Atlantic Fisheries Research Document 1996/050

Biological characteristics of Atlantic cod (Gadus morhua) from three inshore areas of western Trinity Bay, Newfoundland

By J. Brattey

Abstract

Aggregations of cod were found at several locations in shallow (30-100m) waters in Smith Sound and Northwest Arm, but not in Southwest Arm in western Trinity Bay during December 1995. Over 2000 fish caught with jiggers and deathered hooks were tagged with yellow t-bar spaghetti tags and released and another 204 were sampled for length, sex, maturity, and otoliths. Cod were generally large, with most between 40 and 80 cm and mean lengths typically around 56 cm. Ages of cod ranged from 3 to 8 years, but more than 50% were 5 year olds. Beginning of the year mean weights at age were higher than those reported for commercial samples of cod from 3L during recent (1990-95) years. Cod were generally in good condition, with mean values of Fulton's K (based on round weight) in the range 0.85 to 0.94. Most cod sampled were adults and examination of the gonads of females suggested they would spawn in the coming spring. In April 1996, as part of a hydroacoustic survey to estimate the biomass of cod in these inshore areas, further biological sampling of cod was conducted. Aggregations of cod were located in all three areas, particularly in Smith Sound and Southwest Arm. A total of 1542 cod were caught with otter trawl, jiggers and feathered hooks, and gill nets. Cod in all three areas were generally large and of comparable size range and condition to those seen in December 1995. Comparison of the maturities of females revealed a dense aggregation of spawning fish in deep water (>200m) in the outer reaches of Smith Sound. In contrast, the cod in all other regions, including the inner reaches of Smith Sound, were mostly mature but not spawning and appeared destined to spawn later in the spring. The prevalence of the parasitic copepod Lernaeocera branchialis on cod in these inshore areas, particularly among larger fish and all sizes caught in Southwest Arm, was much higher than that of comparable sized fish sampled offshore over the past 13 years. Since transmission of the parasite occurs only during fall and mainly in the inshore, the high prevalences suggest that these fish had resided in inshore waters throughout the fall and winter months.

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