Research Document - 2004/114

Inner Bay of Fundy Atlantic salmon (Salmo salar) critical habitat case study

By Trzcinski, M., A. Kurtis, J.F. Gibson, P. G. Amiro, R.G. Randall

Abstract

Atlantic salmon in the inner Bay of Fundy (iBoF) were common only 30 years ago, but they have declined to such critically low levels that they are now at risk of being extirpated. The Species at Risk Act requires that recovery plans for endangered, threatened and extirpated species include the identification and protection of critical habitat. The purpose of this document is to evaluate the relationships between habitat quality and quantity and the survival and recovery of iBoF Atlantic salmon in order to determine whether habitat protection will aid in this population’s recovery. This evaluation is based on: 1) present status of iBof salmon, 2) an assessment of the amount of freshwater habitat available for iBoF salmon, 3) a review of recovery targets for these populations, 4) a statistical analysis of the life history of an iBoF salmon population to assess which life history parameters changed, and when, 5) equilibrium analyses of population size and viability and 6) a population viability analysis (PVA) to determine whether habitat protection would aid in population recovery.

Despite having over 9,000,000 m² of habitat available in over 22 rivers, iBoF salmon are at very low levels and extirpations have occurred in several rivers. Juvenile salmon are present in rivers with Live Gene Bank (LGB) support, but densities are extremely low in rivers without support. Two possible recovery targets are considered: the conservation limits used for fisheries management and the population size to maintain genetic variability (N_e). The former places recovery targets in the range of 280 small and 420 large salmon for the Big Salmon River and 772 small and 289 large salmon for the Stewiacke River, and the latter in the range of 568 to 1,923 salmon per river.

Analysis of the dynamics of salmon in the Big Salmon River indicate that the annual mortality of immature salmon at sea increased from 0.83 (pre-1990 time period) to 0.97 (post-1990 time period) and that annual mortality of post-spawning adults has increased from 0.49 to 0.64 during the same time. Under present conditions, the equilibrium population is zero and the expectation is that, in the absence of human intervention, the population will go extinct on the time scale of 10 to 15 years. Intervention in the form of captive rearing through the LGB program has at least slowed the decline in some rivers. Both the equilibrium analyses and PVA indicate that population viability cannot be enhanced through changes in freshwater habitat quantity, although persistence of very small populations may be somewhat enhanced through increases in freshwater habitat quality. A change in marine survival is required to reach recovery targets. If marine survival increases, recovery times are sensitive to the quantity and quality of freshwater habitat. These results indicate that a freshwater habitat protection will not reverse current declines but could be important for population recovery if marine survival increases. At present, insufficient data exists to evaluate the efficacy of marine habitat protection for recovering iBoF salmon.

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