Fishery discard consumption rate and scavenging activity in the northwestern Mediterranean Sea

The consumption rate of fishery discards is evaluated and the organisms involved in recycling discarded fish analysed. For this purpose, a fixed baited camera was deployed on the continental shelf and upper slope of the Catalan Sea (northwestern Mediterranean), where trawlers discard large quantities of non-target species. The results showed considerable bait consumption after 12 h of immersion. Between 48 and 64% of the bait was consumed within this period on the shelf, at a mean rate of 23.8 +/- 5.7 g h(-1), and >90% of the bait on the slope, at a mean rate of 30.8 +/- 10.5 g h(-1). After 24 h, generally just the bones of the bait were left. Amphipods, isopods, cephalopods, ophiuroids, nine species of fish, and seven decapods were identified feeding on the bait. Typical scavenger species stayed longer in the vicinity of the bait, but pelagic species exhibited only occasional scavenging behaviour, were slower to arrive at the bait, and remained for a shorter time. The snake eel, Ophichthus rufus, was the most abundant fish attracted to the bait, appearing in 75% of the photographic series. Isopods and amphipods reached the bait 80 minutes after camera deployment and were also involved in the recycling and dispersal of organic matter in the system. In fact, these organisms congregated at the bait and consumed it entirely in just a few hours. For scavenger species that live in areas where discarding is continuous, such additional inputs could be a major trophic resource. For this reason, continuous anthropogenic inputs may bring about environmental perturbations that can alter benthic ecology and community stability. (C) 2002 International Council for the Exploration of the Sea.