Science Advisory Report 2018/012

Impact of the 2015 narwhal (Monodon monoceros) entrapment on the Eclipse Sound narwhal stock

Summary

• An ice entrapment event, where at least 249 narwhals died, occurred in Eclipse Sound in November 2015.
• This study assessed the impact of this entrapment on the current TALC, and the abundance trajectory for the Eclipse Sound narwhal stock.
• It is uncertain if the PBR approach accounts for the mortality caused by a single entrapment event of this size. In the past, it has been assumed these events are encompassed by the natural mortality component of PBR.
• We assessed how entrapments that resulted in the death of 249, or an assumed level of 1,000 whales, would impact the PBR and resulting TALC, if entrapment mortality is considered in addition to natural mortality included in PBR.
• These scenarios were repeated to determine the impacts if the entrapment included individuals from both Eclipse Sound and Admiralty Inlet.
• If PBR fully accounts for the mortality from this entrapment event, the TALC would not need to be adjusted. If mortality from the entrapment event is in addition to natural mortality included in PBR, the TALC would need to be reduced by 3 whales for an entrapment that resulted in the death of 249 whales and 13 whales for an entrapment resulting in the death of 1,000 whales (an estimated upper limit). If some of the whales were assumed to come from Admiralty Inlet, these numbers would be lower.
• Results of several model simulations indicated entrapments occurring every 3, 5 or 10 years may result in a decline in the stock abundance.

This Science Advisory Report is from the October 17-21, 2016 National peer review of the Eclipse Sound narwhal – 2015 ice entrapment impacts. Additional publications from this meeting will be posted on the DFO Science Advisory Schedule as they become available.

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