Reconciling Aquaculture's Influence on the Water Column and Benthos of an Estuarine Fjord – a Case Study from Bay d'Espoir, Newfoundland

Abstract

One unifying principle proposed for the environmental influence of aquaculture is that when flushing is poor (>2 d.), the maximal biomass produced in an area will be constrained by accumulation of waste products in the water column. In the Bay d'Espoir estuarine fjord on the south coast of Newfoundland, under-ice salmonid culture in cages in protected bays with low flushing rates (5 to 20 d.) is a challenging component of the annual production cycle. However, in two years of environmental monitoring of such protected bays, no significant change to water quality was observed. A measurable influence on the benthos was more frequently detected, but localized. Thus the inconsistency of Bay d'Espoir; it has a low flushing rate, yet there was no observable change to the water column. Possible reasons for this are discussed, and include: the sheer amount of water (i.e., potential for within-basin mixing/dilution and biodegradation) in this estuarine fjord; increased surface transport of nutrients; the benefit of fallowing; and, diminished relative loadings to the water column and benthos in winter conditions for an industry in its early stages of development. Further refinement of assimilative capacity estimates for this and other similar suboptimal areas will have to resolve this apparent contradiction prior to espousing “unifying principles”.