Research needs for the management of water quality issues, particularly phosphorus and oxygen concentrations, related to salmonid cage aquaculture in Canadian freshwaters

Abstract

A growing awareness of the difference between the supply and demand for fish products is fueling rapid growth of an aquaculture industry in Canada, including a freshwater sector, based mainly on the cage farming of rainbow trout. Cage farms can release relatively large loads of organic matter and nutrients to the environment. In consequence, federal and provincial resource management agencies need to develop regulatory instruments that will foster the growth of the industry while ensuring minimal water quality impacts. Such instruments should be science based, but there are currently key gaps in our understanding of the water quality implications of the operations of freshwater cage aquaculture. Here I review the state of science of the water quality implications of cage aquaculture and identify 11 knowledge gaps that currently hamper the development of sound, science-based cage culture management instruments. Perhaps the most important finding of the review is the recognition that, while aquaculture has produced significant increases in lakewater total phosphorus (TP) levels in some situations, classic phosphorus mass balance models may substantially overestimate the contributions of cage farms to TP concentrations in some lakes. Research on this, and perhaps the other knowledge gaps identified in this review, should aid the development of sound management instruments for freshwater cage aquaculture in Canada and elsewhere. Key words: aquaculture, cage culture, water quality issues, phosphorus, BOD, review, research needs, freshwaters.