Research Document - 2014/071

Recovery Potential Assessment for Eastern Cape Breton Atlantic Salmon (Salmo salar): Habitat requirements and availability; and threats to populations

By A.J.F. Gibson, T.L. Horsman, J.S. Ford, and E.A. Halfyard

Abstract

The purpose of this Research Document is to provide background information on the habitat characteristics required by Atlantic Salmon in eastern Cape Breton to complete their life-cycle, as well as the stressors and threats impacting those processes. The document includes information related to:

1. functional descriptions of habitat properties,
2. the spatial extent of areas in eastern Cape Breton having these properties,
3. identified threats to habitat, as well as threats to populations that are not habitat-related,
4. the extent to which threats have reduced habitat quality or quantity in eastern Cape Breton, and
5. the potential for mitigation of identified threats.

Each of these components was requested by the Terms of Reference for the Recovery Potential Assessment for eastern Cape Breton salmon. Information is presented for the freshwater and marine (and estuarine where appropriate) environments separately.

Habitat requirements of Atlantic Salmon in freshwater include properties, such as water quality, substrate composition, discharge characteristics, and accessibility. Several life stages (eggs, age-0, age-1 and age-2+ juveniles) have residences that individuals defend and that are required to support essential life-cycle processes. At the current low population sizes of eastern Cape Breton Atlantic Salmon, freshwater habitats are unlikely to be limiting recovery in rivers as there remains a large proportion of accessible area.

Habitat requirements in marine and estuarine environments have not been delineated spatially, but are thought to be primarily related to food availability and oceanographic conditions, as individuals require resources and water conditions that support rapid growth. As such, the areas occupied by Atlantic Salmon populations from eastern Cape Breton likely vary over time with oceanographic environments (currents, temperature, food availability). Tagging data are limited, however, eastern Cape Breton salmon are likely to use much of the northwest Atlantic, in particular the waters of coastal Cape Breton, the southern coast of Newfoundland, western Newfoundland, the Labrador sea and the West Greenland sea. There is no evidence for a residence in the marine environment. Research on population dynamics of Atlantic Salmon demonstrate that survival in the marine environment is not resource-limited, so the availability of habitat in marine environments is not limiting population size.

Threats have been identified that are likely to have an effect on Atlantic Salmon populations in eastern Cape Breton, either historically, currently or in the future. In general, the linkages between threats and changes to Atlantic Salmon populations have been established in the scientific literature, but have not been quantified for specific eastern Cape Breton rivers. Where possible, the relative magnitude of a specific threat has been quantified among watersheds in eastern Cape Breton using GIS (Geographic Information Systems) analyses. In freshwater environments, it is likely that these threats have resulted in an overall reduction in habitat quality. The feasibility of restoring habitats to higher values is likely greater in freshwater environments than in marine because it is possible to quantify the impact of a given threat on a population, and the threats are more localized and tractable to address in the short-term.

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