Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000
Prey-size selectivity by Steller sea lions (Eumetopias jubatus) is relevant for understanding the foraging behavior of this declining predator, but studies have been problematic because of the absence and erosion of otoliths usually used to estimate fish length. Therefore, we developed regression fo...
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ftoceandocs:oai:aquadocs.org:1834/30931 2023-05-15T18:32:51+02:00 Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 Zeppelin, Tonya K. Tollit, Dominic J. Call, Katherine A. Orchard, Trevor J. Gudmundson, Carolyn J. 2004 application/pdf 509-521 http://hdl.handle.net/1834/30931 en eng http://fishbull.noaa.gov/1023/zeppelin.pdf 0090-0656 http://hdl.handle.net/1834/30931 http://aquaticcommons.org/id/eprint/15078 403 2014-05-27 14:41:59 15078 United States National Marine Fisheries Service Ecology Fisheries article TRUE 2004 ftoceandocs 2023-04-06T17:04:16Z Prey-size selectivity by Steller sea lions (Eumetopias jubatus) is relevant for understanding the foraging behavior of this declining predator, but studies have been problematic because of the absence and erosion of otoliths usually used to estimate fish length. Therefore, we developed regression formulae to estimate fish length from seven diagnostic cranial structures of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). For both species, all structure measurements were related with fork length of prey (r2 range: 0.78−0.99). Fork length (FL) of walleye pollock and Atka mackerel consumed by Steller sea lions was estimated by applying these regression models to cranial structures recovered from scats (feces) collected between 1998 and 2000 across the range of the Alaskan western stock of Steller sea lions. Experimentally derived digestion correction factors were applied to take into account loss of size due to digestion. Fork lengths of walleye pollock consumed by Steller sea lions ranged from 3.7 to 70.8 cm (mean=39.3 cm, SD=14.3 cm, n=666) and Atka mackerel ranged from 15.3 to 49.6 cm (mean=32.3 cm, SD=5.9 cm, n=1685). Although sample sizes were limited, a greater proportion of juvenile (≤20 cm) walleye pollock were found in samples collected during the summer (June−September) on haul-out sites (64% juveniles, n=11 scats) than on summer rookeries (9% juveniles, n=132 scats) or winter (February−March) haul-out sites (3% juveniles, n=69 scats). Annual changes in the size of Atka mackerel consumed by Steller sea lions corresponded to changes in the length distribution of Atka mackerel resulting from exceptionally strong year classes. Considerable overlap (>51%) in the size of walleye pollock and Atka mackerel taken by Steller sea lions and the sizes of these species caught by the commercial trawl fishery were demonstrated. Article in Journal/Newspaper Theragra chalcogramma Alaska IODE-UNESCO: OceanDocs - E-Repository of Ocean Publications Atka ENVELOPE(151.789,151.789,60.835,60.835) |
institution |
Open Polar |
collection |
IODE-UNESCO: OceanDocs - E-Repository of Ocean Publications |
op_collection_id |
ftoceandocs |
language |
English |
topic |
Ecology Fisheries |
spellingShingle |
Ecology Fisheries Zeppelin, Tonya K. Tollit, Dominic J. Call, Katherine A. Orchard, Trevor J. Gudmundson, Carolyn J. Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 |
topic_facet |
Ecology Fisheries |
description |
Prey-size selectivity by Steller sea lions (Eumetopias jubatus) is relevant for understanding the foraging behavior of this declining predator, but studies have been problematic because of the absence and erosion of otoliths usually used to estimate fish length. Therefore, we developed regression formulae to estimate fish length from seven diagnostic cranial structures of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). For both species, all structure measurements were related with fork length of prey (r2 range: 0.78−0.99). Fork length (FL) of walleye pollock and Atka mackerel consumed by Steller sea lions was estimated by applying these regression models to cranial structures recovered from scats (feces) collected between 1998 and 2000 across the range of the Alaskan western stock of Steller sea lions. Experimentally derived digestion correction factors were applied to take into account loss of size due to digestion. Fork lengths of walleye pollock consumed by Steller sea lions ranged from 3.7 to 70.8 cm (mean=39.3 cm, SD=14.3 cm, n=666) and Atka mackerel ranged from 15.3 to 49.6 cm (mean=32.3 cm, SD=5.9 cm, n=1685). Although sample sizes were limited, a greater proportion of juvenile (≤20 cm) walleye pollock were found in samples collected during the summer (June−September) on haul-out sites (64% juveniles, n=11 scats) than on summer rookeries (9% juveniles, n=132 scats) or winter (February−March) haul-out sites (3% juveniles, n=69 scats). Annual changes in the size of Atka mackerel consumed by Steller sea lions corresponded to changes in the length distribution of Atka mackerel resulting from exceptionally strong year classes. Considerable overlap (>51%) in the size of walleye pollock and Atka mackerel taken by Steller sea lions and the sizes of these species caught by the commercial trawl fishery were demonstrated. |
format |
Article in Journal/Newspaper |
author |
Zeppelin, Tonya K. Tollit, Dominic J. Call, Katherine A. Orchard, Trevor J. Gudmundson, Carolyn J. |
author_facet |
Zeppelin, Tonya K. Tollit, Dominic J. Call, Katherine A. Orchard, Trevor J. Gudmundson, Carolyn J. |
author_sort |
Zeppelin, Tonya K. |
title |
Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 |
title_short |
Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 |
title_full |
Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 |
title_fullStr |
Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 |
title_full_unstemmed |
Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1999 to 2000 |
title_sort |
sizes of walleye pollock (theragra chalcogramma) and atka mackerel (pleurogrammus monopterygius) consumed by the western stock of steller sea lions (eumetopias jubatus) in alaska from 1999 to 2000 |
publishDate |
2004 |
url |
http://hdl.handle.net/1834/30931 |
long_lat |
ENVELOPE(151.789,151.789,60.835,60.835) |
geographic |
Atka |
geographic_facet |
Atka |
genre |
Theragra chalcogramma Alaska |
genre_facet |
Theragra chalcogramma Alaska |
op_source |
http://aquaticcommons.org/id/eprint/15078 403 2014-05-27 14:41:59 15078 United States National Marine Fisheries Service |
op_relation |
http://fishbull.noaa.gov/1023/zeppelin.pdf 0090-0656 http://hdl.handle.net/1834/30931 |
_version_ |
1766217046058598400 |