Resumen de Differences between demersal fisheries discards: high and low productivity zones of the Northwestern Mediterranean Sea
Aina Carbonell Quetglas, Sandra Mallol
Differences in fishery demersal discards in low and high productive marine ecosystems in the North-western Mediterranean were studied. Analyses were carried in three common fishing tactics carried out in different habitats from coastal to slope bottoms. Though clearly out of date (1996-2000 years), data remain useful when formulating comparisons, and simultaneously establishing a temporal reference values of trawling fishing impact. Results revealed discards were strongly positively correlated with the biomass harvested. In the higher productive zone, in Northern Catalonia, discards varied significantly with the season of the year, whereas in the low productive zone, in the Balearic Islands, discards depend on the characteristics of the biocenosis of the bottom substratum. In the coastal and shelf fisheries, the highest average biomass for retained and discards catches were recorded in spring and summer in Northern Catalonia and autumn and winter in the Balearic Islands. In the slope fishery the maximums were recorded in spring in Northern Catalonia and autumn in the Balearic Islands. By fishing tactic and zone, in the Northern Catalonia discards for coastal and shelf were mainly of fish (44 ± 25 % and 25 ± 12% respectively).
This concurs with the fact that in northern Catalonia bigger quantities of pelagic and epi-benthopelagic species with seasonal fluctuations increase in spring and summer. In contrast, in the coastal Balearic fishery discards are more balanced and mainly composed by flora and invertebrate fauna. In the shelf fishery of Balearic Islands, fish represented the higher proportion of discards (49 ± 13%).
For slope fishery (28± 17% Balearic Islands and 22± 14% Northern Catalonia) discards were foremost due to species without commercial value and by-catch fish species of small size. Differences between biotic and abiotic factors have demonstrate importance in discards impacts and are key factors to understand how can be reduced discards. By delimiting areas of complex biocenoses structures and fish recruitment zones, as well sensitive seasons in what discards increases, as accuracy as possible, may allow a new management scenario adapted to each zone of reduced discards.
