SELECTION OF THE APPROPRIATE DURATION OF EXPERIMENTS TO MEASURE THE SURVIVAL OF ANIMALS DISCARDED FROM TRAWLERS

The survival rate of ten species of invertebrates (n=39-50) and four s pecies of fish (n=50-68) was determined from specimens collected from the by-catch of night trawl catches. They were observed in laboratory tanks for 7 days, as these provide better holding conditions than can normally be achieved at sea. Except for the alpheids, crustaceans and echinoids, the invertebrates were more tolerant than the fish: over 70 % remained alive after 7 days. Although the species of fish were chose n for their relative robustness, only one species (Centropogon marmora tus) had a survival rate above 30% and most deaths occurred during the first 3 days after capture. This result agrees with published data on survival of temperate fish captured in trawls indicating that 4 days is an adequate length of time for experiments to measure survival of a nimals discarded from trawl catches. Animals returned to the sea may c ontinue to die over a longer period but this cannot be determined in t anks.