). The ®sh in this study were necessarily landed on the deck of the vessel for observation and tagging, whereas the application of careful release techniques by a commercial ®sher would result in the ®sh falling into the sea. Care was taken to minimize any injury associated with bringing the ®sh aboard the vessel. The resultant hook removal injuries and ®sh conditions were noted and ®sh were tagged and released. The time period from hook removal to ®nal release was always 3 min or less. Tag recovery rates are used to determine relative mortalities associated with hook removal injury and halibut condition code resulting from each of the four release methods from the two hook styles.
2.1. Fish capture and tagging The ®shing location was chosen to provide both a good probability of tagging large numbers of ®sh, and an area that would be heavily ®shed by the commercial longline ¯eet, facilitating recovery of tagged ®sh. During both the years, halibut were caught with autoline and circle hooks ®xed to the groundline at 1.07 m intervals. The only change in ®shing gear between 1993 and 1994 was in the method used to ®sh the autoline gear. The chartered vessel used a Mustad autoline system (`automatic' baiting during setting, and racking during hauling) during 1993. The autoline system was removed after the 1993 charter, and in 1994 this gear was ®sh `conventionally' (hand coiled
134
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 1 Hook removal methods and numbers of fish tagged by year, hook style, and method Method
Description
Careful shaking
The fish are removed by catching and twisting the hook with the gaff; the hook is held upside down against the tension of the gangion, which allows the fish to fall from the hook. Sometimes a careful `shake' is needed to drop the fish from the hook The gaff holds the bend of the hook against the roller until it is straightened, pulling out of the fish The gangion is cut between the hook and the groundline, resulting in release with the hook still embedded in the fish Automated removal by allowing the fish to be held on the horns of the hook stripper while the hook is torn from the fish as the groundline comes aboard
Hook straightening Gangion cutting Automated hook stripping Year
Hook style
Careful shaking
Hook straightening
1993
Circle Autoline Circle Autoline
277 381 1065 939
0 435 1095 608
109 545 864 790
1358 680 2326 1379
1744 2041 5350 3716
2662
2138
2308
5743
12 851
1994 Total
and baited). The circle hooks were a full circle style (Mustad 39965 13/0). The autoline hooks were an `easy-baiter' style (Mustad 39975 13/0) which was required by the racking and baiting system. All hooks were baited with thawed Loligo sp. squid. Gear was set as early as practical each ®shing day and retrieval was started after a 5±7 h soaking time. If time is allowed, additional gear was set in the afternoon. All gears were usually retrieved before midnight of the day of setting, although on three instances hauling continued two or more hours after midnight. Baiting, setting, and hauling procedures and times were typical of those experienced by commercial ®shers. While the setting and hauling procedures did not control for capture time of day or soak time, gear type and release method were alternated between sets in order to distribute the gear and release treatments as evenly as possible over the course of the experiment. The experiment could not control the area of ®shing for tag recovery. Treatments were distributed evenly among release areas so that uneven distribution of ®shing effort during tag recovery would not bias results. 2.2. Hook removal methods Careful shaking entails sliding the bend of the gaff down the gangion to engage the bend of the hook on the bend of the gaff. Keeping the gangion taut while
Gangion cutting
Automated hook stripping
Total
lifting and twisting the gaff rolls the hook out of the mouth of the ®sh. As the gaff is twisted, it is often given a gentle `shake', thus the term `shaking'. Automated removal of ®sh from the hook is a `hands-off' process. The ®sh is pulled aboard the vessel by the incoming gear and led by the gangion to the hook stripper. As the groundline and gangion are drawn through a constriction, the ®sh is drawn up and held as the hook is torn from the mouth (Kaimmer, 1994). Hook straightening is similar to shaking, in that the gaff is slid down the gangion to engage the bend of the hook, but in this case the gaff is then held against the outer edge of one of the side guide rollers mounted on the vessel's rail. As the gangion draws tight the bend of the hook straightens, and the hook is pulled backwards out of the ®sh's mouth. Gangion cutting involves cutting the gangion close to the hook, allowing the ®sh to fall free with the hook still embedded in the mouth, often with a short piece of the gangion attached to the hook. 2.3. Live holding experiment During both 1993 and 1994, halibut were held in aluminum tanks to assess short-term mortality from hook removal injuries. The tanks were approximately 1 m1.5 m in width and 1.2 m in depth with a grated
