Research Document 98/11

Year-class strength of northern cod (2J3kl) estimated from pelagic juvenile fish surveys in the Newfoundland region, 1994-1997

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

Abstract

Pelagic juvenile fish surveys were carried out in August-September 1994-1997 to index the year-class strength of Atlantic cod (Gadus morhua) in the NAFO Divisions 2J3KL. There were substantial differences in abundance, distributions, spawning times, growth rates, condition and size at settlement of pelagic juvenile cod among years.  The abundance index was highest in 1994, at 81.6, declining to 40.6 in 1995 and to a low of 10.8 in 1996. In 1997, abundance increased to 21.8 In all years except 1994, abundance's were much higher inshore than offshore. In 1994, abundance offshore was approximately equal to that estimated inshore. The occurence of pelagic juvenile cod offshore is indicative of the degree of successful offshore spawning which occured each year. hatching times for cod larvae were primarily unimodal and were derived from spawning times that spanned approximately 6-8 weeks each year. Peak hatching times varied by as much as 25 days among these four y ears, 1994-1997, where hatching was much later in 1995 compared to the other years. We estimate spawning occurred primarily in May 1994, 1996, 1997, and in June 1995, based on estimated egg development times of 25-30 days. Examination of plankton samples collected throughout the survey area indicated that no spawning occurred in July-August each year. Among years, daily growth rates averaged 0.49-0.62 mm d^-1. Projected size at time of settlement in mid-October ranged from 65.3-68.5 mm. Relative condition varied from 1.23-1.35 mg mm^-3 (Fulton's K), 1995-1997. Consideration of abundance's, distributions and biological measures of growth rates, size at settlement and relative condition were combined into a predictive measure of year-class strength where we estimate year-class rank as: 1994>>1995>>1997>>1996.

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