Publication Abstract

Vertical movements of cod, Gadus morhua, in the open sea and the hydrostatic function of the swim baldder

G.P. Arnold and M. Greer-Walker

The vertical movements of 24 individual cod (Gadus morhua ) fitted with 300 kHz transponding acoustic tags were described using a vector scanning sonar operating in vertical mode. The fish, which were 50-76 cm in length, were tracked continuously for periods of up to 52 h in the southern North Sea. Three fish adapted to atmospheric pressure were released at the surface; the others were released on the sea bed at depths of 24 to 73 m, after a period of confinement in a small cage, during which they had the opportunity to adapt, or partially adapt, to the ambient pressure. Most fish spent long periods in midwater and a third of them increased their depth slowly and steadily. Similar predictions indicated that about half the caged fish had achieved neutral buoyancy at the end of the adaptation period.

Reference:

G.P. Arnold and M. Greer-Walker, 1992. Vertical movements of cod, Gadus morhua, in the open sea and the hydrostatic function of the swim baldder. ICES Journal of Marine Science, 49: 357-372.