Tentacle-breakage mechanism for the neon flying squid Ommastrephes bartramii during the jigging capture process

Fisheries Research 121-122 (2012) 9–16

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Tentacle-breakage mechanism for the neon flying squid Ommastrephes bartramii during the jigging capture process Kohei Kurosaka a,b , Hideyuki Yamashita b , Michio Ogawa b , Hiroshi Inada c,∗ , Takafumi Arimoto c a

Graduate Course of Applied Marine Bioscience, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan Marine Fisheries Research and Development Center (JAMARC), Fisheries Research Agency (FRA), Yokohama, Kanagawa 220-6115, Japan c Department of Marine Bioscience, Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan b

a r t i c l e

i n f o

Article history: Received 5 July 2011 Received in revised form 26 December 2011 Accepted 28 December 2011 Keywords: Neon flying squid Ommastrephes bartramii Squid jigging Tentacle breakage Logistic curve analysis

a b s t r a c t In squid jigging operations for neon flying squid (Ommastrephes bartramii), 30–40% of hooked squid are estimated to fall off (i.e., become detached) from the jigs during the drum-hauling process, caused by breakage/severance of the hooked tentacle(s). Reducing fall-off events can lead to higher productivity and more efficient use of the squid resource. In the present study, there were 950 fall-off events either directly observed or assessed from the residue of tentacle(s) left on the jigs compared with the 1720 total captures, which comprises 35.6% of 2670 total hooked squids. The fall-off ratio according to the mantle length (ML) was examined using logistic curve analysis and a higher fall-off ratio for smaller squid was confirmed through size selectivity curve analysis. F50 , the 50% probability of fall off from the jig, was estimated to be 37.4 cm ML. The breaking strength of a single tentacle was determined to be similar to the body weight (BW) of squid smaller than 41.4 cm ML, indicating a high possibility of tentacle breakage in the case of 1 tentacle grabbing the jig for smaller-sized squid. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Neon flying squid (Ommastrephes bartramii) are a highly migratory oceanic species distributed globally in subtropical and temperate regions. However, they are only exploited systematically in the northwestern Pacific Ocean (Roper et al., 2010). This species is also one of the major target species for Japanese squid fisheries, together with other species such as Argentine shortfin squid (Illex argentinus) in the southwestern Atlantic Ocean, Wellington flying squid (Nototodarus sloani) in New Zealand waters and jumbo flying squid (Dosidicus gigas) in the southeastern Pacific Ocean as well as Japanese flying squid (Todarodes pacificus) for coastal and offshore squid jigging near Japan (Yatsu, 2003). Neon flying squid were exploited with high-seas drift gillnets in the North Pacific from the 1970s until the moratorium declaration of the high-seas drift gillnet in 1993 (Burke et al., 1994). To meet the demand resulting from the decline of the Japanese flying squid catch, which had a peak catch of 260,000 tons in 1983 (Ichii et al., 2006) and accounted for half of the total squid caught by Japanese boats, alternative methods of exploitation were required. An alternative fishing strategy using the jigging technique for neon flying squid, developed through exploratory trials with fishing lights and automated jigging systems and improved through

∗ Corresponding author. Tel.: +81 3 5463 0476; fax: +81 3 5463 0360. E-mail address: [email protected] (H. Inada). 0165-7836/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2011.12.016

machinery and jigs for the larger and heavier body of this species, began replacing the drift gillnet (Fisheries Agency, 1994, 1995, 1996). Even with these efforts to establish an efficient jigging technique, the catch has remained low (8000–15,000 tons since 2001) (Kurosaka et al., 2009) as a result of the low primary production level in the North Pacific caused by the regime shift in 1999 (Minobe, 2002) and increased international competition (Ichii et al., 2006). High operation costs with lower profitability in high-seas fishing grounds have led to a decrease in the number of Japanese jigging boats over the last decade. A technical approach to improving catch efficiency is strongly required, especially for minimizing fall-off events during jigging. Fall-off events during jigging for neon flying squid have been previously reported through examinations of tentacle breakage during the jigging process (Ueno and Sakai, 2010). Murata et al. (1981) examined the regeneration of the tentacles caused by damage during both the jigging and drift gillnet catch and concluded that squid without tentacles survived and exhibited a similar growth pattern to that of normal squid. Even with this positive result for the survival of squid after tentacle breakage, the catch loss from jigging needs to be minimized to improve the profitability of jigging fisheries. Several attempts have been made to develop new jig types by modifying the hook shape and size (Guo et al., 1997; Yada et al., 1997). However, these have not been effective in markedly reducing fall-off events or practical to employ. In the present study, the tentacle-breakage mechanism for neon flying squid was investigated through onboard monitoring of conditions

