On the potential impact of shrimping on trophic relationships in the Wadden Sea
Berghahn, R. (1990). On the potential impact of shrimping on trophic relationships in the Wadden Sea, in: Barnes, M. et al. (Ed.) Trophic Relationships in the Marine Environment: Proceedings of the 24th European Marine Biology Symposium. pp. 130-140
In: Barnes, M.; Gibson, R.N. (Ed.) (1990). Trophic relationships in the marine environment: Proceedings of the 24th European Marine Biology Symposium. Aberdeen University Press: Aberdeen. 642 pp., more
Since the early 1970s the by-catch of the shrimp fisheries in the North Frisian Wadden Sea (eastern North Sea) has no longer been landed, but discarded immediately after sorting. Mortality of fish in the catch and the sieving procedure have been investigated for different species and age groups. Dead fish from the bycatch were exposed to predators in tanks and as bait in traps. Intake of fish by sea birds was estimated by means of video recording analysis and re-catch of discards. Thus, clearance rate for fish by various predators was roughly determined. Data concerning clearance rate by harbour seals were adopted from the literature. The "Landesamt fur den Nationalpark Schleswig-Holsteinisches Wattenmeer" provided information on densities of seals and sea birds. The total amount of fish and crustaceans present was derived from synchronous by-catch sampling in the subtidal zone (315 km 2 ) of the entire research area. Finally, food demands of selected predators at the highest trophic level were compared with the amount of discards produced. In June 1988 the seabird population would easily have been capable of clearing the discards of moribund roundfish. The same was true for the former seal population, which was most likely to benefit from flatfish discards.