QUANTITATIVE-ANALYSIS OF DISCARDS FROM BROWN-SHRIMP-TRAWLERS IN THE COASTAL AREA OF THE EAST-FRISIAN-ISLANDS

Trawling for marketable brown shrimp, Crangon crangon, (5 to 8 cm body length) produces a large by-catch of benthic and demersal fish and in vertebrates. After the catch has been sorted, the unwanted organisms a re immediately discarded. To assess the composition of the catch and t he quantity of discards, 111 samples of the unsorted catch of two shri mpers in the Wadden Sea area of Lower Saxony were analysed between Nov ember 1992 and November 1993. Commercial shrimp represented 11% of the mass of the catch, the rest was discarded. The majority of the catch were undersized shrimp (64%), other invertebrates (8%) and fish (11%). Most abundant were flatfish such as plaice, flounder and dab, and rou ndfish such as clupeids and gadoids. The most frequent invertebrates w ere shore crab and swimming crab. To calculate the total amount of the discards for the fleer of Lower Saxony, the average monthly discard/c ommercial shrimp ratios in the samples and data on brown shrimp landin gs Mere used. Different methods of estimation were applied and their r esults compared. Using median values of the discard/commercial shrimp ratios, a total of approximately 4000 tons of fish discards, 27 000 to ns of undersized shrimp and a further 2000 tons of other invertebrate species was calculated for the shrimper fleet in the main fishing seas on (April to November) in 1993. The influence of a higher application rate (+20% of sample number) of selective trawls on the discard quanti fication were described. The results were compared with those from oth er studies on brown shrimp fisheries to check the accuracy of the meth ods used.