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K. Kurosaka et al. / Fisheries Research 121-122 (2012) 9–16

Fig. 1. (a) A photograph showing the elongation of the tentacle above the surface. (b) The remaining tentacles left on the rack as an indication of the breakage point.

leading to successfully hooking, and conditions leading to fall-off events, based on the different body parts hooked during jigging. Measurements of tentacle breaking strength were also conducted. Based on this basic background information, problems related to and possible avenues of research to minimize fall-off events of neon flying squid during the jigging process are discussed.

2. Materials and methods Onboard research was performed on the commercial squid jigging vessel, “Hakurei-maru No. 8” (276 GT, 56 m LOA), employed for the research cruise by the Japan Marine Fisheries Resource Center. The fishing ground was located in the North Pacific (lat. 40◦ N–46◦ N, long. 150◦ E–170◦ W), and the cruise took place from June 6th to September 30th, 2006. The boat was equipped with automated squid-jigging machines (MY-10: Towa Denki Seisakusyo Co., Ltd.); 22 machines on each side were arranged along the gunwale. Each machine had 2 drum reels for releasing and hauling the fishing line with 15 jigs attached. The jigged squid were hauled up by the rotation of the drum reel through the roller set at the tip of the netting rack. The jigging machines repetitively cycle the fishing lines with an up-and-down motion during the fishing operation. We followed the common operation specifications for neon flying squid by utilizing the CM-21 jig (Daiwa Fishing Tackle Co., Ltd.), which has a stem length of 13.5 cm with 2 tiers of 8 hooks with each hook measuring

16 mm long and 1.5 mm in diameter. The drum reel is a diamond type with an octagonal shape and a winding speed of 65 rpm. 2.1. The monitoring of catch and fall-off events Catch and fall-off events were monitored for the 22 jigging machines on the starboard side, from 30 min after sunset and for a total of 2 h each day, from June 23rd to September 25th, 2006. A total of 36 monitoring records (72 h) were completed. The fall-off events can be classified into 3 patterns. The “fell off by the roller” pattern occurred when the squid came into contact with a roller on the rack. The “fell off above the surface” pattern occurred when the squid fell off between the sea surface and the roller. Both of these fall-off events can be monitored and recorded. The last event was recorded by assessing the residue of tentacles remaining on the jig and assuming that the squid tentacle was severed, resulting in the tentacle separating from the body while in the water during the hauling process; this was defined as the “fell off in the water” pattern. Fig. 1a shows the elongation of a tentacle for a squid jigged and hauled up immediately above the surface and before falling off as a result of tentacle breakage. The remaining tentacles left on the rack were carefully inspected to identify the breakage point, which was mostly at the proximal end of the tentacle near the head, as shown in Fig. 1b. In Fig. 2, the breakage positions of the tentacles are identified for an individual that lost 2 tentacles in Fig. 2a, and

Fig. 2. (a) An indication of the breakage points at the proximal end of tentacles for squid having lost 2 tentacles. (b) Squid with the regenerating patterns at the tip of the remaining parts of tentacles. The scale bar indicates 1 cm.

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the jigs (N), the proportion (p) of the fall-off ratio is expressed by the following equation: p=

n

(1)

N

where n is the number of squid that have fallen off, judged from the residue of tentacles on the jigs. The parameters ˛ and ˇ of the logistic curve were then applied for each squid TCL (l) as p=



1 1 + exp(˛ + ˇ × l)



(2)

When n individuals had fallen off out of N individuals hooked on the jig, the log-likelihood (ln L) for captured squid (N − n) can be expressed by the following equation: ln L =





ln(N!) − ln(n!) − ln[(N − n)!] + n ln(ˆp) + (N − n) ln(1 − pˆ )

(3)

The maximized log-likelihood function, using Solver on MS-Excel (Tokai, 1997), was applied to determine the logistic curve parameter of ˛ and ˇ to attain the 50% selection length by means of analogy from fishing gear selectivity (Wileman et al., 1996). The goodness of curve fit was calculated from the deviance, and a significant difference was assessed using the likelihood ratio test (Dobson and Barnett, 2008) by comparing the logistic model and the full model with the monitored data. According to the logistic model analysis, the ML of the 50% fall off (F50 ) is defined as a 50% probability of fall-off events among all the squid hooked on the jig, which were specified by the following: F50 = − Fig. 3. A tentacular club of a neon flying squid.

for another individual in Fig. 2b showing the regenerating pattern at the tip of the remaining part of the tentacles.

