Science Advisory Report 2016/058

Assessment of Dolly Varden from the Rat River, Northwest Territories 2009–2014

Summary

• Mark-recapture techniques were used to estimate abundance of Dolly Varden from the Rat River. The estimated population abundance of Dolly Varden (≥~305–365 mm) increased from 5,820 in 2010 to 11,919 in 2013. The estimates were based on recaptures obtained from seining at the spawning and overwintering area at the end of September in 2010 and 2013.
• Data from community harvest surveys (1972–2014), various sampling programs (1971–1994), and the Rat River Harvest Monitoring Program (RRHMP) (1995–2014) were incorporated into population models (depletion-based stock reduction analysis (DB-SRA), surplus production (SPM) and, statistical catch-at-age models (SCA)) to estimate maximum sustainable yield (MSY) and temporal changes in population abundance.
• The three models predicted the current population size was approximately between 10,509 and 12,205 fish for the fishable component of the population (≥440 mm), and 10,128 fish for all life stages.
• The DB-SRA, SPM and SCA models generated estimates of MSY with the inverse weighted average among the estimates providing a value (± 1 standard deviation [SD]) of 891 (81) fish.
• Biological information collected from the RRHMP and seining at the spawning and overwintering area every year between 2009 and 2014 demonstrated the presence of a wide range of sizes and that length structure of adults appeared relatively stable among years.
• The modal age of harvested fish ranged between 5 and 7 years every year between 2009 and 2014, with an increasing proportion among older ages (≥8 years) over time, suggesting improved survival of adults.
• A high proportion of spawners was observed among years when seining at the spawning and overwintering area (range = 38–81%). Biological data from the mark-recapture studies indicated females spawned in consecutive-years more often than males.
• Genetic mixed-stock fishery analysis of samples collected along the Beaufort Sea coast between 2011 and 2014 indicate that Dolly Varden from the Rat River were mainly harvested at Shingle Point, contributing between 5 and 29% to the harvests at this location among years.
• Estimates of effective population size (NE) determined using genetic data suggest there are no immediate conservation concerns for the population.
• The reported annual harvest of Dolly Varden from the Rat River has been <400 fish since the voluntary closure of the subsistence fishery ended in 2009. Between 2011 and 2014, the estimated average harvest rate was 4.7%.
• The available information indicates that the population is currently stable and is sustainably harvested. There is increased confidence in the assessment given that multiple independent sources of information provided relatively similar trends for indicators and/or conclusions of stock status.

This Science Advisory Report is from the meeting held on February 10 and 11, 2015 on the Assessment of Dolly Varden, Salvelinus malma malma, from the Rat River, Northwest Territories. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Complete document (PDF, 588 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.