Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

Abstract

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 272:257-270 (2004) - doi:10.3354/meps272257 Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation B. J. Laurel1,*, R. S. Gregory1,2, J. A. Brown1, J. K. Hancock1, D. C. Schneider1 1Memorial University of Newfoundland, Ocean Sciences Centre, St. John¹s, Newfoundland A1C 5S7, Canada 2Department of Fisheries and Oceans, St. John¹s, Newfoundland A1C 5X1, Canada *Email: blaurel@mun.ca ABSTRACT: 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. KEY WORDS: Density-dependence · Habitat selection · Atlantic cod · Greenland cod · Aggregation · Shoaling Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 272. Online publication date: May 19, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.