The influence of sea cage aquaculture on cage-associated wild fish

McAllister, Luke (2023) The influence of sea cage aquaculture on cage-associated wild fish. Masters thesis, Memorial University of Newfoundland.

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Abstract

Sea cage aquaculture can alter the spatial distribution of wild fish populations; however, little is known about the dietary habits and subsequent effects on wild fish. In this thesis, I used stable isotopes δ¹³C and δ¹⁵N values and proportions of vegetable oil-based fatty acids (VOFAs) to investigate the dietary habits of wild cage-associated Atlantic cod Gadus morhua and Atlantic redfish Sebastes fasciatus. Furthermore, I compared the length, weight and condition of cage-associated G. morhua ages 2-4 years old to reference sites within the local division and outside divisions removed from aquaculture, and used VOFAs as biomarkers for waste feed consumption to identify any role(s) in explaining differences in length, weight and condition among age classes. Juvenile G. morhua captured around sea cages had depleted δ¹³C and δ¹⁵N values and elevated proportions of VOFAs consistent with waste feed consumption and sea cage residency, whereas differences in δ¹³C, δ¹⁵N, and VOFAs in cage-associated adult G. morhua and S. fasciatus were predominately absent. Interestingly, waste feed consumption by age 2 cage-associated G. morhua resulted in lower condition than age 2 G.morhua from the local reference division; however, age 4 cage-associated G. morhuawere longer and heavier than the local reference division, despite no evidence to support direct or indirect waste-feed consumption. Overall, the results of this thesis suggest that δ¹³C, δ¹⁵N and VOFAs are suitable biomarkers for tracing sea cage residency and dietary habits of cage-associated wild fish, but waste feed consumption patterns and subsequent effects on wild fish were paradoxical and dependent on species and life stage.

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