Research Document 2019/031

Harvest allocation modelling for narwhal (Monodon Monoceros) stocks shared between eastern Canada and West Greenland

By Watt, C.A., Witting, L., Marcoux, M., Doniol-Valcroze, T., Guldborg Hansen, R., Hobbs, R., Lee, D.S., Ferguson, S.H., and Heide-Jørgensen, M.P.

Abstract

Narwhals (Monodon monoceros) from the Baffin Bay population overwinter in the Davis Strait and Baffin Bay and migrate in the summer to fiords and inlets in northern Canada and West Greenland. Based on these summer aggregations, the population is subdivided into stocks for assignment of hunting quotas to individual communities to ensure sustainability of the local aggregations. Previously, stocks have been managed independently of one another, but many animals from the summer stocks are available to hunters in other regions during the migration and winter periods. As a result, a model which considers mixing of stocks is required to ensure quotas are sustainable. We present a model for the exploitation of narwhals in Canada and western Greenland. The model consists of two parts, one that develops the connection between stocks and hunting areas and allocates catches to the different summer aggregations (referred to as the stock exchange model), and one that analyzes the impacts of these catches on the population dynamics of the eight narwhal stocks (referred to as the population dynamics model). We present an example of the model output using abundance estimates and catch statistics from Canada and West Greenland. The stock exchange model could be used in the future to assess the sustainability of catch levels for all stocks. Regarding the population dynamics model, for some stocks there is little information on abundance or distribution and in these cases, rather than using the population dynamics model, a Potential Biological Removal (PBR) can be calculated to determine sustainable catch levels, with the stock exchange model used to determine how catches will distribute across the various stocks. For stocks with sufficient information, modelling using both the stock exchange and a population dynamics model could be useful for determining sustainable catch levels. The population dynamic stock exchange model can advise on catches from the main hunting areas and assess how these are influencing the different stocks; how these catches can be allocated to individual communities in Canada and Greenland will have to be determined with the support of co-management groups. Furthermore, there is a need to develop reference points and corresponding stock status zones using a Precautionary Approach framework that can then be applied to narwhal population management in Canada.

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