Predation-risk in juvenile Atlantic cod with respect to eelgrass patch characteristics in Newman Sound, Bonavista Bay, Newfoundland

Gorman, Ann Marie (2004) Predation-risk in juvenile Atlantic cod with respect to eelgrass patch characteristics in Newman Sound, Bonavista Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Predation risk is a driving force in the distribution of juvenile fish. In coastal Newfoundland, age-0 Atlantic cod (Gadus morhua) use the protective cover of eelgrass (Zostera marina) in preference to exposed, sandy areas. Studies suggest that habitat configuration is closely correlated to the population dynamics of certain species. A relationship between eelgrass patch morphology and predation risk of cod could allow for indirect assessment of natural predation based primarily on eelgrass configuration - a variable more easily quantified than natural predation itself. In three experiments, I used a tethering technique in Newman Sound, Bonavista Bay, Newfoundland, Canada, to quantify the relative predation risk of post-settled age-0 cod in natural eelgrass habitats. I examined the influence of eelgrass patch size (1-80m²) on predation risk based on the assumption that larger patch size results in lower predation compared to small patches. I also tested for the presence of edge effects at an 18 m long, vertical boundary between a mud and an eelgrass habitat. Lastly, I evaluated the effect of patch shape on predation by quantifying the fractal exponent of individual patches. I conclude that predation was correlated to patch area and proximity to patch edge, but not to the shape of individual patches.

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