Sex differences in cod residency on a spawning ground

Telemetric methods were employed to explore behaviour differences between male (n = 21) and female (n = 27) Atlantic cod (Gadus morhua) tagged and released in April 1998 on a spawning ground in coastal Newfoundland. Their distribution was monitored over a grid of listening stations for three consecutive spawning seasons (1998-2000). Of the 48 tagged fish, 32 were relocated acoustically and 15 caught in the fishery (including seven previously relocated) during this study. Only eight were never relocated. On average, males stayed on the spawning ground for at least 10 days, and females for 19 days. The rate of departure from the spawning ground varied between years. There was no effect of body length on the timing of departure from the spawning ground, for either males or females. Males departed from the grounds earlier than females. The relocation rates for males were greater than for females in all years. In any given survey of the spawning ground, resident males were more likely to be relocated, suggesting that females move in and out of male-dominated spawning aggregations. Mobile and intercept fisheries on cod spawning grounds could disrupt the movements of spawning females or lead to sex-biased harvest rates. (C) 2002 Elsevier Science B.V. All rights reserved.