Intra-gear variation in sea turtle bycatch: Implications for fisheries management

Abstract

In the Mediterranean Sea, bottom trawl, bottom longline and set nets are the fishing gears with the highest impact on marine turtle populations. These demersal gear types are characterised by a variety of métiers (fishing operations targeting a specific assemblage of species, using specific gear, during a precise period of the year and/or within a specific area). Data on fishing methods, target species and turtle bycatch were collected through interviews in three different study areas in the central Mediterranean. The results show that, even in the same fishing area, different métiers of the same gear can have a different impact on turtles. These findings have several implications. First, traditional turtle bycatch estimations and comparisons based on a fishing gear as a whole may be spatially or temporally biased by spatial and temporal differences in métier composition, respectively. Second, the efficiency of conservation measures may be different according to the métiers involved and caution is needed when measures developed in small areas with certain métiers are exported to a wider scale with possibly very different métiers. Third, conservation measures may induce shifts among métiers that may have an impact on other species, but such shifts are difficult to detect. All this suggests that, in the Mediterranean, a métier-based approach is needed to provide realistic estimates of turtle bycatch, to increase the efficiency of conservation measures by targeting only the most relevant métiers and to predict the changes in target species and effort distribution that can be driven by conservation measures. The variability of fishing methods and métiers implies that the most effective management strategies should be identified at relatively small geographical scales.