Visibility of St Lawrence belugas to aerial photography, estimated by direct observation
The depleted population of belugas (Delphinapterus leucas) inhabiting the St Lawrence estuary, Canada, was monitored by periodic photographic aerial surveys. In order to correct counts made on aerial survey film and to obtain an estimate of the true size of the population, the diving behaviour and t...
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ftdoajarticles:oai:doaj.org/article:a0590e339a43476cb92590e81edc7375 2023-05-15T15:41:59+02:00 Visibility of St Lawrence belugas to aerial photography, estimated by direct observation Michael CS Kingsley Isabelle Gauthier 2002-07-01T00:00:00Z https://doi.org/10.7557/3.2848 https://doaj.org/article/a0590e339a43476cb92590e81edc7375 EN eng Septentrio Academic Publishing https://septentrio.uit.no/index.php/NAMMCOSP/article/view/2848 https://doaj.org/toc/1560-2206 https://doaj.org/toc/2309-2491 1560-2206 2309-2491 doi:10.7557/3.2848 https://doaj.org/article/a0590e339a43476cb92590e81edc7375 NAMMCO Scientific Publications, Vol 4, Iss 0, Pp 259-270 (2002) belugas Delphinapterus leucas visibility aerial surveys correction factor Ecology QH540-549.5 article 2002 ftdoajarticles https://doi.org/10.7557/3.2848 2022-12-31T02:51:22Z The depleted population of belugas (Delphinapterus leucas) inhabiting the St Lawrence estuary, Canada, was monitored by periodic photographic aerial surveys. In order to correct counts made on aerial survey film and to obtain an estimate of the true size of the population, the diving behaviour and the visibility from the air of these animals was studied. A Secchi-disk turbidity survey in the belugas’ summer range showed that water clarity varied between 1.5 m and 11.6 m. By studying aerial photographs of sheet-plastic models of belugas that had been sunk to different depths below the surface, we found that models of white adults could be seen down to about the same depth as a Secchi disk, but no deeper. Smaller models of dark-grey juveniles could only be seen down to about 50% of Secchi-disk depth. By observing groups of belugas from a hovering helicopter and recording their disappearances and re-appearances, it was found that they were visible for 44.3% of the time, and that an appropriate correction for single photographs would be to multiply the photographic count by about 222% (SE 20%). For surveys in which there was overlap between adjacent frames, the estimated correction would be 209% (SE 16%). This correction factor was slightly conservative and gave an estimate of the true size of the population, based on a single survey, of 1,202 belugas (SE 189) in 1997. An estimate for 1997 based on smoothing 5 surveys 1988–1997 was 1,238 (SE 119). Article in Journal/Newspaper Beluga* Delphinapterus leucas Directory of Open Access Journals: DOAJ Articles Canada NAMMCO Scientific Publications 4 259 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
belugas Delphinapterus leucas visibility aerial surveys correction factor Ecology QH540-549.5 |
spellingShingle |
belugas Delphinapterus leucas visibility aerial surveys correction factor Ecology QH540-549.5 Michael CS Kingsley Isabelle Gauthier Visibility of St Lawrence belugas to aerial photography, estimated by direct observation |
topic_facet |
belugas Delphinapterus leucas visibility aerial surveys correction factor Ecology QH540-549.5 |
description |
The depleted population of belugas (Delphinapterus leucas) inhabiting the St Lawrence estuary, Canada, was monitored by periodic photographic aerial surveys. In order to correct counts made on aerial survey film and to obtain an estimate of the true size of the population, the diving behaviour and the visibility from the air of these animals was studied. A Secchi-disk turbidity survey in the belugas’ summer range showed that water clarity varied between 1.5 m and 11.6 m. By studying aerial photographs of sheet-plastic models of belugas that had been sunk to different depths below the surface, we found that models of white adults could be seen down to about the same depth as a Secchi disk, but no deeper. Smaller models of dark-grey juveniles could only be seen down to about 50% of Secchi-disk depth. By observing groups of belugas from a hovering helicopter and recording their disappearances and re-appearances, it was found that they were visible for 44.3% of the time, and that an appropriate correction for single photographs would be to multiply the photographic count by about 222% (SE 20%). For surveys in which there was overlap between adjacent frames, the estimated correction would be 209% (SE 16%). This correction factor was slightly conservative and gave an estimate of the true size of the population, based on a single survey, of 1,202 belugas (SE 189) in 1997. An estimate for 1997 based on smoothing 5 surveys 1988–1997 was 1,238 (SE 119). |
format |
Article in Journal/Newspaper |
author |
Michael CS Kingsley Isabelle Gauthier |
author_facet |
Michael CS Kingsley Isabelle Gauthier |
author_sort |
Michael CS Kingsley |
title |
Visibility of St Lawrence belugas to aerial photography, estimated by direct observation |
title_short |
Visibility of St Lawrence belugas to aerial photography, estimated by direct observation |
title_full |
Visibility of St Lawrence belugas to aerial photography, estimated by direct observation |
title_fullStr |
Visibility of St Lawrence belugas to aerial photography, estimated by direct observation |
title_full_unstemmed |
Visibility of St Lawrence belugas to aerial photography, estimated by direct observation |
title_sort |
visibility of st lawrence belugas to aerial photography, estimated by direct observation |
publisher |
Septentrio Academic Publishing |
publishDate |
2002 |
url |
https://doi.org/10.7557/3.2848 https://doaj.org/article/a0590e339a43476cb92590e81edc7375 |
geographic |
Canada |
geographic_facet |
Canada |
genre |
Beluga* Delphinapterus leucas |
genre_facet |
Beluga* Delphinapterus leucas |
op_source |
NAMMCO Scientific Publications, Vol 4, Iss 0, Pp 259-270 (2002) |
op_relation |
https://septentrio.uit.no/index.php/NAMMCOSP/article/view/2848 https://doaj.org/toc/1560-2206 https://doaj.org/toc/2309-2491 1560-2206 2309-2491 doi:10.7557/3.2848 https://doaj.org/article/a0590e339a43476cb92590e81edc7375 |
op_doi |
https://doi.org/10.7557/3.2848 |
container_title |
NAMMCO Scientific Publications |
container_volume |
4 |
container_start_page |
259 |
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1766374866354700288 |