Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea
In March-April 1991 a combined expedition using fixed-wing aircraft and ship-borne helicopter was carried out to estimate harp seal pup production in the Greenland Sea (the West Ice). Photographs were taken from the fixed-wing aircraft and analysed from counts made on negatives. Visual surveys were...
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ftimr:oai:imr.brage.unit.no:11250/100313 2023-05-15T16:28:28+02:00 Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea Øien, Nils Øritsland, Torger 1993 471061 bytes application/pdf http://hdl.handle.net/11250/100313 eng eng ICES ICES CM documents 1993/N:9 This report is not to be quoted without prior consultation with the General Secretary. http://hdl.handle.net/11250/100313 9 s. VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920 Working paper 1993 ftimr 2021-09-23T20:15:07Z In March-April 1991 a combined expedition using fixed-wing aircraft and ship-borne helicopter was carried out to estimate harp seal pup production in the Greenland Sea (the West Ice). Photographs were taken from the fixed-wing aircraft and analysed from counts made on negatives. Visual surveys were made fiom helicopter using funnel-shaped shades to limit the search strip. Three separate breeding patches of harp seals were sweyed by either or both of the methods, making direct comparisons between the methods possible. Abundance estimates calculated from the basic data are given for these patches. Bearing in mind that neither survey covered all known patches, the photographic estimate of surveyed areas was about 40,000 pups, and the visual estimate of surveyed patches about 60,000 pups. Both these estimates have an inherent negative bias caused by the fact that known patches were not included (which my account for at least -10%); neither have scattered pups between patches nor the temporal distribution of births been taken into consideration. A specific problem of the photographic survey are the errors made during reading and interpretation of the photographs. These aspects were investigated by reading negatives under slightly different conditions, and parallel reading of negatives and printed copies, which apparently have differing properties with respect to readability definitions of harp seal pups. By these two procedures it was demonstrated that counts increased by 3.2% and 5.5%, respectively. Conclusively, it is recognized that the aerial survey results in general are consistent with pup production estimates based on mark-recapture experiments conducted over the last 15 years. Report Greenland Greenland Sea Harp Seal Institute for Marine Research: Brage IMR Greenland |
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Open Polar |
collection |
Institute for Marine Research: Brage IMR |
op_collection_id |
ftimr |
language |
English |
topic |
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920 |
spellingShingle |
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920 Øien, Nils Øritsland, Torger Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea |
topic_facet |
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920 |
description |
In March-April 1991 a combined expedition using fixed-wing aircraft and ship-borne helicopter was carried out to estimate harp seal pup production in the Greenland Sea (the West Ice). Photographs were taken from the fixed-wing aircraft and analysed from counts made on negatives. Visual surveys were made fiom helicopter using funnel-shaped shades to limit the search strip. Three separate breeding patches of harp seals were sweyed by either or both of the methods, making direct comparisons between the methods possible. Abundance estimates calculated from the basic data are given for these patches. Bearing in mind that neither survey covered all known patches, the photographic estimate of surveyed areas was about 40,000 pups, and the visual estimate of surveyed patches about 60,000 pups. Both these estimates have an inherent negative bias caused by the fact that known patches were not included (which my account for at least -10%); neither have scattered pups between patches nor the temporal distribution of births been taken into consideration. A specific problem of the photographic survey are the errors made during reading and interpretation of the photographs. These aspects were investigated by reading negatives under slightly different conditions, and parallel reading of negatives and printed copies, which apparently have differing properties with respect to readability definitions of harp seal pups. By these two procedures it was demonstrated that counts increased by 3.2% and 5.5%, respectively. Conclusively, it is recognized that the aerial survey results in general are consistent with pup production estimates based on mark-recapture experiments conducted over the last 15 years. |
format |
Report |
author |
Øien, Nils Øritsland, Torger |
author_facet |
Øien, Nils Øritsland, Torger |
author_sort |
Øien, Nils |
title |
Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea |
title_short |
Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea |
title_full |
Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea |
title_fullStr |
Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea |
title_full_unstemmed |
Aerial and visual surveys to estimate harp seal pup production in the Greenland Sea |
title_sort |
aerial and visual surveys to estimate harp seal pup production in the greenland sea |
publisher |
ICES |
publishDate |
1993 |
url |
http://hdl.handle.net/11250/100313 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Greenland Greenland Sea Harp Seal |
genre_facet |
Greenland Greenland Sea Harp Seal |
op_source |
9 s. |
op_relation |
ICES CM documents 1993/N:9 This report is not to be quoted without prior consultation with the General Secretary. http://hdl.handle.net/11250/100313 |
_version_ |
1766018125551108096 |