Feeding habits of two shark species: velvet belly, Etmopterus spinax (Linnaeus, 1758) and blackmouth catshark, Galeus melastomus (Rafinesque, 1810), present in fishing discards in the Gulf of Cádiz

Abstract

In many fisheries, such as trawl fisheries, sharks appear among the catches as bycatch or discards, and these species include velvet belly (Etmopterus spinax) and blackmouth catshark (Galeus melastomus). The objective of this study was to research the feeding habits of both species in the Gulf of Cádiz and to identify possible differences in diet depending on size and time of day. The most frequent sizes were 12–16 cm for E. spinax and 14–20 cm for G. melastomus. Both species preyed mainly on euphausiaceans and teleosts; their Index of Relative Importance (IRI) per species were as follows: E. spinax 42.30% IRI, 21.66% IRI; G. melastomus 52.33% IRI, 27.26% IRI, respectively. Only Etmopterus spinax showed significant variation in diet as a function of the time of day (p < 0.05), although both species showed similar patterns of feeding throughout the day. With respect to size, E. spinax consumes more cephalopods and teleosts as its size increases, while G. melastomus increases its consumption of decapods.