2.2. Squid body size and fall-off ratio The mantle length (ML) and body weight (BW) of the captured squid were measured to determine the effect of body size in relation to the fall-off events. The tentacles of captured and fallen-off squid were also sampled and measured for the tentacular club length (TCL), determined as the length from the first sucker position, the carpus, of the tentacular club base to the tentacular club tip, the dactylus (Roper and Voss, 1983), as shown in Fig. 3. From the relationship between the ML and the TCL of the captured squid, the body size of the fallen-off squid were estimated and analyzed to understand the relationship of fall-off events to squid body size as expressed in ML and TCL. A total of 100 tentacles left on the jig were sampled for TCL measurement. Among the captured squid, detailed measurements were conducted for 60 individuals collected at the same time as the sampling of the residue tentacles to estimate the ML of squid that had fallen off in the water from the measured TCL. The ML and TCL of captured squid were measured for 2897 individuals in total to estimate the relationship. Measurements were conducted after allowing the tentacles to slacken (by leaving them for more than 30 min on a flat floor) for both the fallen-off squid and for captured squid by separating the tentacles pulled off of the body immediately after capture to avoid measurement error caused by tentacular muscle shrinkage by rigor mortis. To estimate the fall-off ratio according to the ML, we assumed a binomial distribution for captured or fall-off events to estimate the relationship between the ML and fall-off ratio (%) using the logistic model (Dobson and Barnett, 2008). Among all the squid hooked on

˛ ˇ

(4)

where ˛ and ˇ are the parameters of the logistic function to be estimated (Sparre et al., 1993). The TCL was then converted to the ML with the linear regression analysis from the data of captured squid. 2.3. The measurement of the tentacle breaking strength The breaking strength of tentacles was measured by a hand scale (Sanko Seikojyo Co., Ltd.) attached to the jig and using the modified methods of Chen (1996) and Chen et al. (2008). Three types of hand scales were used, including 1 kg, 5 kg and 10 kg scales, according to the BW of the sample. Body weight measurements were taken immediately after being hauled onboard. The squid body was laid down on a flat area by fixing the mantle position, and the static breaking strength was recorded by hooking the middle position of a tentacular club to the jig and pulling in a horizontal direction, increasing the pressure progressively until the tentacle was torn from the base (Fig. 4). Both the right and left tentacles were measured for 30–50 squid daily during the survey period, and 1-tentacle measurements of 885 for the left and 891 for the right tentacle (total of 1776) were recorded as well as 871 records for 2-tentacles measurements. The breaking strength (S) is related to the cross-sectional area of the tentacle, which is assumed to be proportional to the square of the ML as S ∝ ML2

(5)

The BW is proportional to the cube of ML as BW ∝ ML3

(6)

The breaking strength (S) can be expressed by the following equation as S = k × BW 0.67

(7)

This equation was applied to examine the fall-off events by considering the breaking strength of tentacles in relation to a squid’s body weight (Guo et al., 1997).

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Fig. 4. The measurement of the breaking strength of tentacle(s) by fixing the mantle position and pulling with a spring-scale attached to the jig stalk until the tentacle was torn off from the base.

The BW of fallen-off squid were calculated from the estimated ML of the sampled tentacles by applying the relationship between TCL and ML and that between ML (cm) and BW (Kg) by converting BW (g) to ML (mm) as BW = 4 × 10−5 ML2.9482 according to Koya et al. (1997). The breaking strength for 1- and 2-tentacles measurements were then analyzed to examine the relationship between ML and BW data.

Table 1 Size range of captured and fallen-off squid accoding to the hooked patterns. Hooked pattern

Situation

3 or more arms Tentacle Tentacle

Captured Captured Fallen-off

Mantle length ± SD (cm) 36.8 ± 6.6a 28.4 ± 4.4b 28.3 ± 5.3b

n 33 4 4

Different superscript letters indicate a significant defference (Periz’s method; p < 0.05).

