Seasonal distribution and spawning of small tunas (Auxis rochei and Sarda sarda) in the Northwestern Mediterranean

Abstract

Bullet tuna, Auxis rochei and Atlantic bonito, Sarda sarda are the most abundant small tuna species in the Mediterranean Sea. Both species are commercially exploited by a small-scale inshore fishery off the Catalan coast. Catches of A. rochei are highly seasonal, with maximum values in the warmest months (June to September), which is also the spawning period. Larvae of A. rochei were collected between July and September and were particularly abundant in July, when the mean sea surface temperature was 25.4ºC. In summer, adults of this species migrate from the Atlantic to the Western Mediterranean, including the Catalan Sea, to spawn, but they are not found in this last region during the colder months. S. sarda is taken all year round in the Catalan Sea, with maximum catches from September to March, and minimum levels during the spawning period (May to July). Larvae of this species were only observed in July and larval abundance was considerably lower than that of larval A. rochei. Unlike A. rochei, S. sarda is resident over the continental shelf in the Western Mediterranean all year long, but at the beginning of summer, coinciding with the arrival of the other species, it moves to other areas in order to spawn.