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
outlet near the top of the tank. A hose fastened near the bottom of the tank supplied fresh seawater, and a loose cover was ®xed over the top. Fish were observed daily for signs of stress or mortality. Halibut ranged in size from 56 to 90 cm, and were selected to cover the extremes of hook removal injuries observed during the charters, with about equal numbers of minor injuries and more severe injuries put into each tank. Eight halibut were held for four days in one tank in 1993. All eight were robust after four days, and on release swam directly into deep water. Two of the four ®sh tanked with autoline hooks in their mouths shed their hooks during the holding. During 1994, 35 halibut were held in four tanks, 8±9 to a tank, for 10 days. Fifteen of them had torn face wounds, and were coded as likely to die. Seven ®sh caught on autoline hooks, and eight ®sh caught on circle hooks, had hooks in their mouths resulting from the hook release method. Three of the autoline hooks had been shed during handling and tagging. Two more of the autoline hooks and four of the circle hooks were shed during the tank holding. All ®sh were very robust at the time of release. We observed no short-term mortality during either year, nor any apparent difference in either vitality or behavior among ®sh with different injuries. 2.4. Data analysis Observed frequencies of hooking and hook removal injuries, tag recovery rates, and mean growth in length of recovered ®sh were compared among treatment groups and across sizes of halibut to determine signi®cant differences between the groups. Differences in the distribution of injuries and tag recovery rates were examined using the 2 test. Expected values were calculated assuming that if the null hypothesis were true, then the distribution of tags across the groups would be the same for both the releases and the recoveries. In some groupings by injury classes, release numbers were so small that the expected returns were less than 5. These classes were either pooled with similar injury classes, or in some cases not included in the analyses. To determine differences in growth rates, the t-test was used. For both tests, the level of signi®cance was set at 0.05. Relative survival was determined by comparing the ratio of tag recovery rates between the groups. Absolute survival was estimated by taking a ratio of the recovery rate of a group
135
to the recovery rate of excellent condition ®sh, and multiplying by the estimated 96.5 survival assumed for excellent condition ®sh. 3. Results In all, 12 851 halibut (8879 sublegal-sized and 3972 legal-sized ®sh) were examined, tagged and released from both years (Table 1). The fork length of tagged ®sh ranged from 34 to 191 cm, with an average length of 77 cm (9.4 cm SD). Fishing depths ranged from 46 to 290 m with an average depth over both years of 116 m. In 1993, hook straightening was used with the autoline hooks only. About half as many ®sh were tagged during 1993 as during 1994. During both the years, approximately equal numbers of ®sh were removed by each of the careful release methods being used, and about twice the number were released using the hook stripper. The 1993 capture and release area was relatively large, extending 240 nm along the top and the edge of the coastal shelf. The weather during 1993 was extremely poor, and the ®shing area was forced each day to move away from an approaching storm. The 1994 releases were from a much smaller geographic area, extending 50 nm along the coastal edge and the shelf (Fig. 1). To avoid biases that may arise from possible different recapture probabilities from the two release years, these release years are treated as separate experiments. Within either year, all releases were in areas of subsequent commercial removals. The commercial catch in these areas was similar for the recovery years over the areas of recovery, and there should be no signi®cant variation in recovery probability for the treatments. 3.1. Hooking location Combining information from both years, 98% of the halibut caught on circle hooks and 94% of the halibut caught on autoline hooks were hooked in either the left or the right jaw (Table 2), with the point of the hook encircling the jawbone. A further 1% of the ®sh caught on circle hooks and 4% of the ®sh caught on autoline hooks were caught with the hook protruding through the eye (an extreme form of a right jaw hooking). While small differences in hooking location between the size of the ®sh or hook styles are statistically
