Research Document 2020/066

Population abundance and biological characteristics of Dolly Varden (Salvelinus malma malma) from the Rat River collected from a mark-recapture program: 2009–2014

By Gallagher, C.P., Howland, K.L., and Sandstrom, S.J.

Abstract

The anadromous northern-form of Dolly Varden (Salvelinus malma malma) from the Rat River, Northwest Territories was assessed through a mark-recapture program between 2009 and 2014 which evaluated trend in abundance and biological characteristics to determine if the population was sustainably harvested. Seining was conducted annually in late-September at the spawning and overwintering location in Fish Creek to collect live-sampled biological data (length, sex, reproductive status, and growth) and periodically to apply tags. Recapture of tagged fish occurred the following year in either the subsistence fishery near the mouth of the Rat River or while seining in the headwaters (Fish Creek). The two recapture methods generated independent abundance estimates for 2009, 2010, and 2013. These estimates suggest the population has increased to ~ 12,000–15,000 fish from a low of 2,900 estimated in 2004 and were amongst the highest abundances observed since 1995 when the mark-recapture program was initiated. Biological information collected during seining between 2009 and 2014 revealed a wide range of sizes with an increase in the proportion of larger sizes in more recent years. Female spawners were mainly between 450 and 575 mm in length while male spawners tended to be larger and primarily distributed between 500 and 600 mm. Non-spawners were typically smaller in size compared to spawners. Males had higher annual growth compared to females and spawned in consecutive years less frequently (12.5%) than females (50.9%). The growth of females spawning in consecutive-years in 2009-2014 was higher compared to 1995–1996, yet was lower than during 2004-2005. Sampling conducted in the upper most reaches of Fish Creek detected a high proportion of anadromous spawners and a large number of both the resident life history (sexually mature non-anadromous) and pre-smolt juveniles, suggesting this recently examined location provides important spawning and rearing habitat. Data from the mark-recapture program suggest the population is currently stable and sustainably harvested.

Research Document 2020/066 (PDF, 6,380 KB)

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