Research Document 2019/062

Updated stock status of commercially harvested Arctic Char (Salvelinus alpinus) from the Jayko and Halokvik rivers, Nunavut: A summary of harvest, catch-effort and biological information

By Harris, L.N., Cahill, C.L., Jivan, T., Zhu, X., and Tallman, R.F.

Abstract

Anadromous Arctic Char, Salvelinus alpinus, are the focus of commercial fisheries in several communities in Nunavut. In the Cambridge Bay region of the territory, two water bodies, the Jayko and Halokvik (locally known as 30 Mile) rivers, started as open-water gill-net commercial fisheries in the 1960s. These transitioned to conduit weir fisheries in the 1990s. Fisheries and Oceans Canada (DFO) has been collecting fishery-dependent biological data (i.e., data collected through sampling commercially harvested fish at the processing plant) from these fisheries since the 1970s. More recently DFO collected fishery-independent biological and catch and effort data from 2010–2015 at both locations. Using data collected from these multiple programs, trends in fishery-dependent (1971–2015) and fishery-independent (2010–2015) biological and catch-effort data were summarized to inform the population status of Arctic Char from the Jayko and Halokvik rivers. Mean age, fork length, round weight, and condition each exhibited sinusoidal patterns through time and all, with the exception of mean age, have increased significantly since commercial fishing commenced. The observed trends in these biological metrics raise no concern on stock health but it is not clear if the variability among years is the result of environmental variability, varying responses to harvest over time, or changes in gear type over time. Of concern, length (L₅₀) and age (A₅₀) at 50% maturity have declined over the course of fishery-independent sampling at both the Jayko and Halokvik rivers. Both metrics were lower in the last year of sampling compared to initial values at both sites (Jayko L₅₀ from 587 mm to 537 mm and Halokvik L₅₀ from 554 mm to 533 mm; Jayko A₅₀ from 15.2 years to 12.1 years and Halokvik A₅₀ from 11.8 years to 9.1 years) from years 1 to 4 (year five was excluded due to concerns over maturity status identification that year). These results, however, were within ranges reported when historical data were used in the analysis. The overall Brody growth coefficient (k), calculated using fishery-dependent data, varied without trend and was similar among commercial water bodies, with median values of 0.20 and 0.21 across all years assessed for the Jayko and Halokvik rivers, respectively. Towards the latter years of the assessment k appears to be quite stable at both locations. Finally, estimates of total instantaneous mortality (Z) and annual finite survival (S) calculated using fishery-dependent data have varied without trend since commercial fishing commenced at both locations. Across all years, Z has ranged from 0.27–0.84 at Jayko (mean = 0.46) and 0.23–1.26 at Halokvik (mean = 0.64). This results in annual survival rates (S, the percentage of a stock surviving annually) ranging from 0.43–0.76 at Jayko (mean across all years = 0.66) and 0.28–0.79 at Halokvik (mean across all years = 0.55). At both locations, mortality has been decreasing and survival has been increasing since 2007–2008. Updated ageing results, however, may change estimates of mortality and survival. Given all available information and the current understanding of these fisheries, there is likely a low to moderate risk of decline in these populations if harvest remains the same. The available analyses cannot support an increase or a decrease in harvest at either fishery. It is recommended that monitoring of biological parameters (in particular, age structure and estimates of mortality and survival) continue.

Research Document 2019/062 (PDF, 6,140 KB)

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