- Email: [email protected]
Biology, spatial distribution and population dynamics of Lepidotrigla cavillone (Pisces: Triglidae) in the Central Tyrrhenian Sea
ELSEVIER
Fisheries Research 32 (1997) 21-32
Biology, spatial distribution and population dynamics of Lepidotrigla caviLZone [ Pisces: Triglidae) in the Central Tyrrhenian Sea F. Colloca, M. Cardinale, G.D. Ardizzone
*
Department ofAnimal and Human Biology, UnicersiQ ‘La Sapienza’, Viale dell’lJniuersith 32, 00185 Rome, Italy
Accepted 2 April 1997
Abstract Specimens of Lepidorrigla cavillone (the large-scaled gurnard) were collected in the Central Tyrrhenian Sea during trawl surveys carried out in April-May and September 198.5, 1986, 1987, 1994, and in October 1995. The species was fished between 30 and 200 m depth. A significant size-depth relationship ( p < O.OOl), was observed for juveniles (S.L. < 7 cm) and adults: the former migrated deeper from the coastal nursery, at the end of the first year of life; the latter moved shallower toward the spawning grounds at 60-100 m depth. Principal Component Analysis, indicated gonadal development as the main factor affecting L. cavillone depth-size relationships. Mature females were observed with significantly higher abundance ( p < 0.001) at depth of 80- 100 m. Large-scaled gumards accomplished more than half of their growth during the first two years. Reduction of growth coincided with attainment of sexual maturity. An increase of the mesh size towards the legal size may bring the age at first capture from 1.5 years up to the age of first maturity (second year) improving current Y/R. 0 1997 Elsevier Science B.V. Keywords: tepidotrigla cauillone;
Spatial distribution; Reproduction; Growth; Stock assessment; Tyrrhenian Sea
1. Introduction The large-scaled gumard, Lepidotrigla cavillone (Lacepede, 1802), is the most common gumard species in the Meditenanean Sea. In the Aegean sea it is fished at depths of 30-440 m and reaches maximum abundance at 60-200 m depth (Papacostantinou, 1983). Along the Cretan shelf (Greece) the species occurs between 30 and 295 m (Tsimenides et
* Corresponding author. Tel. and fax: +39-6-4991-4773; email: [email protected] 0165-7836/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SOl65-7836(97)00041-6
al., 1992). In the northern Tyrrhenian Sea it inhabits soft bottom from 20 to 330 m (Serena et al., 1990); in the southern Adriatic and along the Moroccan coast it is distributed between 30 and 200-250 m (Rizzi and Belle, 1986; Collignon, 1979). The species is found in eastern Atlantic from the Portuguese to the Mauritanic coast (Fisher et al., 1987). Published information on the ecological features of the large scaled-gumard, just as for other Lepidotrigla species (Richards et al., 1977a), is rather limited. The feeding habits of the species have been investigated in the Central Tyrrhenian Sea (Colloca et al., 1990, 1994), in the Aegean Sea (Caragitsou
F. Colloca et al. /Fisheries
22
Research 32 (1997) 21-32
and Papacostantinou, 19881, along the eastern Spanish coasts (Moreno and Matallanas, 1983) and at Banylus in France (Kartas, 1974). Reproduction and growth of the species have been studied in the Aegean Sea and in the Gulf of Lions (Papacostantinou, 1982a, 1983; Campillo, 1992). Raffaele described its larval development stages in 1888 (Padoa, 1956). Despite the abundance and commercial importance of gumards in the Mediterranean Sea there is a lack of knowledge on the exploited status of the stocks. This study describes some aspects of the biology of L. cavilZone in the Central Tyrrhenian Sea relevant to future management of the fishery. In particular, spatial distribution and abundance, age and growth, population structure, reproduction and mortality are considered. Finally, stock and yield assessment have been analysed.
In the Central Tyrrhenian Sea (Latium coasts) specimens of L. cavillone were collected during eight trawl surveys carried out in April-May and September of 1985, 1986 and 1987, in May 1994 and in October 1995. The sampling area was of 5.062 km during the years 1985-1987 and 15.289 km2 in 1994-1995. A total of 222 one-hour daytime hauls were divided into five depth strata (O-50, 51-100, 101-200,201-450,451-700 ml: 160 hauls were obtained in 1985-1987 (Table 1) and 31 both in May 1994 and October 1995 (Fig. 1). Each stratum was divided into 3 square nautical miles areas, several of which were randomly chosen to be investigated. The hauls were conducted with commercial trawlers (24-48 tons gross tonnage; 400-430 hp engine) using otter-trawl nets with a cod-end mesh size of 18 mm in 1985-1987 and of 22-24 mm in 1994-1995. The increase of the mesh size employed was due to the change in the commercial trawlers used for the trawl surveys in the two periods. Data from 1985-1987 surveys were used to analyse catch, seasonal abundance, size-depth relationship and reproduction of the large-scaled gumard in the study area. Data from 1994 and 1995 were utilized to study, respectively, reproduction and growth patterns of the species. The standard length (S.L.) and total body weight of the fish collected were measured to the nearest 0.5 cm and 1 g, respectively. The sex and maturity stage for each specimen were verified by macroscopic examination of the gonads using the Holden and
2. Materials and methods Trawl surveys in the Italian seas (CGPM statistical subareas 1.3, 2.1, 2.2 of area 37) were financed by Direzione Generale Pesca Marittima (Minister0 delle Risorse Agricole, Alimentari e Forestali) from 1985 to 1996. The general objective of the surveys was to determine the distribution, abundance, and biological characteristics of demersal fish (for details of 1985-1996 surveys see Relini and Piccinetti, 1996).
Table 1 Number of one-hour depth strata (m)
hauls carried out in Anzio (A) and Terracina O-50 A
April-May 1985 1986 1987 TOTAL September 1985 1986 1987 TOTAL
51-100 T
A
(T) fishing area per trawl survey and depth strata 201-450
101-200 T
A
T
A
3 4 3 10
4 5 3 12 3 4 4 11
451-700 T
A
T
F. Colloca et al. /Fisheries
Raitt (1974) partial-spawner scale. The gonads were weighed to the nearest 0.001 g and the mean gonosomatic index was calculated. For female fish the length at first maturity was established as the shortest l-cm length group at which more than 50% of the sample was sexually mature (Elder, 1976). The mean number per hour of l-cm size class individuals fished every 25 m depth was analysed in 1985- 1987 according the sampling period and the sampling area (Anzio and Terracina). Differences in the observed CPUE (number of individuals fished per one-hour trawling) between fishing areas and depth strata were tested using the Mann-Whitney U-test (Sokal and Rohlf, 1980). Analysis of variance (ANOVA) and TukeyKramer test (Sokal and Rohlf, 1980) were used to determine if significant differences in fish size among depths were consistent. Dependence of depth of capture on maturity stage and of CPUE on sampling area was tested with the G-test with Wilson correction (Sokal and Rohlf, 1980). Principal Components Analysis was run using
A APRIL- MAY n - ,, ,,
85 86
:
85 87
SiPTEMbER
: OCToBER o MAY
Research 32 (1997) 21-32
23
the mean yield of each l-cm size class every 25 m depth to emphasize the main factors affecting the spatial distribution of the large-scaled gumard in the study area. To study growth, 335 otoliths were taken in October 1995 and prepared using abrasive paper and xylol. A non-linear calculation of the von Bertalanffy growth parameters (least squares method) was carried out using the FISAT software program (Gayanillo et al., 1994). The Bhattacharya (1967) method was used to separate normal distributions, each representing a cohort of fish, from the overall seasonal distribution (Sparre et al., 1989). Natural mortality rate (M) was calculated using the models of Pauly (1980): In M = -0.0152
- 0.2791n L,
+ 0.65431n K
+ 0.4631n T, and Djabali et al. (1994) for the Mediterranean stocks: log,,M
= -0.736
- O.l14log,,L,
+ 0.5831og,,T.
86 95 94
Fig. 1. Location of sampling stations where L. cauillone were collected.
fish
+ 0.5581og,,K
24
F. Colloca et al. /Fisheries
Research 32 (1997) 21-32
T is the average annual temperature at the surface in degrees Centigrade. Total mortality rate (Z) for sampling year was estimated using the linearized length-converted catch curve (Pauly, 1984a):
SPRING 1985
where N is the number of fish in length class i, n t is the time needed for the fish to grow through length class i, ti is the age corresponding to the midlength of class i, b is equal to -Z. The analysis was performed with FISAT which required lengthfrequency data and von Bertalanffy growth parameters as input. The Z values calculated were employed to obtain the fishing mortality rate (F) with its confidence intervals at 95%. The length at which 50% of fishes is retained by the gear (Lc) was obtained using the logistic curve, which assumes selection to be sin-metrical (Pauly, 1984b):
SUMMER 198.5
SPRING 1986
ln((l\P,)-l)=S,-S,,
SUMMER 1986
where: Pr, is the probability of capture for length L, and S,, S, are constants. Lc = S,/S,. Finally the yield per recruit analysis was carried out utilizing the model of Beverton and Holt (1966), modified by Pauly and Soriano (1986) with the FISAT stock assessment program (Gayanillo et al., 1994) in which the absolute Y/R values have no direct relation to fisheries management. The model is especially suitable for assessing the effect of mesh size regulation (Sparre et al., 1989). The F,,,, defined as fishing mortality corresponding to the point on the yield/effort curve where the slope is l/ 10 of that at the origin (Gulland and Boerema, 1973), was calculated for the years 1985-1987 and 1994-1995.
