The wrong time for the right whale: modelling the decline of North Atlantic right whales

<p dir="ltr">The exploitation of marine mammal populations has been happening for centuries, with commercial whaling beginning around the 11th century, modernising in the 1860’s which decimated whale populations globally. The formation of the International Whaling Commission in 1946 is seen by many to be the onset of international protection for whale populations. However, for many species, such as the North Atlantic right whale (<i>Eubalaena glacialis</i>), these efforts came far too late, with the population estimated to be approximately 100 individuals by the end of the 1700’s. With complete protection, the North Atlantic right whale population saw a small recovery, reaching possibly 500 individuals by 2010, however since that year their numbers have been inexorably declining. Like all whale species, the North Atlantic right whale faces numerous threats including fisheries interactions (entanglements), vessel strikes, noise and chemical pollution and anthropogenic climate change. This thesis aims to understand the demographic factors driving the recent decline and quantify the potential impact of entanglements on this decline. Based on a ~40-year photo-identification dataset on all known North Atlantic right whales across their range, I have used classical mark-recapture techniques to provide estimates of abundance and demographic parameters for the whole North Atlantic right whale population. To facilitate uptake of this approach, I have developed an R Shiny tool, thereby allowing interested managers, government and conservation groups to simply generate up-to-date estimates as new data become available. In order to understand drivers of this decline, I then looked at how abundance and demography of female right whales has changed over time based upon their breeding state. Using models that deal with state uncertainty in reproductive status, I show that the number of breeding females in the population has decreased over time with only an estimated 72 still present at the beginning of 2018, and that fewer females have been recruited to the breeding population since 2000. To understand how this change in recruitment was influenced by anthropogenic factors, I looked at the influence of entanglement severity and the number of entanglements an individual has had in their lifetime on recruitment. I showed a strong influence on recruitment into the breeding population and breeding events. Unexpectedly I found that individuals with so called “minor” entanglements had the lowest recruitment probability. However, females only tell half the story of the North Atlantic right whale decline, thus I also developed a separate sex specific model of male demography, to investigate how the demography has changed over time by sex. The male North Atlantic right whale model highlights the importance of model development in addressing changes in the population, as differences in demography caused by intrinsic differences between sexes could be accounted for. This single sex model revealed considerable differences in survival compared to whole population models using sex as an additive effect. Finally, I reanalysed the estimates for female abundance using updated data to 2020 and found that the number of breeding females had declined to 64 individuals, similar to the numbers present in 1989, which implies that ~30 years of growth in the number of breeding females has been lost. Altogether, these results highlight the precarious state of the North Atlantic right whale, and also illustrate how we can gain new insights into contemporary declines by taking a simple, robust approach. However, unless management actions change, the North Atlantic right whale will soon be in a position where they are unlikely to recover, meaning they will decline to extinction. This research contributes to our understanding of whale conservation and the importance of data-driven models for conservation.</p>