Todaropsis Eblanae

BULLETIN OF MARINE SCIENCE, 71(2): 711–724, 2002 RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE (BALL, 1841), IN THE AREA FISHED BY FRENCH ATLANTIC TRAWLERS J. P . R obin, V . D enis, J. Royer and L. Challier ABSTRACT Short-finned squid landed by the French fishery are by-catch of trawlers operating in the Northern Bay of Biscay and Southern Celtic sea. In the period November 1997–June 1999 samples of commercial specimen were collected monthly. A total 1065 Todaropsis eblanae were analysed for biological parameters. In a subsample of animals age was determined using statoliths. Mature animals are observed almost all year round, however juvenile recruitment occurred mainly in winter and sexual maturation increased in spring. Size at sexual maturity (DML50) was 16.5 cm in females and 13.5 cm in males. Length frequencies showed that the range of exploited stages was 9–29 cm in females and 8–22 cm in males. Statolith analysis indicated that youngest recruits were about 4 mo old and that growth was faster in females than in males (3.41 and 1.86 cm mo−1, respectively). Sex-related differences in growth and size at maturity are in agreement with previously published data from the Galician coast. T o daropsis eblanae (Ball, 1841) is an oceanic squid, which lives near the bottom on the shelf break. In the Mediterranean, it has been observed at depths between 200 and 600 m in the Western area (Quetglas et al., 2000) and in shallower waters in the Central and Eastern areas (Belcari and Sartor, 1993; Tursi and D’Onghia, 1992). In theAtlantic, southeast populations of this species were considered by Roeleveld et al. (1992) as an indicator of the necto-benthic community in the upper slope (300–800 m) off Africa whereas the species occurs on the continental shelf to the west and south of Ireland (Lordan et al., 1998). In spite of a deeper distribution than Loliginids, T. eblanae is said to have lifetraits and behavior more similar to neritic squids than to oceanic ones (Clarke, 1966). Geographically, T. eblanae is widely distributed from eastern Atlantic to Mediterranean sea between 60°N and 36°S (Roper et al., 1984). The species was also recorded in Southwest Indian Ocean (Nesis, 1979) and in Australian waters (Lu, 1982). T. eblanae is, together with Illex coindettii, the only Ommastrephid squid exploited by the French Fishery. This resource is mainly a by-catch for trawlers operating in the Northern Bay of Biscay and Celtic Sea. It is only a minor component of the catch which is still discarded in areas of low abundance like in the English Channel. The two species are not distinguished by fishermen and landings are not split into commercial categories. Little published information exists on T. eblanae. In European waters studies carried out to describe exploited stages concern Galician waters (Gonzales et al., 1994) and Scottish waters (Hastie et al., 1994). This study presents results on the Northeast Atlantic population exploited by French trawlers. The study of the proportion of this species in the landings and investigations into its population biology were based on the sampling of commercial landings in Le Guilvinec (Southwest Brittany) in the period November 1997–June 1999. In addition, the spatial distribution was derived from fishery statistics. 711 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 712 Figure 1. Location of the fishing harbour where biological samples were collected and ICES statistical divisions fished by French trawlers (white zone). MATERIALS AND METHODS Biological samples of landings of the trawl fishery were collected in Le Guilvinec fish-market (Fig. 1). Geographic origin of each catch was not recorded but during the study period 93% of short finned squid landed by Le Guilvinec trawlers came from two ICES divisions (Fig. 1-8A,1-7H). From November 1997 until June 1999 a 40-kg box of unsorted short-finned squid was collected monthly. Fishermen store the catch on ice and samples were kept frozen from transport until processing in the University laboratory. In Caen, species were determined and basic biological data recorded (i.e., dorsal mantle length, body weight, sex, maturity stage -according to Lipinski (1979) modified by Gonzales and Guerra (1996), total reproductive system weight, separated gonad weight and digestive gland weight). A total of 1065 T. eblanae were analysed during the sampling period. Reproduction timing was analysed with temporal variations of both gonado-somatic index (GSI) and maturity stages, histological observations having shown that GSI should not be used alone (Lipinski and Underhill, 1995). The gonado-somatic index (Mangold-Wirz, 1963) is: GSI = 100 × GW/(BW − GW) where GW is gonad weight (ovary or testis) and BW is total body weight. Length-weight relationships were described by the power model: ROBIN ET AL.: RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE 713 W = aLb where W is body weight, L is DML, a and b