SUMMER 1987 10
II=151 I
3. Results 3.1. Catch and seasonal abundance During 1985-1987, 2899 individuals of L. cauilZone, ranging in size from 3 to 12 cm S.L. (Fig. 21, were collected throughout the study area at depths of 30-200 m. In April-May there was a significantly greater abundance of the species (p < 0.05) between 61 and 150 m depth for each year. In September
Fig. 2. Length frequency distributions of L. cavillone in the Central Tyrrhenian Sea during the years 1985-1987.
significantly higher CPUEs (p < 0.05) were observed in the Terracina fishing area down to 100 m depth (Table 2). In the first six trawl surveys non-significant dif-
25
F. Colloca et al./ Fisheries Research 32 (1997) 21-32
Table 2 Depth abundance of L. cauillone in the study area during the trawl surveys carried out in the years 1985-1987. individuals caught per one-hour trawling in Anzio and Terracina fishing areas. n = number of hauls Depth (m)
Summer
Spring Anzio
30-60 61-100 101-150 151-200
n/h is the mean number of
Anzio
Terracina
(n/h)
s.d.
n
0.0 4.0 25.0 1.2
2.8 11.5 1.8
5 6 2 5
(n/h)
s.d.
n
0.0 35.4 34.0 0.4
40.5 33.4 0.8
6 5 4 6
ferences (p > 0.05) in abundances were observed between the fishing areas. In Terracina, L. cavillone yielded 21.0 (s-d. = 31.8) and 73.05 (s.d. = 151.5) specimens per hour trawling in April-May and September, respectively. At Anzio, the mean number of individuals per hour trawling was 19.3 (s.d. = 46.9) in April-May and 48.7 (s.d. = 69.1) in September. The mean fish length was 6.2 cm (range: 5-12 cm S.L.) in April-May. In September the mean length decreased to 5 cm S.L., and the stock was composed mainly of individuals of 4-6 cm S.L. which seemed to be recruited at 30-50 m depth around the lower limit of the Posidonia oceanica
Summer
Fig. 3. Mean yield of L. cauillone size-classes per sampling season and area. n/h = number of individuals caught per hour trawl.
Terracina
(n/h)
s.d.
n
(n/h)
s.d.
n
18.2 116.2 62.8 11.8
28.1 81.1 82.3 30.5
5 4 4 5
182.4 67.8 24.2 22.0
268.9 52.5 5.3 10.5
7 5 6 4
meadows. A significantly greater abundance (p < 0.05) of juveniles (L.S. < 7 cm) in September was observed for each sampling year. The two sampling areas showed differences in the stock structure. In Terracina the abundance of specimens of 7-10 cm S.L. in April-May and of 5.0-7.5 cm S.L. in September was significantly (p < 0.001) greater than at Anzio (Fig. 3).
3.2. Reproduction Females with mature gonads were observed from April to September. In April-May more than 70% of the females over 7 cm S.L. were sexually mature, while in the beginning of September and in late October the mature females decreased to 63% and 0% respectively. The mean ovaries weight was 7.2% (s.d. = 0.017) of the fish body weight. The sizes of minimum maturity and first maturity of females were 7 cm S.L. and 6 cm S.L. in spring and 7 cm and 8 cm S.L. in summer. The males sampled did not show gonads at the third or fourth stages of the scale of Holden and Raitt (1974) and it was not possible to quantify macroscopically the percentage of mature individuals. The testis appeared much smaller than the female gonads (0.44% of the body weight, s.d. = 0.0039). The male-female ratio was 51.9% for fish of 6-10 cm S.L. The mean number of mature females fished per hour trawling increased as depth of capture decreased (Fig. 4). A significantly higher abundance of spawning females ( p < 0.001) at depth of 80-100 m was found in the Terracina area. The minimum depth at which sexually mature females were fished was 60 m.
F. Colloca et al. /Fisheries
26 Spring1985.87
61.100
101-120 JJM
121-160
(ml
100 80
61-100
101-120 4th
Fig. 4. Depth distribution in the Central Tyrrhenian 1994.
121-160
W
of L. cavillone female maturity stages Sea in the springs of 1985-1987 and
3.3. Size-depth relationships
The mean length of L. cavillone showed significant differences according to the depth of capture. In April-May 1986, the mean fish length around 70 m depth was significantly greater (p < 0.05) than at
Research 32 (1997) 21-32
1lo-120 m depth (Table 3B) and there was a quite low but significant negative relationship (d.f. = 221, r = -0.567, p < 0.001) between increasing size and increasing depth of capture. In spring 1994, a similar relationship had been observed for fish 2 7 cm S.L. (d.f. = 186; I = -0.354; p < 0.001). In the summers 1985-1986, the fish distributed at intermediate and greater depth (90-100 m and 150160 m) showed a significantly (p < 0.05) larger mean fish length than those caught at depths of 30-80 m and 110-120 m (Table 3A, 0. The depthbody size correlation was significantly positive (d.f. = 637; r = 0.554; p < 0.001) in summer 1986. In summer 1985, this relationship was analyzed separately for the fish less than 7 cm S.L. and for individuals greater or equal than 7 cm S.L. The body size of the former was found to increase with depth (d.f. = 413; r = 0.3; p < O.OOl>,while an opposite relationship was found between depth and body size (d.f. = 323; r = -0.32; p < 0.001) for the latter. The mean CPuEs of female l-cm size classes in September 1985 were used to carry out a Principal Component Analysis to analyse the factors affecting the size-depth distribution of the species in the study area. Fig. 5 shows the projection of the species points along Axes I and II. The two axes are strongly correlated and variance explained is of 93.83%. The left part of the figure gives the distribution of fish size classes from 6 to 8.9 cm S.L., while size classes 9-l 1.9 cm are given on the right. The upper part presents intermediate fish sizes (7-9.9 cm S.L.) as
Table 3 Mean standard lengths of L. cavillone in the study area at different depths Summer 1985 (A), Spring 1986 (B), Summer 1986 CC), and results of Tukey-Kramer test (all depth not underlined by a common line have means that are significantly (p < 0.05) different from each other) Summer I985 (A) Depth (m) n S.L. (cm)
63 66 6.00
66 90 6.20
87 67 6.40
Spring ‘86 (B) Depth (m) n S.L. (cm)
101 66 6.00
115 90 6.20
-
Summer ‘86 ICJ Depth (m) n S.L. (cm)
-
-
32 27 4.40 -
54 133 5.72 -
108 81 6.50
70 67 6.40
64 81 6.50 -
36 650 6.01
74 133 6.20
155 70 8.40
148 55 8.70
100 85 8.90
101 143 6.27 -
108 155 6.29 -
117 39 6.93
162 57 7.30
F. Colloca et al. / Fisheries Research 32 (1997) 21-32
27
spectively. On the left side of Axis II, fish size increases, while on the right, decreases with depth. 3.4. Age and growth
9-9 9cm .
Otoliths collected in October 1995 from 335 fish throughout the study area, were examined. Only the otoliths on whose interpretation all readers agreed (88% of otholits read) were taken as part of age-atlength data (Table 4). No animal older than the fourth year class was found in the sample. The corresponding Von Bertalanffy’s growth equations are:
Fig. 5. Principal Components Analysis carried out using the mean yield (n/h) of each L. cacillone size class every 25 m depth.
= 1.53) ;
males: L, = 10.85(s.e. K = 0.53(s.e.
opposed to the largest and smallest fish sizes (5-6.9 cm S.L. and lo-II.9 cm S.L.) found in the lower part. Axis I can be translated into a gonadal development factor and axis II into a depth factor. Sexual maturation increases from left to the right on the first axis, with the origin of the axis defined as the moment in which reproductive migration begins. The depth distribution of size classes increase from the lower to the upper part of the second axis. The 8-8.9 cm S.L. and the 5-6.9/10-l 1.9 cm S.L. size classes showed the deepest and shallowest distribution, re-
Table 4 Age-length 1996
r2 = 0.68 K = 0.38(s.e.
= 0.12); t0 = -0.427(s.e.
= 0.4);
r2 = 0.82 both sexes: L, = 11.7(s.e. K = 0.414(s.e.