3. Results 3.1. The monitoring of catch and fall-off events During the jigging operation, the catch and fall-off events were monitored using the detailed recordings of the hooked conditions classified in Fig. 5 and summarized in Fig. 6. The 950 fall-off events either observed or assessed from the residue of tentacles remaining on the jigs (compared with a total of 1720 captures) accounted for 35.6% of fall-offs among a total of 2670 records of all hooked squid, which was estimated as the total number of specimens captured and fall-offs. The fall-off events were further classified into 3 categories as fell off in the water (838 events, 31.4% among all hooked squids), fell off above the surface (71 events, 2.66% among all hooked squids) and fell off by the roller (41 events, 1.54% among all hooked squids). The hooked squid were classified into 4 patterns depending on which part of the body was hooked: the tentacle(s), by 1 or 2 arms, by 3 arms or more, or at the buccal mass, as shown in Fig. 5.

Among all of the fall-off individuals, the fell off in the water pattern was dominant and was observed from the residue of tentacles. The fell off above the surface and fell off by the roller patterns were observed relatively rarely, and the majority were tentaclehooked individuals, with some arm-hooked squid. This finding was markedly different from the hooking patterns of captured squid: 1618 individuals were firmly hooked by the arms, whereas there were only a few cases of the tentacle-hooked pattern. This implies that tentacle breakage is the major cause of fall-off events, especially when the squid are still in the water during the hauling process. Table 1 shows the size range of squid by the ML measured for captured squid and estimated for the fall-off squid from the residue TCL according to the hooked position. Nearly all captured squid were hooked firmly by 3 or more arms, which was significantly more than in the other cases (Table 1; p < 0.05, Peritz’s method). Although there were too few observations of tentacle-hooked squid

Fig. 5. Hooking patterns of different hooked position of neon flying squid.

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Fig. 6. Hooking patterns of neon flying squid according to the catch and fall-off events.

in both captured and fall-off specimens for a statistically robust analysis, the smaller squid tended to attack and hold the jigs with their tentacles rather than their arms.

were much larger than the squid that had fallen off, indicating that smaller squid tended to fall off from the jig more frequently than larger squid. The logistic curve for the fall-off ratio according to the TCL was estimated as

3.2. Squid body size and fall-off ratio Fig. 7 shows the frequency histogram of TCL for comparison between the size of the captured and fall-off squid; these values were applied to the logistic model of Eq. (2) to evaluate the falloff ratio through a selectivity-curve analysis. The captured squid

p=



1 1 + exp((−6.517) + 0.337 × l)

(8)

By substituting the ˛ and ˇ values in Eq. (4), F50 was determined as 19.3 cm, as shown in Fig. 7. To compare the size range of captured and fallen-off squid, the body size of squid that had fallen off were estimated from the residue tentacle size with the TCL. The relationship between the TCL and the ML was analyzed from the data of captured squid and is shown in Fig. 8. The linear regression line is determined as

ML = 1.09 TCL + 16.3

Fig. 7. The fall-off ratio according to the mantle length, indicating an F50 of 19.3 cm in TCL.



r = 0.75

(9)

The ML of squid that had fallen off was estimated using this equation based on the length of the residual tentacle. F50 , which shows the size of half of the individuals that fell off from the jig, was then estimated as 37.4 cm ML. As a result of the likelihood ratio test (deviance = 27.4, df = 35, p = 0.82), no statistically significant difference (p > 0.05) was observed between the full model and the logistic model. Therefore, the logistic model can be effectively used as a goodness-of-fit curve.

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60

10.0

Breaking strength of tentacle (kgf)

R = 0.76

n=2897

Mantle length (cm)

50 40 30 20

10.0

2 -Tentacles 1-Tentacle Body Weight

9.0 8.0

9.0 8.0

7.0

7.0

6.0

6.0

5.0

5.0

4.0

4.0

3.0

3.0

2.0

2.0

1.0

1.0 0.0

0.0

10

Body weight (kgf)

14

20

25

30

35

40

45

50

55

60

Mantle length (cm) 0 0

10

20

30

40

Tentacularclub length (cm)

Fig. 10. A comparison of tentacle breaking strength and body weight in air according to the mantle length.

Fig. 8. The mantle length according to the tentacular club length.