are the regression coefficients. Length at sexual maturity was estimated via the DML50 parameter (length at which 50% of the individuals are maturity stages 4, 5 and 6). This parameter was derived from the fitting of a Logistic curve to the frequencies of mature animals per length class (DML) (Coelho et al., 1994): 1P = i1+ e− a+bL <ul style="display: flex;"><li style="flex:1">(</li><li style="flex:1">)</li></ul>iwhere Pi is the percentage of mature individuals in length class Li, a and b are the regression coefficients and DML50 = −a/b. In a preliminary step, an estimation of growth was sought by studying mean length progression, which provides underestimates of the phenomenon (Caddy, 1991). Regression lines were fitted between average DML and time in males and females. A sub-sample of T. eblanae was selected for the analysis of age and growth during a recruitment period (November 1997–February 1998). In a preliminary stage, 57 statoliths of specimens ranging from 8 to 27 cm (27 females and 30 males) were ground and polished. Statolith preparation techniques followed a protocol named by Dawe and Natsukari (1991) “method of Arkhipkin and Villanueva” in which both sides of the statolith are ground, starting with the concave side. The main difference with Arkhipkin’s protocol is that statoliths were mounted with a heat-melting resin (Crystal Bond™) with which it was easier to invert. Grinding papers had grain sizes ranging from 3 to 0.3 mm. Increments counts often differ between light microscopy and scanning electron microscopy (Lipinski and Durholtz, 1994). In this case, increments were counted in light microscopy using the T.N.P.C.® software from the nucleus to the dome edge (Fig. 2). This analysis was based on the hypothesis of daily deposition of statolith increments which had not been tested in T. eblanae but which was validated in Alloteuthis subulata (Lipinski, 1986) Idiosepius pygmaeus (Jackson, 1987) Todarodes pacificus (Nakamura and Sakurai, 1990) and in Loligo vulgaris (Natsukari and Komine, 1992). Fisheries statistics for French trawlers were obtained from the official database held by Centre Administratif des Affaires Maritimes. Monthly short-finned squid landings per ICES rectangle in the period January 1989–December 1998 were included in the Caen Cephalopods GIS Application (Pierce et al., 1998). RESULTS PROPORTION OF T. EBLANAE IN LE GUILVINEC LANDINGS.—During the study period T. eblanae was observed in all samples, although it was generally a minor component of shortfinned landings (about 30%, Fig. 3). The two Ommastraephid species seemed to be exploited simultaneously and not in a sequence as described in English Channel loliginids. Changes in species proportions showed that the percentage of T. eblanae was minimal in December 1997 and maximal in September 1998. Todaropsis dominated during 4 mo in summer 1998. In the light of the species life-cycle, unbalanced proportions in these 2 mo were likely a consequence of lags in the recruitment or the spawning of these two species. SEX RATIO.—Out of 1065 squid collected, 610 were females and 455 were males, which corresponds to an overall ratio of 0.75. Sex ratio in monthly samples was not significantly different from the 1:1 equilibrium except in summer 1998 and in April 1999 (Fig. 2). The unbalanced situation observed in March 1998 (68% of males) do not represent a BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 714 Figure 2. Statolith of a male Todaropsis eblanae; DML = 18 cm; Increment number = 177. ROBIN ET AL.: RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE 715 Figure 3. Monthly proportion (bars) of Todaropsis eblanae in Le Guilvinec short-finned squid landings and monthly sex ratio (males:females) (line). Monthly sex ratio significantly different from 1 are indicated with white circles (χ2 test P < 0.05). significant departure from the equilibrium but rather a statistical error related to a small sample size (n = 19 in this month). SPATIAL DISTRIBUTION.—Abundance indices in Ommastrephid squid were derived from French trawlers CPUE (Fig. 4). Although fishery records are not species specific, this series of maps underlines that in the area fished by French trawlers short-finned squid are mainly observed at the shelf edge. Month-to-month variations suggest that stock spread is higher in late spring than in winter (when the distribution looks more patchy). The spread of Todaropsis and Illex in the Bay of Biscay and Celtic sea in spring is consistent with the lack of genetic differences between Irish and Spanish samples (Dillane et al., 2000). LENGTH-FREQUENCIES.