136
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 2 Hooking locations in numbers and percent observed for autoline and conventional gears and size of fish (1993 and 1994 observations combined) Code
Description
Number (and percentage) by length category and hook style Circle hooks
LJ RJ EYE RM PP TO JB JH NO
Left (blind side) jaw or cheek Right (eyed side) jaw or cheek Eye Roof of mouth Pharyngeal pad Tongue Jig or snag body Jig or snag head No injury apparent
Total
Autoline hooks
<82 cm
82 cm
Total
<82 cm
82 cm
Total
4165 (79.3) 980 (18.6) 66 (1.3) 11 (0.2) 0 (0.0) 20 (0.4) 6 (0.1) 4 (0.1) 3 (0.1)
1471 (80.0) 351 (19.1) 8 (0.4) 4 (0.2) 0 (0.0) 2 (0.1) 0 (0.0) 0 (0.0) 3 (0.2)
5636 (79.4) 1254 (18.8) 151 (1.0) 15 (0.2) 0 (0.0) 22 (0.3) 6 (0.1) 4 (0.1) 6 (0.1)
2932 (80.9) 489 (13.5) 153 (4.2) 11 (0.3) 0 (0.0) 10 (0.3) 8 (0.2) 8 (0.2) 13 (0.4)
1678 (78.7) 323 (15.1) 96 (4.5) 9 (0.4) 1 (0.0) 6 (0.3) 4 (0.2) 7 (0.3) 9 (0.4)
4610 (80.1) 730 (14.1) 331 (4.3) 20 (0.3) 1 (0.0) 16 (0.3) 12 (0.2) 15 (0.3) 22 (0.4)
5255
1839
7094
3624
2133
5757
signi®cant, the only difference of biological signi®cance to this study is the increased incidence of eye hooking from the autoline hooks, which is identi®ed as a more severe wound after the hook is removed. 3.2. Hook removal injury Hook removal injuries were classi®ed into one of the 14 categories (Table 3), ranging from minor injuries NI, CO, JO, TL, TC, through the moderate TJ, CJ,
and EYE, and to the severe TF, SJ and TS, and jig injuries. The minor wounds NI±TC are generally only the hooking injury, with no further injury caused during hook removal. During both the years, just over half of the ®sh exhibited these less severe removal injuries. More severe wounds are the result of the hook being torn from the ®sh during removal, or the hook puncturing the eye. Forty-three percent of the ®sh examined had the moderate TJ, CJ, or EYE injuries, while just over 4% had more severe injuries.
Table 3 Hook removal injuries and codes in increasing order of apparent severity and frequency of occurrence (1993 and 1994 observations combined) Severity
Code
Description
Overall percent frequency
Minor
NI CO JO TL TC
No apparent injury Cheek only; point of hook partially penetrates the cheek Jaw only; point of hook partially penetrates the jaw Torn lip Torn cheek; small hole through cheek only
0.7 5.3 1.4 0.4 44.5
Moderate
TJ CJ EYE
Torn jaw; jaw is torn on one side or the other, little or no tearing in cheek area Cheek and jaw; tear in cheek extending through jaw Hook penetrates eye
16.6 26.4 0.3
Severe
TF SJ JB JH TS
Torn face; torn through cheek and jaw as above but large flap of side of head is ripped or missing Split jaw: lower jaw is split laterally Jig body; fish was snagged by hook somewhere on body other than head Jig head; as above but snagged in head area Torn snout; upper jaw is split laterally, usually tearing through snout as well
3.8 0.3 0.1 0.0 0.1
UN
Unknown or unrecorded
0.1
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
137
Table 4 Most common hook removal injury or class of hook removal injuries by hook removal method and hook style (1993 and 1994 observations combined) Removal method
Hook style
Hook removal injury TC or less
TJ
CJ
TF
Others
Total observed
Careful shaking
Circle Autoline
1188 (88.5) 1043 (79.0)
88 (6.6) 80 (6.1)
56 (4.2) 169 (12.8)
1 (0.1) 2 (0.2)
9 (0.7) 26 (2.0)
1342 1320
Hook straightening
Circle Autoline
667 (60.9) 644 (61.7)
62 (5.7) 186 (17.8)
346 (31.6) 202 (19.4)
11 (1.0) 6 (0.6)
9 (0.8) 5 (0.5)
1095 1043
Gangion cutting
Circle Autoline
918 (94.3) 1227 (91.9)
20 (2.1) 67 (5.0)
24 (2.5) 34 (2.5)
1 (0.1) 0 (0.0)
10 (1.0) 7 (0.5)
973 1335
Automated hook stripping
Circle Autoline
494 (13.4) 543 (26.4)
1112 (30.2) 522 (25.4)
1722 (46.7) 836 (40.6)
325 (8.8) 140 (6.8)
31 (0.8) 18 (0.9)
3684 2059
