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English Channel Cuttlefish ( Sepia officinalis ) stock structure in the reproduction period

ICES ASC 2010 / S 16. CRESH PROJECT. English Channel Cuttlefish ( Sepia officinalis ) stock structure in the reproduction period. Michael Gras, Olivier Goetz, Jehane Lepoittevin and Jean-Paul Robin

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English Channel Cuttlefish ( Sepia officinalis ) stock structure in the reproduction period

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  1. ICES ASC 2010 / S 16 CRESH PROJECT English Channel Cuttlefish (Sepia officinalis) stock structure in the reproduction period Michael Gras, Olivier Goetz, Jehane Lepoittevin and Jean-Paul Robin UMR-Ifremer-Physiology and Ecophysiology of Marine Molluscs, University of Caen Lower-Normandy, France Contact author : michael.gras@unicaen.fr

  2. OUTLINE • INTRODUCTION • Context • Objectives • MATERIAL AND METHODS • Sample • Analysis • RESULTS • Length structure • Size at maturity • DISCUSSION ICES ASC 2010 / S:16

  3. INTRODUCTION • Distribution area of Sepia officinalis • from West Africa • to English Channel • Shared resource • UK : 4000 tons • French : 10 000 tons ICES ASC 2010 / S:16

  4. INTRODUCTION • Sepia officinalis is a migratory species • Sepia officinalis is a semelparous species • Life cycle varies with environmental conditions : • Lasts one year in the South (Portugal, Med.) • Lasts two years in the North (English Channel) ICES ASC 2010 / S:16

  5. Life cycle of English Channel Sepia officinalis ICES ASC 2010 / S:16

  6. English Channel Warming • Hawkins et al. (2003) published results of MBA survey • Increase in sea temperature • During all the 20th century • Mainly during 1970-2000 • Leads to a change in species composition ICES ASC 2010 / S:16

  7. Previous Description of the life cycle in the English Channel • Boucaud-Camou et al. (1991) : • Study based on French coast specimens • Maturity stages determined using microscopic tools • Age determination based on modal progression • The entire population studied has a 2 year lifespan • Dunn (1999): • Study based on English coast specimens • Maturity stages determined using macroscopic key • Age determination based on modal progression • 4 % of the male population mature in the first year ICES ASC 2010 / S:16

  8. Description of the life cycle in theSouth Brittany, Gulf of Morbihan • Gauvrit et al. (1997): • South Brittany, Gulf of Morbihan cuttlefish • Age groups defined according to length-structure (modes) • 45 % of males are mature the first year • 20 % of females are mature the first year ICES ASC 2010 / S:16

  9. Objectives of the work • Update the previous pattern described • Boucaud-Camou et al. (1991) • Dunn (1999) • Provide population parameters not taken into account before (length at maturity) ICES ASC 2010 / S:16

  10. Sample composition • Number of individuals sampled: • Number of individuals = 738 • Number of males = 395 • Number of females = 339 • Length • Ranges between 6 and 35 cm DML • Mean length : 13.6 cm DML ICES ASC 2010 / S:16

  11. Maturity stage macroscopic determination (Dunn, 1999) ICES ASC 2010 / S:16

  12. Data analysis • Cohort determination: • Polymodal decomposition (normal modes) using maximum likelihood method • Gonado-Somatic Index: • Length-at-maturity ogives • Fitted by GLM (binomial distribution) to derive DML50, (size at 50 % mature specimens) ICES ASC 2010 / S:16

  13. Length-structure per sex ♂ M1 = 10.98 M2 = 16.71 M3 = 24.37 ♀ M1 = 10.98 M2 = 16.71 13 cm 99% 1st cohort 12% of C1 are mature 14% of C1 are mature ICES ASC 2010 / S:16

  14. Trend in reproductive indices (GSI vs length) ♂ ♀ Increase point: 14 cm Inflexion point: 12 cm ICES ASC 2010 / S:16

  15. Length at maturity DML50 = 12.94 cm At 13 cm, 86% belongs to C1 DML50 = 12.64 cm At 12 cm, 100% belongs toC1 ♂ ♀ ICES ASC 2010 / S:16

  16. DISCUSSION • 14 % of the males have a one year life cycle • 12 % of the females have a one year life cycle • Maturity occurs when the GSI increases • GSI shows: • The storage of the vitellus for the females • The storage following by the emptying of the spermatophoric sac for the males • Growth rate is very variable ICES ASC 2010 / S:16

  17. DISCUSSION • Age assessment must be confirmed using ring counts on the statoliths (Challier et al. 2002) • It is worth knowing if the one year old adults actually mate and if intergeneration breeding exists (as suggested by Gauvrit et al., 1998) • Interannual variability should be checked (2010 reproduction follows a cold winter) • Consequences of a shorter lifespan for a part of the population should be included in models ICES ASC 2010 / S:16

  18. THANK YOU FOR YOUR ATTENTION !

  19. ACKNOWLEDGEMENTS CRESH PROJECT (INTERREG IVA PROGRAM) Co-funding by the Conseil Régional _ de Basse-Noramndie ICES ASC 2010 / S:16

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