Examen de quatre nouveaux sites de pisciculture marine proposés dans la baie St. Mary’s, dans le comté de Digby en Nouvelle-Écosse

Abstract

Canadian Salmon Ltd. has applied to the Province of Nova Scotia to lease four new marine finfish aquaculture sites in St. Mary’s Bay, Digby County, Nova Scotia, as well as for associated licences for Atlantic Salmon (Salmo salar) and Rainbow Trout (Oncorhynchus mykiss) for a total production of up to 3 million fish. The proponent has indicated a primary intent to culture Atlantic Salmon. St. Mary’s Bay is an inlet of water measuring approximately 60 km in length and 15 km in width that has large tidal heights, medium to high current speeds, and exposure to offshore waves. To help inform DFO’s review of this application, DFO Science identified Ecologically and Biologically Significant Areas (EBSA), Species at Risk, and a number of pertinent fish and benthic species within the area. Susceptibility of species to organic enrichment, exposure to in-feed drugs (emamectin benzoate) and/or pesticides (azamethiphos and hydrogen peroxide) used to control sea lice in farmed fish was considered. In addition, direct genetic interactions between wild and farmed salmon, species entanglement with infrastructure, and cumulative anthropogenic stressors were also considered. The advice primarily considered the culture of Atlantic Salmon with some consideration to Rainbow Trout. A Predicted Exposure Zone (PEZ) estimates a distance that a dissolved chemical or particulate material could travel from a proposed finfish aquaculture site. The PEZ approach is precautionary and used to characterize potential exposure of marine ecosystems and species to associated aquaculture activities. It does not provide a detailed analysis of impact, intensity, or risk associated with the potential exposure. A benthic-PEZ is an estimate of benthic (seabed) areas that may be exposed to deposited feed waste, feces, and bound substances (e.g., medications) released from a proposed aquaculture site. Two benthic-PEZ were estimated (one for feed waste and one for feces). There is no overlap between site-specific benthic-PEZs for potential feed waste, but there are overlaps in the benthic-PEZs for feces. When considering these PEZs, most of the seabed in St. Mary’s Bay could be exposed to feces deposition. Adjacent coastal areas outside of St. Mary’s Bay may also be exposed. A pelagic-PEZ is an estimate of the pelagic (water column) areas that may be exposed to registered bath pesticides from a proposed aquaculture site at levels above which adverse effects may occur, if used. The pelagic-PEZs demonstrate that most of the pelagic area and some shallower water benthos in St. Mary’s Bay could be exposed. Adjacent coastal areas outside of St. Mary’s Bay may also be exposed. An increase in aquaculture infrastructure may increase the potential for entanglement for some species at risk. These may include White Shark (Carcharodon carcharias) and North Atlantic Right Whale (Eubalaena glacialis), which have been detected within the vicinity of the proposed aquaculture sites. Reports of entanglement of marine mammals, sea turtles, and sharks in marine finfish aquaculture gear in Atlantic Canada remain low or nil for these large-bodied species. The proposed aquaculture sites, and their associated PEZs, are within Lobster Fishing Area (LFA) 34 (LFA 34 represents greater than 20% of total Canadian landings). Within LFA 34, St. Mary’s Bay consistently exhibits a higher presence and density of American Lobster (Homarus americanus) compared to the offshore area. A higher abundance of Lobster at all life stages, including berried females, is observed in the bay. Juvenile patterns of settlement also indicate that the overlying water column is important habitat for pelagic larval stages. The proposed aquaculture sites fall within Scallop Production Area (SPA) 3 which is an important area for wild Sea Scallop (Placopecten magellanicus); this area is important for scallop habitat at all life stages of the species. Scallop are relatively sedentary; three of the four proposed aquaculture site leases overlap areas of high abundances of young and adult scallop. Scallop in St. Mary’s Bay have some of the highest physical quality attributes of scallop found in the Bay of Fundy and its approaches. Jonah Crab (Cancer borealis), Rock Crab (Cancer irroratus), and Snow Crab (Chionoecetes opilio) have also been observed in St. Mary’s Bay and within the PEZs. Shrimp and krill species identified within the benthic-PEZ and pelagic-PEZ include: Bristled Longbeak (Dichelopandalus leptocerus); Sand Shrimp (Crangon septemspinosa); Northern Shrimp (Pandalus borealis); Northern Krill (Meganyctiphanes norvegica); and krill (Euphausiacea sp.). St. Mary’s Bay is also a productive area for Soft-shell Clam (Mya arenaria), Quahog (Mercenaria mercenaria), Bar