= 0.9);
= 0.1); t,, = -0.38(s.e.
= 0.29);
r? = 0.77 Growth
rates
gurnard
of females
collected
and males
in the Central Tyrrhenian
are virtually
Sea during October
Age group (years) 0.5 m
4.5-4.99 5-5.49 5.5-5.99 6-6.49 6.5-6.99 7-7.49 7.5-7.99 8-8.49 8.5-8.99 9-9.49 9.5-9.99 lo- 10.49 10.5- 10.99 II-1 1.49 Total
= 0.5);
females: L, = 12(s.e. = 1.2);
matrix of 142 males (m) and 154 females (f) of large-scaled
Length group cm
= 0.27); t0 = -0.17(s.e.
1.5 f
2.5
m
f
2 4 12 6 12 16 12
2 4 6 10 20 8 4
m
0 4 12 8 32 6 2
3.5 f
2 6 10 8 20 8 2
m
2 8 2
4.5 f
m
4 6 10 2 2
0
0
64
54
64
56
12
22
2
Total f
4 8 6 4 22
m 2 4 12 6 12 20 24 8 34 14 2 2 2 0 142
f 2 4 6 10 22 14 14 8 24 14 16 10 6 4 154
F. Colloca et al. /Fisheries
28
Fig. 6. Length frequency distribution of L. cauillone in the Central Tyrrhenian Sea in October 1995. The arrows indicate the modal classes identified with Bhatthacharya’s method.
Research 32 (I 997) 21-32
identical. Large-scaled gurnards accomplished more than one-half of their growth during their first two years of life. Reduction of growth coincided with attainment of sexual maturity which occurred in both sexes at the end of their second year. The length frequency distributions in October 1995 analysed with the Bhatthacharya method, showed two distinct cohorts with mean length of 6.18 and 8.46 cm S.L., matching those obtained from age-at-length data for the 1 + (1.5 years) and 2 + (2.5 years) age classes (mean length 6.32 and 8.14 cm S.L. respectively) (Fig. 6).
1994-95
140 120
MO _
l-l
1985
100
c
60 60 40 20 0
s
K
9
2
2
S.L. (cm)
Fig. 7. Annual length-frequency
distributions
and linearized length-converted
catch curves of the large-scaled
gumard in the study area.
F. Colloca et al. /Fisheries
Research 32 (1997) 21-32
29
at around the end of first and second 1985-1987 and 1994-1995, respectively.
3.5. Stock assessment The natural mortality coefficients adopted in this study (m = OS), were estimated with the Djabali et al. (1994) equation. The Pauly method, with a mean habitat temperature of 16°C furnished a value of 1.O, which was assessed as being too high for the species, considering that the Z value observed in the 1985 was 0.68. Annual length-frequency distributions and linearized catch curves are showed in Fig. 7. The mean Z values ranged from 0.68 in 1985 to a maximum of 1.91 in 1986. In 1985, a very low fishing mortality (0.18) rate, compared with the other sampling years (1.41, 1.25, 1.09, respectively in 1986, 1987, 19941995), was pointed out (Table 5). The length structure of the stock showed changes from year to year (Fig. 7), suggesting that the yield per recruit analysis be carried out separately for each sampling year. The F,,, values ranged between 0.52 and 0.62 in the 1985-1987 and was of 1.16 in 1994-1995. A growth overfishing state was indicated in 1986 and 1987, while there was an opposite state in 1985. In 1994-1995, the observed fishing mortality being close to optimum. Better exploitation of the stock from the years 1986-1987 to the 19941995 was the result of an increase in the selectivity parameter c, that rose from 0.36-0.47 in eighties to 0.55 in nineties. The Lc of L. cauillone during the trawl surveys ranged from 4.26 in 1987 to the 5.47 in 1986 using a code-end mesh (stretched mesh) of 18 mm, while the Lc in 1994-1995 was 6.46 using nets with mesh between 22 and 24 mm (Table 5). Therefore the age of first capture can be estimated
Table 5 Mean annual values of mesh size, Lc, T,,, Tvrrhenian Sea
2, F, F,,
years
for
4. Discussion Sexual development appeared to be the main factor affecting size-depth distribution of L. cavillone in the Central Tyrrhenian Sea. Females reach the size of first sexual maturity (around 7 cm S.L.) at the age 1 + . The smallest fish with ripe ova measured 6 cm in spring. In summer, the size of first sexual maturity and the minimum size of maturity of the females increased respectively to 8 and 7 cm S.L. The increase in the size of maturity from the beginning to the end of the spawning period can be due to the partial spawning of L. cavillone typical of gumard species (Priol, 1932; Elder, 1976; Baron, 1985) which induces a somewhat prolonged breeding period. Rapid development of male testis and their small weight and volume compared with female gonads was documented by Baron (1985) for gumard species of east-Atlantic coasts. The same large difference in gonosomatic index between males and females was reported in the Mediterranean for Scorpaena porcus (Bradai and Bouain, 1990) and could be related to the sexual behaviour of the species. L. cavillone in the study area seems to grow more slowly than in the Gulf of Lions (Campillo, 1992) and in the Greek seas (Papacostantinou, 1982a). Both sexes accomplish more than half of their growth during the first two years of life. The reduction in growth rate after the second year coincided with the attainment of sexual maturity, as described for others
of the large-scaled
gumard
during
the trawl surveys
carried
Mesh size mm
1985 18
I986 18
1987 18
1994-1995 22-24
Lc T,, Z C.I. 95% F C.I. 95% F 0.1
5.16 1.03 0.68 0.5-0.86 0.18 O-O.36 0.61
5.41 1.14 1.91 1.46-2.36 1.41 0.96- 1.86 0.62
4.37 0.70 1.75 1.39- 2.12 1.25 0.88-1.62 0.52
6.47 1.56 1.59 1.31-1.81 1.09 0.81-1.31 1.16
out in the Central
30
F. Colloca et al. /Fisheries
gurnard species (Papacostantinou, 1982b), and a change in the feeding strategy of the species (Colloca et al., 1994). In the two sampling seasons, a low but significant relationship between body size and depth was found. As observed by Papacostantinou (1983), juveniles in the Creek seas appeared on P. oceanica meadows at 30-50 m depth and showed a positive size-depth relationship. Depth migration of the immature during growth is a common behaviour in fish (Helfman, 1978) and particularly in gurnard species (Meek, 1915; Elder, 1976; Lewis and Yerger, 1976; Ross, 1978; Richards et al., 1977b). Juveniles of L. cavillone migrated offshore from nurseries around the end of the first year of life, as the high summer abundance of fish aged 1 + on 30-60 m depth suggests, juveniles were absent from these bottoms in spring. The importance of gonadal development in the depth-size relationships of L. cavillone in the study area was shown by the Principal Components Analysis. The gonadal development factor explains the 59.8% variance, while the fish size factor explains only the 34%. This value confirms that the latter factor alone plays a secondary role to determine the depth distribution of the species in the study area, as the correlation analysis emphasized. In summer, the fish were separated into two groups according to
Life
cycle
Research 32 (1997) 21-32
sexual maturation: individuals in the 5-8 cm S.L. range that migrate offshore during growth and individuals over 9 cm S.L. that migrate shallower towards the spawning grounds. This pattern resulted in a similar depth distribution of younger (5-6 cm S.L.) and older (lo-11 cm S.L.) fish. Individuals of intermediate size (8 cm S.L.) not also in reproductive migration appeared distributed deeper than bigger and smaller fish. This agrees with the size at first maturity which was 8 cm S.L. for females in summer. Migration of gumards associated with their spawning activity has been recorded by Fulton (18991, Meek (1915) and Marshall (1946). Harden Jones (1968) stated that spawning fish undertake a contranatant migration to a spawning ground because of its position in relation to a favorable nursery area. L. cavillone carries out such migration during growth, but before gonad maturation, juveniles reach bottoms deeper than the spawning grounds. Fig. 8 shows life cycle of L. cavillone in the study area. The differences in the species abundance observed between the Anzio and Terracina fishing areas could be related to the distribution of the nursery and spawning grounds in the sampling area: latter were observed between 60-100 m offshore of the nurseries, and furthermore, P. oceunica meadows colonize larger areas in Terracina than in Anzio
of L. cavillone
Ufiflte,
1+ /5+
Fig. 8. Hypothetical
life cycle of L. cadlone
in the Central Tyrrhenian
200
Sea.
m
F. Colloca et al. /Fisheries
(Ardizzone and Pelusi, 1984). It can be hypothesized that the fish hatch in a limited zone of Terracina area and subsequently spread throughout the study area. The exploitation level of the species could be optimized by raising the cod-end mesh size normally used by the commercial fleet to the legal size (40 mm). The mesh size adopted (22-24 mm) results in an age at first capture (Lc) of 1.5 year, close to the age at first maturity. An increase in mesh size, bringing the age of first capture over this age, is desirable. The mortality values of the L. cavillone stock in the study area showed differences in the various sampling years. Fishing mortality did not exceed the F,,, in 1985 and 1994-1995, while the opposite status was observed in 1986-1987, according to the differences in observed stock structure. Such a differences can not be related to variations in fishing effort, since it did not change during the last 10 years in the study area. In the Central Tyrrhenian sea large-scaled gurnard nursery areas and spawning zones occur in restricted areas along the shelf. Thus, fluctuations in fishing mortality were caused by the characteristics of sampling design used rather than actual variations in fishing effort. In spite of the strong fishing effort in the area, large-scaled gumard is a common species. The over-exploitation risks of the species seem to be reduced by a rapid growth and short length at maturation as well as by low catchability of juveniles.
