Time series analysis of flatfish landings in the Portuguese coast

Flatfish fisheries are widely spread over the Portuguese coast and traditionally have a high social and economical relevance in some coastal communities. The artisanal multi-gear fleet is responsible for the largest share of flatfishes landings. However, only a fraction of these vessels actively target flatfishes, since many other species are caught in these multi-species fisheries. To explain the variability of flatfish landings we used the data set of official landings of commercially important flatfish species (monthly landings values, from 1992 to 2005) and applied generalized linear models (GLM) using the NAO index (NAO), sea surface temperature (SST), scalar wind (WIND), rainfall (RAIN) and month as explanatory variables. Flatfish landings did not showed a common trend for different species group between 1992 and 2005. For the majority of the species, significant relationships were found between month and SST and landings per unit effort (LPUE). The seasonal pattern in LPUE reflected migrations to spawning grounds, when flatfishes concentrate in some areas of the continental shelf and become more vulnerable to fishery. Temporal closures should be implemented for the stocks that evidence overexploitation. More studies focused in species abundance and fishing effort estimation are necessary on Portuguese flatfish fisheries in order to determine the status of stocks and adopt adequate management measures.