Science Advisory Report 2015/052
Updated abundance estimate and harvest advice for the Eastern Canada-West Greenland bowhead whale population
- Bowhead whales from the Eastern Canada-West Greenland (ECWG) population range widely around Baffin Island in the summer and aggregate in Prince Regent Inlet, Gulf of Boothia, Foxe Basin, Cumberland Sound, Isabella Bay and Repulse Bay in August. This population was historically overharvested by commercial whalers. Current evidence indicates that the ECWG bowhead whale population has increased considerably since the end of commercial whaling.
- No previous aerial surveys covered the entire summer range of the ECWG bowhead population. A winter survey took place in Hudson Strait in March 1981 and a summer survey was conducted over Eclipse Sound, Prince Regent Inlet and Gulf of Boothia in August 2002. The partial abundance estimate obtained from the 2002 survey was imprecise due to the small number of whales observed and the large uncertainty associated with the estimate.
- In August 2013, a large scale aerial survey was conducted over all the major aggregation areas of the ECWG bowhead whale population, with the exception of Foxe Basin, Repulse Bay and Lancaster Sound. To account for bowhead whales that were diving and not visible to aerial survey observers, survey results were adjusted using dive data from August 2012 and 2013 obtained from 22 bowhead whales fitted with satellite-linked time depth recorders near Igloolik and Pangnirtung, Nunavut. Depending on the area and time of month, bowhead whales were visible for detection by observers from 17.6% to 29.1% of the time. Applying this correction to the August 2013 survey resulted in an updated abundance estimate of 6,446 bowhead whales (Coefficient of Variation, CV = 26%).
- Population abundance of ECWG bowhead whales was also estimated using a genetic capture-mark-recapture approach. Analysis of 1,177 biopsy samples from nine locations within the population’s range produced a best estimate of population abundance of 7,660 individuals (range of uncertainty: 4,500-11,100).
- The genetic capture-mark-recapture approach, while promising, relies on several assumptions. The effects of violating these assumptions require more thorough exploration. For this reason, we recommend using only the 2013 aerial survey abundance estimate to calculate sustainable harvest levels for ECWG bowhead whales.
- Given that our knowledge of current population size is based on only a few incomplete surveys over a 34 year period, and given uncertainty about the size of the ECWG bowhead whale population prior to commercial whaling, we recommend a recovery factor (FR) of 0.5 for use in the potential biological removal (PBR) calculation of sustainable harvest.
- Using the 2013 aerial survey estimate and a recovery factor of 0.5, the ECWG bowhead whale population can support a total human-induced mortality of 52 whales annually resulting from all sources of anthropogenic mortality (e.g., harvest, struck and loss, net entanglements, ship collisions).
This Science Advisory Report is from the October 20-24, 2014 Annual Meeting of the National Marine Mammal Peer Review Committee (NMMPRC). Additional publications from this meeting will be posted on the DFO Science Advisory Schedule as they become available.
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