References Ardizzone, G.D., Pelusi, P., 1984. Yield and damage evaluation of bottom trawling on Posidonia meadows, in: Bouuresque, C.F., Jeudy de Grissac, A., Olivier, J. (Eds.), GIS International Workshop Posidonia oceanica Beds, Posidonie Publ., 1, 6372. Baron, J., 1985. Les Ttiglidae (Teleosteens, Scorpaeniformes) de la baie de Douamenez. La reproduction de E. gumardus, 7’. lastouiza, A. cuculus, T. lucema. Cybium 9 (41, 255-281. Beverton and Holt, 1966. Manual of methods for fish stock assessment. FAO Fish. Tech. Pap., (38) Rev. 1, 67 pp. Bhattacharya, C.G., 1967. A simple method of resolution of a distribution into gaussian components. Biometrics 23, 115 135. Bradai, M.N., Bouain, A., 1990. Donnets sur la reproduction de Scorpaena porcus du Golfe de Gab&s. Rapp. Comm. Int. Mer. MCdit. 32 (1). 265.
Research 32 (1997) 21-32
31
Campillo, A., 1992, Les pecheries francaises de Mediterranee: synthese des connaissances. Rapports Intemes de la Direction des Ressources Vivantes de I’Ifremer. IFREMER, DRV92/019-RH/SL?te, 206 pp. Caragitsou, E., Papacostantinou, C., 1988. Food habits and dietary overlap of Lepidotrigla cauillone in Greek Seas. Rapp. Comm. Int. Mer. Mtdit. 31 (21, 13. Collignon, J., 1979. Catalogue raisonne des poissons des mers marocaines (4.eme pat-tie). Bull. Inst. Pech. Marit. Marocco 81, 37-60. Colloca, F., Belluscio, A., Schintu, P., Ardizzone, G.D., 1990, Alimentazione dei triglidae de1 Tirreno Centrale. Oebalia, Suppl., XVI, (21, 643-646. Colloca, F., Gravina, M.F., Ardizzone, G.D., 1994. Trophic ecology of gumards (Pisces: Triglidae) in the Central Mediterranean Sea. Marine Life 4 (2), 45-57. Djabah, F., Mehailia, A., Koudil, M., Brahmi, B., 1994. A reassessment of equations for predicting natural mortality in Mediterranean teleosts. Naga, ICLARM Q. 17 (11, 33-34. Elder, R.D., 1976. Studies on age and growth, reproduction and population dynamics of red gumard, Chelidonichthys kutnu in the Hauraky Gulf, New Zealand. Fish. Res. Bull. 12, 77. Fisher, W., Bauchot, M.L., Schneider, M., 1987, Fiches FAO d’identification des especes pour les besoins de la p&he. (revision 1). Mediterrante et mer Noire. Zone de p&he 37. vol. 2, 761-1530. Fulton, T.W., 1899. On the migratory movements and rate of growth of the grey or common gumard. Ann. Rep. Fish. Board Scotland 3, 210-231. Gayanillo, F.C., Sparre, P., Pauly, D., 1994. The FAO-ICLARM Stock Assessment Tools (FISAT) user’s guide. FAO Comput. Info. Series (Fisheries) 6, 186. Gulland, J.A., Boerema, K., 1973. Scientific advice on catch levels. Fish. Bull. 71 (2). 325-335. Harden Jones, F.R., 1968. Biological aspect of migration. In: Arnold, Edward (Ed.) Fish Migration, 325 pp. Helfman, G.S., 1978. Patterns of community structure in fishes: summary and overview. Env. Biol. Fish. 3, 129-148. Holden, M.J., Raitt, D.F.S., 1974. Sex, maturity and fecundity. Manual of fisheries science. Part 2. Method of resource investigation and their application. FAO, Fish. Tech. Pap. 115 (Rev. 11, 214. Kartas, F., 1974. Regime alimentaire des especes du genre Lepidotrigla (Gunther, 1860) de la mer Catalane. Rapp. Comm. Int. Mer. Medit. 22 (71, 47. Lewis, T.C., Yerger, R.W., 1976. Biology of five species of searobins (Ttiglidae) from the Northeastern Gulf of Mexico. Fish. Bull. 74 cl), 93-103. Marshall, N., 1946. Observation of the comparative ecology and life history of two searobins Prionotus carolinus and Prionotus ecolans strigatus. Copeia 1946, 118- 144. Meek, A., 1915. The migration of the grey gumard Trigla gumardus. Rep. Dove. Mar. Lab., (n.s.) 4, 9-15. Moreno, R., Matallanas, J., 1983. Etude du regime alimentaire de Lepidotrigla cal,illone (Lacepede, 1801) (Pisces: Triglidae) dans la mer Catalane. Cybium 7 (3), 93-103.
F. Colloca et al. /Fisheries
32
Padoa, E., 1956. Triglidae. Uova e stadi giovanili di Teleostei. Fauna e Flora de1 Golfo di Napoli 38, 627-640. Papacostantinou, C., 1982a. Em 71)~ /3~ohoywm TOV l~Gova A&-L~OTPQ’~~
,yawhihova
(TPL~ALBoE)
TOV
LhhCKOV
Thalassographica 1 (51, 33-59. Papacostantinou, C., 1982b. Age and growth of grey gumard (Eurrigla gurnardus) in the Pagassitikos Gulf (Greece). Inv. Pesq. 46 (2), 191-213. Papacostantinou, C., 1983. Observations on the ecology of gumards (Pisces: Triglidae) in the Greek Seas. Cybium 7 (4). 71-88. Pauly, D., 1980. On the interrelationships between natural mortality, growth parameters and mean environmental temperature in 175 fish stock. J. Cons. CIEM. 39 (31, 175-192. Pauly, D., 1984a. Length-converted catch curves: a powerful tool for fisheries research in the tropics. Part. II. ICLARM Fishbyte 2 (0, 17-19. Pauly, D., 1984b. Fish population dynamics in tropical waters: a manual for use with programmable calculators. ICLARM Stud. Rev. 8, 325. Pauly, D., Soriano, M.L., 1986. Some practical extensions to Beverton and Holt’s relative yield-per-recruit model. In: Maclean, J.L., Dizon, L.D., Hosillo, L.V. (Eds.), The First Asian Fisheries Forum, Asian Fisheries Society, Manila, Philippines, 49 l-496 pp. Priol, E., 1932. Remarques sur les especes des grondins les plus communes des totes de France. Rev. Trav. Inst. Pech. Marit. 5 (21, 223-272. Oahauuov.
Research 32 (1997) 21-32
Relini, G., Piccinetti, C., 1996. Ten years of trawl surveys in Italian seas (1985-1995). FAO Fish. Rep. 533, 21-42. Richards, J., Vishnu, P., Saksena, P., 1977a. Systematics of the gumards, genus Lepidorrigla (Pisces, Triglidae), from the Indian Ocean. Bull. Mar. Sci. 27 (2), 208-222. Richards, J., Mann, J.M., Walker, J., 1977b. Comparison of spawning season, age, growth rates and food of two sympatric searobins, Prionotus evolans and P. carolinus, from Long Island Sound. Estuaries 2 (4). 255-268. Rizzi, E., Bello, G., 1986. Triglidi (Osteichthyes) de1 basso Adriatico. Nova Thalassia 8 (3), 665-666. Ross, S., 1978. Trophic ontogeny of the Leopard searobin Prionotus scitulus (Pisces: Triglidae). Fish. Bull. 76 (11, 225-234. Serena, F., Baino, R., Voliani, A., 1990. Distribuzione dei Triglidi (Osteichthyes, Scorpaeniformes) nell’Alto Tirreno. Oebalia, Suppl., XVI (11, 269-278. Sokal, R.R., Rohlf, F.J., 1980. Biometry, 2nd edn., W.H. Freeman, New York, 859 pp. Sparre, P., Ursin, Venema, SC., 1989, Introduction to tropical fish stock assessment. Part 1, Manual FAO Fish. Tech. Paper, 306,429 pp. Tsimenides, N., Machias, A., Kallianotis, A., 1992. Distribution pattern of triglids (Pisces: Triglidae) on the Cretan shelf (Greece), and their interspecific associations. Fish. Res. 15, 83-103.