—T. eblanae length-frequencies at monthly intervals were plotted in Figure 5. The largest specimen was a 29 cm female, although most individuals ranged between 9 cm and 25 cm in females and between 8 cm and 22 cm in males. The highest percentage of small animals (<12 cm) occurred in December 1997 and in November 1998 for both sexes, which indicated a recruitment in late autumn to early winter. Body size increased over the winter to reach maximum size in June 1998. Females grew faster and reached a larger size than males. From June 1998 to November 1998 average DML did not seem to increase. This plateau is likely be related to adults post-spawning mortality. Several minor modes were observed in addition to the main mode in some particular months (like in February 1999). However, such micro-cohorts could not be followed over a significant period of time. AGE AND GROWTH.—In the period December 1997 to June 1998 a significant relationship was observed between mean length and time (P < 0.05). Calculated growth rates (and 95% confidence limits) were respectively 0.76 cm mo−1 (0.12–1.24) in males and 1.22 cm mo−1 (1.18–1.86) in females. Figure 6 shows the relationship between the DML and the number of statolith increments for each sex. Because of the limited number of statoliths counted, only provisional conclusions were drawn. Studied samples did not contain any specimens having reached BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 716 Figure 4. Distribution and abundance of Ommastrephid squid in 1998: French bottom trawlers CPUE (kg h-1) bathymetry contours between 20 and 200 m depths underline the shelf edge); a. period January–June; b. (opposite page) period July–December (in each month an inset sector diagram shows the percentage of Todaropsis eblanae in Le Guilvinec short-finned squid samples). the age of 1 yr (highest number of increments: 255). Also, this analysis underlined that inter-individual variability in growth is very high. Average growth rates based on statoliths counts were estimated with simple linear regression. Significant fits (P < 0.05) were obtained in both sexes (correlation coefficient r = 0.72 in females and 0.67 in males), although growth rates (1.86 cm mo−1 in males and 3.41 in females) could not be considered significantly different: standard deviation for growth rate is 0.68 and 0.46 cm mo–1 ROBIN ET AL.: RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE 717 in females and males respectively. Statoliths-derived growth rates resulted unsurprisingly higher than estimates based on mean DML (P < 0.05). LENGTH-WEIGHT RELATIONSHIP.—The relationship between DML and Weight are expressed by following equations: In females: In males: W = 0.33L2.41 W = 0.67L2.15 (sample size: n = 610) (r = 0.93) (sample size: n = 455) (r = 0.90) Regression fittings were all highly significant (P < 0.001). Difference in the power coefficient b suggest that females are broader and males thinner. BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 718 Figure 5. Monthly length-frequency distribution in female (a) and male (b) T o daropsis eblanae. MATURATION.—Gonado-somatic index (GSI), presented in Figure 7, suggested clearly an annual maturation cycle for both sexes. Female GSI was minimal in November 1997– January 1998 and again in January 1999. This index increased progressively to a maximum in summer, in May–September 1998 and May 1999. High values were observed during a longer period in females than in males. Male GSI was minimal in November– December and maximal in May 1998 and in March–April 1999. ROBIN ET AL.: RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE 719 Figure 6. Relationship between number of growth increments in polished statoliths and dorsal mantle length (DML) in female (a) and male (b) Todaropsis eblanae. Proportions of maturity stages (Fig. 8) were at first sight consistent with the GSI trends. Immature individuals (stages I to III) dominated in winter (80%) and the greatest proportion of mature animals (stages IV and V) appeared in summer (85%). Post-spawning specimen were only observed in males (July and November). Maturity stages underlined the heterogeneity of the maturation process (with stages II to V present almost all year round). SIZE AT MATURITY.—In both females and males (Fig. 9.), size at maturity (DML50) is derived from the following equations 1P = i<ul style="display: flex;"><li style="flex:1">In females, </li><li style="flex:1">(number of length-classes k = 15, r = 0.99) </li></ul>1+ e− −17.7+1.07L <ul style="display: flex;"><li style="flex:1">(</li><li style="flex:1">)</li></ul>iBULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 720 Figure 7. Mean monthly Gonado-somatic index (GSI) in female and male Todaropsis eblanae. 