The loliginid squid Loligo forbesi has a flexible life-cycle, involving variable size and age at maturity, presence of summer and winter breeding populations, and extended periods of breeding and recruitment. This paper reviews life history data collected since 1983 from the commercial fishery in Scottish (UK) waters, alongside fishery data collected since 1970, and examines (a) the relationship between body size and timing of maturation, (b) evidence for shifts in the relative abundance of the summer and winter breeding populations, and (c) the possible role of environmental signals in determining the timing of breeding. Evidence from fishery data suggests that, since the 1970s, the summer breeding population has declined while the winter breeding population now dominates and breeds later than was previously the case. Length-weight relationships and size at maturity showed significant inter-annual and seasonal variation during the period 1983-2001. Males are shown to decline in relative weight as they mature while females increase in relative weight; possible interpretations are discussed. High autumn/winter temperatures (high winter NAO values) were associated with high squid abundance and precocious maturation and tended to favour high abundance in the following year, along with increased body weight at length and a decrease in the proportion of animals breeding in December. High abundance in summer, conversely, leads to a fall of body weight at length in the following year. Thus there may be alternation of precocious and slow maturation, and/or summer and winter breeding, driven by a combination of environmental conditions and intraspecific competition.

Despite many previous studies on the life history of the squid Loligo forbesi, the roles of internal and external factors in growth and maturation have not previously been investigated in detail. The present study takes advantage of the availability of statistical techniques, namely generalised additive models, which permit simultaneous evaluation of the effects of multiple explanatory variables while avoiding the need to assume linear relationships. This has the further advantage that the size of body parts can be entered directly into the models rather than expressed as indices (e.g., gonado-somatic index). The present analysis is based on measurements taken from monthly market samples during 1989-1991 and aims to infer patterns of reproductive and somatic investment though comparison of large numbers of individuals at different (post recruit) life-cycle stages. Results indicate that, once the effect of body size is removed, gonad weight in both sexes is affected by month and digestive gland weight, consistent with seasonal triggering of maturation, and with energy for gonad growth being derived from food. There is also evidence of a negative relationship between somatic and ovary growth in females, possibly indicating remobilisation of somatic tissue to grow the ovary. In males, relationships between variables tended to have more complex forms, probably related to the existence of two or more growth patterns leading to different sizes at maturity. As found in previous work, maturation begins around 1-2 months earlier in males, suggesting that sensitivity to external triggers is controlled by a sex-dependent internal factor.

Recruitment variability is commonly attributed to variation in spawning stock size and environmental variability. Here, the abundance of Loligo forbesi in the English Channel was estimated using cohort analysis. Environmental and adult biomass effects on recruitment variation were then tested. A stochastic length-age key was included in the cohort analysis, considering inter-individual variability in age at length. The number of recruits and parental stock biomass per monthly age-class were computed for a series of 13 fishing seasons (1989-2002). Recruitment was examined in relation to adult biomass and environmental parameters (sea surface temperature, SST, and the North Atlantic Oscillation, NAO) at the time of hatching. Recruits were approximately 7 months old and recruitment for each annual cohort occurred between April and August. Squid bigger than the length at maturity were assumed to be spawners. In the spawning season (September December), spawners were 11–13 months old. Parametric stock-recruitment curves (Ricker, Beverton and Holt, Shepherd, etc.) fitted poorly, while SST was negatively correlated with recruitment in a simple linear model. Recruitment was unrelated to NAO. A model combining SST and adult biomass showed that recruitment is probably density-dependent when stock size is high, and negatively correlated with temperature. The study did not indicate obvious recruitment overfishing in the English Channel L. forbesi population.

The Argentine shortfin squid (Illex argentinus) is a common neritic species occurring in waters off Brazil, Uruguay, Argentina, and the Falkland/Malvinas Islands in the southwest Atlantic. Illex argentinus is the most important fished cephalopod species in the area and plays a significant role in the ecosystem. It is object of major fisheries using both trawlers (mostly from European countries) and jigging vessels (mainly from Asian countries) and estimated total annual average catch for the last 15 years (1988-2003) is about 700 000 tons. The present paper aims to develop predictive models of squid abundance in relation to physical and environmental conditions, models that could ultimately be applied to fishery forecasting. Fishery and biological data collected by scientific observers aboard commercial trawlers between 1988 and 2003 were analysed in relation to physical and environmental factors to establish the spatio-temporal pattern of the species' distribution and quantify the influence of environmental variables (e.g. SST, depth) on local abundance. The data included 26 168 fishing haul records, of which 11 103 were positive for Illex. CPUE (Catch Per Unit Effort, kg h−1) was used as abundance index. The analyses were based on time-series maps created using Geographical Information Systems (GIS). GIS maps showed that highest CPUE values were recorded during the first four months of the year (the Austral summer-autumn), with peak values higher than 5000 kg h−1 mainly located within 42° S, 46° S and MN (North part of Malvinas/Falkland) areas. Generalised additive models (GAMs) were used to describe variation in Illex argentinus abundance in relation to geographical and environmental variables. The presence/absence (PA) of Illex and its abundance (CPUE) in areas of presence were modelled separately. Predictors retained in the optimal models included SST, latitude, longitude, month, average fishing depth and year. Both models suggest a clear seasonal effect: maximum catchability was found during March (PA model) and the maximum abundances were found during the first quarter of the year (CPUE model). GAM models also demonstrated that higher catches and maturity of squid were related, in general terms, to warmer and deeper water.

