Trawl and acoustic survey in southern Bonavista Bay - observations on demersal distribution of Atlantic cod / John T. Anderson and Edgar L. Dalley.: Fs70-1/2000-095E-PDF

A trawling and acoustic survey was conducted throughout southern Bonavista Bay in December 1999. The most abundant species caught in the trawl was Atlantic cod, followed by American plaice and Arctic cod. Atlantic cod were predominantly juveniles <40 cm length caught most abundantly in water depths <125 m. The largest catch of juvenile cod was 10,509 for a 10 minute tow, while the largest catch of large juvenile and adult cod was 652 for a 10 minute tow. Water temperatures ranged from approximately 0°C at 100 m to 3.5°C at the surface. Minimum water temperatures of -1.5°C occurred at approximately 175 m, rising to 0°C at 300 m in the deep trenches. Acoustically, small juvenile cod were observed throughout the survey area at depths of <100 m. One concentration of large, adult cod, was located at depths <30 m within a narrow channel in Southern Bay, inside of Sandy Point. These cod were relatively good condition, although all stomachs were empty. No fish concentrations were observed in the deep trenches. A diurnal pattern was observed, where cod lay near, or on, the seabed during daytime and rose into the water column at night. This diurnal pattern indicates that night time trawling will be biased low due to fish occurring above the trawl headline, while daytime acoustics will be biased low by cod lying within the acoustic dead zone. Therefore, design of an inshore survey must address diurnal behaviour in Atlantic cod.

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