Clam (Spisula solidissima), and Blue Mussel (Mytilus edulis). Some groundfish and small pelagic species are also found in the bay. Within the feed waste benthic-PEZs, shelter-restricted benthic juvenile lobsters and other crustaceans may be vulnerable to localized impacts such as hypoxia from increased organic deposition due to their restricted movement and preferential selection for shelter. The sedentary nature of scallops and other bivalves makes them vulnerable to excessive organic deposition. Within the benthic-PEZs, emamectin benzoate may have toxic effects on non-target organisms, especially crustaceans. Effects of emamectin benzoate on crustaceans include premature moulting, reduced growth rates, and mortality. Bivalves are currently considered less sensitive to emamectin benzoate, however data are limited. Within the pelagic-PEZs, azamethiphos and hydrogen peroxide may have toxic effects on non-target organisms, including all life stages of crustaceans (e.g., lobster, shrimp, krill, crab). Berried female (egg-bearing) lobsters specifically are more sensitive to azamethiphos during the summer months based on reproductive and moulting cycles. Impacts on bivalves are possible, however data are limited. Populations within the Nova Scotia Southern Upland – West (SU–W) and Outer Bay of Fundy (OBOF), as well as the Inner Bay of Fundy (IBOF) Designatable Units (DU) of Atlantic Salmon, are within the range that escapees from the four proposed finfish aquaculture farms could be expected to travel. The farms themselves are physically located within the Nova Scotia Southern Upland – West DU. Both the SU–W and OBOF DUs are assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), and the IBOF DU is listed as Endangered under the Species at Risk Act (SARA). Modelling of the demographics and genetics of populations predicts that impacts from interbreeding between fertile farmed Atlantic Salmon escapes and wild Atlantic Salmon occur when the proportion of farmed salmon in a river exceeds 10% of the wild population. Dispersal modelling of escapees at two different escape rates predicts that a large number of rivers in the OBOF and SU–W DUs are already expected to be above the threshold of impacts. The same dispersal model predicts that with the addition of the four proposed aquaculture sites, there will be an increase in the proportion of escapees in most of the rivers within 200 km of the proposed St. Mary’s Bay sites, both in the proposed SU–W and OBOF DUs, and to a lesser extent in the IBOF DU. Interbreeding between escaped Rainbow Trout and wild Atlantic Salmon would not be expected. However, interaction between them may still result in ecological or indirect genetic impacts on wild salmon populations. An analysis of the relative intensities of human activities and stressors, using cumulative impact mapping, on the St. Mary’s Bay area, bounded by the pelagic-PEZ, estimated that the existing and proposed finfish aquaculture sites contributed 5.1% to the total cumulative impact score, which is lower relative to some other human stressors. This analysis also highlighted the current high complexity of human uses and relative effects of overlapping stressors on the benthic and pelagic habitats in the St. Mary’s Bay area. After the addition of the proposed sites, the greatest change in cumulative impact score was within several kilometres of the proposed leases, where additional finfish aquaculture, warming waters, acidification, and bottom-contact fishing may interact to impact species found in pelagic, hard bottom and soft bottom habitats. Climate change was considered as a factor of anticipated changes in St. Mary’s Bay that may alter the interactions between the ecosystem and the proposed aquaculture sites. Projected ocean warming due to climate change may increase the abundance of lobsters in St. Mary’s Bay, including earlier and increased residence time for berried females, with potential for increased interactions of all life stages with farms (e.g., physical interactions and therapeutant use relating to timing of larval release). Sea scallops and bivalves are vulnerable to ocean acidification, which is predicted to increase. However, the potential for eutrophication and localized acidification from algal blooms related to fish farm nutrient inputs is considered low. Climate warming and freshwater availability in general may influence sea lice, disease, and the subsequent use of pesticides and drugs. Increased likelihood of storm incidence and severity, projections of increased wave height and sea level may all affect aquaculture infrastructure and increase the potential risk of escapees without additional mitigation. Various data sources and methodologies were incorporated into this report. Each of these components has uncertainties which should be considered when interpreting this information.