Science Advisory Report 2018/021

Stock Status and Sustainable Harvest Levels for Arctic Char in Ijaruvung Lake, Iqalujjuaq Fiord and Irvine Inlet, Cumberland Sound, Nunavut

Summary

• Ijaruvung Lake (DFO waterbody code PG003), Iqalujjuaq Fiord (PG027), and Irvine Inlet (PG018) were declared commercially licensed water bodies in 1984-1985 for fishing with 140 mm gillnets.
• Fisheries and Oceans Canada (DFO) has been collecting fisheries harvest data since 1985, test fishery data (in late 1970’s and early 1980’s) and fishery-dependent (plant sampling in mid-2000’s and in 2012-2013) data from these water bodies.
• DFO collected fishery-independent biological and catch and effort data from 2010-2014 at Iqalujjuaq Fiord and Irvine Inlet, and from 2011-2015 at Ijaruvung Lake.
• Fork length, age, round weight, and derived indices showed annual variation, but there were no significant trends in the mean values of these metrics.
• Irvine Inlet appears to have substantially lower fishing mortality among the three stocks.
• Three population models, the Baranov catch equation, Catch-Maximum Sustainable Yield (MSY) and Depletion-corrected average catch, were used to estimate population abundance, MSY and evaluate stock status.
• For the Irvine Inlet stock, the Baranov catch equation estimated biomass as 53,304 kg. Keeping an exploitation rate of 5 % gives a harvest level of 2,665 kg per year, which is more than the current mean level of harvest but less than the current quota. The Catch-MSY model provided an MSY limit of 2,733 kg, which is also close to the 5 % level. Fishers have observed no issues or concerns with this stock. Fish tissue is observed to be healthy and fat, indicating to the locals that the population is healthy. Traditional knowledge states that fish need to be taken from the lakes to keep them stable.
• For Ijaruvung Lake, the Baranov catch equation calculated standing stock biomass to be 25,732 kg. Keeping an exploitation rate 5 % gives a harvest level of 1,287 kg per year. The calculated 5 % level is slightly above the current mean level of harvest, while 10 % is higher than the quota limit. The Catch-MSY model calculated standing stock biomass to be
  29,916 kg and suggested MSY was 1,683 kg.
• For the Iqalujjuaq Fiord stock, the Baranov catch equation estimated standing stock biomass to be 35,214 kg. Keeping an exploitation rate of 5 % gives a harvest level of
  1,761 kg per year, which is above the current quota and mean level of harvest. The Catch-MSY model calculated standing stock biomass to be 40,879 kg and suggested MSY was 2,626 kg, which includes harvest for subsistence purposes. Fishers have traditionally taken a consistent amount from the lake to meet their basic needs.
• In Ijaruvung Lake and Irvine Inlet, estimated MSY was less than the prescribed quotas for these water bodies. MSY for Irvine Inlet was near the present harvest rate, while Ijaruvung Lake MSY was higher than the mean harvest level. For Iqalujjuaq Fiord, estimated MSY was higher than the allocated quota. However, these MSY calculations included the subsistence harvest, which is high relative to the other two water bodies assessed.
• From the biomass calculation using the Baranov catch equation, present quotas were below a 10 % exploitation rate, while recent annual commercial harvests were lower than 5 % of the calculated standing stock biomass.
• Upper and limit reference points (URP, LRP) were calculated using the provisional reference points from the DFO Sustainable Fisheries Framework Precautionary Approach (DFO 2009). The LRP of 0.4 B_MSY and the URP of 0.8 B_MSY were calculated based on Catch-MSY results.
• These median reference point values for the stocks were in the healthy zone with minimum probability range in the cautious zone.
• Overall, the results of the trends in size and age data, population indices, quantitative models and observations from the local fishers all suggest the Arctic Char stocks in Ijaruvung Lake, Iqalujjuaq Fiord and Irvine Inlet are in the Healthy Zone of the Precautionary Approach framework and the current harvest levels are sustainable.

This Science Advisory Report is from February 14–15, 2017 Stock status and sustainable harvest levels for Arctic Char in Ijaruvung Lake, Iqalujjuaq Fiord and Irvine Inlet, Cumberland Sound, Nunavut. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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