Research Document - 2000/092

Distribution and abundance of demersal juvenile cod (Gadus morhua) on the Northeast Newfoundland Shelf and the Grand Banks (Divisions 2J3KLNOP): implications for stock identity and monitoring.

By G. Lilly, E. Murphy, and M. Simpson

Abstract

The distributions of juvenile cod in Divisions 2J3KLNO in the autumns of 1995-1998 and in Divisions 3LNOP in the springs of 1996-1998 (plus 1999 for Subdivision 3Ps only) were inferred from catches during resource assessment bottom-trawl surveys. Since autumn 1995 these surveys have been conducted with the Campelen 1800 shrimp trawl, which is far more effective at catching small cod than the Engel 145 Hi-rise trawl that it replaced. In 2J3KL, there was an ontogenetic change from a mainly coastal distribution at ages 0 and 1 to a more mid- and outer shelf distribution by ages 3 and 4. Of those year-classes observed with the autumn surveys, only the 1994 year-class was broadly distributed across the shelf, including much of 2J, by age 1. Subsequent year-classes were distributed almost entirely inshore at age 1, and moved with increasing age onto the Northeast Newfoundland Shelf in 3K and northern 3L, and to a much lesser extent into 2J. In 3P, age 1 cod were distributed mainly toward the coast and on western St. Pierre Bank, age 2 cod were more broadly distributed across the Division, and older fish were concentrated in the northwest and the southeast. The only distinct offshore aggregation of cod of ages 0 and 1 was seen on the plateau of Grand Bank in 3NO. The ontogenetic changes in distribution complicate the interpretation of stock structure and the monitoring of recruitment.

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