Modeling population trajectory and probability of decline in northern Hudson Bay narwhals (Monodon monoceros)

Abstract

Narwhals (Monodon monoceros) are an important subsistence harvest species for Inuit communities and their conservation is important for Inuit culture and ecosystem function. The northern Hudson Bay (NHB) narwhal population, which spends summer in northern Hudson Bay, Canada, has been assessed through periodic aerial surveys from 1981 to 2018. To estimate the population trajectory and predict future population trends under various harvest scenarios, a Bayesian population model was fit to four aerial survey estimates and harvest data from 1951 to 2018. The model resulted in a 2019 population estimate of ~14,400, 95% CI [10,300, 20,400] and an estimated starting population of 7,200, 95% CI [1,400, 19,000] in 1951. The model was extended 10 years into the future under three annual harvest scenarios (current harvest: 157, low harvest: 50, and high harvest: 300) and the probability of population decline was estimated. The model predicted a 6% chance of decline with an annual harvest quota of 50 narwhals, 78% for a harvest of 157, and 95% for a harvest of 300. This updated model provides the opportunity to shape conservation efforts by estimating past population trends and how those trends, combined with management action, can affect future population dynamics.