Abundance, survival and population growth of killer whales Orcinus orca at subantarctic Marion Island
Abundance, survival and population growth of killer whales Orcinus orca at subantarctic Marion Island
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.
abundance, calving rate, demography, environmental variation, fisheries
Jordaan, Rowan K.
4d8c99fa-ad76-4da5-a9f3-f9dd8a634ae4
Oosthuizen, W. Chris
1b94648f-2c36-4d46-bc75-ca5b394a3f98
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Nico De Bruyn, P. J.
90bf3f93-34ab-40aa-98be-e5a5ada56565
2020
Jordaan, Rowan K.
4d8c99fa-ad76-4da5-a9f3-f9dd8a634ae4
Oosthuizen, W. Chris
1b94648f-2c36-4d46-bc75-ca5b394a3f98
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Nico De Bruyn, P. J.
90bf3f93-34ab-40aa-98be-e5a5ada56565
Jordaan, Rowan K., Oosthuizen, W. Chris, Reisinger, Ryan R. and Nico De Bruyn, P. J.
(2020)
Abundance, survival and population growth of killer whales Orcinus orca at subantarctic Marion Island.
Wildlife Biology, 2020 (4), [00732].
(doi:10.2981/wlb.00732).
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.
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wlb.00732
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Published date: 2020
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Acknowledgements – We thank the many fieldworkers and individuals who collected long-term data on killer whales at Marion Island. Marion Island killer whale research was conducted pursuant to the provisions of the Marine Living Resources Act, 1998 (Act 18 of 1998) and the Prince Edward Islands Management Plan v0.2 (2010). Funding – Funding was provided through the Department of Science and Innovation (DSI) by the National Research Foundations’ SANAP and Thuthuka Funding instruments, and additionally supported through the International Whaling Commission Southern Ocean Research Partnership, as well as the Mohamed bin Zayed Species Conservation Fund (project number: 10251290). Additionally, RKJ was supported by a FILAMO Mobility grant. Permits – The project has ethics clearance from the Animal Ethics Committee (AEC) of the Faculty of Veterinary Science, University of Pretoria, under EC077-15. All research was also carried out under permit from the Director-General: Department of Environment, Forestry and Fisheries (DEFF), South Africa. The DEFF provided logistical support for on-going fieldwork at Marion Island, through the South African National Antarctic Program (SANAP).
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Copyright 2021 Elsevier B.V., All rights reserved.
Keywords:
abundance, calving rate, demography, environmental variation, fisheries
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Local EPrints ID: 453566
URI: http://eprints.soton.ac.uk/id/eprint/453566
ISSN: 0909-6396
PURE UUID: 5fa04138-f07d-4773-8633-93cbcca0ee42
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Date deposited: 19 Jan 2022 18:13
Last modified: 18 Mar 2024 04:03
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Author:
Rowan K. Jordaan
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W. Chris Oosthuizen
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P. J. Nico De Bruyn
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