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

Acoustic surveys were used to locate coastal Atlantic cod (Gadus morhua) sp awning grounds and examine spatial and temporal patterns of spawning in Pla centia 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 spawnin g timing differed between years. Mean spawning female densities were highes t at Cape St. Mary's in 1997 (1.6 x 10(-2) fish.m(-2)) and Oderin Bank in 1 998 (1.0 x 10(-2) fish.m(-2)). At all grounds, spawning peaked earlier in 1 997 (April) than in 1998 (June-July). In both years, cod spawned at sub- or near-zero temperatures. "Spawning columns" were observed at sites and time s having high densities of spawning females. Sex ratios suggested that male s arrived first and stayed later, while females followed when ready to spaw n, accompanied by juveniles. Older females spawned earlier and later than y ounger females. Peaks in density of spawning females and the proportion of females spawning did not coincide. Hence, the location and timing of spawni ng cannot be quantified solely from the proportions of females in spawning condition.