Between-patch movement behaviour of juvenile Atlantic cod (Gadus morhua)

Ryan, Mary R. (2009) Between-patch movement behaviour of juvenile Atlantic cod (Gadus morhua). Masters thesis, Memorial University of Newfoundland.

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Abstract

Complex habitat provides a predator refuge for many animals. When such habitat is fragmented, movement between patches may be driven by many factors including foraging opportunities, density effects, abiotic factors, and predator distribution. Although the effects of these factors are well-studied in terrestrial environments, few studies have focussed on inter-patch movement in the marine environment beyond the role of foraging success in patch selection and departure. I examined the effects of release density, gap distance, and predator presence on the inter-patch movements of juvenile Atlantic cod (Gadus morhua) in a 12 m by 3 m raceway tank containing patches of artificial eelgrass. In addition to the main factors examined, I also collected data to test the effects of fish length and average group size on between-patch movement. Results show that between-patch distance and predator location each have significant effects on the total number of times juvenile Atlantic cod cross gaps in complex habitat. Interactions among experimental conditions had significant effects on the time taken to depart the release patch, and on the duration of the first completed between-patch movement. I also conducted mark-recapture experiments in Newman Sound, Terra Nova National Park. In 2006,1 released 348 juvenile Greenland cod (Gadus ogac) into artificial eelgrass patches following tagging with visual implant alphanumeric tags (VI Alpha™). In 2007,1 released 450 juvenile Atlantic cod, also tagged with VI Alpha tags into artificial eelgrass patches. Because of low recovery rates, I was unable to confirm laboratory findings in the field. However, I was able to demonstrate that standard length negatively affects recapture of juvenile Atlantic cod, and that the presence of conspecifics affects the movement of juvenile Atlantic cod in highly fragmented habitat. My laboratory and field results indicate that the inter-patch movements of fishes may be determined by several factors other than foraging success, and that movement decisions in juvenile cod are based on evaluation of multiple risks and benefits.

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