Consumption Rates And Interaction With Fisheries Of Mediterranean Common Dolphins In The Alboran Sea

Common dolphins (Delphinus delphis) are top predators, feeding on a wide variety of prey species, several of which are also targeted by fisheries. The last remaining healthy group of the endangered Mediterranean common dolphin subpopulation is located in the Alboran Sea. Their feeding grounds overlap with the fishing grounds of trawlers targeting European hake (Merluccius merluccius) and blue whiting (Micromessistius poutassou) as well as purse seiners targeting small pelagic species such as European sardine (Sardina pilchardus), European anchovy (Engraulis encrasicolus), horse mackerel (Trachurus spp.) and mackerel (Scomber spp.). In the present study, we estimated that individual common dolphins in the Alboran Sea have a food consumption of 3.35 +/- 0.67 kg/day, based on scaling equations applied to stranded animals. This figure is similar to the ones reported for other European populations. Although common dolphins mainly feed on mesopelagic species of none or little commercial interest, they also feed on commercial species, which could lead to a potential conflict with fisheries in the area. We estimated common dolphins in the Alboran Sea could consume more than 16,000 tonnes of fish annually, including ca 7365 (95% CI: 3838-11,639) tonnes of Madeira lanternfish (Ceratoscopelus maderensis), 2,888 (1123-5223) tonnes of bogue (Boops boops), 2770 (879-5270) tonnes of European sardine, 1,850 (170-4116) tonnes of gobies (Gobiidae), and 1497 (65-3352) tonnes of European hake (reference period 2006-2011). Estimated sardine, anchovy and blue whiting consumption was low when compared to the landings in the area, however estimated hake consumption was above the reported hake landings in recent years (393.4 +/- 146 tonnes landed annually between 2006 and 2011). Additionally, direct interactions between common dolphins and main fisheries were evaluated in a total of 111 observed fishing trips (70 in trawlers and 41 in purse seiners) in the area. Although no bycatch of common dolphin was recorded, non-lethal interactions between dolphins and the fishing activity were detected from observations of this on-board observer program. These interactions, together with the high prevalence of stranding with signs of fishing interactions from the study area, may imply an additional threat to this endangered cetacean subpopulation. (C) 2021 Elsevier B.V. All rights reserved.