SCI. AR., 65 (): 75-8 SCIENIA ARINA 2 Populaion size and exploiaion of gian squid (Dosidicus gigas D Orbigny, 835) in he Gulf of California, exico* ENRIQUE ORALES-BOJÓRQUEZ, AGUSÍN HERNÁNDEZ-HERRERA 2, ANUEL O. NEVÁREZ-ARÍNEZ 3, IGUEL ANGEL CISNEROS-AA 3 and FRANCISCO JAVIER GUERRERO-ESCOBEDO Insiuo Nacional de la Pesca. Cenro Regional de Invesigación Pesquera, La Paz. Carreera a Pichilingue km, CP 232, La Paz, Baa California Sur, éxico. E-mail: emboorq@redipn.ipn.mx 2 Cenro Inerdisciplinario de Ciencias arinas. IPN. Ap. Posal 592. Col. Cenro CP 23. La Paz, Baa California Sur, éxico. 3 Insiuo Nacional de la Pesca. Cenro Regional de Invesigación Pesquera, Guaymas. Calle 2 Sur No. 65. CP 854, Guaymas, Sonora, éxico. SUARY: he mos imporan landing sies of he gian squid (Dosidicus gigas D Orbigny, 835) fishery in he Gulf of California, exico are Guaymas, in Sonora and Sana Rosalía, in Baa California Sur. An increase in he species biomass resuled in increased landings, ranging from 6, 2 ons in 994 o 4, ons in 996. he developmen of a managemen sraegy for his fishery based on he proporional escapemen has been suggesed. his necessiaes he esimaion of he populaion size when he fishing season begins in order o deermine he amoun of fishing effor. Weekly cach and effor daa were repored from Ocober 995 o arch 996 for hree flees operaing in he Gulf of California. he populaion size esimaed using a maximum likelihood model was 82, ons wih a proporional escapemen of 66%. Key words: recruimen, likelihood, muliflee model, proporional escapemen. INRODUCION he gian squid fishery in he Gulf of California (Fig. ) began in 974 wih a small arisanal flee composed of small boas called pangas using ouboard moors wih a crew of wo fishermen using hand igs. his flee fished wo o hree monhs during he summer when he sock was near he coas. he producion was small and he cach was consumed locally (Ehrhard e al., 983). *Received January 8, 2. Acceped Sepember 9, 2. In 978, par of he shrimp rawler flee of he Gulf of California was devoed o he gian squid fishery during he summer monhs, fishing wih six o en fishermen wih hand igs per vessel. High abundance of squid was recorded from 979 o 98 (Fig. 2). his promoed he involvemen of hree fishing flees, a vessel flee comprising 285 shrimp rawlers of various characerisics wih six o en fishermen wih hand igs, 5 Japanese vessels wih an auomaic igging sysem, and a small arisanal flee wih wo fishermen using hand igs. POPULAION SIZE AND EXPLOIAION OF DOSIDICUS GIGAS 75
FIG.. Sudy zone in he Gulf of California, exico. Beween 983 and 987, he fishery disappeared because he abundance of he sock was reduced (Fig. 2). he causes of he collapse were no defined, bu a relaion beween recruimen overfishing and unfavorable environmenal condiions associaed o El Niño 982-983 were assumed (Kle, 996). From 989 o 992, some exploraory squid fishing was carried ou by a flee of six Japanese vessels equipped wih auomaic igging sysem. During 995 an increase in squid abundance was observed. In 996 a cach above 4, ons was obained by hree flees (fig. 2) which were composed respecively of 5 shrimp rawlers from Sonora wih six o en fishermen using hand igs (subsequenly called vessel flee ), and wo arisanal flee of 646 pangas from Baa California Sur and 342 pangas from Sonora. FIG. 2. Landing records of Dosidicus gigas from Sonora and Baa California Sur, éxico. During fishing seasons previous o collapse, he biomass esimaions for he deerminaion of he poenial cach were based on virual populaion analysis (Ehrhard e al., 983), and analysis of survey daa in he Gulf of California (Kle, 996). Subsequenly, orales-boórquez e al. (997) conduced an evaluaion of he sock, using he DeLury depleion model and cach equaion, whereas Nevárez-arínez and orales-boórquez (997) deermined he biological reference poin (BRP) for he gian squid fishery based on he proporional escapemen. Recenly a single cohor biomass model was