Hook removal injuries by hook style and hook removal method show differences between the careful release methods and the automated hook stripper (Table 4). The smallest proportion of severe injuries was observed in ®sh that were released by gangion cutting. Gangion cutting leaves the hook embedded in the jaw or the mouth. It is likely that most of these hooks either quickly fall out or erode away after a period of time. In the few minutes between gangion cutting and our inspection and tagging, almost 15% (355 out of 2380) of the then unattached hooks had fallen from the ®sh' mouths. This percentage was similar for both circle and autoline hooks (16.5% and 13.9%, respectively). During the 1994 holding experiment, half of the 12 ®sh put into the holding tanks with hooks embedded in their mouths shed their hooks during the 10 days of the experiment. Careful shaking and hook straightening had higher proportions of ®sh with more severe injuries. To some extent, we think that this was due to our application of the techniques. Shaken ®sh were guided over the vessel's rail before hook removal, and hook straightening was performed on an inboard roller, both of which allowed ®sh to fall to the deck rather than into the sea. Our requirement to have the ®sh fall into the boat made the techniques more dif®cult and in all likelihood contributed to more severe injuries. Under normal commercial application the releases would occur while the ®sh hung vertically, outboard of the rail, resulting in a more direct removal process. Injuries were far more severe with ®sh removed by the hook stripper, less than 25% exhibited minor hook
removal injuries (Table 4). In only a few instances with each hook style (33 circle, 14 autoline), the gangion broke during the removal process, leaving the hook embedded in the mouth. Small but signi®cant differences were found between the severity of injuries resulting from all of the release methods from the two hook styles (Table 5). When the removal technique involved stressing (hook stripping) or deforming (hook straightening) the hook, injuries were more severe for removal from the stronger circle hooks compared to removal from the weaker autoline hooks. Construction from a lighter, smaller size wire makes autoline hooks easier to bend or straighten than similar sized full circle hooks (A. Forsberg, personal communication, O. Mustad&Son (USA), NY). 3.3. Condition codes Condition codes were assigned based on a close inspection of hook removal injuries, bleeding and gill color, evidence of predation, and muscle tone (Table 6). Condition codes assigned closely followed the hook removal injury (Table 7), with very few ®sh receiving codes more severe than those suggested by the hook injury. Generally, ®sh with minor injuries were coded as excellent; moderate injuries were coded as poor; and severe injuries were coded as dead. Jig injuries were coded as either poor or dead depending on hook location and penetration. Codes more severe than those suggested by the hooking injury were given most often as the result of bleeding associated with the
138
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 5 Results of 2- and t-tests (pooled data are indicated by square brackets) Groups
Treatments
Test value
df
p
Comments
2
Hook removal injuries by release method and hook style ± -test [TC], TJ, CJ for careful shaking Hook style [TC], TJ, CJ, TF for hook straightening Hook style [TC], TJ, CJ for gangion cutting Hook style [TC], TJ, CJ, TF for hook stripper Hook style
66.0 69.1 13.5 140.5
2 3 2 3
<0.00025 <0.00025 <0.0025 <0.00025
More More More More
Hook removal injuries by hook style and release method ± 2-test [TC], [TJ] for circle hooks Release method 3565.3
3
<0.00025
[TC], [TJ] for autoline hooks
3
<0.00025
More severe with hook stripper More severe with hook stripper
Release method
1737
Tag recovery rates by year and injury class, release method, or condition code ± 2-test 1993 releases Injury classa 15.1 2 1994 releases Injury classa 6.4 2 1993 circles Release method 10.2 2
<0.0005 <0.05 <0.005
1993 1994 1993 1994
<0.00025 <0.0025 <0.0025 <0.0025
releases releases releases releases
Condition Condition Condition Condition
(E, P, D) (E, P, D) (E, P) (P, D)
Growth in length by condition code ± t-test Annual growth for all releases Condition (P, D) a
18.9 13.7 13.8 10.9 3.483
2 2 2 2 145
<0.001
severe severe severe severe
with with with with
autoline circles circles circles
Minor>moderate>severe Minor>moderate>severe Shaking>gangion cutting> hook stripper E>P>D E>P>D E>P P>D Greater growth for better condition
Minor, moderate and severe.
