AMOUNTS OF DISCARDS BY COMMERCIAL FISHERIES AND THEIR SIGNIFICANCE ASFOOD FOR SEABIRDS IN THE NORTH-SEA

Most types of fishery produce discards and offal in considerable quant ities which are fed upon by seabirds. This paper demonstrates the impo rtance 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, 262 200 t of roundfish, 299 300 t of flatfish, 15 000 t of elas mobranchs and 149 700 t of benthic invertebrates per year, representin g 4% of the total biomass of fish and 22% of the total landings. This equals an energy value of about 3.4 x 10(12) kJ. Beam trawl fisheries discharge discards at the highest rates of all fishing fleets. Their d iscard fraction is dominated by flatfish which are less favoured by se abirds because of their shape. In contrast, the amounts of discards fr om pelagic and gadid fisheries are less, but fish species and lengths are more appropriate as food for seabirds. The number of seabirds pote ntially supported by fishery waste in the North Sea is estimated to be roughly 5.9 million individuals in an average scavenger community (co mposition in proportion to the seasonal abundance of scavenging specie s). During experimental discard studies, the proportions of fishery wa ste 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 o f elasmobranchs and 9000 t of benthic invertebrates.