4. Discussion 3.3. The measurement of the tentacle breaking strength During the measurement of the tentacle breaking strength (as previously described), the breakage position was also monitored as the tentacle elongated by the thinning of the proximal end before breakage. The other parts of the tentacle, where the suckers were distributed, did not elongate before breakage, and the same breakage position pattern was confirmed in the inspected residual tentacles. The breaking strength of a tentacle ranged from 0.2 to 5.8 kgf for 1-tentacle measurement and 0.5–9.5 kgf for 2 tentacles, which were related to BW as shown in Fig. 9. This finding indicates that greater breaking strengths were associated with larger squid, based on the regression analysis of breaking strength (S) results for 1 tentacle (n = 1847) versus the BW. It was applied to Eq. (7) and determined that S = 1.38 × BW 0.67 (r = 0.84) for 1 tentacle and S = 2.29 × BW 0.67 (r = 0.84) for 2 tentacles. The breaking strength, according to the ML, is shown in Fig. 10, which was derived together with the BW curve from the equation of Koya et al. (1997); for 1 tentacle, the breaking strength was found as S = 1.29 × 10−3 ML2.0 ; for 2 tentacles, S = 1.81 × 10−3 ML2.0 . The ML at which the BW is greater than the breaking strength was 41.4 cm for 1 tentacle and 57.7 cm for 2 tentacles. However, the 1-tentacle breaking strength approximated the BW even for squid smaller than 41.4 cm ML.

2 -Tentacles(n=871) 1 -Tentacle (n=1776)

Breaking strength of tentacle (kgf)

10

r=0.84

9 8 7 6

r=0.84

5 4 3 2 1 0 0

1

2

3

4

5

6

Body weight (kg) Fig. 9. The breaking strength of tentacle(s) according to body weight in air.

Jigging fisheries for neon flying squid are operated in the North Pacific around the fishing grounds east of 170◦ E longitude and from 35◦ N to 45◦ N latitude. The season runs from mid-May to late July, targeting squid of approximately 35 cm ML of the autumn cohort together with smaller squid of the winter/spring cohort (Ichii et al., 2004; Murata, 1990). In the 2007 research cruise report of Yoshi maru No. 2 (Yamashita et al., 2008b), the size composition of the neon flying squid was recorded as 36 cm ML (ranging from 26 to 46 cm) for peak mode size in May, 36 cm ML (ranging from 21 to 49 cm) in June, and 38 cm ML (ranging from 24 to 50 cm) in July. According to the monitoring analysis results in this paper, half of the jigged squid in the 37.4 cm ML size fell off the jigs as a result of tentacle breakage, indicating the need to reduce the loss of hooked squid of the main target size group. Tentacles can be severed from the body during the hauling process, mainly while the squid are still in the water, and occasionally above the surface and in the roller position. The breaking strength of tentacles is related to the body size and is stronger in larger squids, whereas the BW exceeds the tentacle breaking strength for ML over 41.4 cm for squid attached by 1 tentacle and over 57.7 cm ML for squid attached by 2 tentacles, as illustrated in Fig. 10. This finding implies that larger sized squid can be lost as a result of tentacle breakage, while the observed results of the hauling process indicated a higher catch for larger squid that were hooked not by the tentacle(s) but mainly by 3 or more arms, ensuring a firmly hooked condition, as shown in Table 1. Chen (1996) and Chen et al. (2008) reported that the breaking strength of the arms was 2–3 times higher than that of the tentacle, which agrees with the findings of the present study of the higher catch ratio of larger squid as a result of the arm-hooked patterns. Tentacle breakage during hauling is likely caused by dynamic processes, such as the escape reactions of hooked squid against the upward-moving jig. As a result, the static measurements of breaking strength of the tentacle in this paper are unlikely to accurately recreate the situation during such dynamic activity and are probably an underestimate of the actual impact to the tentacle(s). The major cause of tentacle breakage was estimated to occur during the hauling process in the water as a result of the body drag resistance by upward movement and by the escape response involving jet blowing (Thompson and Kier, 2002), producing an increased strain on the tentacle(s). This finding implies that most of the tentacle-hooked squid fell off in the water, with a lower number of observations of fall-off events above the surface and by the roller. A high strain can be produced by the muscular contraction of the