Table 6 Halibut condition codes and criteria for assignment (adapted from Williams and Wilderbuer (1995)) Code
Description
Criteria
E
Excellent, no sign of stress
(1) Hook injuries are minor (limited to hook entrance/exit hole, torn lip) and located in jaw or cheek (2) Bleeding, if present, is minor and limited to jaw area (3) No penetration of the body by sand fleas (check eyes, fins, anus) (4) Muscle tone or physical activity is strong (5) Gills are deep red
P
Poor, alive but showing signs of stress
(1) Hook injuries may be severe: broken jaw; punctured eye (2) Vital organs are not injured (3) Bleeding may be moderate but not from gills (4) No penetration of the body by sand fleas (check eyes, fins, anus) (5) Muscle tone or physical movement may be weak or intermittent; little, if any, response to stimuli (6) Gills are red
D
Dead, no sign of life or, if alive, likely to die from severe injuries or suffocation
(1) Vital organs may be damaged: torn gills; gaff wound to head or body; jig injury to viscera; side of face torn loose or missing jaw (2) Sand fleas have penetrated the body (they usually attack the eyes first, but also fins and anus) (3) Severe bleeding may occur, especially from the gills (4) No sign of muscle tone; physical activity absent or limited to fin ripples or twitches (5) Gills may be red, pink, or white
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144 Table 7 Number of observations by condition codes and hook removal injury (1993 and 1994 observations combined) Hook removal injury
Number (and percentage) by condition code E
P
D
NI CO JO TL TC TJ CJ EYE TF SJ JB or JH TS
87 (93.5) 665 (98.2) 174 (95.1) 48 (98.0) 5516 (96.4) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0)
5 (5.4) 10 (1.5) 8 (4.4) 1 (2.0) 93 (1.6) 2104 (98.5) 3296 (97.3) 38 (100.0) 0 (0.0) 34 (97.1) 7 (43.8) 8 (100.0)
1 (1.1) 2 (0.3) 1 (0.5) 0 (0.0) 113 (2.0) 33 (1.5) 93 (2.7) 0 (0.0) 486 (100.0) 1 (2.9) 9 (56.3) 0 (0.0)
Total
6506 (50.6)
5604 (43.6)
741 (5.8)
139
3.4. Tag returns A total of 631 tags were recovered by the end of the 1996 ®shing season for an overall tag recovery rate of 5% (4.5% for 1993 releases and 5.2% for 1994 releases). Most of the tags were recovered in the area of tag release by commercial longline ®sheries (of 602 tags returned with recovery location, 505 were recovered less than 35 km from their release locations). 3.4.1. Tag return rate by hook removal injury Least severe injury classes showed higher recovery rates than the more severe injury classes (Table 9). While the overall recovery rate for the 1994 releases is higher than that for the 1993 releases, a signi®cant trend towards higher recovery rate for less severely injured ®sh holds for both the years. There is no signi®cant trend of declining recovery numbers for the more severe injuries in subsequent years, suggesting that injury-induced mortality does not increase over time. However, the small number of releases in these categories could mask this effect.
hooking and hook removal process (46 cases) and occasionally as the result of amphipod (sand ¯ea) predation (17 cases). Condition codes by hook removal method and hook style (Table 8) were consistent with the trend for hook removal injuries by these criteria. Generally, ®sh released by one of the three careful release methods were coded as excellent, with the particular exception of those ®sh which received poor codes as the result of our hook straightening technique. Depending on the hook style, about 66±76% of the ®sh removed by the hook stripper were coded as poor, with an additional 9±10% coded as dead.
3.4.2. Tag return rate by hook removal method Generally, the return rate for any of the three careful release methods is higher than that for ®sh removed using the hook stripper (Table 10). However, the return rates for all methods are very close, and signi®cant differences in return rate by removal method are seen only in one of the four possible hook style and release year combinations: 1993 releases from circle hooks.
