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Knowledge of stock structure is a priority for effective assessment of commercially-fished cephalopods. Loligo forbesii squid are thought to migrate inshore for breeding and offshore for feeding and long-range movements are implied from past studies showing genetic homogeneity in the entire neritic population. Only offshore populations (Faroe and Rockall Bank) were considered distinct. The present study applied mitchondrial and microsatellite markers (nine loci) to samples from Rockall Bank, north Scotland, North Sea, various shelf locations in Ireland, English Channel, northern Bay of Biscay, north Spain, and Bay of Cadiz. No statistically significant genetic sub-structure was found, although some non-significant trends involving Rockall were seen using microsatellite markers. Differences in L. forbesii statolith shape were apparent at a subset of locations, with most locations showing pairwise differences and statoliths from north Ireland being highly distinct. This suggests that (i) statolith shape is highly sensitive to local conditions and (ii) L. forbesii forms distinguishable groups (based on shape statistics), maintaining these groups over sufficiently long periods for local conditions to affect the shape of the statolith. Overall evidence suggests that L. forbesii forms separable (ecological) groups over short timescales with a semi-isolated breeding group at Rockall whose distinctiveness varies over time. [ABSTRACT FROM AUTHOR]

Cephalopods have become an important global food source, but their sustainable management is challenged by unique life history characteristics associated with short lifespans and semelparous reproduction, high natural mortality rates, rapid and often nonasymptotic growth, and complex population structures. Weak stock-recruitment relationships together with the time-consuming work required for age validation and high-volume annual age determinations make traditional age-based modelling impractical. We propose that the best method for cephalopod assessment involves innovative depletion models, fitted with in-season data on catch numbers and fishing effort, to produce realistic estimates of stock biomass. A "fast lane" assessment approach is suggested that includes high-frequency data collection for separate, in-season stock assessments of each cohort to ensure sustainable exploitation of these short-lived resources. However, most cephalopod fisheries are data-poor and/or lack the infrastructure and resources needed to apply depletion methods; therefore, we also present alternative assessment methods that have been recently applied worldwide. We also offer suggestions for further research on the remaining challenges of cephalopod stock assessment and management. [ABSTRACT FROM AUTHOR]

The English Channel cuttlefish (Sepia officinalis) is the most abundant cephalopod resource in the Northeast Atlantic and one of the three most valuable resources for English Channel fishers. Depletion methods and age-structured models have been used to assess the stock, though they have shown limitations related to the model assumptions and data demand. A two-stage biomass model is, therefore, proposed here using, as input data, four abundance indices derived from survey and commercial trawl data collected by Ifremer and Cefas. The model suggests great interannual variability in abundance during the 17 years of the period considered and a decreasing trend in recent years. Model results suggest that recruitment strength is independent of spawning–stock biomass, but appears to be influenced by environmental conditions such as sea surface temperature at the start of the life cycle. Trends in exploitation rate do not reveal evidence of overexploitation. Reference points are proposed and suggestions for management of the sustainable utilization of cuttlefish in the English Channel are advanced. [ABSTRACT FROM AUTHOR]

The cuttlefish Sepia officinalis is an important fishery resource in the English Channel, and one of the largest stocks of cephalopods in the Northeast Atlantic. Cuttlefish live for approximately 2 years and catches consequently depend largely on recruitment. Early life stages were analysed for differences in juvenile growth and age-at-recruitment to the commercial fisheries. Recruits were sampled monthly between October 2000 and June 2003, and pre-recruits from the coastal waters of the UK and France in the summers of 2000 and 2002. Age (days) was determined from statoliths. Although most cuttlefish were recruited during autumn, there was some recruitment throughout the year. Age-at-recruitment varied significantly between season and cohort, but was consistently in the range 3–4 months, so although there was some hatching throughout the year, most cuttlefish hatched during summer. Fitted growth models indicated that the growth rates of pre-recruits (7–59mm mantle length) were significantly higher in 2002 than in 2000. Spatial differences in growth rate were apparent in 2000, suggesting that pre-recruit growth may depend on local environmental conditions. Pre-recruits and recruits combined (7–106mm mantle length) also showed significant variation in growth between hatching months and years. Hypotheses explaining the observed patterns of growth and recruitment are presented. [Copyright &y& Elsevier]

The spatial and temporal distribution patterns of cuttlefish abundance and the relationships between cuttlefish abundance and environmental variables in the French Atlantic coast, the English Channel, and adjacent waters were studied using both geographical information system and statistical methods. Cuttlefish have a clear general annual migration pattern, consistently occurring in broadly the same areas in different years. The strength of the Atlantic currents into the west part of the English Channel and the south part of the Celtic Sea may be the dominant influence on the timing of cuttlefish migration to these areas. Local abundance shows a positive correlation with SST, although it is difficult to determine if this reflects any causal link. Cuttlefish expand their distribution further north in the spawning season in warm years and shift south in cool years. The centre of high abundance in offshore deep water shifts north in warm winters and south in cool winters. [Copyright &y& Elsevier]