1 / 19

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

dustin
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related