Fisheries Research 32 (1997) 21-32
Biology, spatial distribution and population dynamics of Lepidotrigla caviLZone [ Pisces: Triglidae) in the Central Tyrrhenian Sea F. Colloca, M. Cardinale, G.D. Ardizzone
*
Department ofAnimal and Human Biology, UnicersiQ ‘La Sapienza’, Viale dell’lJniuersith 32, 00185 Rome, Italy
Accepted 2 April 1997
Abstract Specimens of Lepidorrigla cavillone (the large-scaled gurnard) were collected in the Central Tyrrhenian Sea during trawl surveys carried out in April-May and September 198.5, 1986, 1987, 1994, and in October 1995. The species was fished between 30 and 200 m depth. A significant size-depth relationship ( p < O.OOl), was observed for juveniles (S.L. < 7 cm) and adults: the former migrated deeper from the coastal nursery, at the end of the first year of life; the latter moved shallower toward the spawning grounds at 60-100 m depth. Principal Component Analysis, indicated gonadal development as the main factor affecting L. cavillone depth-size relationships. Mature females were observed with significantly higher abundance ( p < 0.001) at depth of 80- 100 m. Large-scaled gumards accomplished more than half of their growth during the first two years. Reduction of growth coincided with attainment of sexual maturity. An increase of the mesh size towards the legal size may bring the age at first capture from 1.5 years up to the age of first maturity (second year) improving current Y/R. 0 1997 Elsevier Science B.V. Keywords: tepidotrigla cauillone;
Spatial distribution; Reproduction; Growth; Stock assessment; Tyrrhenian Sea
1. Introduction The large-scaled gumard, Lepidotrigla cavillone (Lacepede, 1802), is the most common gumard species in the Meditenanean Sea. In the Aegean sea it is fished at depths of 30-440 m and reaches maximum abundance at 60-200 m depth (Papacostantinou, 1983). Along the Cretan shelf (Greece) the species occurs between 30 and 295 m (Tsimenides et
* Corresponding author. Tel. and fax: +39-6-4991-4773; email: [email protected] 0165-7836/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SOl65-7836(97)00041-6
al., 1992). In the northern Tyrrhenian Sea it inhabits soft bottom from 20 to 330 m (Serena et al., 1990); in the southern Adriatic and along the Moroccan coast it is distributed between 30 and 200-250 m (Rizzi and Belle, 1986; Collignon, 1979). The species is found in eastern Atlantic from the Portuguese to the Mauritanic coast (Fisher et al., 1987). Published information on the ecological features of the large scaled-gumard, just as for other Lepidotrigla species (Richards et al., 1977a), is rather limited. The feeding habits of the species have been investigated in the Central Tyrrhenian Sea (Colloca et al., 1990, 1994), in the Aegean Sea (Caragitsou
F. Colloca et al. /Fisheries
22
Research 32 (1997) 21-32
and Papacostantinou, 19881, along the eastern Spanish coasts (Moreno and Matallanas, 1983) and at Banylus in France (Kartas, 1974). Reproduction and growth of the species have been studied in the Aegean Sea and in the Gulf of Lions (Papacostantinou, 1982a, 1983; Campillo, 1992). Raffaele described its larval development stages in 1888 (Padoa, 1956). Despite the abundance and commercial importance of gumards in the Mediterranean Sea there is a lack of knowledge on the exploited status of the stocks. This study describes some aspects of the biology of L. cavilZone in the Central Tyrrhenian Sea relevant to future management of the fishery. In particular, spatial distribution and abundance, age and growth, population structure, reproduction and mortality are considered. Finally, stock and yield assessment have been analysed.
In the Central Tyrrhenian Sea (Latium coasts) specimens of L. cavillone were collected during eight trawl surveys carried out in April-May and September of 1985, 1986 and 1987, in May 1994 and in October 1995. The sampling area was of 5.062 km during the years 1985-1987 and 15.289 km2 in 1994-1995. A total of 222 one-hour daytime hauls were divided into five depth strata (O-50, 51-100, 101-200,201-450,451-700 ml: 160 hauls were obtained in 1985-1987 (Table 1) and 31 both in May 1994 and October 1995 (Fig. 1). Each stratum was divided into 3 square nautical miles areas, several of which were randomly chosen to be investigated. The hauls were conducted with commercial trawlers (24-48 tons gross tonnage; 400-430 hp engine) using otter-trawl nets with a cod-end mesh size of 18 mm in 1985-1987 and of 22-24 mm in 1994-1995. The increase of the mesh size employed was due to the change in the commercial trawlers used for the trawl surveys in the two periods. Data from 1985-1987 surveys were used to analyse catch, seasonal abundance, size-depth relationship and reproduction of the large-scaled gumard in the study area. Data from 1994 and 1995 were utilized to study, respectively, reproduction and growth patterns of the species. The standard length (S.L.) and total body weight of the fish collected were measured to the nearest 0.5 cm and 1 g, respectively. The sex and maturity stage for each specimen were verified by macroscopic examination of the gonads using the Holden and
2. Materials and methods Trawl surveys in the Italian seas (CGPM statistical subareas 1.3, 2.1, 2.2 of area 37) were financed by Direzione Generale Pesca Marittima (Minister0 delle Risorse Agricole, Alimentari e Forestali) from 1985 to 1996. The general objective of the surveys was to determine the distribution, abundance, and biological characteristics of demersal fish (for details of 1985-1996 surveys see Relini and Piccinetti, 1996).
Table 1 Number of one-hour depth strata (m)
hauls carried out in Anzio (A) and Terracina O-50 A
April-May 1985 1986 1987 TOTAL September 1985 1986 1987 TOTAL
51-100 T
A
(T) fishing area per trawl survey and depth strata 201-450
101-200 T
A
T
A
3 4 3 10
4 5 3 12 3 4 4 11
451-700 T
A
T
F. Colloca et al. /Fisheries
Raitt (1974) partial-spawner scale. The gonads were weighed to the nearest 0.001 g and the mean gonosomatic index was calculated. For female fish the length at first maturity was established as the shortest l-cm length group at which more than 50% of the sample was sexually mature (Elder, 1976). The mean number per hour of l-cm size class individuals fished every 25 m depth was analysed in 1985- 1987 according the sampling period and the sampling area (Anzio and Terracina). Differences in the observed CPUE (number of individuals fished per one-hour trawling) between fishing areas and depth strata were tested using the Mann-Whitney U-test (Sokal and Rohlf, 1980). Analysis of variance (ANOVA) and TukeyKramer test (Sokal and Rohlf, 1980) were used to determine if significant differences in fish size among depths were consistent. Dependence of depth of capture on maturity stage and of CPUE on sampling area was tested with the G-test with Wilson correction (Sokal and Rohlf, 1980). Principal Components Analysis was run using
A APRIL- MAY n - ,, ,,
85 86
:
85 87
SiPTEMbER
: OCToBER o MAY
Research 32 (1997) 21-32
23
the mean yield of each l-cm size class every 25 m depth to emphasize the main factors affecting the spatial distribution of the large-scaled gumard in the study area. To study growth, 335 otoliths were taken in October 1995 and prepared using abrasive paper and xylol. A non-linear calculation of the von Bertalanffy growth parameters (least squares method) was carried out using the FISAT software program (Gayanillo et al., 1994). The Bhattacharya (1967) method was used to separate normal distributions, each representing a cohort of fish, from the overall seasonal distribution (Sparre et al., 1989). Natural mortality rate (M) was calculated using the models of Pauly (1980): In M = -0.0152
- 0.2791n L,
+ 0.65431n K
+ 0.4631n T, and Djabali et al. (1994) for the Mediterranean stocks: log,,M
= -0.736
- O.l14log,,L,
+ 0.5831og,,T.
86 95 94
Fig. 1. Location of sampling stations where L. cauillone were collected.
fish
+ 0.5581og,,K
24
F. Colloca et al. /Fisheries
Research 32 (1997) 21-32
T is the average annual temperature at the surface in degrees Centigrade. Total mortality rate (Z) for sampling year was estimated using the linearized length-converted catch curve (Pauly, 1984a):
SPRING 1985
where N is the number of fish in length class i, n t is the time needed for the fish to grow through length class i, ti is the age corresponding to the midlength of class i, b is equal to -Z. The analysis was performed with FISAT which required lengthfrequency data and von Bertalanffy growth parameters as input. The Z values calculated were employed to obtain the fishing mortality rate (F) with its confidence intervals at 95%. The length at which 50% of fishes is retained by the gear (Lc) was obtained using the logistic curve, which assumes selection to be sin-metrical (Pauly, 1984b):
SUMMER 198.5
SPRING 1986
ln((l\P,)-l)=S,-S,,
SUMMER 1986
where: Pr, is the probability of capture for length L, and S,, S, are constants. Lc = S,/S,. Finally the yield per recruit analysis was carried out utilizing the model of Beverton and Holt (1966), modified by Pauly and Soriano (1986) with the FISAT stock assessment program (Gayanillo et al., 1994) in which the absolute Y/R values have no direct relation to fisheries management. The model is especially suitable for assessing the effect of mesh size regulation (Sparre et al., 1989). The F,,,, defined as fishing mortality corresponding to the point on the yield/effort curve where the slope is l/ 10 of that at the origin (Gulland and Boerema, 1973), was calculated for the years 1985-1987 and 1994-1995.
