Patterns of investment in reproductive and somatic tissues in the loliginid squid Loligo forbesii and Loligo vulgaris in Iberian and Azorean waters

Abstract

The veined squid, Loligo forbesii, is found throughout the northeast Atlantic, including the waters off the Iberian Peninsula, and is a socio-economically important cephalopod species, sustaining several small-scale commercial and local artisanal fisheries. This study uses Iberian and Azorean trawl survey and fishery landings data from 1990 to 1992 and employs additive modelling to examine the relationships amongst somatic growth, season and gonad growth, in an attempt to determine the relative importance of intrinsic (e.g. nutritional state and body size) and extrinsic (temperature and daylight) factors which contribute to maturation in L. forbesii. We compare the results with those from a comparative analysis of contemporaneous data on Loligo vulgaris from the Iberian coast, and with a re-analysis of previously published results for L. forbesii in Scottish waters. Reproductive organ weight in both sexes of L. forbesii from all ports shows seasonal patterns with a fall/winter peak in maturation, as is expected with the animals' year-long life cycle. Two maturity peaks (spring and winter) were found for both Azores L. forbesii males and females, possibly evidence of two breeding cohorts, with males maturing approximately 1 month earlier than females in both seasons. For L. vulgaris, three annual peaks in reproductive weight were identified. With the exception of L. forbesii males from Scottish waters, in all study animals, the partial effect of mantle length and mantle weight on reproductive weight is positive up to large body sizes. The relationship between nutritional status and reproductive weight is also generally positive. Geographic variation in the relationships, as seen between Scottish males and samples from the other study areas, is hypothesised to be largely attributable to local differences in environmental conditions (productivity, food availability, temperature, upwelling),

Distribution and habitat modelling of common dolphins (Delphinus delphis) in the eastern North Atlantic

“…Distance to coast and depth were the only pair of variables highly positively correlated. Since both were of interest, a GAM model was fitted, with depth as predictor and distance to coast as response variable, and both depth and the residuals of this model were used as predictors in the common dolphin models (see Smith et al ., 2011). Moreover, multiple correlation among explanatory variables was assessed through the Variance Inflation Factor (VIF, with a threshold of 3) (Zuur et al ., 2010).…”

Predicting Cetacean Distributions in the Eastern North Atlantic to Support Marine Management

“…Both were of interest, hence, we first fitted a GAM model with depth as the predictor and distance to coast as the response variable. The depth and the residuals of this model were then used as explanatory variables in subsequent models (see Smith et al, 2011). The resulting spline for the residuals term should be interpret as the effects of proximity to coast in the species occurrence, at a given depth.…”

The Role of Environmental Factors on the Fishery Catch of the Squid Uroteuthis chinensis in the Pearl River Estuary, China

“…For this reason, environmental factors play a critical role in the life cycle of U. chinensis. Studies showed that cephalopods are sensitive to water temperature [5][6][7][8][9], marine primary productivity [10], and food supply [11], with temperature being the key factor affecting the population biomass and the species' distribution [12,13]. Such conditions could impact the population dynamics by acting on the spawning activity and recruitment [7,8,14].…”