Research Document - 2002/087
Relative strength of the 1999 and 2000 year-classes, from nearshore surveys of demersal age 0 & 1 Atlantic cod in 3KL and in Newman Sound, Bonavista Bay
By Robert S. Gregory, Benjamin J. Laurel, Dan W. Ings and David C. Schneider
Abstract
From 1959 to 1964 and 1992 to 1997 (i.e., 1990s), demersal age 0 Atlantic cod (Gadus morhua) in the nearshore (<10 m deep) were surveyed by seine from St. Mary's Bay to Notre Dame Bay, Newfoundland during the Fleming survey, conducted annually in September and October. In the absence of a coastwide Fleming survey in 1998-2000, we conducted a qualitative assessment of the strength of four 1997-2000 year-classes. Our assessment was based on abundance of demersal age 0 and age 1 Atlantic cod sampled at 6 - 13 nearshore sites in Newman Sound, Bonavista Bay in five summer-autumn periods during 1995-2000. Sampling techniques and collection dates for the Fleming survey and Newman Sound study were similar. Therefore, cod abundances in the two studies were comparable, albeit at different geographic scales. Abundance trends of age 0 and 1 cod covaried between the studies in 1995 and 1996, when both were conducted concurrently, suggesting that abundances of juvenile cod in Newman Sound mirrored those observed in the spatially broader Fleming survey. In 1997, age 0 abundance in the Fleming survey was the highest observed in the 1990s, leading to the prediction that age 1 cod would be high the following year. High age 1 abundance in 1998 compared to 1995 and 1996 in Newman Sound supported this prediction. Compared with the historical low in 1996 observed in both studies, age 0 abundance was 10 times higher in 1998 and 40 times higher in 1999. These results suggest that the 1997, 1998, and 1999 year classes should be strong compared to those in 1995 and 1996. Analysis of length frequency data collected from July to November in Newman Sound indicated that age 0 Atlantic cod settled in the nearshore in two distinct recruitment pulses in "good years" - i.e., 1998 and 1999 - the first pulse arriving in early August, the second in late September. In "bad years" - i.e., 1995 and 1996 - only the second of these pulses was evident. The length frequency data also suggest that the pulse structure may remain intact through the first winter and appears to be detectable in age 1 cod the subsequent year. In 2000, we (Gregory et al. 2000) predicted that the 1999 year class of Atlantic cod will prove to be the strongest since the 1992 moratorium. Catches of the 1999 year class in 2000 as age 1 fish, support this prediction. Age 1 Atlantic cod in Newman Sound in 2000 were the highest we have ever recorded at these sites. In contrast to 1997-1999, we anticipate that the 2000 year class will be weak, based on nearshore densities of age 0 Atlantic cod in Newman Sound. Densities of age 0 Atlantic cod were consistently low throughout much of the season, and were comparable to 1996, the poorest year class on record in three independent surveys of age 0 abundance off the northeast Newfoundland coast.
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