K. Kurosaka et al. / Fisheries Research 121-122 (2012) 9–16

mantle during jet blowing during the escape response in water, and this is likely to induce a high probability of tentacle breakage. The tentacle strike movement for prey capture in the squid Loligo pealei was analyzed by Kier and van Leeuwen (1997) using highspeed film recordings to examine the elongation of the tentacle stalk when the club is in contact with the prey and when attacking using the suckers. These authors also reviewed the sequential phases of prey capture by squid, observing the squid’s body positioning during the strike, to explain the squid’s use of its arms to subdue and manipulate the prey into an appropriate position to be eaten. Additionally, Kier and van Leeuwen determined that after initial capture, the tentacles are not involved in further prey manipulation. This previous research can assist in understanding the capture process involved with jigging machines; the tentacle(s) strike the jig first, and the arms are then manipulated to hold the jig firmly, which could be achieved during the hauling process of the jig line. The jig line is hauled upward by the drum reel motion of the jigging machine to haul up the squid body, and the tentacle is elongated in response to the body drag resistance as it is towed upward in the water and by an escape response involving the squid’s propulsive jet. This escape response may cause the tentacle(s) to break, as observed by the residual tentacles on the jig, especially for large-bodied squid such as neon flying squid. The size ranges of captured and fallen-off squids in Fig. 8 show that smaller squid tended to fall off as a result of tentacle breakage in accordance with the lower tentacle breaking strength of smaller squid (Fig. 9). The comparison of BW and breaking strength based on the ML of squid, shown in Fig. 10, indicates that 1 tentacle cannot hold the BW in air for squid with an ML over 41.4 cm, whereas even in the case of the smaller squid, the tentacle breaking strength closely approximates the BW. The breaking of tentacles during the jigging process is not directly related to the BW in air, as described above, but to the strong strain on the tentacle(s) in response to the body drag resistance during the upward jig movement and the squid’s jet-blowing action during the struggle to escape. Cephalopod species can autotomize limbs as a defense mechanism by losing 1 or more arms/tentacles, similar to the tails of reptiles or claws of crabs (Fleming et al., 2007). As another response, Ocythoe tuberculata can use a specially modified arm, the hectocotylus, during mating behavior to transfer spermatophores by placing this limb into the female’s mantle cavity (Okutani, 1990). The tentacle breakage for neon flying squid during jigging may be a different mechanism than autotomy, such as a mechanical severance due to a given strain. However, this breakage can also effectively work as a defensive strategy by which the tentacle is severed, enabling escape from a potentially lethal situation. Even after losing tentacles, individuals are able to maintain the same growth pattern and the regeneration of the lost tentacle(s), as described previously (Murata et al., 1981), likely indicating minimal damage to the stock. However, the high amount of catch loss as a result of tentacle breakage should be minimized to increase efficiency. The solution for minimizing the catch loss as a result of fall-off events may be increasing arm-hooking catches (not by the tentacles), as shown in Fig. 6. Nearly all of the captured squid were hooked by the arms. According to Table 1, squid captured by the arm-hooked pattern are much larger than tentacle-hooked squid in both captured and fallen-off specimens. This result is related to the feeding behavior of squid, as the tentacles strike first and then the arms hold the prey (Kier and van Leeuwen, 1997). Squid are forced to move upward at the same speed as the jig motion. However, holding the jig by the arms after the tentacles strike alleviates the strain on the tentacles resulting from the high drag resistance of the squid’s body, thereby reducing the potential for tentacle breakage. The swimming performance of squid may be the key to understand why larger squid are mainly hooked by the arms, which

