Science Advisory Report  2013/072

Recovery Potential Assessment for Eastern Cape Breton Atlantic Salmon

Summary

• The Eastern Cape Breton Designatable Unit of Atlantic Salmon (Salmo salar) was assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada in November 2010.
• There are 46 rivers that are thought to either contain or to have historically contained Eastern Cape Breton Atlantic Salmon populations. It is likely that salmon either presently use, or have in the past used, other rivers, at least on an intermittent basis.
• There is considerable life history and genetic diversity among Atlantic Salmon populations in Eastern Cape Breton, the maintenance of which is considered important for the long term persistence of the Designatable Unit.
• Adult population monitoring for Atlantic Salmon in Eastern Cape Breton has been focused on five river systems: Middle, Baddeck, North, Grand and Clyburn. 
• Adult abundance trends during the last three generations (15 years) indicate abundance declines of 97% and 89% in Grand and Clyburn rivers respectively, whereas abundance in North River is thought to have increased by 159% during the same time period. Trends in adult abundance in Middle and Baddeck rivers are less evident.
• Only the North River population is assessed to be above its conservation requirement. During the last ten years, the Middle River and Baddeck River populations have been fluctuating in the vicinity of 20 to 75% of their respective conservation requirements. Abundance in Grand and Clyburn rivers is assessed to be very low relative to their conservation requirements.
• Status of salmon in other rivers is inferred from recreational fisheries and limited electrofishing surveys and with less certainty than in rivers where adult population monitoring has been focused.
• Although there are some exceptions, both the recreational catch and fishing effort have declined to very low levels throughout most of the Designatable Unit.
• The electrofishing data generally indicates that juvenile abundance is low throughout much of the Designatable Unit. However, in contrast with both the Southern Upland and Inner Bay of Fundy DUs, there is no evidence in the surveys that river-specific extirpations have occurred.
• Recommended recovery targets for Atlantic Salmon populations in the Eastern Cape Breton Designatable Unit include both abundance and distribution components. It is proposed that the abundance target for individual river populations be the conservation (egg) requirement. The distribution target should encompass the range of genetic and phenotypic variability among populations and environmental variability among rivers, and it should allow for gene flow between the rivers/populations.
• Taking these principles into consideration, a long term abundance target could be to consistently achieve the conservation (egg) requirements in a suite of watersheds that reflect the population diversity of the Eastern Cape Breton Designatable Unit, with a distribution target of supporting the persistence of salmon in the 46 known salmon rivers. A subset of the 46 rivers could be selected for the distribution target (using the science-based criteria provided) if practical aspects of recovering salmon in a specific river are limiting.
• Recovery targets will need to be revisited as information about the dynamics of the recovering populations becomes available.
• There are only two populations with sufficient data for modeling population dynamics (Middle River and Baddeck River populations, which are considered to be two of the healthier populations). Given the life history variability seen throughout Eastern Cape Breton, these two populations are not considered to be representative of other populations in the Designatable Unit.
• Subject to the uncertainties associated with the limited data available for the analyses, modeling for the Middle River population indicates that productivity (including the combined effects of in-river productivity and at-sea survival) has not declined from the mid-1980s to present. In contrast, productivity for the Baddeck River population is estimated to have declined slightly.
• Population viability analyses for the Middle and Baddeck populations indicate a low probability of extinction if conditions in the future are similar to those in the recent past. Similarly, neither population is expected to reach and remain above their conservation requirements unless overall productivity (including reproduction and/or survival) is improved.
• Freshwater habitat supply is not thought to be limiting salmon abundance in Eastern Cape Breton rivers at present, and evidence of significant habitat loss was not found during this Recovery Potential Assessment.
• While the quantity of habitat currently available in Eastern Cape Breton rivers is considered capable of supporting salmon populations at or above the proposed recovery targets, information is insufficient to determine whether habitat quality may be impeding the survival or recovery of salmon populations in some rivers.
• On the watershed scale, important freshwater habitat can be allocated based on the rivers selected for the distribution component of the recovery target. Within a watershed, sufficient quantities of the habitat types needed to support each life stage are required.
• Estuaries associated with rivers containing important freshwater habitats are also considered to be important habitat for Eastern Cape Breton salmon as successful migration through these areas is required to complete the life cycle.
• The Bras d’Or Lakes are a large and very unique estuary in Eastern Cape Breton. Their role in the life cycle of Atlantic Salmon in the area is not well understood, although regional specific Mi’kmaq traditional ecological knowledge indicates that, in addition to serving as a migratory pathway, they also serve as a staging area for returning adults and as an over-wintering area for kelts.
• While there is likely to be important marine habitat for Eastern Cape Breton Atlantic Salmon, given broad temporal and spatial variation, it is not currently possible to link important life-history functions with specific marine features and their attributes.
• Three dwelling places used by four life stages of Atlantic Salmon were evaluated for their potential consideration as residences. Redds most closely match the criteria for a residence because they are constructed.
• There have been many anecdotal reports of illegal fishing activities (i.e. poaching) for Atlantic Salmon in eastern Cape Breton, both using recreational fishing gear and using gillnets. The magnitude of this threat to specific populations is not possible to quantify.
• Threats in freshwater environments with a medium level of overall concern are (importance not implied by order): infrastructure (roads, power lines, etc.); culverts; genetic effects of small population size; forestry; illegal targeting of Atlantic Salmon while fishing under a general license; stocking of rainbow, brown and brook trout; salmon stocking for fisheries enhancement; changes in predator or prey abundance; non-native fish; silt and sediment; and altered hydrology.
• Threats in estuarine and marine environments identified with a high level of overall concern are (importance not implied by order): salmonid aquaculture; marine ecosystem changes; and diseases and parasites. Threats in estuarine and marine environments identified with a medium level of overall concern are: bycatch in other fisheries and international fisheries.
• In general, estimated status and trends of the five index populations suggests that the North River population would be the most resilient to harm. Under present conditions, North, Middle and Baddeck river populations may be able to sustain existing levels of harm without going extinct. However, existing levels of harm may be impeding recovery for the Middle and Baddeck river populations. The smaller populations that are in decline such as the Grand and Clyburn rivers may not be able to sustain existing levels of harm.

This Science Advisory Report is from the January 28 – February 1, 2013, Recovery Potential Assessment for Atlantic Salmon (Eastern Cape Breton Designatable Unit). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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