developed for he managemen of gian squid fishery in he sae of Sonora, using proporional escapemen as a reference o conrol fishing effor for gian squid (Hernández-Herrera e al., 998). In he presen sudy an esimaion of he iniial recruimen of he gian squid in he Gulf of California, exico is calculaed, based on he analysis of cach per uni effor daa from Sana Rosalía B. C. S. and Guaymas, Sonora, éxico. Beween hese wo fishing grounds 9% of he oal landings is recorded. In his way he implicaions for managemen of he resource were deermined. AERIAL AND EHODS Weekly cach (ons) and effor (fishing nighs) daa were repored during he period Ocober 22, 995 o arch 3, 996. hese records were obained from hree differen flees fishing simulaneously in he Gulf of California using hand igs as fishing gear. he landing por for wo of hem, an arisanal and a vessel flee, is Guaymas, whereas for he oher (an arisanal flee), Sana Rosalía. he cach in weigh per week was convered o cach in number of individulas per week, using he average individual weigh per week (Hernández-Herrera e al., 998). he following muliflee model described by Rosenberg e al. (99) was used: () Where N = Populaion size a ime, C = oal cach of all he flees in he fishery during ha period of ime, and = Naural moraliy. he expression in erms of he iniial recruimen is as follows: / N = N e e Ce 2 N = N e C e / / 2 ( ) 2 ( i ) (2) 76 E. ORALES-BOJÓRQUEZ e al.
N = recruimen in he beginning of he fishing season. his expression showed he size of he populaion as he number of individuals ha survive he naural moraliy, minus hose individuals capured. he lower limi of he recruimen for a susainable yield is expressed as: / N e Ce (3) Which means, ha he iniial recruimen mus be a leas equal o he sum of he caches. he esimae of he iniial recruimen was obained using a maximum likelihood model (L) considering he ineracion of differen flees according o he following expression (Rosenberg e al., 99; Pierce and Guerra, 994): J / 2 2 = ln L K 2 2 = lnσ σ C q f Nexp 2 2 = 2 i ( ) J = (4) In his model, i is assumed ha cach is derived from a known effor series (f). Effor from represenaive groups of he paricipaing fishing flees can be used as indicaors and no necessarily he oal effor of all he vessel. However, cach per uni effor (CPUE) is assumed o be direcly proporional o he abundance of he sock during his period of ime (Rosenberg e al., 99). he maximum likelihood model was derived assuming ha he cach obained by each flee is disribued normally wih mean = q f N exp -/2 and variance = var(c )=σ 2. he unknown variables o be esimaed are N, q ( =,2,...J), and σ 2 ( =,2...J); indicaes he number of flees in he fishery and = ime in weeks ( =,2...). hus all he N can be expressed in erms of N (For deails o see Appendix I). o compue q of he arisanal flee of Guaymas and Sana Rosalía, previous esimaes of (. per week; Hernández-Herrera e al., 998) and of q (4.29 E-4; orales-boórquez e al., 997) for he adaped shrimp flee of Guaymas were used (Appendix II). hese values were used as fixed parameers in he muliflee model. he sock exploiaion by he vessel flee was considered o be represenaive of he whole populaion, because of he wide coverage of fishing grounds wihin he Gulf of California (Guaymas and Sana Rosalía) by he flee. he proporional escapemen (K) was esimaed per week as follows: K= exp -F (Beddingon e al., FIG. 3. Variaion in fishing effor observed, vfg = vessel flee in Guaymas, afg = arisanal flee in Guaymas, afsr = arisanal flee in Sana Rosalía. 