Research Document - 1999/080

Year-class strength of Northern cod (2J3KL) and southern Grand Bank cod (3NO) estimated from the pelagic juvenile fish survey in 1998.

By J.T. Anderson, E.L. Dalley and D.J. Davis

Abstract

The pelagic juvenile fish survey was carried out from August 24 to September 10, 1998 from southern Labrador to the southern Grand Bank, including the inshore areas of the northeast coast of Newfoundland (NAFO 2J3KLNO). Abundance of pelagic juvenile Atlantic cod (Gadus morhua) was relatively high in 1998, compared to surveys carried out 1994-1997. The high abundance in 1998 resulted from high abundance on the Grand Bank (3LNO) compared to other years. Abundance on the Northeast Newfoundland Shelf (2J3K) was relatively low offshore while inshore it was mid-range compared to the previous four years. Over the five years during which the survey has been carried out, abundance in 2J3KL declined from 1994 to 1996 and has increased since then. However, abundance in 1997 and 1998 remained below that measured in 1994 and 1995.

Juvenile cod were most abundant in White Bay and Notre Dame Bay along the northeast coast of Newfoundland (3K). Bonavista Bay was not sampled in 1998 due to the early termination of the research trip. However, in previous years Bonavista Bay has ranked among the highest in terms of abundance. Abundance in Trinity and Conception Bays was relatively low and very few cod were found offshore in 2J3K. On the Grand Banks, juvenile cod were found throughout the surveyed area, with the distribution extending onto the northern Grand Bank.

Juvenile cod averaged 18 mm larger and 26 days older on the Grand Banks (3LNO) compared to the northern area (2J3K). Cod in 3NO averaged 62.7 mm and in 3L averaged 67.2 mm in length compared to the north within the inshore bays where cod averaged 43.0-50.3 mm in length.

Growth rates were not different between northern and southern areas in 1998, averaging 0.569 mm d^-1. These growth rates fell within the range observed in previous years, 1994-1997.

Larval hatching dates were earlier and spanned a longer period of time in 1998, compared to 1994-1997. On the Grand Banks (3LNO) larval hatching occurred from late April until late July, whereas to the north hatching did not begin until late June and continued into the middle of July. Peak spawning is predicted to have occurred in April on the Grand Banks and in May along the northeast Newfounland coast.

The relatively large year-class measured on the southern Grand Bank in 1998 appears to be a positive response by Atlantic cod to a warmer environment. Warm bottom water temperatures during spring (Colbourne 1999) appear to be related to a successful spawning by cod. To the north, in 2J3K, the production of young fish continues to be low with no sign of recovery six years after the introduction of the fishing moratorium on northern cod.

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