1P = i<ul style="display: flex;"><li style="flex:1">In males, </li><li style="flex:1">(number of length-classes k = 13, r = 0.97) </li></ul>1+ e− −12.4+0.92L <ul style="display: flex;"><li style="flex:1">(</li><li style="flex:1">)</li></ul>iCorrespondingly DML50 are 165 mm and 135 mm in females and in males, respectively. DISCUSSION The set of samples collected in Le Guilvinec provide the first opportunity to describe T. eblanae exploited by French trawlers. In this fishery the short-finned squid resource is a mix of T. eblanae and I. coindetii and both species are observed throughout the year. This rather constant occurrence of T. eblanae is worth noting because further North the species appears more scarce: it was absent from Scottish landings during several years (Hastie et al., 1994) and was not caught in summer in Irish waters (Lordan et al., 1998). The appearance of T. eblanae in Le Guilvinec short-finned squid samples looks similar to what was observed in Spanish landings in Galicia (Gonzales et al., 1994). Maximum size recorded (29 cm for female and 22 cm for male) are higher than those indicated by Roper et al. (1984) for this species (27 and 16 cm for females and males respectively). Sex related differences in growth, maximum size and size at maturity are consistent with previous observations of T. eblanae (Clarke, 1966; Gonzales et al., 1994; Hastie et al., 1994; Mangold-Wirz, 1963). Female reach a larger size than males also in I. coindetii (Sanchez et al., 1998), in T. pacificus (Okutani, 1983) and in most other Ommastraephid species (Roper et al., 1984). ROBIN ET AL.: RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE 721 Figure 8. Maturity stages in female (a) and in male (b) T o daropsis eblanae. Growth rates, calculated from monthly average DML, are largely underestimated in both sex in comparison with the estimations by the statoliths method. Analysing the origin of this bias Caddy (1991) suggested that length-frequency estimates were influenced by three main phenomena: juvenile recruitment, gear selectivity and post-spawning mortality. Statolith readings suggest that females have higher growth rates than males. However, statistical analysis of growth curves did not reveal significant difference in growth rate BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 722 Figure 9. Sigmoid curves of size frequency produced from mantle length measurement of mature between the sexes. This is clearly related to the low number of studied statoliths and to the high individual variation in growth. Nevertheless, these preliminary readings are in agreement with a one year life-span in this species as suggested by Arkhipkin and Laptikhovsky (2000) in the Northwest African shelf. Additional ageing of large specimens is required to confirm this, although statolith ring deposition can be less clear in oldest animals (Lipinski et al., 1993). Sex ratio in pooled samples is different from that observed by Gonzalez et al. (1994) who found males more numerous in Galician waters. However, this overall result can be influenced by temporal changes in sample size. In both areas monthly ratios are generally not significantly different from the equilibrium. Significant differences observed in Le Guilvinec samples in summer 1998 suggest that post-spawning behavior (or survival) could be different according to the sex. All results on maturation clearly describe an annual cycle of maturation. Mature individuals were collected throughout the sampling period but the peak of the spawning season began in March–April and apparently lasted until September. This period is similar to that observed by Mangold-Wirz (1963), Gonzales et al (1994) and Arkhipkin and Laptikhovsky (2000) but earlier than that described by Hastie et al. (1994) in Scottish waters (June–September). The main recruitment period (November–December) seems to be shorter in French waters than in Galicia or further South. The age of recruits suggests that they hatched in late spring as observed also by Gonzales et al. (1994) or Arkhipkin and Laptikhovsky (2000). Males are more precocious than females as recorded by Coehlo and Borges (1982), Gonzales et al. (1994) and Mangold-Wirz (1963) and mature at smaller size. Size at maturity of French fishery samples fall within the size range of maturation estimated by Mangold-Wirtz (1963), (110–140 mm for males and 160–190 mm for females). In conclusion, additional information on T. eblanae provided by the sampling of French landings is consistent with biological parameters collected in other parts of its Atlantic range. In comparison with study areas more to the South shorter periods for spawning and recruitment and more pronounced seasonality are observed. This latitudinal trend is very likely related to a-biotic environmental factors which determine life history. ROBIN ET AL.: RECRUITMENT, GROWTH AND REPRODUCTION IN TODAROPSIS EBLANAE 723 Ommastraephid squids are only a minor component of French cephalopod production, however from the biological point of view they provide an interesting example of a lifecycle timing totally different from that of Loliginid populations in the same area (Collins et al., 1997; Guerra and Rocha, 1994). Such differences will have to be taken into account when times come to propose management measures for French squid stocks. LITERATURE CITED Arkhipkin, A. I. and V. V. Laptikhovsky<a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(2000)80L.747[aid=7455805]" target="_blank">. 