The return of cod transplanted from a spawning ground in southern Newfoundland

Abstract

To investigate the navigation mechanisms used by Atlantic cod (Gadus morhua) to locate spawning grounds we conducted a biotelemetric study in which 23 large (74-98 cm) spawners were displaced in small groups up to 35 km from a coastal Newfoundland spawning ground at Bar Haven, Placentia Bay. Overall, approximately 60% of the transplanted fish returned to the grounds, most within a few days. The data derived from this exercise allow the development of hypotheses regarding the navigatory mechanisms used by cod during movements on a small scale spatially. The return success was negatively related to distance of the release sites from the spawning ground (p<0.05) but was higher when fish were released along a known migratory pathway, or when released upcurrent of the spawning site. There was no support for the hypotheses that cod conducted contra-natant spawning migrations or tracked water-borne chemical-olfactory signals respectively. Transplanted groups did not stay together but a group transplanted near a large cod aggregation stayed there for some time, although 50% eventually returned to Bar Haven. Finally, our data suggest that cod moved towards an omnidirectional “attractor”, such as a characteristic sound or geophysical signature, that dissipates with distance perhaps in combination with spatial memory of bathymetry or current structures and the presence of maturing conspecifics.