Examining the effects of in-situ aquaculture on marine ecosystem structure and function

Piersiak, Michael G. (2021) Examining the effects of in-situ aquaculture on marine ecosystem structure and function. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Marine aquaculture operations in Atlantic Canada have been steadily increasing for decades. Along Newfoundland’s southern coast, Atlantic salmon (Salmo salar) are farmed in two of the three major oceanographic bays, and development of hatchery and farm operations in the third are ongoing. Marine farm operations attract wild animals, and resulting changes to local ecosystem properties may also affect wild salmon during coastal phases of their marine migrations to and from their natal rivers. In this thesis, I explore the mechanisms responsible for the aggregative effect generated by farm activity, and examine the effects of changing ecosystem properties on wild salmon populations with natal rivers in close proximity to farm operations. I show that fish schools are an effective proxy measure for predation risk, and that in sea cage environments, attraction of large predators to active farm sites can be quantified using acoustic measurements of fish schools. I also show that basal resource availability does not differ between active and fallow farm sites, while basal productivity trends differ annually between bays and as well across years within the same major oceanographic bay regardless of the presence of aquaculture operations. Finally, I show that wild salmon exhibit little fidelity to active farm sites compared to farm fish, and differences in movement behavior and changes to local ecosystem properties resulting from farm activity leads to increased mortality risk via natural predation for escaped farm-raised salmon. Cumulatively, results from this thesis suggest that marine pelagic ecosystems and natural processes therein are changing in response to aquaculture activities. Within these changing ecosystems, marine survival for escaped farm salmon is likely low due to the combination of reduced antipredator behavior and fidelity to active farm sites where encounter probability with naturally-occurring predators is high.

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