SUMMER 1987 10
II=151 I
3. Results 3.1. Catch and seasonal abundance During 1985-1987, 2899 individuals of L. cauilZone, ranging in size from 3 to 12 cm S.L. (Fig. 21, were collected throughout the study area at depths of 30-200 m. In April-May there was a significantly greater abundance of the species (p < 0.05) between 61 and 150 m depth for each year. In September
Fig. 2. Length frequency distributions of L. cavillone in the Central Tyrrhenian Sea during the years 1985-1987.
significantly higher CPUEs (p < 0.05) were observed in the Terracina fishing area down to 100 m depth (Table 2). In the first six trawl surveys non-significant dif-
25
F. Colloca et al./ Fisheries Research 32 (1997) 21-32
Table 2 Depth abundance of L. cauillone in the study area during the trawl surveys carried out in the years 1985-1987. individuals caught per one-hour trawling in Anzio and Terracina fishing areas. n = number of hauls Depth (m)
Summer
Spring Anzio
30-60 61-100 101-150 151-200
n/h is the mean number of
Anzio
Terracina
(n/h)
s.d.
n
0.0 4.0 25.0 1.2
2.8 11.5 1.8
5 6 2 5
(n/h)
s.d.
n
0.0 35.4 34.0 0.4
40.5 33.4 0.8
6 5 4 6
ferences (p > 0.05) in abundances were observed between the fishing areas. In Terracina, L. cavillone yielded 21.0 (s-d. = 31.8) and 73.05 (s.d. = 151.5) specimens per hour trawling in April-May and September, respectively. At Anzio, the mean number of individuals per hour trawling was 19.3 (s.d. = 46.9) in April-May and 48.7 (s.d. = 69.1) in September. The mean fish length was 6.2 cm (range: 5-12 cm S.L.) in April-May. In September the mean length decreased to 5 cm S.L., and the stock was composed mainly of individuals of 4-6 cm S.L. which seemed to be recruited at 30-50 m depth around the lower limit of the Posidonia oceanica
Summer
Fig. 3. Mean yield of L. cauillone size-classes per sampling season and area. n/h = number of individuals caught per hour trawl.
Terracina
(n/h)
s.d.
n
(n/h)
s.d.
n
18.2 116.2 62.8 11.8
28.1 81.1 82.3 30.5
5 4 4 5
182.4 67.8 24.2 22.0
268.9 52.5 5.3 10.5
7 5 6 4
meadows. A significantly greater abundance (p < 0.05) of juveniles (L.S. < 7 cm) in September was observed for each sampling year. The two sampling areas showed differences in the stock structure. In Terracina the abundance of specimens of 7-10 cm S.L. in April-May and of 5.0-7.5 cm S.L. in September was significantly (p < 0.001) greater than at Anzio (Fig. 3).
3.2. Reproduction Females with mature gonads were observed from April to September. In April-May more than 70% of the females over 7 cm S.L. were sexually mature, while in the beginning of September and in late October the mature females decreased to 63% and 0% respectively. The mean ovaries weight was 7.2% (s.d. = 0.017) of the fish body weight. The sizes of minimum maturity and first maturity of females were 7 cm S.L. and 6 cm S.L. in spring and 7 cm and 8 cm S.L. in summer. The males sampled did not show gonads at the third or fourth stages of the scale of Holden and Raitt (1974) and it was not possible to quantify macroscopically the percentage of mature individuals. The testis appeared much smaller than the female gonads (0.44% of the body weight, s.d. = 0.0039). The male-female ratio was 51.9% for fish of 6-10 cm S.L. The mean number of mature females fished per hour trawling increased as depth of capture decreased (Fig. 4). A significantly higher abundance of spawning females ( p < 0.001) at depth of 80-100 m was found in the Terracina area. The minimum depth at which sexually mature females were fished was 60 m.
F. Colloca et al. /Fisheries
26 Spring1985.87
61.100
101-120 JJM
121-160
(ml
100 80
61-100
101-120 4th
Fig. 4. Depth distribution in the Central Tyrrhenian 1994.
121-160
W
of L. cavillone female maturity stages Sea in the springs of 1985-1987 and
3.3. Size-depth relationships
The mean length of L. cavillone showed significant differences according to the depth of capture. In April-May 1986, the mean fish length around 70 m depth was significantly greater (p < 0.05) than at
Research 32 (1997) 21-32
1lo-120 m depth (Table 3B) and there was a quite low but significant negative relationship (d.f. = 221, r = -0.567, p < 0.001) between increasing size and increasing depth of capture. In spring 1994, a similar relationship had been observed for fish 2 7 cm S.L. (d.f. = 186; I = -0.354; p < 0.001). In the summers 1985-1986, the fish distributed at intermediate and greater depth (90-100 m and 150160 m) showed a significantly (p < 0.05) larger mean fish length than those caught at depths of 30-80 m and 110-120 m (Table 3A, 0. The depthbody size correlation was significantly positive (d.f. = 637; r = 0.554; p < 0.001) in summer 1986. In summer 1985, this relationship was analyzed separately for the fish less than 7 cm S.L. and for individuals greater or equal than 7 cm S.L. The body size of the former was found to increase with depth (d.f. = 413; r = 0.3; p < O.OOl>,while an opposite relationship was found between depth and body size (d.f. = 323; r = -0.32; p < 0.001) for the latter. The mean CPuEs of female l-cm size classes in September 1985 were used to carry out a Principal Component Analysis to analyse the factors affecting the size-depth distribution of the species in the study area. Fig. 5 shows the projection of the species points along Axes I and II. The two axes are strongly correlated and variance explained is of 93.83%. The left part of the figure gives the distribution of fish size classes from 6 to 8.9 cm S.L., while size classes 9-l 1.9 cm are given on the right. The upper part presents intermediate fish sizes (7-9.9 cm S.L.) as
Table 3 Mean standard lengths of L. cavillone in the study area at different depths Summer 1985 (A), Spring 1986 (B), Summer 1986 CC), and results of Tukey-Kramer test (all depth not underlined by a common line have means that are significantly (p < 0.05) different from each other) Summer I985 (A) Depth (m) n S.L. (cm)
63 66 6.00
66 90 6.20
87 67 6.40
Spring ‘86 (B) Depth (m) n S.L. (cm)
101 66 6.00
115 90 6.20
-
Summer ‘86 ICJ Depth (m) n S.L. (cm)
-
-
32 27 4.40 -
54 133 5.72 -
108 81 6.50
70 67 6.40
64 81 6.50 -
36 650 6.01
74 133 6.20
155 70 8.40
148 55 8.70
100 85 8.90
101 143 6.27 -
108 155 6.29 -
117 39 6.93
162 57 7.30
F. Colloca et al. / Fisheries Research 32 (1997) 21-32
27
spectively. On the left side of Axis II, fish size increases, while on the right, decreases with depth. 3.4. Age and growth
9-9 9cm .
Otoliths collected in October 1995 from 335 fish throughout the study area, were examined. Only the otoliths on whose interpretation all readers agreed (88% of otholits read) were taken as part of age-atlength data (Table 4). No animal older than the fourth year class was found in the sample. The corresponding Von Bertalanffy’s growth equations are:
Fig. 5. Principal Components Analysis carried out using the mean yield (n/h) of each L. cacillone size class every 25 m depth.
= 1.53) ;
males: L, = 10.85(s.e. K = 0.53(s.e.
opposed to the largest and smallest fish sizes (5-6.9 cm S.L. and lo-II.9 cm S.L.) found in the lower part. Axis I can be translated into a gonadal development factor and axis II into a depth factor. Sexual maturation increases from left to the right on the first axis, with the origin of the axis defined as the moment in which reproductive migration begins. The depth distribution of size classes increase from the lower to the upper part of the second axis. The 8-8.9 cm S.L. and the 5-6.9/10-l 1.9 cm S.L. size classes showed the deepest and shallowest distribution, re-
Table 4 Age-length 1996
r2 = 0.68 K = 0.38(s.e.
= 0.12); t0 = -0.427(s.e.
= 0.4);
r2 = 0.82 both sexes: L, = 11.7(s.e. K = 0.414(s.e.
= 0.9);
= 0.1); t,, = -0.38(s.e.