99), where F = Fishing moraliy. In his sudy, he conservaive level of arge escapemen K = 4%, was used as recommended by Rosenberg e al. (99). RESULS Effor and is rend during he sudy period varied grealy beween he hree flees (Fig. 3). he effor of he vessel flee showed a slow increase unil week 3 and subsequenly varied beween 5 o 4 fishing nighs/week. he effor of he arisanal flee of Guaymas was raher erraic unil week 4 showing a decreasing effor oward he end of he period. he aciviy of he arisanal flee of Sana Rosalía was inerruped for several weeks due o changes in he availabiliy of he resource. During his period, gian squid are concenraed principally off he coas of Guaymas. However, from week 8, effor increased dramaically from o fishing nighs/week in only four weeks. CPUE for he vessel flee showed a peak of 47 ons, followed by a sharp decline he nex 4 weeks FIG. 4. rends of he cach per uni effor (CPUE) by flee in he Gulf of California, exico, vfg = vessel flee in Guaymas, afg = arisanal flee in Guaymas, afsr = arisanal flee in Sana Rosalía. POPULAION SIZE AND EXPLOIAION OF DOSIDICUS GIGAS 77
FIG. 5. Populaion size esimaed in he Gulf of California, exico. FIG. 6. rend of he proporional escapemen during 2 weeks. and he remained quie sable in 4 ons/vessel/week. he CPUE of he arisanal flee of Guaymas varied beween 48 and ons/panga/week. CPUE of he arisanal flee of Sana Rosalía was smaller, beween 7 and 7 ons/panga/week (Fig. 4), while no clear paern was defined, due o he scarciy of he daa. he biomass esimae of gian squid was 82, ons, wih a range of 63, and 97, ons (95% CI) (Fig. 5). he cachabiliy was.486 E-5 (s.d..857 E-6) for he arisanal flee of Guaymas and q = 6.432 E-6 (s.d. 2.35 E-6) for ha of Sana Rosalía. During 2 fishing weeks he proporional escapemen decreased o a final value of 66%, higher han he 4% used as a reference in he fishery (Fig. 6). DISCUSSION Cach and effor daa of hree squid flees were used o esimae gian squid biomass. Our esimae does no differ from ha of orales-boórquez e al. (997) for he same period using only daa from wo flees from Guaymas, Sonora. his is because he disribuion of squid is principally off he coas of Guaymas, herefore, squid were no available o he arisanal flee of Sana Rosalía during 2 weeks in he winer. he evoluion of he CPUE for he vessel flee reflecs he rend of biomass of D. gigas in he Gulf of California. Weekly variaions of CPUE in he arisanal flee of Guaymas are due o movemens of squid wihin he fishing ground, raher han o he vessels accessibiliy problems. According o some observaions made during a survey carried ou in 996, 997 and 998 zones wih high concenraion of D. gigas have been shown beween Sana Rosalía and Guaymas, whereas no cach was recorded Souh of Loreo, B.C.S, and Yavaros, Sonora. In his case, he squid fishery is developed principally beween Sana Rosalía and Guaymas (Nevárez-arínez e al., 2). Rosenberg e al. (99) showed, wih CPUE daa, he possibiliy of applying a managemen sraegy for squid fisheries using he proporional escapemen as a ool for he conrol of he fishing effor. hey suggesed wo alernaive managemen opions: a) Limiing he number of licenses and deermining allowable levels of effor prior o he sar of he fishing season, or b) Limiing he lengh of he fishing season, monioring he sock during he fishing season, and deermining wheher he fishing season needs o be shorened (Basson and Beddingon, 993; Beddingon e al., 99; Rosenberg e al., 99). Proporional escapemen is considered as a valuable ool for a managemen sraegy if his value is direcly relaed o a biological reference poin (Nevárez- arínez and orales-boórquez, 997). I is more reliable hen o avoid recruimen overfishing, which is defined as he level of fishing pressure ha reduces he spawning biomass produced by a year class over is lifeime below he spawning biomass of is parens. Recruimen overfishing, implies exploiaion of fishery resource a such an inensive level ha compensaory sock responses are insufficien o mainain a normal paern of recruimen (Overholz e al., 986; Sissenwine and Shepherd, 987). Some biological reference poins used o avoid recruimen overfishing are: a) F max defined as he fishing moraliy rae ha maximizes yield per recrui, b) F msy defined as he fishing moraliy rae a an equilibrium condiion, c) F., which corresponds o he poin a which he yield per marginal 78 E. ORALES-BOJÓRQUEZ e al.