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may be associated with the higher jet propulsion force in response to mantle muscle contraction in the squid’s efforts to follow the movement of the jig. This action provides larger squid with the opportunity to manipulate the jig with its arms as a result of their higher speed and maneuverability during the jigging process (Bartol et al., 2001a,b; Webber and O’Dor, 1986). Yamashita et al. (2008a) reported that the fall-off ratio differed according to the position of the jigging machine along the boat, as the ship’s motion was affected by sea conditions. This finding may suggest another approach to adjust the motion of the jig and jig-line hauling speed to increase the arm-hooked pattern even among the smaller squid and minimize the catch loss resulting from tentacle breakage. Acknowledgments We would like to thank Dr. T. Watanabe, Dr. M. Sakai, Dr. Y. Ochi, the Fisheries Research Agency and Dr. T. Ichii of the Fisheries Agency for their encouragement and useful comments in preparing the manuscript. We would also like to thank the Fishing Master, Mr. K. Miyazaki, and his crew on the research cruise of R/V Hakurei-maru No. 8 for their help with onboard tasks. We gratefully acknowledge Mr. T. Miki from Towa Denki Seisakusho Co., Ltd., for programming the automated jigging machine. Dr. E. Kenjo critically read earlier versions of the manuscript. References Bartol, I.K., Mann, R., Patterson, M.R., 2001a. Aerobic respiratory costs of swimming in the negatively buoyant brief squid Lolliguncula brevis. J. Exp. Biol. 204, 3639–3653. Bartol, I.K., Patterson, M.R., Mann, R., 2001b. Swimming mechanics and behavior of the shallow-water brief squid Lolliguncula brevis. J. Exp. Biol. 204, 3655–3682. Burke, W.T., Freeberg, M., Miles, E.L., 1994. United Nations Resolutions on driftnet fishing: an unsustainable precedent for high seas and coastal fisheries management. Ocean Dev. Int. Law. 25, 127–186. Chen, X.J., 1996. On the broken strength of Todarodes pacificus and Ommastrephes bartramii tentacles. J. Shanghai. Fish. Univ. 5, 115–118 (in Chinese). Chen, X.J., Liu, B.L., Chen, Y., 2008. A review of the development of Chinese distantwater squid jigging fisheries. Fish. Res. 89, 211–221. Dobson, A.J., Barnett, A.G., 2008. Binary variables and logistic regression. In: Dobson, A.J., Barnett, A.G. (Eds.), An Introduction to Generalized Linear Models. , third ed. CRC Press, London, pp. 123–147. Fisheries Agency, 1994. Cruise Report 1993 on Fishing Ground Survey for Neon Flying Squid Ommastrephes bartramii. Fisheries Agency, Japan (in Japanese). Fisheries Agency, 1995. Cruise Report 1994 on Fishing Ground Survey for Neon Flying Squid Ommastrephes bartramii. Fisheries Agency, Japan (in Japanese). Fisheries Agency, 1996. Cruise Report 1995 on Fishing Ground Survey for Neon Flying Squid Ommastrephes bartramii. Fisheries Agency, Japan (in Japanese). Fleming, P.A., Muller, D., Bateman, P.W., 2007. Leave it all behind: a taxonomic perspective of autotomy in invertebrates. Biol. Rev. 82, 481–510. Guo, B.H., Yada, S., Toda, M., Inada, H., 1997. Mechanical characteristics of improved jigs to prevent squid falling off in the capturing process. Fish. Sci. 63, 9–14. Ichii, T., Mahapatra, K., Okamura, H., Okada, Y., 2006. Stock assessment of the autumn cohort of neon flying squid (Ommastrephes bartramii) in the North Pacific based on past large-scale high seas driftnet fishery data. Fish. Res. 78, 286–297. Ichii, T., Mahapatra, K., Sakai, M., Inagake, D., Okada, Y., 2004. Differing body size between the autumn and the winter-spring cohorts of neon flying squid (Ommastrephes bartramii) related to the oceanographic regime in the North Pacific: a hypothesis. Fish. Oceanogr. 13, 295–309. Kier, W.M., van Leeuwen, J.L., 1997. A kinematic analysis of tentacle extension in the squid Loligo pealei. J. Exp. Biol. 200, 41–53. Koya, I., Katto, K., Inada, H., 1997. The 1996 New Fishery Ground Development Study Report (North Pacific Central Sea Area). JAMARC, Tokyo (in Japanese). Kurosaka, K., Yamashita, H., Ochi, Y., Ogawa, M., Akamatsu, T., Inada, H., Watanabe, T., 2009. Influence of autojigger’s winding velocity on lure holding behavior of neon flying squid Ommastrephes bartramii. Nippon Suisan Gakkaishi 75, 83–85 (in Japanese). Minobe, S., 2002. Interannual to interdecadal changes in the Bering Sea and concurrent 1998/99 changes over the North Pacific. Prog. Oceanogr. 55, 45–64. Murata, M., 1990. Oceanic resources of squids. Mar. Behav. Physiol. 18, 19–71. Murata, M., Ishii, M., Osako, M., 1981. On the regeneration of tentacle of the oceanic squid Ommastrephes bartramii (Lesueur). Bull. Hokkaido Reg. Fish. Res. Lab. 46, 1–14. Okutani, T., 1990. Squids, cuttlefish and octopuses. Mar. Freshw. Behav. Physiol. 18, 1–17. Roper, C.F.E., Nigmatullin, C., Jereb, P., 2010. Family Ommastrephidae. In: Jereb, P., Roper, C.F.E. (Eds.), Cephalopods of the World. An Annotated and

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