= 0.29);
r? = 0.77 Growth
rates
gurnard
of females
collected
and males
in the Central Tyrrhenian
are virtually
Sea during October
Age group (years) 0.5 m
4.5-4.99 5-5.49 5.5-5.99 6-6.49 6.5-6.99 7-7.49 7.5-7.99 8-8.49 8.5-8.99 9-9.49 9.5-9.99 lo- 10.49 10.5- 10.99 II-1 1.49 Total
= 0.5);
females: L, = 12(s.e. = 1.2);
matrix of 142 males (m) and 154 females (f) of large-scaled
Length group cm
= 0.27); t0 = -0.17(s.e.
1.5 f
2.5
m
f
2 4 12 6 12 16 12
2 4 6 10 20 8 4
m
0 4 12 8 32 6 2
3.5 f
2 6 10 8 20 8 2
m
2 8 2
4.5 f
m
4 6 10 2 2
0
0
64
54
64
56
12
22
2
Total f
4 8 6 4 22
m 2 4 12 6 12 20 24 8 34 14 2 2 2 0 142
f 2 4 6 10 22 14 14 8 24 14 16 10 6 4 154
F. Colloca et al. /Fisheries
28
Fig. 6. Length frequency distribution of L. cauillone in the Central Tyrrhenian Sea in October 1995. The arrows indicate the modal classes identified with Bhatthacharya’s method.
Research 32 (I 997) 21-32
identical. Large-scaled gurnards accomplished more than one-half of their growth during their first two years of life. Reduction of growth coincided with attainment of sexual maturity which occurred in both sexes at the end of their second year. The length frequency distributions in October 1995 analysed with the Bhatthacharya method, showed two distinct cohorts with mean length of 6.18 and 8.46 cm S.L., matching those obtained from age-at-length data for the 1 + (1.5 years) and 2 + (2.5 years) age classes (mean length 6.32 and 8.14 cm S.L. respectively) (Fig. 6).
1994-95
140 120
MO _
l-l
1985
100
c
60 60 40 20 0
s
K
9
2
2
S.L. (cm)
Fig. 7. Annual length-frequency
distributions
and linearized length-converted
catch curves of the large-scaled
gumard in the study area.
F. Colloca et al. /Fisheries
Research 32 (1997) 21-32
29
at around the end of first and second 1985-1987 and 1994-1995, respectively.
3.5. Stock assessment The natural mortality coefficients adopted in this study (m = OS), were estimated with the Djabali et al. (1994) equation. The Pauly method, with a mean habitat temperature of 16°C furnished a value of 1.O, which was assessed as being too high for the species, considering that the Z value observed in the 1985 was 0.68. Annual length-frequency distributions and linearized catch curves are showed in Fig. 7. The mean Z values ranged from 0.68 in 1985 to a maximum of 1.91 in 1986. In 1985, a very low fishing mortality (0.18) rate, compared with the other sampling years (1.41, 1.25, 1.09, respectively in 1986, 1987, 19941995), was pointed out (Table 5). The length structure of the stock showed changes from year to year (Fig. 7), suggesting that the yield per recruit analysis be carried out separately for each sampling year. The F,,, values ranged between 0.52 and 0.62 in the 1985-1987 and was of 1.16 in 1994-1995. A growth overfishing state was indicated in 1986 and 1987, while there was an opposite state in 1985. In 1994-1995, the observed fishing mortality being close to optimum. Better exploitation of the stock from the years 1986-1987 to the 19941995 was the result of an increase in the selectivity parameter c, that rose from 0.36-0.47 in eighties to 0.55 in nineties. The Lc of L. cauillone during the trawl surveys ranged from 4.26 in 1987 to the 5.47 in 1986 using a code-end mesh (stretched mesh) of 18 mm, while the Lc in 1994-1995 was 6.46 using nets with mesh between 22 and 24 mm (Table 5). Therefore the age of first capture can be estimated
Table 5 Mean annual values of mesh size, Lc, T,,, Tvrrhenian Sea
2, F, F,,
years
for
4. Discussion Sexual development appeared to be the main factor affecting size-depth distribution of L. cavillone in the Central Tyrrhenian Sea. Females reach the size of first sexual maturity (around 7 cm S.L.) at the age 1 + . The smallest fish with ripe ova measured 6 cm in spring. In summer, the size of first sexual maturity and the minimum size of maturity of the females increased respectively to 8 and 7 cm S.L. The increase in the size of maturity from the beginning to the end of the spawning period can be due to the partial spawning of L. cavillone typical of gumard species (Priol, 1932; Elder, 1976; Baron, 1985) which induces a somewhat prolonged breeding period. Rapid development of male testis and their small weight and volume compared with female gonads was documented by Baron (1985) for gumard species of east-Atlantic coasts. The same large difference in gonosomatic index between males and females was reported in the Mediterranean for Scorpaena porcus (Bradai and Bouain, 1990) and could be related to the sexual behaviour of the species. L. cavillone in the study area seems to grow more slowly than in the Gulf of Lions (Campillo, 1992) and in the Greek seas (Papacostantinou, 1982a). Both sexes accomplish more than half of their growth during the first two years of life. The reduction in growth rate after the second year coincided with the attainment of sexual maturity, as described for others
of the large-scaled
gumard
during
the trawl surveys
carried
Mesh size mm
1985 18
I986 18
1987 18
1994-1995 22-24
Lc T,, Z C.I. 95% F C.I. 95% F 0.1
5.16 1.03 0.68 0.5-0.86 0.18 O-O.36 0.61
5.41 1.14 1.91 1.46-2.36 1.41 0.96- 1.86 0.62
4.37 0.70 1.75 1.39- 2.12 1.25 0.88-1.62 0.52
6.47 1.56 1.59 1.31-1.81 1.09 0.81-1.31 1.16
out in the Central
30
F. Colloca et al. /Fisheries
gurnard species (Papacostantinou, 1982b), and a change in the feeding strategy of the species (Colloca et al., 1994). In the two sampling seasons, a low but significant relationship between body size and depth was found. As observed by Papacostantinou (1983), juveniles in the Creek seas appeared on P. oceanica meadows at 30-50 m depth and showed a positive size-depth relationship. Depth migration of the immature during growth is a common behaviour in fish (Helfman, 1978) and particularly in gurnard species (Meek, 1915; Elder, 1976; Lewis and Yerger, 1976; Ross, 1978; Richards et al., 1977b). Juveniles of L. cavillone migrated offshore from nurseries around the end of the first year of life, as the high summer abundance of fish aged 1 + on 30-60 m depth suggests, juveniles were absent from these bottoms in spring. The importance of gonadal development in the depth-size relationships of L. cavillone in the study area was shown by the Principal Components Analysis. The gonadal development factor explains the 59.8% variance, while the fish size factor explains only the 34%. This value confirms that the latter factor alone plays a secondary role to determine the depth distribution of the species in the study area, as the correlation analysis emphasized. In summer, the fish were separated into two groups according to
Life
cycle
Research 32 (1997) 21-32
sexual maturation: individuals in the 5-8 cm S.L. range that migrate offshore during growth and individuals over 9 cm S.L. that migrate shallower towards the spawning grounds. This pattern resulted in a similar depth distribution of younger (5-6 cm S.L.) and older (lo-11 cm S.L.) fish. Individuals of intermediate size (8 cm S.L.) not also in reproductive migration appeared distributed deeper than bigger and smaller fish. This agrees with the size at first maturity which was 8 cm S.L. for females in summer. Migration of gumards associated with their spawning activity has been recorded by Fulton (18991, Meek (1915) and Marshall (1946). Harden Jones (1968) stated that spawning fish undertake a contranatant migration to a spawning ground because of its position in relation to a favorable nursery area. L. cavillone carries out such migration during growth, but before gonad maturation, juveniles reach bottoms deeper than the spawning grounds. Fig. 8 shows life cycle of L. cavillone in the study area. The differences in the species abundance observed between the Anzio and Terracina fishing areas could be related to the distribution of the nursery and spawning grounds in the sampling area: latter were observed between 60-100 m offshore of the nurseries, and furthermore, P. oceunica meadows colonize larger areas in Terracina than in Anzio
of L. cavillone
Ufiflte,
1+ /5+
Fig. 8. Hypothetical
life cycle of L. cadlone
in the Central Tyrrhenian
200
Sea.
m
F. Colloca et al. /Fisheries
(Ardizzone and Pelusi, 1984). It can be hypothesized that the fish hatch in a limited zone of Terracina area and subsequently spread throughout the study area. The exploitation level of the species could be optimized by raising the cod-end mesh size normally used by the commercial fleet to the legal size (40 mm). The mesh size adopted (22-24 mm) results in an age at first capture (Lc) of 1.5 year, close to the age at first maturity. An increase in mesh size, bringing the age of first capture over this age, is desirable. The mortality values of the L. cavillone stock in the study area showed differences in the various sampling years. Fishing mortality did not exceed the F,,, in 1985 and 1994-1995, while the opposite status was observed in 1986-1987, according to the differences in observed stock structure. Such a differences can not be related to variations in fishing effort, since it did not change during the last 10 years in the study area. In the Central Tyrrhenian sea large-scaled gurnard nursery areas and spawning zones occur in restricted areas along the shelf. Thus, fluctuations in fishing mortality were caused by the characteristics of sampling design used rather than actual variations in fishing effort. In spite of the strong fishing effort in the area, large-scaled gumard is a common species. The over-exploitation risks of the species seem to be reduced by a rapid growth and short length at maturation as well as by low catchability of juveniles.
