Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging
During Arctic summers, sea ice provides resting habitat for Pacific walruses as it drifts over foraging areas in the eastern Chukchi Sea. Climate-driven reductions in sea ice have recently created ice-free conditions in the Chukchi Sea by late summer causing walruses to rest at coastal haulouts alon...
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ftpubmed:oai:pubmedcentral.nih.gov:3729469 2023-05-15T15:16:23+02:00 Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging Monson, Daniel H. Udevitz, Mark S. Jay, Chadwick V. 2013-07-31 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729469 http://www.ncbi.nlm.nih.gov/pubmed/23936106 https://doi.org/10.1371/journal.pone.0069806 en eng Public Library of Science http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729469 http://www.ncbi.nlm.nih.gov/pubmed/23936106 http://dx.doi.org/10.1371/journal.pone.0069806 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. PDM CC0 Research Article Text 2013 ftpubmed https://doi.org/10.1371/journal.pone.0069806 2013-09-05T03:15:53Z During Arctic summers, sea ice provides resting habitat for Pacific walruses as it drifts over foraging areas in the eastern Chukchi Sea. Climate-driven reductions in sea ice have recently created ice-free conditions in the Chukchi Sea by late summer causing walruses to rest at coastal haulouts along the Chukotka and Alaska coasts, which provides an opportunity to study walruses at relatively accessible locations. Walrus age can be determined from the ratio of tusk length to snout dimensions. We evaluated use of images obtained from a gyro-stabilized video system mounted on a helicopter flying at high altitudes (to avoid disturbance) to classify the sex and age of walruses hauled out on Alaska beaches in 2010–2011. We were able to classify 95% of randomly selected individuals to either an 8- or 3-category age class, and we found measurement-based age classifications were more repeatable than visual classifications when using images presenting the correct head profile. Herd density at coastal haulouts averaged 0.88 walruses/m2 (std. err. = 0.02), herd size ranged from 8,300 to 19,400 (CV 0.03–0.06) and we documented ∼30,000 animals along ∼1 km of beach in 2011. Within the herds, dependent walruses (0–2 yr-olds) tended to be located closer to water, and this tendency became more pronounced as the herd spent more time on the beach. Therefore, unbiased estimation of herd age-ratios will require a sampling design that allows for spatial and temporal structuring. In addition, randomly sampling walruses available at the edge of the herd for other purposes (e.g., tagging, biopsying) will not sample walruses with an age structure representative of the herd. Sea ice losses are projected to continue, and population age structure data collected with aerial videography at coastal haulouts may provide demographic information vital to ongoing efforts to understand effects of climate change on this species. Text Arctic Chukchi Chukchi Sea Chukotka Climate change Sea ice Alaska walrus* PubMed Central (PMC) Arctic Chukchi Sea Pacific PLoS ONE 8 7 e69806 |
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Research Article Monson, Daniel H. Udevitz, Mark S. Jay, Chadwick V. Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging |
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Research Article |
description |
During Arctic summers, sea ice provides resting habitat for Pacific walruses as it drifts over foraging areas in the eastern Chukchi Sea. Climate-driven reductions in sea ice have recently created ice-free conditions in the Chukchi Sea by late summer causing walruses to rest at coastal haulouts along the Chukotka and Alaska coasts, which provides an opportunity to study walruses at relatively accessible locations. Walrus age can be determined from the ratio of tusk length to snout dimensions. We evaluated use of images obtained from a gyro-stabilized video system mounted on a helicopter flying at high altitudes (to avoid disturbance) to classify the sex and age of walruses hauled out on Alaska beaches in 2010–2011. We were able to classify 95% of randomly selected individuals to either an 8- or 3-category age class, and we found measurement-based age classifications were more repeatable than visual classifications when using images presenting the correct head profile. Herd density at coastal haulouts averaged 0.88 walruses/m2 (std. err. = 0.02), herd size ranged from 8,300 to 19,400 (CV 0.03–0.06) and we documented ∼30,000 animals along ∼1 km of beach in 2011. Within the herds, dependent walruses (0–2 yr-olds) tended to be located closer to water, and this tendency became more pronounced as the herd spent more time on the beach. Therefore, unbiased estimation of herd age-ratios will require a sampling design that allows for spatial and temporal structuring. In addition, randomly sampling walruses available at the edge of the herd for other purposes (e.g., tagging, biopsying) will not sample walruses with an age structure representative of the herd. Sea ice losses are projected to continue, and population age structure data collected with aerial videography at coastal haulouts may provide demographic information vital to ongoing efforts to understand effects of climate change on this species. |
format |
Text |
author |
Monson, Daniel H. Udevitz, Mark S. Jay, Chadwick V. |
author_facet |
Monson, Daniel H. Udevitz, Mark S. Jay, Chadwick V. |
author_sort |
Monson, Daniel H. |
title |
Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging |
title_short |
Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging |
title_full |
Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging |
title_fullStr |
Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging |
title_full_unstemmed |
Estimating Age Ratios and Size of Pacific Walrus Herds on Coastal Haulouts using Video Imaging |
title_sort |
estimating age ratios and size of pacific walrus herds on coastal haulouts using video imaging |
publisher |
Public Library of Science |
publishDate |
2013 |
url |
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729469 http://www.ncbi.nlm.nih.gov/pubmed/23936106 https://doi.org/10.1371/journal.pone.0069806 |
geographic |
Arctic Chukchi Sea Pacific |
geographic_facet |
Arctic Chukchi Sea Pacific |
genre |
Arctic Chukchi Chukchi Sea Chukotka Climate change Sea ice Alaska walrus* |
genre_facet |
Arctic Chukchi Chukchi Sea Chukotka Climate change Sea ice Alaska walrus* |
op_relation |
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729469 http://www.ncbi.nlm.nih.gov/pubmed/23936106 http://dx.doi.org/10.1371/journal.pone.0069806 |
op_rights |
This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. |
op_rightsnorm |
PDM CC0 |
op_doi |
https://doi.org/10.1371/journal.pone.0069806 |
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PLoS ONE |
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8 |
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7 |
container_start_page |
e69806 |
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