Research Document - 2010/118
Assessments of Atlantic Salmon Stocks in South Western New Brunswick (Outer Portion of SFA 23): An Update to 2008
By R.A. Jones, L. Anderson, A.J.F. Gibson, and T. Goff
Abstract
The purpose of this document is to provide a review of DFO Science information for Southwest New Brunswick Atlantic salmon (Salmo salar) populations in support of a review of the conservation status of Atlantic salmon in Eastern Canada by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Information pertaining to populations in New Brunswick’s outer Bay of Fundy (oBoF) portion of Salmon Fishing Area (SFA) 23 is compiled in this review, including the Saint John River upriver of Mactaquac Dam, the Nashwaak River (a tributary to the Saint John River downriver of Mactaquac Dam), the Magaguadavic River and the St. Croix River.
Adult salmon counts and estimates of returns to counting facilities (fishway, counting fence) are evaluated against conservation requirements that were determined for each index river based on accessible habitat area and the biological characteristic information of the returning adult salmon. Estimates of emigrating juvenile salmon (pre-smolt, smolt) using rotary screw traps as well as mean parr densities by electrofishing on two tributaries of the Saint John River are assessed against reference levels.
Overall, the available data on salmon in the outer portion of SFA 23 indicates that populations are persisting at low abundance levels. Estimated adult abundance on the Saint John River upriver of Mactaquac and on the Nashwaak River is presently 5% and 23% of their respective conservation requirements, and estimated egg deposition has declined at rates in excess of 65% over the last 15 years. Pre-smolt and smolt estimates for the Tobique River in 2008 were approximately half those in 2007, and smolt abundance on the Nashwaak River was 67% lower. Juvenile densities in the Tobique and Nashwaak rivers were an order of magnitude below reference values (Elson’s norm) in 2008. Adult returns to other rivers in SFA 23 were extremely low, and decline rates in excess of 95% over the last 15 years were predicted for these populations (Magaguadavic and St. Croix rivers). Considering total escapement to SFA 23 over the last 15 years, declines of 62% and 87% respectively, are predicted for 1SW and MSW returning adults.
Within this region, numerous threats are likely affecting the current status and trends in abundance of these populations. Mortalities associated with the operation of hydro facilities are predicted to result in a 5-30% loss in spawner abundance on an annual basis. Freshwater threats include the effects of forestry and agriculture activities, invasive fish predators and escapes from the nearby aquaculture industry, but their population-level impact has yet to be quantified. Although some illegal fishing persists, commercial fisheries affecting these populations have been closed since 1984, and the recreational and native fisheries have been closed since 1998. To deal with the issue of low marine survival, the salmon enhancement program at the Mactaquac Biodiversity Facility was re-focused in 2001 to produce captive spawning adults from wild-caught juvenile salmon. However, freshwater threats, combined with low marine survival, still appear to be limiting recovery of the populations in the region.
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