Research Document 1997/73

Year-class strength of northern cod (2J3KL) estimated from pelagic juvenile fish surveys in the Newfoundland Region, 1994, 1995, and 1996

By J.T. Anderson and E.L. Dalley

Abstract

Pelagic juvenile fish surveys were carried out in August-September 1994-1996 to index the year-class strength of Atlantic cod (Gadus morhua) in the NW Atlantic ocean (NAFO Div. 2J3KL). The abundance of pelagic juvenile cod decreased by a factor of eight from 1994 to 1996. This decline occurred first in the offshore in 1995, and occurred both inshore and offshore in 1996. Year-class estimates from these surveys predict that recruitment at age three of the 1996 year-class will be extremely low. Growth rates of 0-group cod estimated from micro-otoliths averaged 0.57 mm d^-1 in 1994, 0.67 mm d^-1 in 1995 and 0.55 mm d^-1 in 1996. Mean survey lengths were 45.1 mm, 45.3 mm, and 41.2 mm, respectively. When lengths were adjusted to a common date based on measured growth rates, cod were larger in 1994 than in 1995 or 1996. Peak hatching dates were June 1994 and June-July in 1995 and 1996, indicating that spawning occurred primarily in May and June of these three years. The observed decline in abundance coincided with the disappearance of spawning cod offshore. There is some evidence of declining abundance and reduced spawning of cod inshore, in Trinity Bay. There is no evidence of poor survival in 1996, based on the abundance of larval capelin and pelagic juvenile Arctic cod (Boreogadus saida) sampled in these surveys. The decline in abundance and geographical contraction in the range of pelagic juvenile cod is consistent with declining production associated with depensation for an extremely low spawning population.)

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