Amounts of discards by commercial fisheries and their significance as food for seabirds in the North Sea

Abstract

Most types of fishery produce discards and offal in considerable quantities which are led upon by seabirds. This paper demonstrates the importance to seabirds of fishery waste in the North Sea. The total amount of fishery waste in the North Sea region is estimated at 62 800 t of offal, 262200 t of roundfish, 299 300 t of flatfish, 15 000 t of elasmobranchs and 149 700 t of benthic invertebrates per year, representing 4 % of the total biomass of fish and 22 % of the total landings. This equals an energy value of about 3.4 x 1012 kJ. Beam trawl fisheries discharge discards at the highest rates of all fishing fleets. Their discard fraction is dominated by flatfish which are less favoured by seabirds because of their shape. In contrast, the amounts of discards from pelagic and gadid fisheries are less, but fish species and lengths are more appropriate as food for seabirds. The number of seabirds potentially supported by fishery waste in the North Sea is estimated to be roughly 5.9 million individuals in an average scavenger community (composition in proportion to the seasonal abundance of scavenging species). During experimental discard studies, the proportions of fishery waste consumed by seabirds was calculated. We estimated that the mass of discards and offal consumed by birds during our study amounted to 55 000 t of offal, 206 000 t of roundfish, 38 000 t of flatfish, 2000 t of elasmobranchs and 9000 t of benthic invertebrates.