Gear-Independent Patterns of Variation in Catch of Juvenile Atlantic Cod (Gadus morhua) in Coastal Habitats

Lead Researcher and Department
D. A. Methven; D.C. Schneider, Ocean Sciences Centre, Memorial University

Funding Resources
Northern Cod Science Program, Department of Fisheries and Oceans

Summary
Habitat and size of juvenile Atlantic cod (Gadus morhua) changes substantially during the first 3 years after settlement, and hence, cohort size cannot be followed using a single gear. Whether catch could be calibrated across gear types was investigated by deploying pairs of gears repeatedly in the same habitat. As expected, size selectivity differed substantially among gears. Trawls and seines generally collected individuals <200 mm. Gillnets and jiggers collected individuals >150 mm. Size modes corresponding to age-classes, were common to catches of most gears. Highest catches were taken by trawls and seines. Gillnet catches were orders of magnitude lower. Standardized catches could not be calibrated across pairs of gears deployed in the same habitat at approximately the same time. It was possible to identify spatial depth gradients and diel changes in catch that were independent of gear.

Consistent spatial and temporal patterns across gears were interpreted as characteristic of fish populations, not just of gears. Density in coastal habitats was higher at night and was higher at 4-7 m than at greater depths. These results, in conjunction with other studies, establish that coastal depths of 4-7 m, represent the centre, and not the edge of the distribution of age 0 cod in Newfoundland, during autumn. Hence nursery areas during the early 1990s, a time of historically low spawning stock biomass, must be identified as the coastal zone, not offshore.

Published in: Canadian Journal of Fisheries and Aquatic Sciences. 55 (6), 1430-1442.1998.

Dates
1998

Keywords
Juvenile cod, Inshore distribution, Comparison of catch methods, Coastal zone

Locations
Bonavista Bay
Conception Bay
Notre Dame Bay
Trinity Bay
Avalon Peninsula
Clarenville - Bonavista
Gander - New-Wes-Valley
Grand Falls-Windsor - Baie Verte - Harbour Breton
Zone 11 - Emerald
Zone 12 - Exploits Valley
Zone 14 - Kittiwake
Zone 15 - Discovery
Zone 17 - Mariner

Industry Sectors
Salt water fishing (Agriculture, forestry, fishing and hunting — Fishing, hunting and trapping — Fishing)
Fisheries research and development laboratories (Professional, scientific and technical services — Scientific research and development services — Research and development in the physical, engineering and life sciences)

Thematic Categories
Fishery Research (Fisheries)
Cod (Fisheries — Species)

Departments
Ocean Sciences, Faculty of Science (STJ)