Habitat use and movement patterns of juvenile Atlantic cod (Gadus morhua) in a coastal area of eastern Newfoundland

In this thesis I address fundamental aspects of the ecology of juvenile Atlantic cod (Gadus morhua); a species of economic and cultural importance.{09}A multi-faceted approach, using SCUBA observations, conventional mobile telemetry and a prototype fixed telemetry system, was employed to study the movement patterns and habitat use of juvenile Atlantic cod (age 0 to age 2) in a coastal area of Newfoundland, Canada.; Age 0 cod did not appear in the study area until September and their abundance increased throughout autumn. Age 1 and age 2 cod were present through the study period (August–January) with their abundance peaking in mid-October. In mid-November, a time coinciding with the disappearance of the thermocline, approximately 70% of the tagged age 2 individuals migrated seaward from autumn home ranges.; During late summer and autumn, cod maintained home ranges (mean = 6 ha) in areas of mid (5–10°) to high (>10°) bathymetric relief and over structurally complex substrates (boulder and kelp) to a greater degree than would be expected given available habitat. Younger juveniles (age 0 and 1) were found in structurally complex habitats diurnally, however, did not exhibit preference for any habitats nocturnally.; Age 0 and 1 cod were observed to exhibit nocturnal inshore migrations through a thermocline. Previous studies have shown that movements through a thermocline provide energetic benefits to cod however, since these fish continued this behaviour when the water column became isothermal, other mechanisms must be involved. The depth distributions of age 2 cod did not differ over the diel period.; Age 2 cod were found to be active throughout the diel cycle, although reduced activity was observed during nocturnal periods during September and October and diurnal periods in December. Although temperature did not appear to have an effect on swimming speed, greater swimming speeds were observed over open substrates (sand and gravel); possibly a response to increased vulnerability to predators.; The results of this thesis suggest that structurally complex substrates are important to juvenile life stages of cod and activities resulting in reduced structural complexity (i.e. bottom trawling) could have negative impacts on the recovery of the species. Habitat protection initiatives, such as Marine Protected Areas, could also benefit survivorship of juvenile cod as old as age 2, given their spatial requirements.