Table 8 Number of observations and percent by condition codes, hook removal method, and hook style (1993 and 1994 observations combined) Hook removal method
Hook style
Number (and percentage) by condition code E
P
D
Careful shaking
Circle Autoline
1170 (87.2) 1010 (76.5)
158 (11.8) 267 (20.2)
14 (1.0) 43 (3.3)
Hook straightening
Circle Autoline
653 (59.6) 631 (60.5)
412 (37.6) 396 (38.0)
30 (2.7) 16 (1.5)
Gangion cutting
Circle Autoline
891 (91.6) 1159 (86.8)
55 (5.7) 142 (10.6)
27 (2.8) 34 (2.5)
Automated hook stripping
Circle Autoline
489 (13.3) 503 (24.4)
2804 (76.1) 1370 (66.5)
391 (10.6) 186 (9.0)
140
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 9 Tag recoveries by year of release and hook removal injury (number and percent) Hook removal injury
Year of release 1993
1994
Releases
Returns
%
Releases
Returns
%
Minor NI CO JO TL TC Total minor
51 283 109 35 1371 1849
7 14 5 4 72 102
(13.7) (4.9) (4.6) (11.4) (5.3) (5.5)
42 394 74 14 4351 4875
0 25 7 0 243 275
(0.0) (6.3) (9.5) (0.0) (5.6) (5.6)
Moderate TJ CJ EYE Total moderate
1229 599 1 1829
36 20 0 56
(2.9) (3.3) (0.0) (3.1)
908 2790 37 3735
40 140 2 184
(4.6) (5.0) (5.4) (4.9)
85 12 0 5 3 105
1 1 0 0 0 2
(1.2) (8.3) (±) (0.0) (0.0) (1.9)
401 23 8 5 3 440
13 0 1 0 0 14
(3.2) (0.0) (12.5) (0.0) (0.0) (3.2)
3783
160
(4.2)
9050
471
(5.2)
Severe TF SJ TS JB JH Total severe Total all injuries
3.4.3. Tag return rate by condition code The difference in return rates by condition code was signi®cant for both of the release years. Trends were similar between years (Table 11) and also similar to those seen by injury class. A notable difference between rates by injury class and rates by condition code are the return rates for dead ®sh `D'. In Table 9, rates for ®sh with more severe injuries were 1.9% and 3.2% in 1993 and 1994, respectively, while rates for
®sh coded dead in those years are 0.8% and 2.1%. While all ®sh with most severe injuries were coded as dead, the return rate of code `dead' ®sh is lower by about 50% when compared to the ®sh grouped by hook removal injury only. The difference arises from the additional dead codings as the result of bleeding or sand ¯ea infestation. There were 46 and 17 releases of ®sh with these conditions overall, with no subsequent recoveries.
Table 10 Tag recoveries by year of release, hook style, and hook removal method (number and percent) Release year
Hook style
Hook removal method Careful shaking
Hook straightening
Gangion cutting
Automated hook stripping
Total
1993
Circle Autoline
16 (5.8) 27 (7.1)
0 (±) 19 (4.4)
4 (3.7) 26 (4.8)
31 (2.3) 37 (5.4)
51 (2.9) 109 (5.3)
1994
Circle Autoline
56 (5.3) 57 (6.1)
45 (4.1) 38 (6.3)
52 (6.0) 44 (5.6)
116 (5.0) 64 (4.6)
269 (5.0) 203 (5.5)
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
141
Table 11 Tag recoveries by year of release and recovery, and condition code (number and tag recovery rate) Release year
Recovery year
Condition code E
P
D
1993
1993 1994 1995 1996 1993±1996 Total
29 29 18 23 99
(1.7) (1.7) (1.0) (1.3) (5.7)
12 20 9 19 60
(0.6) (1.0) (0.5) (1.0) (3.1)
0 0 0 1 1
(0.0) (0.0) (0.0) (0.8) (0.8)
1994
1994 1995 1996 1994±1996 Total
27 129 112 268
(0.6) (2.7) (2.4) (5.6)
16 99 76 191
(0.4) (2.7) (2.1) (5.2)
0 6 7 13
(0.0) (1.0) (1.1) (2.1)
3.5. Growth in length
3.6. Relative and absolute survival
Recovery fork lengths were recorded for 331 of the tag recoveries where the time at liberty ranged from 90 to 1263 days. The increase in the overall length ranged from 0 to 31 cm. Growth in centimeters was divided by the fractions of years at liberty to determine an annual growth rate (cm yearÿ1). The trends in growth by either hook removal injury or condition code are similar to those seen in recovery rate by both the criteria (Table 12). Fish with more severe injuries, or in poorer condition, appeared to grow in length more slowly than those ®sh in either better condition or with less severe injuries. The difference in growth rate was signi®cant between ®sh in poor and dead condition.
Survival rates for injury classes or conditions were estimated by using the proportion of ®sh recovered in each class, and applying that proportion to the estimated survival of ®sh in excellent condition (Table 13). Sixty-nine percent of halibut with moderate injuries are expected to survive, while about 2/3 as many, or 43%, of ®sh with severe injuries survive. While the 73% survival estimate of poor condition ®sh is similar to that for ®sh with moderate injuries, the survival of ®sh judged to be in dead condition is only 26%, just over half the survival rate of ®sh with severe hook removal injuries. While the dead condition ®sh have the worst
Table 12 Annual growth in length by hook removal injury and condition code (includes recoveries from both 1993 and 1994 releases) Number of observations
Annual growth (cm)
Std. dev.
