Abstract
Killer whales, Orcinus orca, are a cosmopolitan species with large ecological and demographic variation across populations. Population‐specific demographic studies are, therefore, crucial in accurately assessing the status and trends of local killer whale populations. Such studies require long‐term datasets and remain scarce, particularly in the Southern Ocean where detailed population specific studies have only been conducted at a single archipelago – Îles Crozet. Here, we analysed 12 years of capture–recapture data (comprising nearly 90 000 identification photographs taken from 2006 to 2018) of killer whales at subantarctic Marion Island (46°54′S, 37°45′E) to estimate the abundance, survival and growth rate of this population. Demographic parameters were estimated using multistate capture recapture models, and Pradel Survival‐Lambda and POPAN single‐state models implemented in the program MARK. Annual survival probability (0.98 [95% CI: 0.96–0.99]) was constant over time, and no important differences between sexes and age‐classes (calves, juveniles, adults) were found. This estimate of survival suggests a life expectancy of approximately 48 years. Realised mean population growth rate (λ) was 1.012 (0.987–1.037) with an estimated population size of 54 (54–60) individuals and a mean calving rate of 0.13 (0.06–0.20) calves born per year per reproductive female. The survival and reproduction rates of killer whales at Marion Island are similar to those of killer whale populations in the eastern North Pacific, Norway and Îles Crozet. However, subtle differences in survival and reproduction rates are present. These are likely the result of local differences in resource abundances, historical impacts on social structure and/or stressors. Also, the presence and scale of fisheries (legal and illegal) in the area may provide opportunities for direct interactions with fishing activities impacting survival and reproduction rates.
Highlights
BioOne Complete is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses
19 killer whales were born into the population during the study period and were excluded from the discovery curve which shows the number of individuals identified plotted against the total number of identifications (Fig. 2)
This study provides a demographic baseline for Marion Island’s killer whales and increases our knowledge of this population and of killer whales in the Southern Ocean
Summary
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses. Local adaptation and variation in diet, behaviour, morphology and demographic parameters (e.g. survival and reproductive rates) are common among such populations (McMahon et al 2003, Tremblay and Cherel 2003, Gabrey 2010, Jordaan et al 2019b). These population differences are often overlooked in ecological studies. The license permits use, distribution and reproduction in any medium, provided the original work is properly cited
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