The Argentine short-finned squid Illex argentinus in the food webs of southern Brazil

Abstract

Predation on Illex argentinus (Cephalopoda, Ommastrephidae) in southern Brazil (26°S to 34°S) was studied from its presence in contents of over 14 000 stomachs from 63 potential predator species including fishes, cephalopods, penguins and marine mammals. The size composition of I. argentinus in the diet of their main predators was estimated using regression equations that relate mantle length and body weight to beak size. The short-finned squid was found in the diet of 32 species and appears to play an important role in the trophic relations along the upper slope and adjacent oceanic waters, where it was found in the diet of the swordfish Xiphias gladius, the tunas Thunnus obesus, T. alalunga and T. albacares, and the wreckfish Polyprion americanus. These five species stand for more than half of the landings from the upper slope demersal and oceanic pelagic fisheries in the region. On the shelf, where the dominant squid was Loligo sanpaulensis, Illex argentinus was only occasionally found in the diet of a few neritic predators. In southern Brazil, overall predation was more intense on subadults and adults of the winter-spring spawning group on the upper slope and oceanic adjacent waters, differently from its southern range along Uruguay and Argentina waters where the short-finned squid is abundant on the shelf and is preyed upon mainly by the demersal fish assemblage.