Hook removal injury NI CO JO TL TC TJ CJ TF TS
2 22 9 2 183 45 87 6 1
6.10 4.09 2.36 3.03 3.46 3.19 2.90 2.53 0.00
3.18 2.59 1.69 ± 2.58 2.68 2.55 2.00 ±
Condition code E P D
210 141 6
3.51 2.99 2.53
2.56 2.56 2.00
142
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
Table 13 Relative survival by injury class and condition code as inferred by tag recovery rates (includes recoveries from both 1993 and 1994 releases) Survival by injury class Injury Class
Injuries in class
Tag recovery rate*
Survival
Minor Moderate Severe
NI, CO, JO, TL, TC TJ, CJ, EYE TF, SJ, TS, JB, JH
5.5% 4.3% 2.6%
97% 76% 46%
Condition code
Description
Tag recovery rate*
Survival
E P D
Excellent Poor Dead
5.6% 4.4% 1.5%
97% 76% 26%
Survival by condition code
a
Determined as average of recovery rates from 1993 and 1994 releases
survival, clearly the term `dead' is a misnomer for this group. 4. Discussion Hooking locations are consistent with our earlier study of hook removal injuries (Kaimmer, 1994); the great majority of halibut, over 95% overall, are captured on either hook style with the hook encircling the jaw bone, usually with the point of the hook penetrating the tissue of the cheek muscle. This hooking location is characteristic of the circle or modi®ed circle hook for many species (Johannes, 1981; Bjordahl and Lokkeborg, 1996; Kaimmer and Trumble, 1997). Proper execution of any of the three careful release techniques either leave the hook in place, which may eventually fall out (gangion cutting), or result in the hook being removed back out the same way as it entered (careful shaking and hook straightening). They leave no additional injury beyond that caused by the hooking itself. No short-term mortality was observed over periods of 4 or 10 days, even for ®sh with severe injuries. This observation is conservative, since small tank sizes and rough weather during the tank holding could be expected to increase stress conditions during holding. Tag recovery rates, by either class of hook removal injury or condition code, showed signi®cant differences. From these tag returns, the survival of poor condition halibut is estimated at 73%, while the survival of dead halibut is estimated as 26%. From
the perspective of mortality, the mortality of poor ®sh is almost eight times as great (27% compared to 3.5%), while the mortality of dead ®sh is over 21 times greater than that of excellent ®sh (74% compared to 3.5%). These numbers agree with those currently used for the management in direction, but not in magnitude, and suggest that poor and dead condition ®sh survive at higher rates than currently assumed. While more severe hook injuries appear to associate with reduced growth rates in ®sh which are subsequently recaptured, even these are shown only as trends in the data, the differences not being large enough to be statistically signi®cant. These differences were signi®cant in an earlier study with heavier gear (Kaimmer, 1994), and, if present, reduced growth of survivors could represent an additional component of loss to the ®shery. 5. Conclusion All three of the careful release methods used in this study are approved methods to remove halibut from longline gear. However, differences in hook strength or operator skill can alter the success of any of these techniques. Since hook strength and operator skill appear to be important variables, removal method alone is not suf®cient to estimate survival rates. We achieved fairly consistent, and signi®cantly different, estimates of survival based on the condition factors developed by IPHC for use by ®shery observers.
