The feeding behaviour of some demersal fish species in response to artificial discarding

Abstract

SUMMARY:In an attempt to detect changes in the diet and the feeding intensity of demersal fish caused by fishery discarding, two hauls were carried out 22 h apart at a depth of 90 m in an area of the Cantabrian Sea closed to trawling. Before the second haul, dead fauna that were not common in the sampling area under natural conditions, such as Micromesistius poutassou and squat lobster (Munida spp.), which are both usually discarded by the fleet and mainly found in deeper water, were thrown overboard. A total of 319 stomach contents from 12 demersal fish species caught in both hauls were analysed. The percentage emptiness decreased in the second haul (32%) with respect to the first (43%), and at the same time the feeding intensity of scavenger species such as Trachinus draco, Pagellus acarne, Scyliorhinus canicula, Raja montagui and Leucoraja naevus increased. Discards of M. poutassou was actually found in the stomach of a typically planktophagous species, Pagellus bogaraveo. Observed changes in trophic structure of the species analysed as a response to discards are discussed.Key words: Cantabrian Sea, diet, feeding behaviour, fisheries discards, scavengers. RESUMEN: CONDUCTA ALIMENTICIA DE ALGUNOS PECES DEMERSALES ANTE EL DESCARTE ARTIFICIAL. -Con el objetivo de detectar los cambios que producen los descartes de las pesquerías en la intensidad de alimentación y la dieta de los peces demersales se realizaron, en un intervalo de tiempo de 22 horas, dos lances de arrastre de fondo semejantes a una profundidad de 90 metros y en un área cerrada a la pesca comercial de arrastre del Mar Cantábrico. Antes del segundo lance, se arrojó al mar fauna muerta que se encuentra en condiciones naturales en aguas más profundas, como Micromesistius poutassou y Munida spp, especies que suelen ser descartadas por la flota. Se analizaron 319 contenidos estomacales de 12 especies de peces demersales capturados en ambos lances. El porcentaje de estómagos vacíos decreció en el segundo lance (32%) con respecto al primero (43%), y al mismo tiempo aumentó la intensidad de alimentación de las especies carroñeras como Trachinus draco, Pagellus acarne, Scyliorhinus canicula, Raja montagui y Leucoraja naevus. La especie descartada M. poutassou se encontró en estómagos de la especie típicamente planctófaga Pagellus bogaraveo. Asimismo se discuten los cambios producidos en la estructura trófica de las especies analizadas como respuesta al alimento suplementario que constituye el descarte.

The Role of Elasmobranchs in the Cantabrian Sea Shelf Ecosystem and Impact of the Fisheries on Them

“…For the catshark group, this biomass comprises blue whiting (probably discarded), benthic invertebrate carnivores (mainly crustacea) and discards. The opportunistic behaviour of this group of elasmobranchs in taking advantage of feeding on discards from the fleet (2.3 tons per km 2 per year estimated), as confirmed by previous studies (Olaso et al, 2002a), and its high survival after being discarded (Rodríguez-Cabello et al, MS 2001) confers many adaptive advantages. For rays, most of the biomass consumed comprises benthic invertebrates carnivores (mainly brachiura crustaceans) and shrimps (natantia crustaceans).…”

“…Other heavily discarded trophic groups were S. canicula, some of which (78%) survive the process (Rodriguez-Cabello et al, 2004), include benthic invertebrate carnivores, small demersal fish and other invertebrates. To determine the species that benefit from discards, some studies have been carried out in the area Olaso et al, 2002a), and their results have been included in the present model.…”

Trophic Relations of Lesser-Spotted Catshark (Scyliorhinus canicula) and Blackmouth Catshark (Galeus melastomus) in the Cantabrian Sea

“…This combination of vision and smell makes it possible for lesser-spotted catshark to be scavengers and consumers of fishery discards (Kaiser and Spencer, 1994;Olaso et al, 1998 and. In the diet of adult lesser-spotted catshark, many of the M. poutassou in the stomach contents are also discards, or consumed when dead or damaged Olaso et al, 2002). It is likely that large quantities of M. poutassou consumed by blackmouth catshark are also discards.…”

“…Trawling may change the benthos and so modify the abundance of their preferred prey, as well as increase the availability of discards upon which these catshark species feed Rodríguez-Cabello et al, MS 2001;Olaso et al, 2002). Studies of the feeding of blackmouth catshark (Capapé and Zaouali, 1976;Macpherson, 1980;Mattson, 1981) suggest that this species may also be changing its feeding habits due to the supply of energy from fishing discards.…”

Feeding habits of small-spotted catshark (Scyliorhinus caniculaLinnaeus, 1758) from the eastern central Adriatic Sea

“…However, small-spotted catshark have also been shown to have generalistic diets in Mediterranean (Capapé 1974;Valls et al 2011) and eastern Atlantic waters (Lyle 1983;Serrano et al 2003;Olaso et al 2005;Martinho et al 2012). This species has also been considered an opportunistic scavenger, taking advantage of the discards from local trawling fisheries (Olaso et al 2002).…”