MEPS prepress abstract  -  DOI:

Sex and age-biased mortality of three shearwaters species in longline fisheries of the Mediterranean

Verónica Cortés*, Salvador García-Barcelona, Jacob González-Solís


ABSTRACT: Bycatch rates in longline fisheries are unsustainable for many seabirds worldwide. Nevertheless, to understand its effects at population level it is essential assessing sex and age-biased mortalities, since uneven mortalities may exacerbate bycatch impacts. In the Mediterranean, bycatch is the main cause of population decline for the three endemic shearwater species (Scopoli’s Calonectris diomedea, Balearic Puffinus mauretanicus and Mediterranean shearwater P.yelkouan), but little is known about population biases of the birds caught in longliners. From 2003 to 2015, we collected 639 shearwater carcasses from Spanish longliners operating in the north-western Mediterranean, dissected them to determine their age and sex and examined their spatial and temporal patterns and the origin of ringed birds. Most shearwaters caught in longliners were adults, but the proportion of immatures and subadults increased in the late breeding period. Adult Scopoli’s shearwaters were mostly caught around the breeding colonies. In contrast, all Puffinus birds were caught in the Iberian shelf. Scopoli’s shearwater catches were male-biased, particularly during the prelaying and close to the breeding colonies. Puffinus shearwaters catches were also male-biased during the prelaying, but adult catches were female-biased during chick-rearing. Ring recoveries revealed most birds were ringed in the nearby Balearic Islands, but some Scopoli’s shearwaters ringed in France and Italy were also caught during their migration period, showing impacts of the Spanish longliners are spread well beyond Spanish colonies. The adult-biased and sex-biased mortality found in this study may aggravate bycatch impacts on populations and highlights the urgent need for conservation action.