Science Advisory Report 2008/050

Recovery Potential Assessment for Inner Bay of Fundy Atlantic Salmon

Summary

• Wild iBoF salmon have declined to critically low levels and are currently at risk of extinction. Population projections under current conditions indicate a very high probability that, without human intervention, iBoF salmon will be extinct within 10 years.
• To date, the primary activity that has been used to prevent the extinction of iBoF salmon has been Live Gene Banking (LGB), a form of captive breeding and rearing designed to minimize the loss of the genetic diversity and support the recovery of salmon populations into iBoF rivers once conditions are suitable for their survival. Extirpations in rivers without the support of LGB are ongoing; however, juvenile abundance has increased in rivers receiving LGB support. This increase is due to the release of salmon into these rivers combined with their subsequent survival and a low level of natural reproduction occurring as a result.
• Population modeling for iBoF salmon indicates that the average annual at-sea mortality of immature salmon increased from an average of 83% to 97% from the 1964-1989 to the 1990-2003 time periods. Mortality of post-spawning adults increased from an average of 49% to 64% during the same period. Estimates of recent at-sea mortality are higher again (~99%).
• Modeling indicates that while iBoF salmon would rapidly become extinct without the LGB program, populations are expected to persist at low population sizes in the longer term with the LGB program in place. These populations consist of LGB progeny combined with salmon resulting from the low level of reproduction that is still occurring in the wild.
• The Conservation Spawner Requirement for the designatable unit (DU) (~9,919 spawning adults) is considered to be a reasonable abundance target for iBoF salmon for recovery, representing about 25% of its past abundance. It is recommended that the distribution target include as many of the 32 rivers that iBoF salmon are known to have occupied just prior to their collapse as can be achieved. As iBoF salmon begin to recover, recovery targets will need to be re-evaluated.
• The factors that caused the collapse of iBoF salmon since the 1980s are not well understood, though the observed change in marine survival is large enough to explain the decline. Similarly, while current threats to iBoF salmon have been identified, the primary factors limiting the survival and recovery of iBoF salmon are not known.
• Freshwater habitat is not thought to be currently limiting the recovery of iBoF salmon.
• Modeling indicates that at current levels of at-sea mortality (~99%), increasing freshwater productivity would have little effect on the probability of extinction or recovery. However, if marine survival increases (e.g., at-sea mortality drops to 92-94%), both population growth rates and the size of the recovered population are very sensitive to the quantity and quality of freshwater habitat available.
• Modeling also indicates that under current conditions, neither the probability of extinction nor the probability of recovery is very sensitive to low levels of human-induced mortality. However, if marine survival increased and iBoF salmon began to recover, modeling suggests that recovery would be sensitive to low levels of human-induced mortality.
• The leading marine threats identified to date are (importance not implied by order): interactions with farmed and hatchery salmon, ecological community shifts, environmental shifts, fisheries, and depressed population phenomena. The leading threats identified in freshwater habitats are: changes in environmental conditions, contaminants, barriers to passage, freshwater fisheries, and depressed population phenomena. Additional details on these threats are provided in the Threats to Inner Bay of Fundy Salmon section (starting on Page 16).
• Mitigation measures of particular importance from a DFO Science perspective are: continued restrictions on season, area and gear to minimize incidences of IBoF salmon capture, and release of captured salmon with minimum harm possible; improved containment of aquaculture salmon, fish health management and hatchery/salmon farm site selection to reduce or eliminate ecological and genetic interactions between wild and aquaculture salmon; measures to reduce the impacts of predators; and the maintenance/restoration of watershed integrity to maintain natural flow regimes, to provide access to habitat, and habitat/water quality.
• High priority research recommendations include investigation into the causes of the change in at-sea survival, marine habitat use by iBoF salmon, as well as other factors that may limit recovery, including genetic effects of inbreeding depression, outbreeding depression, domestication selection, interactions with farmed and hatchery salmon, predation, and food web shifts, together with mitigation options. Research into the role of freshwater habitat on recovery, including effects and methods of improved fish passage, if at-sea survival improves, is also recommended.

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