Research Document - 2006/038

Relative strength of the 2003 and 2004 year-classes, from nearshore surveys of demersal age 0 and 1 Atlantic cod in Newman Sound, Bonavista Bay

By Gregory, R.S., C. Morris, G.L. Sheppard, M.E. Thistle, J.E. Linehan, and D.C. Schneider

Abstract

We surveyed demersal age 0 Atlantic cod (Gadus morhua) in the nearshore (<10 m deep) using a seine net to conduct a qualitative assessment of the strength of eight 1997-2004 year-classes of Atlantic cod early in their life. 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 9 summer-autumn periods during 1995-2004. Our results were qualitatively similar to those of the geographically broader Fleming Survey (1959-64, 1992-1997, 2001) during years were the two surveys could be compared. Therefore, we have some confidence that Newman Sound data may be indicative of broader geographic patterns. Compared with the benchmark historical low in 1996 observed in several pre-recruit studies in the waters off the northeast Newfoundland coast, 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 were 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" – e.g. 1998 and 1999 - the first pulse arriving in early August, the second in late September. In "bad years" – e.g. 1995 and 1996 – the first pulse has been weak and late to recruit to the nearshore. The length frequency data in years following strong age 0 recruitment 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. We have predicted (Gregory et al. 2003) that the 2000-02 year-classes of Atlantic cod will prove to be weak relative to the strong 1998 and 1999 year-classes which preceeded it. In contrast to 1997-1999, densities of age 0 Atlantic cod have been consistently low throughout much of the season in the past five years (2000-04), and were comparable to 1996, the poorest year class on record in three independent surveys of age 0 abundance off northeastern Newfoundland. The 2002 year class appeared the exhibit strong overwinter survival, showing higher than expected densities as age 1 individuals throughout 2003.

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