Research Document - 2012/073

2011 Harvest Attributions for Baffin Bay Narwhals

By C. Abraham

Abstract

The Canadian portion of the Baffin Bay population consists of at least four narwhal stocks which aggregate in summer: the Somerset Island, Admiralty Inlet, Eclipse Sound and East Baffin Island stocks. DFO Science requested a retrospective analysis of the sustainability of the 2011 Baffin Bay narwhal catches using a previously reviewed narwhal allocation model to attribute historical recorded catches and seasonal catch proportions; this analysis included both moderate and extreme sensitivity analyses to evaluate (1) the risk associated with the assumption of proportional stock size, and (2) the risk associated with the assumption of separate Admiralty Inlet (AI) and Eclipse Sound (ES) stocks. The attribution model results demonstrated that the 2011 narwhal catches were sustainable (TALC-TC >0). In both sets of sensitivity analyses applied, results demonstrated no risk associated with the harvests of all stocks in 2011. When the attribution model was revised to treat AI and ES summering aggregations as one stock, results again demonstrated that narwhal catches in 2011 were sustainable. However, in this case, the moderate risk scenario demonstrated a ~35% risk associated with the harvest of the combined AI/ES stock in 2011, while the risk to other stocks remained negligible. However, if the AI/ES harvest was reduced to, for example, 90% of the observed value, the risks of overexploiting that stock would be negligible. The extreme risk scenario demonstrated a substantial risk of ~85% associated with the harvest of the combined AI/ES stock in 2011, while the risks to other stocks remained negligible. However, if the AI/ES harvest was reduced to 80% of the observed value, the risks of overexploiting that stock would be negligible.

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