The vertical distribution of southern North Sea Crangon crangon (brown shrimp) in relation to towed fishing gears as influenced by water temperature

Abstract

The behaviour of Crangon crangon in the southern North Sea was studied in sea trials and aquarium experiments to establish whether water temperature influenced the vertical escape reaction of shrimp. The sea trials involved the use of a three-tier beam trawl, with horizontal compartments of 15 cm in height. The aquarium experiments involved a series of stimulation tests at varying seawater temperatures, designed to elicit vertical movement. The seawater temperature did influence the vertical escape response of the shrimp to towed gear. The temperature effect on vertical movement was identified in an analysis of the catch distribution between the three tiers of the trawl. Shrimp with a total body length >5 cm moved higher in the water column than smaller shrimp. At colder temperatures, a higher proportion of the catch was found in the lower tier. The inhibiting effect of temperature was supported by data obtained in the aquarium experiments.