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Research Document - 2013/059

Dolly Varden (Salvelinus malma malma) from the Big Fish River: abundance estimates, effective population size, biological characteristics, and contribution to the coastal mixed-stock fishery

By C.P. Gallagher, K.L. Howland, L.N. Harris, R. Bajno, S. Sandstrom, T. Loewen, and J. Reist

Abstract

The population of Dolly Varden (Salvelinus malma malma) from the Big Fish River, Northwest Territories was assessed using mark-recapture, biological, genetic, and harvest data. Mark-recapture studies conducted in the fall of 2009, 2010 and 2011 indicate there are between 1,477 and 7,265 anadromous Dolly Varden ≥365 mm present at the spawning and overwintering site. The stock appears to have a low and stable abundance, which has not changed considerably over the past 20 years. Counts of migrating Dolly Varden collected using a DIDSON camera in the summer of 2010 likely underestimated abundance due to timing of camera deployment. Microsatellite data were used to determine that the effective population size (NE) was between 210 and 615 adults, suggesting current estimated abundance is sufficient to maintain long-term genetic sustainability. Two independent abundance calculations were done using the NE data which produced estimates between 1,500 and 4,393 fish, similar to the mark-recapture estimates. Biological data collected in the fall at the spawning and overwintering area found an increase in both the proportion of spawning males and those ≥550 mm compared to previous surveys in the 1980s and 1990s. Data from recaptured fish indicates that growth has also not changed significantly from past surveys. Contribution of the Big Fish River population to the harvest along the Beaufort Sea coast in 2011 was examined using genetic mixed-stock analysis. The results, combined with catch information collected from a harvest monitoring program and the abundance estimates, revealed the population experienced a harvest rate of approximately 0.77% in 2011. Overall, results presented here indicate the population is stable, with improvement in some measures, since its decline in the 1980s.

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