References Ardizzone, G.D., Pelusi, P., 1984. Yield and damage evaluation of bottom trawling on Posidonia meadows, in: Bouuresque, C.F., Jeudy de Grissac, A., Olivier, J. (Eds.), GIS International Workshop Posidonia oceanica Beds, Posidonie Publ., 1, 6372. Baron, J., 1985. Les Ttiglidae (Teleosteens, Scorpaeniformes) de la baie de Douamenez. La reproduction de E. gumardus, 7’. lastouiza, A. cuculus, T. lucema. Cybium 9 (41, 255-281. Beverton and Holt, 1966. Manual of methods for fish stock assessment. FAO Fish. Tech. Pap., (38) Rev. 1, 67 pp. Bhattacharya, C.G., 1967. A simple method of resolution of a distribution into gaussian components. Biometrics 23, 115 135. Bradai, M.N., Bouain, A., 1990. Donnets sur la reproduction de Scorpaena porcus du Golfe de Gab&s. Rapp. Comm. Int. Mer. MCdit. 32 (1). 265.
Research 32 (1997) 21-32
31
Campillo, A., 1992, Les pecheries francaises de Mediterranee: synthese des connaissances. Rapports Intemes de la Direction des Ressources Vivantes de I’Ifremer. IFREMER, DRV92/019-RH/SL?te, 206 pp. Caragitsou, E., Papacostantinou, C., 1988. Food habits and dietary overlap of Lepidotrigla cauillone in Greek Seas. Rapp. Comm. Int. Mer. Mtdit. 31 (21, 13. Collignon, J., 1979. Catalogue raisonne des poissons des mers marocaines (4.eme pat-tie). Bull. Inst. Pech. Marit. Marocco 81, 37-60. Colloca, F., Belluscio, A., Schintu, P., Ardizzone, G.D., 1990, Alimentazione dei triglidae de1 Tirreno Centrale. Oebalia, Suppl., XVI, (21, 643-646. Colloca, F., Gravina, M.F., Ardizzone, G.D., 1994. Trophic ecology of gumards (Pisces: Triglidae) in the Central Mediterranean Sea. Marine Life 4 (2), 45-57. Djabah, F., Mehailia, A., Koudil, M., Brahmi, B., 1994. A reassessment of equations for predicting natural mortality in Mediterranean teleosts. Naga, ICLARM Q. 17 (11, 33-34. Elder, R.D., 1976. Studies on age and growth, reproduction and population dynamics of red gumard, Chelidonichthys kutnu in the Hauraky Gulf, New Zealand. Fish. Res. Bull. 12, 77. Fisher, W., Bauchot, M.L., Schneider, M., 1987, Fiches FAO d’identification des especes pour les besoins de la p&he. (revision 1). Mediterrante et mer Noire. Zone de p&he 37. vol. 2, 761-1530. Fulton, T.W., 1899. On the migratory movements and rate of growth of the grey or common gumard. Ann. Rep. Fish. Board Scotland 3, 210-231. Gayanillo, F.C., Sparre, P., Pauly, D., 1994. The FAO-ICLARM Stock Assessment Tools (FISAT) user’s guide. FAO Comput. Info. Series (Fisheries) 6, 186. Gulland, J.A., Boerema, K., 1973. Scientific advice on catch levels. Fish. Bull. 71 (2). 325-335. Harden Jones, F.R., 1968. Biological aspect of migration. In: Arnold, Edward (Ed.) Fish Migration, 325 pp. Helfman, G.S., 1978. Patterns of community structure in fishes: summary and overview. Env. Biol. Fish. 3, 129-148. Holden, M.J., Raitt, D.F.S., 1974. Sex, maturity and fecundity. Manual of fisheries science. Part 2. Method of resource investigation and their application. FAO, Fish. Tech. Pap. 115 (Rev. 11, 214. Kartas, F., 1974. Regime alimentaire des especes du genre Lepidotrigla (Gunther, 1860) de la mer Catalane. Rapp. Comm. Int. Mer. Medit. 22 (71, 47. Lewis, T.C., Yerger, R.W., 1976. Biology of five species of searobins (Ttiglidae) from the Northeastern Gulf of Mexico. Fish. Bull. 74 cl), 93-103. Marshall, N., 1946. Observation of the comparative ecology and life history of two searobins Prionotus carolinus and Prionotus ecolans strigatus. Copeia 1946, 118- 144. Meek, A., 1915. The migration of the grey gumard Trigla gumardus. Rep. Dove. Mar. Lab., (n.s.) 4, 9-15. Moreno, R., Matallanas, J., 1983. Etude du regime alimentaire de Lepidotrigla cal,illone (Lacepede, 1801) (Pisces: Triglidae) dans la mer Catalane. Cybium 7 (3), 93-103.
F. Colloca et al. /Fisheries
32
Padoa, E., 1956. Triglidae. Uova e stadi giovanili di Teleostei. Fauna e Flora de1 Golfo di Napoli 38, 627-640. Papacostantinou, C., 1982a. Em 71)~ /3~ohoywm TOV l~Gova A&-L~OTPQ’~~
,yawhihova
(TPL~ALBoE)
TOV
LhhCKOV
Thalassographica 1 (51, 33-59. Papacostantinou, C., 1982b. Age and growth of grey gumard (Eurrigla gurnardus) in the Pagassitikos Gulf (Greece). Inv. Pesq. 46 (2), 191-213. Papacostantinou, C., 1983. Observations on the ecology of gumards (Pisces: Triglidae) in the Greek Seas. Cybium 7 (4). 71-88. Pauly, D., 1980. On the interrelationships between natural mortality, growth parameters and mean environmental temperature in 175 fish stock. J. Cons. CIEM. 39 (31, 175-192. Pauly, D., 1984a. Length-converted catch curves: a powerful tool for fisheries research in the tropics. Part. II. ICLARM Fishbyte 2 (0, 17-19. Pauly, D., 1984b. Fish population dynamics in tropical waters: a manual for use with programmable calculators. ICLARM Stud. Rev. 8, 325. Pauly, D., Soriano, M.L., 1986. Some practical extensions to Beverton and Holt’s relative yield-per-recruit model. In: Maclean, J.L., Dizon, L.D., Hosillo, L.V. (Eds.), The First Asian Fisheries Forum, Asian Fisheries Society, Manila, Philippines, 49 l-496 pp. Priol, E., 1932. Remarques sur les especes des grondins les plus communes des totes de France. Rev. Trav. Inst. Pech. Marit. 5 (21, 223-272. Oahauuov.
Research 32 (1997) 21-32
Relini, G., Piccinetti, C., 1996. Ten years of trawl surveys in Italian seas (1985-1995). FAO Fish. Rep. 533, 21-42. Richards, J., Vishnu, P., Saksena, P., 1977a. Systematics of the gumards, genus Lepidorrigla (Pisces, Triglidae), from the Indian Ocean. Bull. Mar. Sci. 27 (2), 208-222. Richards, J., Mann, J.M., Walker, J., 1977b. Comparison of spawning season, age, growth rates and food of two sympatric searobins, Prionotus evolans and P. carolinus, from Long Island Sound. Estuaries 2 (4). 255-268. Rizzi, E., Bello, G., 1986. Triglidi (Osteichthyes) de1 basso Adriatico. Nova Thalassia 8 (3), 665-666. Ross, S., 1978. Trophic ontogeny of the Leopard searobin Prionotus scitulus (Pisces: Triglidae). Fish. Bull. 76 (11, 225-234. Serena, F., Baino, R., Voliani, A., 1990. Distribuzione dei Triglidi (Osteichthyes, Scorpaeniformes) nell’Alto Tirreno. Oebalia, Suppl., XVI (11, 269-278. Sokal, R.R., Rohlf, F.J., 1980. Biometry, 2nd edn., W.H. Freeman, New York, 859 pp. Sparre, P., Ursin, Venema, SC., 1989, Introduction to tropical fish stock assessment. Part 1, Manual FAO Fish. Tech. Paper, 306,429 pp. Tsimenides, N., Machias, A., Kallianotis, A., 1992. Distribution pattern of triglids (Pisces: Triglidae) on the Cretan shelf (Greece), and their interspecific associations. Fish. Res. 15, 83-103.