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
While the nomenclature and mortalities associated with the condition codes may need to be changed or realigned, the applications of the codes themselves seem to function well as a predictor of individual halibut survival. Currently, setline bycatch mortality is assessed at 3.5% for ®sh in an excellent condition, 52% for ®sh in poor condition, and 100% for ®sh in dead condition. Although not designed to assess mortalities associated with condition, the results of Kaimmer (1994) suggest that less than about 50% of poor condition ®sh actually die while only about 75% of dead condition ®sh die. Our study is the ®rst designed speci®cally to determine longline bycatch mortality rates associated with hook removal method, hook removal injury, or condition code, and suggests that even lower mortality rates should be used, 27% and 74% for poor and dead condition ®sh. It will be necessary to reassess both the nomenclatures used for condition codes and the parameters used in bycatch calculations for the light gear longline ¯eets in the north Paci®c. The need for a change in nomenclature is obvious. The use of `dead' as a description of a category where all ®sh do not die is clearly inappropriate. The implementation of these changes requires further study. One complicating factor lies in the application of the condition code criteria. In our study, most ®sh in dead condition were so coded as the result of hook removal injuries (criteria 1, 3, or 5 in Table 6), with only a small proportion of the dead codings resulting from predation by sand ¯eas (criterion 2). A survey of observers at the end of the 1996 ®shing season gave sand ¯ea predation as the most common reason for coding halibut as dead (Sadorus, 1996). Although less than 10% of the halibut bycatch in the sable®sh and Paci®c cod longline ®sheries are coded as dead (Williams, 1996), it is very likely that our releases of ®sh in this condition do not adequately represent those observed in the ®shery. None of the ®sh released in our study in which sand ¯eas had penetrated the body were subsequently recovered, for an implied survival of these ®sh of 0%. A survival of 0% for the dead condition ®sh in the commercial ®shery might be very appropriate. The most common reason given for coding ®sh as poor condition was the injuries sustained while being released from the hook, suggesting that the mortality estimated for poor condition ®sh from this study should be representative of
143
that experienced by ®sh coded as poor condition in the commercial ®shery. Acknowledgements We are grateful to J. Nielson, B. Leaman, and an anonymous reviewer for their comments on an earlier draft. Thanks are also due to Ron Hegge, skipper of the Rebecca B, and his crew for their co-operation and assistance during the experiments.
References Bjordahl, A., Lokkeborg, S., 1996. Longlining. Fishing News Books, Oxford, UK. Johannes, R.E., 1981. Words of the Lagoon ± Fishing and Marine Lore in the District of Micronesia. University of California Press, CA. Kaimmer, S.M., 1994. Halibut injury and mortality associated with manual and automated removal from setline hooks. Fisheries Res. 20, 165±179. Kaimmer, S.M., Trumble, R.J., 1997. Survival of Pacific halibut released from longlines: hooking location and release methods. In: Fisheries Bycatch: Consequences and Management. Alaska Sea Grant College Program Report No. 97 (2), University of Alaska Fairbanks, pp. 101±105. Myhre, R.J., 1974. Minimum size and optimum age of entry for Pacific halibut. Int. Pac. Halibut Comm. Rep. 55, IPHC, Seattle, WA. Nielson, J.D., Waiwood, K.G., Smith, S.J., 1989. Survival of Atlantic halibut (Hippoglossus hippoglossus) caught by longline and otter trawl gear. Can. J. Fish. Aquat. Sci. 46(5), 887± 897. Peltonen, G.J., 1969. Viability of tagged Pacific halibut. Int. Pac. Halibut Comm. Rep. 52, IPHC, Seattle, WA. Sadorus, L.L., 1996. Results from 1996 NMFS observer questionnaires. Int. Pac. Halibut Comm. Report of Assessment and Research Activities (unpublished), IPHC, Seattle, WA, pp. 235±248. Sadorus, L.L., Williams, G.H., 1996. The 1996 groundfish fishery off Alaska: Groundfish catches, halibut bycatches, and bycatch rates. Int. Pac. Halibut Comm. Report of Assessment and Research Activities (unpublished), IPHC, Seattle, WA, pp. 169±188. Williams, G.H., 1996. Pacific halibut discard mortality rates in the 1990±1995 Alaskan groundfish fisheries, with recommendations for monitoring in 1997. Int. Pac. Halibut Comm. Report of Assessment and Research Activities (unpublished), IPHC, Seattle, WA, pp. 211±228. Williams, G.H., Wilderbuer, T.K., 1995. Discard mortality rates of Pacific halibut bycatch: Fishery differences and trends during 1990±1993. In: Proceedings of the International Symposium on
144
S.M. Kaimmer, R.J. Trumble / Fisheries Research 38 (1998) 131±144
North Pacific flatfish. Alaska Sea Grant College Program Report No. 95 (4), University of Alaska Fairbanks, pp. 611± 622. Wilson, W.J., Weeks, H.J., 1996. Policy and regulatory measures to control incidental mortality of Pacific halibut in groundfish
fisheries of the North Pacific ocean. In: Meyer, R.M., Zhang, C., Windsor, M.L., McCay, B.J., Hushak, L.J., Muth, R.M. (Eds.), Fisheries Resource Utilization and Policy, Proceedings of the World Fisheries Congress, Theme 2. Oxford and IBH Publishing, New Delhi, pp. 219±239.