MEPS 511:223-235 (2014)  -  DOI: https://doi.org/10.3354/meps10939

ABSTRACT: Fish body size is a key life history trait that influences population dynamics. Individual growth and size distribution are generally affected by both intrinsic and extrinsic factors. However, the drivers of body size changes are still poorly understood. The NW Iberian Peninsula is one of the most important fishing regions in Europe, where there is a special emphasis on artisanal fisheries. Despite the large contribution of small-scale fisheries to local communities, there is a lack of knowledge of the biotic and abiotic factors influencing the performance of coastal key species. In this study, we analyzed spatio-temporal changes in body size of Pollachius pollachius at the population level in response to a set of intrinsic and extrinsic factors. Generalized additive mixed-effects models were fit to a data set of ~11000 records of individual body size of catch sampled by onboard observers during the last 13 yr in a complex multi-gear artisanal fishing fleet. Pollack body size showed strong spatio-temporal patterns, with an inshore–offshore geographic gradient where smaller fish were associated with shallower waters. Moreover, body size displayed a seasonal cycle, with larger individuals occurring mainly in winter months. This seasonality matches the annual reproductive cycle of the species. In addition, body size was affected by the interaction between population density and the temperature experienced by fish the year preceding the catch, with smaller individuals occurring at elevated temperatures and higher densities. 

KEY WORDS: Generalized additive mixed model · Size-based indicators · Growth · Environmental drivers · Pollachius pollachius