Using opportunistic photo-identifications to detect a population decline of killer whales (Orcinus orca) in British and Irish waters

Abstract

An assemblage of killer whales that has been sighted in waters off the west coast of the British Isles and Ireland has previously been shown to be isolated from other North Atlantic killer whale communities based on association patterns. By applying a Bayesian formulation of the Jolly -Seber mark-recapture model to the photo-identification data compiled from opportunistic photographic encounters with this population of killer whales, we show that such sparse and opportunistically-collected data can still be valuable in estimating population dynamics of small, wide-ranging groups. Good quality photo-identification data was collected from 32 encounters over 19 years. Despite a cumulative total of 77 identifications from these encounters, just ten individuals were identified and the remaining 67 identifications were re-sights of these ten animals. There was no detected recruitment through births during the study and, as a result, the population appears to be in a slight decline. The demography of the population was highly skewed towards older individuals and had an unusually high ratio of adult males, and we suggest that demographic stochasticity due to a small population size may be further impacting the population growth rate. We recommend that this population be managed as a separate conservation unit from neighbouring killer whale populations.

Runs of homozygosity in killer whale genomes provide a global record of demographic histories

“…The inbreeding coefficient of the Scottish killer whale was comparable to those estimated for the iconic inbred populations of the grey wolves (Canis lupus) of the Isle Royale [27] and Scandinavia [28]. Longterm monitoring of this Scottish population using photo-identification data estimated anextremely small census size (< 10 individuals) and zero fecundity during over two decades of data collection [29]. As previously argued, the low adult mortality rate in this small population 8 suggests that bioaccumulation of organic pollutants, prey depletion and lethal interactions with fisheries are not the principle drivers of the small size of this population [29].…”

“…extremely small census size (< 10 individuals) and zero fecundity during over two decades of data collection [29]. As previously argued, the low adult mortality rate in this small population 8 suggests that bioaccumulation of organic pollutants, prey depletion and lethal interactions with fisheries are not the principle drivers of the small size of this population [29].…”

“…However, the potential fitness impacts of inbreeding are evident in the small (< 10 individuals) Scottish West Coast population, which has had zero recruitment over the past two decades [29].…”

“…Longterm monitoring of this Scottish population using photo-identification data estimated anextremely small census size (< 10 individuals) and zero fecundity during over two decades of data collection [29]. As previously argued, the low adult mortality rate in this small population 8 suggests that bioaccumulation of organic pollutants, prey depletion and lethal interactions with fisheries are not the principle drivers of the small size of this population [29]. However, lack of recruitment through reproduction suggests that the population has reached a critical point whereby it experiences inverse density dependence (the 'Allee' effect) due to a loss of fitness from inbreeding, demographic stochasticity and reduced benefits of sociality [29].…”

Killer whale genomes reveal a complex history of recurrent admixture and vicariance

“…Samples were selected from a global data set of 452 individuals that best represented the known global geographic and genetic diversity of this species (Morin et al, 2015). Where possible, we selected identifiable individuals from longitudinally studied populations, e.g., Crozet Archipelago (Guinet & Tixier, 2011), Gibraltar (Esteban et al, 2016), Iceland (Samarra & Foote, 2015) and Scotland (Beck et al, 2014).…”