Behavioural Consequences of Density-Dependent Habitat Use In Juvenile Cod Gadus morhua and G. ogac: The Role of Movement and Aggregation

Lead Researcher and Department
B.J. Laurel; R.S. Gregory; J.A. Brown; J.K. Hancock; D.C. Schneider, Ocean Sciences Centre, Memorial University

Collaborators and Students
Terra Nova National Park

Funding Resources
NSERC Strategic Grant

Summary
Fish behaviour can change to accommodate a variable environment, but changes in behaviour have not been considered in the context of density-dependent habitat use. In Bonavista Bay, Newfoundland, we measured how fish density movement and schooling behaviour changed with habitat in 2 gadids, Atlantic cod Gadus morhua and Greenland cod Gadus ogac, using a combination of field-seines, mark-recapture, and laboratory experiments. Density estimates from seines (n = 427) over 5 yr (1996, 1998 to 2001) indicated that these species associated with eelgrass but periodically were detected in high abundance over unvegetated habitat (i.e. sand). Within-site catch variation indicated both species aggregated more in sand than eelgrass habitat, and, in Atlantic cod, aggregations over sand increased as density in eelgrass increased. Although such patterns in catch data could be interpreted as due to the effects of differential mortality between habitats, a mark-recapture experiment indicated that both species of cod were not site-attached and moved between seine locations. Furthermore, video-analysis from laboratory experiments demonstrated that cod formed tighter aggregations over sand compared to eelgrass habitats. Our results suggest that juvenile cod modify their behaviour with changing density, possibly as a means of exploiting poor-quality habitats when high-quality habitats are saturated with conspecifics. Consequently, habitat suitability for Atlantic cod may be a dynamic rather than fixed variable in density-dependent habitat models.

Published in: Marine Ecology - Progress Series. 272, 257-270. 2004.

Dates
2004

Keywords
Juvenile Cod, Habitat, Eelgrass, Terra Nova Park, Atlantic cod, Greenland cod

Locations
Terra Nova National Park
Gander - New-Wes-Valley
Zone 14 - Kittiwake

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)
Oceanographic 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)