recrui wih an increase of he fishing effor beyond. will no increase in any imporan way he yield derived from fishing (Gulland, 983), and d) F rep defined as he moraliy rae by fishing ha corresponds o an average replacemen level of he populaion. In principle, a good biological reference poin mus consider: a) inrinsic biological aspecs of he populaion, b) he variabiliy induced by he environmen, and c) he error wihin he esimae (Walers and Ludwing, 98). In he case of he gian squid fishery, Nevárez-arínez and orales- Boórquez (997) used as BRP F %SB which is he fishing moraliy ha allows survival of a cerain percenage of he spawning biomass (SB) (Caddy and ahon, 995). Rosenberg e al. (99) defined he 4% arge proporional escapemen as an adequae level for he conservaion of he spawning sock of he squid Illex argeninus off he Falkland islands. his policy is considered also in oher squid fisheries in he world (Beddingon e al., 99). he goal of his managemen sraegy is o allow an escapemen value of aduls such ha he probabiliy of a low recruimen is reduced (Rosenberg e al., 99; Beddingon e al., 99). In our case, a final escapemen of 66% a week 2 was esimaed, which is higher han he obecive of managemen. he esimae of recruimen is imporan o decide he number of fishing licenses. orales- Boórquez e al. (997) and Hernández-Herrera e al. (998) showed ha he squid fishery is suppored by one cohor wih a recruimen in ay. For proper managemen, we mus consider ha he size of recruimen can vary considerably from one year o anoher. oreover, he number of licenses mus also consider he effor and he efficiency of he flees. hus, recruimen esimaes will allow o amend problems associaed wih changes in he efficiency of he flees, principally variaions in he cachabiliy (Basson e al., 996) or in he fishing power (Rosenberg e al., 99; Basson and Beddingon, 993). ACKNOWLEDGEENS We hank Araceli Ramos, Everardo iranda and Aleandro Balmori, of Cenro Regional de Invesigación Pesquera de Guaymas, for heir suppor in obaining saisical daa on gian squid. Ellis Glazier, CIBNOR, S. C., edied he English version of his work in manuscrip form. REFERENCES Basson,. and J.R. Beddingon. 993. Risks and uncerainies in he managemen of a single-cohor squid fishery: he Falkland Islands Illex fishery as an example. In: S. J. Smih, J. J. Hun and D. Rivard (eds.), Risk evaluaion and biological reference poins for fisheries managemen. Can. Spec. Pub. Fish. Aqua. Sci., 2: 253-259. Basson,., J.R. Beddingon, J.A. Crombie, S.J. Holden, L.V. Purchase and G.A. ingley. 996. Assessmen and managemen echniques for migraory annual squid socks: he Illex argeninus fishery in he Souhwes Alanic as an example. Fish. Res., 28: 3-27. Beddingon, J.R., A.A. Rosenberg, J.A. Crombie and G.P. Kirkwood. 99. Sock assessmen and he provision of managemen advice for he shor fin squid fishery in Falkland Island waers. Fish. Res., 8: 35-365. Caddy, J. and R. ahon. 995. Reference poins for fisheries managemen. FAO Fish. ech. Pap., 343: -83. Ehrhard, N.., P.S. Jacquemin, F. García, G. González, J.. López, J. Oriz and A. Solis. 