Research Document 2020/001

Genetic mixed-stock analyses, catch-effort, and biological characteristics of Dolly Varden (Salvelinus malma malma) from the Rat River collected from subsistence harvest monitoring programs: 2009-2014

By Gallagher, C.P., Bajno, R., Reist, J.D., and Howland, K.L.

Abstract

Data collected from fishery dependent monitoring programs between 2009 and 2014 were used to inform a population assessment of the anadromous Dolly Varden (Salvelinus malma malma) from the Rat River, Northwest Territories. Dolly Varden from the Rat River stock are harvested in subsistence fisheries by Gwich’in and Inuvialuit people on the Beaufort Sea coast during summer and in the Mackenzie Delta and Rat River in late summer and early fall during their return (upstream) migration to spawning and overwintering habitats. Coastal monitoring programs collected harvest information and tissue samples between 2011 and 2014 to use in genetic mixed-stock analyses to estimate the contribution of the stock to the harvest. The annual monitoring program in the Mackenzie Delta and Rat River, established in its current form in 1995, collected harvest, catch-effort, and biological data including tissues for genetic mixed-stock analysis (starting in 2011). Genetic mixed-stock fishery analyses of coastal samples revealed the Rat River stock accounted for 5.1%–28.7% of the harvest at Shingle Point, represented by 21–40 fish. There were no confident detections of individuals from this stock occurring in fisheries further west. The fisheries in the Mackenzie Delta and Rat River were almost exclusively comprised of the Rat River stock. The estimated total number of Dolly Varden harvested from the Rat River from all fisheries averaged 362 fish, ranging between 300 (in 2009) and 427 (in 2014), with an estimated annual harvest rate averaging 4.7%. Catch-per-unit-effort was variable with relatively high values in 2010–2012 and low values in 2013–2014 (i.e., mean of ~ ≥10 and ~ ≤5 fish/25 m gillnet/24 hours, respectively). The sizes of fish captured between 2009 and 2014 were among the largest observed since 1995 (range of mean sizes = 463–509 mm) and demonstrated an increasing trend since 2006. Furthermore, an increasing trend in the presence of older ages between 2009 and 2014 suggested a higher rate of annual survival (increase from 33% to 55%). Additionally, a high proportion of current-year spawners (range = 29–67%) was observed in most years between 2009 and 2014. The time-series of information from the Rat River Harvest Monitoring Program indicates that the Rat River population of Dolly Varden is currently stable and sustainably harvested.

Research Document 2020/001 (PDF, 3,819 KB)

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