DAILY ACTIVITY, FEEDING AND RATIONS IN GOBIES AND BROWN SHRIMP IN THENORTHERN WADDEN SEA

A 24 h trawl fishery was conducted near the island of Sylt, northern W adden Sea, Germany, to investigate and compare daily patterns of activ ity and feeding among the gobies Pomatoschistus microps Kroyer and P. minutus Pallas and the brown shrimp Crangon crangon L. Relative occurr ence of the 3 species was generally consistent, with C. crangon domina ting at about 93%, except at midnight, when P. minutus and P. microps occurred at 68% and 12%, respectively. Peak abundances of C. crangon a nd P. minutus occurred at dawn and of P. microps at sunrise, coincidin g with rising tide. Size distributions for the 3 species were constant on a diurnal basis. Intensity of feeding among the gobies was highest during daylight hours, at dusk and sunrise, whereas a feeding peak in shrimp occurred at dawn, with very little feeding at noon. Feeding pe aks of the 3 species therefore roughly coincided with peak activity pe riods. Smaller specimens of the 3 species fed mostly on meiofauna, swi tching gradually to macrofauna with increase in size. Over a 24 h peri od, C. crangon cannibalism was low, but predation of P. minutus on C. crangon was prevalent, ranging from about 28% of total gut contents by ash-free dry weight (<55 mm gobies) to 77% (>55 mm gobies). On a popu lation basis, however, this predation was only equivalent to 0.3% of t he total available biomass of shrimp, although with highest proportion s among the new recruits. Gastric evacuation rates and resulting daily rations are comparable with the range of values in the literature.