983. On he fishery and biology of he gian squid Dosidicus gigas in he Gulf of California, exico. In: Caddy, J. F. (ed.), Advances in assessmen of world cephalopods resources. FAO Fish. ech. Pap., 23, pp. 36-34. Gulland, A.J. 983. Fish sock assessmen. A manual of basic mehods. FAO/Wiley series on food and agriculure. Hernández-Herrera, A., E. orales-boórquez,.a. Cisneros- aa,.o. Nevárez-arínez and G. Rivera-Parra. 998. anagemen sraegy for he gian squid (Dosidicus gigas) from Gulf of California, éxico. Calif. Coop. Oceanic Fish. Inves. Repors., 39: 22-28. Kle,.A. 996. Pesquería del calamar gigane Dosidicus gigas. In: Casas-Valdéz,. and G. Ponce-Díaz (eds.), Esudio del poencial pesquero y acuícola de Baa California Sur (): 27-49 orales-boórquez, E., A. Hernández-Herrera,.O. Nevárez- arínez, A.J. Díaz de León, G. I. Rivera-Parra and A. Ramos. 997. Abundancia poblacional del calamar gigane (Dosidicus gigas) en las cosas de Sonora, éxico. Oceánides, 2 (2): 9-95. Nevárez-arínez,., A. Hernández-Herrera, E. orales- Boórquez, A. Balmori-Ramírez,.A. Cisneros-aa and R. orales-azpeiia. 2. Biomass and disribuion of he umbo squid (Dosidicus gigas d Orbigny, 835) in he Gulf of California, exico. Fish. Res., 49: 29-4. Nevárez-arínez,. and E. orales-boórquez. 997. El escape proporcional y el uso del puno de referencia biológico, F %BR, para la exploación del calamar gigane, Dosidicus gigas, en el Golfo de California, éxico. Oceánides, 2 (2): 97-5. Overholz, W.J.,.P. Sissenwine and S.H. Clark. 986. Recruimen variabiliy and is implicaion for managing and rebuilding he Georges Bank haddock (elanogrammus aeglefinus) sock. Can. J. Fish. Aqua. Sci., 43: 748-753. Pierce, G.J. and A. Guerra. 994. Sock assessmen mehods used for cephalopod fisheries. Fish. Res., 2: 255-285. Rosenberg, A.A., G.P. Kirkwood, J.A. Crombie and J.R. Beddingon. 99. he assessmen of socks of annual squid species. Fish. Res., 8: 335-35. Sissenwine.P. and J.G. Shepherd. 987. An alernaive perspecive on recruimen overfishing and biological reference poins. Can. J. Fish. Aqua. Sci., 44: 93-98. Walers, C.J. and D. Ludwing. 98. Effecs of measuremen errors on he assessmen of sock-recruimen relaionships. Can. J. Fish. Aqua. Sci., 38: 74-7. Scien. ed: P. Abelló APPENDIX I he cachabiliy coefficiens and variances can be expressed as funcions of he esimaed iniial populaion size according o Rosenberg e al. (99): POPULAION SIZE AND EXPLOIAION OF DOSIDICUS GIGAS 79
q = = = σ 2 = C q f N 2 2 exp / = / C f Nexp / ( f Nexp ) J 2 5 2 ( C q f Nexp / ) qf exp. = = σ = 2 2 2 A A2 A3 Equaion A3 canno be solved analyically; however, i is possible o maximize he se equaions for N (Rosenberg e al., 99). APPENDIX II he esimaion of cachabiliy for shrimp rawler flee was using a modificaion of he Leslie analysis proposed by Rosenberg e al. (99) in accord wih he nex model: + 5. CPUE = qn exp q C exp C i In his model he independen variable is: exp ( ) i ( ) A4 A5 8 E. ORALES-BOJÓRQUEZ e al.