Atlantic Fisheries Research Document 1996/046

Results of the 1995 Fleming survey of demersal juvenile cod in the coastal zone of eastern Newfoundland

By D.C. Schneider; P. Hennebury; D. Methven; D. Ings; J. Howell; S. White; D. Pinsent; W. Bailey

Abstract

Research carried out under the Northern Cod Science Program (Methven, unpublished) showed that 0-group and 1-group cod currently (1992 onward) concentrate in coastal areas, with highest densities at depths of 4-7 m. 0-group cod are also concentrated in time, arriving in coastal nursery areas as distinct and predictable pulses in April-June, mid-August, mid-October, and possibly late December-January. Surveys were made during the October recruitment pulse at depths with maximum density by setting seines at 10-20 metres then hauling them shoreward. The primary objective during 1995 was to test for enhanced density of first year demersal juvenile cod resulting from a well documented spawning aggregation in Smith Sound in April and May of 1995. Enhanced density of juveniles settling to the bottom in suitable coastal habitats were expected circa 3-4 months later, in August and September. The second objective was to compare the abundance of identifiable length groups (corresponding to ages 0+ 1+ 2+ fish) to the abundance of the same length groups in previous years. The survey revisited sites sampled in 1959-1964 and 1992-1994. The density of first year (0+) demersal juvenile fish (LGO = length group 0) did not exceed the average for 1992-1994 for the entire survey area (St. Mary's Bay north to Notre Dame Bay). Within this area the density of LGO demersal juveniles in Trinity and Conception Bay did not exceed that in previous years. The density of second year (1+) juveniles (LG1 = length group 1) fish was expected to be higher in 1995 that 1994, based on higher density of LGO fish in 1994 than in 1993. Instead, the number of LG1 fish in 1995 was the lowest in the 10 years record of comparable counts. Third year (2+) juveniles (LG2 = length group 2) were expected to be more abundant in 1995 than 1994, again based on strength of that cohort in previous years. Contrary to expectation the density of LG2 was lower in 1995 that 1994. The apparent increase in mortality of LG1 fish in the coastal zone was 258% relative to the expected density calculated from cohort strength the prior year. This calculation assumes no change in performance of gear, and no greater shift of LG1 into deep water than in previous years. Potential sources of mortality include incidental catch, predation by seals or large cod moving into shallow water.

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