A total of 324 specimens of the ommastrephid squid Todaropsis eblanae, collected from bottom trawl surveys in the North Sea was examined. Information on seasonal length frequency distributions and relationships of beak size to mantle length and wet body mass from the northernmost distribution of the species is supplied. The overall male: female ratio was 1: 0.78. Maturing males and females were found in winter and summer, while fully mature animals were observed only in summer. Sexual maturity in females occurred in bigger sizes than in males. Specimens were caught in water depths between 56 and 170 m throughout the whole investigated area except from the German Bight. This paper presents the first biological data on T. eblanae in the North Sea derived from scientific surveys.

Age and size-at-maturity of Loligo vulgaris from Portuguese waters were evaluated in order to explain its complex population structure, which is strongly influenced by continuous spawning. Age was obtained by increment counting in statoliths. Maturity ogives by age group indicated that males mature one month earlier (at 277 days) than females (at 298 days). Females mature at a ML50% of 17.6 cm, while males mature at smaller sizes. The later, however, showed a high degree of complexity in the size at maturity with evidence of two size at maturity groups. In both sexes, maturity was ultimately found to be primarily dependent on size rather than age. The effect of hatching season on age-at-maturity, size-at-maturity and reproductive investment was analysed by comparing two groups of squid hatched under distinct environmental conditions, namely the temperature during the first 3 months of life, the cold cohort (CC), hatching between December and March and the warm cohort (WC), hatching between May and September. Significant differences were found between cohorts on age-at-maturity, size-at-maturity and reproductive investment, giving indication of the environmental influences on sexual maturity. CC squid mature ca. 2 months later in life than WC squid and at a significantly larger size. The reproductive investment as measured by GSI was higher in the WC squid. Much of the variability in age and size-at-maturity of females in the population was due to differences between cohorts but this was not the case for males.

To understand the mechanisms that influence recruitment of the commercially important chokka squid Loligo vulgaris reynaudii, knowledge of its early life history is required. This paper evaluates the influence of food supply on yolk utilization, metabolism and growth of paralarvae. Eggs collected on the spawning grounds were incubated and the paralarvae reared in the laboratory under “fed” and “starved” conditions for 22 d at 16 ± 1 °C. Some paralarvae lasted 42 d in the laboratory. Mantle length (ML), wet and dry weights (WW and DW) and yolk weight (YW) were measured daily from samples of ~30 (10−51) paralarvae from each group. Yolk weight was estimated using image analysis to determined yolk volume. Three methods (growth model, O2 consumption rates and yolk utilization rates) were used to estimate metabolic rates. Input parameters included daily mean wet weight of paralarvae and temperature. Mean ML, WW, DW and YW at hatching were found to be 2.3 mm, 1.86 mg, 0.45 mg and 0.21 mg, respectively. The experiment revealed that daily yolk utilization rates were 86 and 95% d−1 for fed and starved paralarvae respectively, and that the yolk reserve was almost exhausted 3−4 d after hatching. Starved paralarvae survived for 6 days (with 80% mortality), while fed paralarvae attained a growth rate of 7.8% body WW d−1 over the first 22 days after hatching. Results illustrate that temperatures on the chokka squid spawning grounds allow paralarvae to grow at the fastest rates possible without being subjected to a growth “slow down” caused by a high temperature dependent imbalance between sustaining high metabolic and commitment high feeding rates.

Domoic acid (DA), the toxin responsible for the illness known as amnesic shellfish poisoning (ASP), is an algal toxin produced naturally by some species of the diatom genus Pseudo-nitzschia. The toxin has been detected in a diverse array of marine organisms from copepods to whales. Cephalopods, which are important members of the food chain and active predators of known toxin vectors such as bivalves, crabs and some fishes, have just recently been implicated in DA transfer or accumulation. Here we present data showing detectable values of DA determined by HPLC-UV (high-performance liquid chromatography and ultraviolet detection) and confirmed by HPLC-MS (mass spectrometric detection) in two octopus species collected along the Portuguese continental coast: Eledone cirrhosa and E. moschata. Domoic acid was frequently detected in the digestive gland of E. moschata and occasionally reached concentrations exceeding 100 µg g−1. In contrast, E. cirrhosa contained lower concentrations of DA on the few occasions that it was detected. This suggests that E. moschata is a potential vector for DA transfer to higher trophic levels in the coastal marine food web, not excluding humans. These data, combined with known aspects of the life history of the species, are a necessary step towards achieving an understanding of the accumulation of phycotoxins in cephalopods.