Spatio-temporal factors affecting variations in biomass and mean length of three commercially important species of crustaceans along the Algarve coast, (South Portugal)

Manuel Thibaud Blonc

Rhythmic displacements of marine species affect their catchability, playing a major role in fisheries activity. Therefore, understanding such activity patterns is paramount for pursuing profitable fishing activities and guaranteeing sampling representativeness, improving fisheries management. Portuguese trawl crustacean fisheries target mainly Nephrops norvegicus, Aristeus antennatus, and Parapenaeus longirostris. In this study, data collected by IPMA, the Portuguese Institute for Sea and Atmosphere, through 398 hauls during 15 campaigns were analysed using Generalised Additive Models (GAMs) with the aim to understand the factors driving spatio-temporal fluctuations in biomass (g/Km²) and mean carapace length of the aforementioned species along the Algarve coast, and to attempt to understand the factors driving such variations, including longitude, depth, year, month and time of the day. Important interannual and seasonal variations were evident for all three species, strongly linked to the organisms’ reproductive cycle. Additionally, differences in distribution with depth and longitude, driven by hydrographic and ecological processes, emerged from the results. Furthermore, P. longirostris and N. norvegicus displayed diel fluctuations in biomass and mean length. These results might have been affected by the lack of a dedicated experimental design.; however, they should be taken into consideration for the design and implementation of future management measures in this fishery.