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.

Unraveling the genetic legacy of commercial whaling in bowhead whales and narwhals

“…Aerial survey abundance estimates suggest that the northern Hudson Bay narwhal population is increasing, albeit with slowing growth rate as it reaches carrying capacity [78]. At this slowed growth rate Biddlecombe and Watt [78] predicted that even modest harvests could result in a decline in abundance. Our low estimates of N e also suggest this population may be vulnerable to harvest and highlight the need to consider both abundance and genetic population structure and genetic resilience when assessing management and conservation strategies [79].…”

“…The northern Hudson Bay subpopulation warrants conservation priority within Canadian Arctic narwhals in the context of genetic diversity, due to greater levels of inbreeding, and lower effective population size. Aerial survey abundance estimates suggest that the northern Hudson Bay narwhal population is increasing, albeit with slowing growth rate as it reaches carrying capacity [78]. At this slowed growth rate Biddlecombe and Watt [78] predicted that even modest harvests could result in a decline in abundance.…”

Spatiotemporal modeling of mature‐at‐length data using a sliding window approach

“…For example, surveys, biotelemetry, and sample collection programs in Arctic marine ecosystems are often impacted by logistical challenges and high costs (Mallory et al, 2018) that can result in infrequent sampling (Yurkowski et al, 2019, Table 1). In particular, aerial surveys of marine mammal abundance are conducted in different areas and years, and recently they have been expanding to areas not previously surveyed (Biddlecombe & Watt, 2021). There are also spatial and temporal gaps in other types of data (e.g., fatty acids and stable isotopes) used to examine food‐web trends in marine ecosystems that can lead researchers to group data into broad categories to try to address sampling gaps (Watt & Ferguson, 2015).…”

Biology and Cultural Importance of the Narwhal

“…Yet in 2010, the total number of narwhal was estimated to be 80,000, with variation between 58,000 and 86,000 (11). Population modeling currently projects declining future narwhal populations (12) due to environmental changes associated with climate change indicators such as sea ice decline and the associated increase in killer whale populations (13) and reduced prey availability (14).…”