Diurnal Variation in the Feeding Intensity and Catchability of Silver Hake (Merluccius bilinearis)

Abstract

Feeding intensity and catchability of silver hake (Merluccius bilinearis) during periods of daylight and darkness were examined. Silver hake feed at night from just after dark until predawn, but mostly between dusk and midnight. After ~15 h in the stomach, partly digested food passes into the intestine where it continues to be digested for another 9 h before being evacuated. A variety of free-swimming crustaceans (i.e. Crangon septemspinosa, Dichelopandalus leptocerus, and Monoculodes intermedius) make up the largest part of the diet. Silver hake are located on or immediately above the bottom during the day and off bottom at night. Pelagic trawls, off-bottom trawls, and bottom trawls with roller gear tend to pass over silver hake during the day, while bottom trawls with chain-disc sweeps and cable sweeps catch large quantities. A high opening trawl combined with a chain-disc sweep would substantially increase the mean yield per tow by a vessel operating on a 24-h basis.Key words: silver hake, Merluccius bilinearis; feeding, food, diurnal variation, catchability, availability