2000. Age and growth of the squid </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(2000)80L.747[aid=7455805]" target="_blank">T</a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(2000)80L.747[aid=7455805]" target="_blank">o</a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(2000)80L.747[aid=7455805]" target="_blank">daropsis eblanae </a> <a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(2000)80L.747[aid=7455805]" target="_blank">(Cephalopoda: Ommastrephidae) on the north-west African shelf. J. Mar. Biol. Ass. U.K. 80: </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(2000)80L.747[aid=7455805]" target="_blank">747–748. </a> Belcari, P. and P. Sartor. 1993. Bottom trawling teuthofauna of the northern Tyrrhenian Sea. Sci. Mar. 57: 145–152. Caddy, J. F. 1991. Daily rings on squid statoliths: An opportunity to test standard population models? Page 53–66 in P. Jereb, S. Ragonese and S. von Boletzky, eds. Squid age determination using statoliths, NTR-ITPP, Spec. Publ. 1. Clarke, M. R. 1966. A review of the systematics and ecology of oceanic squids. Adv. Mar. Biol. 4: 91–300. Coelho, M. L. and M. T. Borges. 1982. Preliminary results of research on squids, Loliginidae and Ommastrephidae, from the portuguese coastal waters. ICES CM/K. 34 p. __________, J. Quitela, V. Bettencourt, G. Olavo and H. Villa. 1994. Population structure, maturation patterns and fecundity of the squid Loligo vulgaris from southern Portugal. Fish. Res. 21: 87–102. Collins, M. A., G. J. Pierce and P. <a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0021-8901(1997)34L.778[aid=7455804]" target="_blank">R. Boyle. 1997. Population indices of reproduction and recruit- </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0021-8901(1997)34L.778[aid=7455804]" target="_blank">ment in </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0021-8901(1997)34L.778[aid=7455804]" target="_blank">Loligo forbesi </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0021-8901(1997)34L.778[aid=7455804]" target="_blank">(Cephalopoda: Loliginidae) in Scottish and Irish waters. J. Appl. Ecol. </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0021-8901(1997)34L.778[aid=7455804]" target="_blank">34: 778–786. </a> Dillane, E., P. Galvin, J. Coughlan, P. G. K. Rodhouse and T. F. Cross. 2000. Polymorphic VNTR loci in the Ommastrephid squid, Illex coindetii (Verany,1839) and Todaropsis eblanae (Ball, 1841). Mol. Ecol. (in press). Dawe, E. G. and Y. Natsukari. 1991. Light microscopy. Pages 83–95 in P. Jereb, S. Ragonese and S. von Boletzky, eds. Squid age determination using statoliths, NTR-ITPP. Spec. Publ., vol. 1. Guerra, A. and F. Rocha. 1994.The life history of Loligo vulgaris and Loligo forbesi (Cephalopoda: Loliginidae) in Galician waters (NW Spain). Fish. Res. 21: 43–69. Gonzales, A. F. and <a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0036-4827(1996)81L.107[aid=7452049]" target="_blank">A. Guerra. 1996. Reproductive biology of the short finned squid </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0036-4827(1996)81L.107[aid=7452049]" target="_blank">Illex coindetii </a> <a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0036-4827(1996)81L.107[aid=7452049]" target="_blank">(Cephalopoda, Ommastrephidae) of the Northeastern Atlantic. Sarsia 81: 107–118. </a> ____________, M. Rasero and A. Guerra. 1994. Prelminary study of Illex coindetii and Todarpsis eblanae (Cephalopoda: Ommastrephidae) in northern spanish Atlantic waters. Fish. Res. 21: 115–126. Hastie, L. C., J. B. Joy, G. J. Pierce and C. Y<a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(1994)74:2L.367[aid=7455807]" target="_blank">au. 1994. Reproductive biology of </a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(1994)74:2L.367[aid=7455807]" target="_blank">T</a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(1994)74:2L.367[aid=7455807]" target="_blank">o</a><a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(1994)74:2L.367[aid=7455807]" target="_blank">daropsis eblanae </a> <a href="/goto?url=http://www.ingentaconnect.com/content/external-references?article=0025-3154(1994)74:2L.367[aid=7455807]" target="_blank">(Cephalopoda: Ommastrephidae) in Scottish waters. J. Mar. Biol. Ass. U. K. 74(2): 367–382. </a> Jackson G. D. 1987. The use of statolith microsturctures to analyze life-history events in the small tropical cephalopod Idiosepius pygmaeus. Fish. Bull., 87 (2) : 265–272. Lipinski, M. R. 1979. Universal Maturity Scale for the Commercially-important squids (Cephalopoda: Teuthoidea). The Results of Maturity Classification of the Illex illecebrosus Population for the years 1973–1977. I.C.N.A.F., 79/II/38 : 40 pp. _____________. 1986. Methods for the validation of squid age from statoliths. J. Mar. Biol. Assoc. U. K., 66: 505–526. _____________ and Durholtz M.D. 1994. Problems associated with ageing squid from their statoliths: towards a more structured approach. Antarct. Sci. 6(2): 215–222.

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<I>Todaropsis Eblanae</I>