Small-scale spatial and temporal patterns in spawning of Atlantic cod (Gadus morhua) in coastal Newfoundland waters

Abstract

Acoustic surveys were used to locate coastal Atlantic cod (Gadus morhua) spawning grounds and examine spatial and temporal patterns of spawning in Placentia Bay, Newfoundland, Canada. The same three grounds were used in 1997 and 1998 (Bar Haven in the inner bay and Cape St. Mary's and Oderin Bank in the outer bay). Grounds had densities >0.1 fish·m-2 over scales of 100 m and >13% of mature females in spawning condition. Ground use and spawning timing differed between years. Mean spawning female densities were highest at Cape St. Mary's in 1997 (1.6 × 10-2 fish·m-2) and Oderin Bank in 1998 (1.0 × 10-2 fish·m-2). At all grounds, spawning peaked earlier in 1997 (April) than in 1998 (June-July). In both years, cod spawned at sub- or near-zero temperatures. "Spawning columns" were observed at sites and times having high densities of spawning females. Sex ratios suggested that males arrived first and stayed later, while females followed when ready to spawn, accompanied by juveniles. Older females spawned earlier and later than younger females. Peaks in density of spawning females and the proportion of females spawning did not coincide. Hence, the location and timing of spawning cannot be quantified solely from the proportions of females in spawning condition.