Stock structure of the English Channel common cuttlefish Sepia officinalis (Linnaeus, 1758) during the reproduction period

Within the English Channel, the common cuttlefish Sepia officinalis is a semelparous species for which a 2-year life cycle was
exclusively described in the 1980s. In the 1990s, new research indicated that whilst a 2-year life cycle was still evident for
females and the large majority of males, a small proportion of males were actually maturing at only 1 year of age. Since
1980, the interest of French and UK fishers for this resource has increased and it is nowadays one of the most important
demersal species of the area and is considered to be fully exploited. From the start of the 20th century, fishing effort
and sea surface temperatures have increased in the English Channel and have probably impacted the life history traits of
S. officinalis. A 2-year sampling programme was undertaken at French landing sites of the English Channel during the reproduction
season in 2010 and 2011 to estimate if the proportion of 1-year-old mature animals has changed. Age determination
was carried out by coupling polymodal decomposition and lipofuscin measurement. Size-at-maturity for each year and each
sex was estimated by fitting a binomial error GLM. Results highlight that a variable percentage of males and females belonging
to the first cohort are mature and that size-at-maturity was lower than that observed in the 1990s. Finally, different parameters,
such as temperature and fishing pressure are explored to discuss changes in life history traits suggesting that cuttlefish
could be an indicator of the temperature regime shift in the English Channel.