Variation in harbour seal counts obtained using aerial surveys
Aerial surveys of harbour seals ( Phoca vitulina ) are usually carried out to provide an index of population size. This can be normalized, either by design or by post-hoc analysis to reduce the effects that date, time of day, tide and weather might have on the number of seals counted. In order for l...
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Online Access: | http://dx.doi.org/10.1017/s002531540999155x https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002531540999155X |
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crcambridgeupr:10.1017/s002531540999155x 2024-03-03T08:45:09+00:00 Variation in harbour seal counts obtained using aerial surveys Cunningham, Louise Baxter, John M. Boyd, Ian L. 2010 http://dx.doi.org/10.1017/s002531540999155x https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002531540999155X en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Journal of the Marine Biological Association of the United Kingdom volume 90, issue 8, page 1659-1666 ISSN 0025-3154 1469-7769 Aquatic Science journal-article 2010 crcambridgeupr https://doi.org/10.1017/s002531540999155x 2024-02-08T08:27:54Z Aerial surveys of harbour seals ( Phoca vitulina ) are usually carried out to provide an index of population size. This can be normalized, either by design or by post-hoc analysis to reduce the effects that date, time of day, tide and weather might have on the number of seals counted. In order for long-term trends to be determined from these counts it is assumed that the mean number of seals at a particular site does not vary during the survey period, and that the start and duration of the survey window does not vary with location or between years. This study used a combination of repeat land-based and aerial surveys to test the assumption for constancy of counts during the survey period. The study focused on harbour seal abundance at haul-out sites around the Isle of Skye in north-west Scotland. The coefficient of variation in these counts was estimated to be 15%, based on repeat aerial surveys using thermal imaging. Land-based counts were used to examine the effect of covariates on seal numbers using generalized additive modelling. This site-specific model predicted that the current aerial survey window for harbour seals in the UK, which is a three-week period during the moult, is about a week too early and that count variation could be reduced by surveying 1 1/2 hours earlier in the tidal cycle. Furthermore, the pupping period showed even higher (though more variable) abundance of hauled out seals than during the moult. Article in Journal/Newspaper harbour seal Phoca vitulina Cambridge University Press Journal of the Marine Biological Association of the United Kingdom 90 8 1659 1666 |
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Cambridge University Press |
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crcambridgeupr |
language |
English |
topic |
Aquatic Science |
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Aquatic Science Cunningham, Louise Baxter, John M. Boyd, Ian L. Variation in harbour seal counts obtained using aerial surveys |
topic_facet |
Aquatic Science |
description |
Aerial surveys of harbour seals ( Phoca vitulina ) are usually carried out to provide an index of population size. This can be normalized, either by design or by post-hoc analysis to reduce the effects that date, time of day, tide and weather might have on the number of seals counted. In order for long-term trends to be determined from these counts it is assumed that the mean number of seals at a particular site does not vary during the survey period, and that the start and duration of the survey window does not vary with location or between years. This study used a combination of repeat land-based and aerial surveys to test the assumption for constancy of counts during the survey period. The study focused on harbour seal abundance at haul-out sites around the Isle of Skye in north-west Scotland. The coefficient of variation in these counts was estimated to be 15%, based on repeat aerial surveys using thermal imaging. Land-based counts were used to examine the effect of covariates on seal numbers using generalized additive modelling. This site-specific model predicted that the current aerial survey window for harbour seals in the UK, which is a three-week period during the moult, is about a week too early and that count variation could be reduced by surveying 1 1/2 hours earlier in the tidal cycle. Furthermore, the pupping period showed even higher (though more variable) abundance of hauled out seals than during the moult. |
format |
Article in Journal/Newspaper |
author |
Cunningham, Louise Baxter, John M. Boyd, Ian L. |
author_facet |
Cunningham, Louise Baxter, John M. Boyd, Ian L. |
author_sort |
Cunningham, Louise |
title |
Variation in harbour seal counts obtained using aerial surveys |
title_short |
Variation in harbour seal counts obtained using aerial surveys |
title_full |
Variation in harbour seal counts obtained using aerial surveys |
title_fullStr |
Variation in harbour seal counts obtained using aerial surveys |
title_full_unstemmed |
Variation in harbour seal counts obtained using aerial surveys |
title_sort |
variation in harbour seal counts obtained using aerial surveys |
publisher |
Cambridge University Press (CUP) |
publishDate |
2010 |
url |
http://dx.doi.org/10.1017/s002531540999155x https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002531540999155X |
genre |
harbour seal Phoca vitulina |
genre_facet |
harbour seal Phoca vitulina |
op_source |
Journal of the Marine Biological Association of the United Kingdom volume 90, issue 8, page 1659-1666 ISSN 0025-3154 1469-7769 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s002531540999155x |
container_title |
Journal of the Marine Biological Association of the United Kingdom |
container_volume |
90 |
container_issue |
8 |
container_start_page |
1659 |
op_container_end_page |
1666 |
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1792500688568188928 |