Science Advisory Report 2016/037
Status of beluga (Delphinapterus leucas) in Cumberland Sound, Nunavut
Summary
- Cumberland Sound belugas (CSB) are managed as a distinct stock and are thought to remain within Cumberland Sound throughout the year. They are designated as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).
- CSB are harvested by hunters from the hamlet of Pangnirtung. Since 2002, the quota for the community has been 41 whales.
- An aerial survey was flown in August 2014 to estimate the abundance of CSB. After correcting for animals that were diving and therefore not visible to the survey aircraft, the survey produced an abundance estimate of 1,200 belugas (Standard Error (SE) = 200, rounded to the nearest 100 animals).
- A population model that incorporates reported harvest information, was fitted to abundance estimates from the Cumberland Sound beluga stock using Bayesian methods to obtain an estimate of current abundance and population trend. Multiple model runs using different combinations of survey data from 1980–2014 and harvest data from 1960–2015 were completed. All runs yielded similar estimates with a current stock estimate of around 1,000 animals and indicate that the stock may be declining. These estimates are lower than those predicted by the previous assessments on which the current quota was based.
- The preferred model used the harvest data from 1960–2015 and fitted to four aerial surveys flown between 1990 and 2014. The estimated current stock abundance from this run is 1,000 (95% Credibility Intervals: 500–2,000, rounded to the nearest 100) belugas.
- The current management objective is for the stock to recover to 5,000 animals by 2091. This would require reaching an interim management objective of 1,235 animals by 2025.
- If CSB is to recover to the identified management objective, then harvest reductions are required. However, based upon the model used, the probability of the stock increasing to the interim target level within 10 years is very low, even under conditions where no harvesting occurs. The estimated probability of the stock recovering to the interim target level is estimated to be 10%, 21%, 26% and 32% for a Total Allowable Landed Catch (TALC) of 25, 10, 5 and 0 whales, respectively.
- Harvest advice was also generated using the Potential Biological Removal (PBR) method. Based upon the model estimate of current abundance, and using a recovery factor of 0.5, the estimated PBR is eight belugas. The PBR estimate includes all sources of human mortality, such as landings, struck and lost, non-reporting, and bycatch.
- The TALC estimated using the PBR method is the PBR minus other sources of mortality not included in reported catch (e.g., struck and lost, non-reported harvest and other human related mortality). If levels of other sources of mortality are assumed to be 42% of the actual harvest, then the TALC would be five belugas.
- Correlation among some model parameters was identified. This is not likely to affect model estimates, but suggests that our estimates of uncertainty may be conservative. A longer time series of survey estimates, improved survey correction factors and improved harvest reporting (including struck and lost estimates) are required to reduce uncertainty associated with estimating CSB abundance and trend.
This Science Advisory Report is from the April 6, April 20 and May 10, 2016 National Marine Mammal Peer-Review Meeting: Cumberland Sound Beluga. Additional publications from this meeting will be posted on the DFO Science Advisory Schedule as they become available.
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