A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats
The lengths of otoliths and other skeletal structures recovered from the scats of pinnipeds, such as Steller sea lions (Eumetopias jubatus), correlate with body size and can be used to estimate the length of prey consumed. Unfortunately, otoliths are often found in too few scats or are too digested...
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ftaquaticcommons:oai:generic.eprints.org:15077 2023-05-15T18:32:51+02:00 A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats Tollit, Dominic J. Heaslip, Susan G. Zeppelin, Tonya K. Joy, Ruth Call, Katherine A. Trites, Andrew W. 2004 application/pdf http://aquaticcommons.org/15077/ http://fishbull.noaa.gov/1023/tollit1.pdf http://aquaticcommons.org/15077/1/tollit1.pdf en eng http://aquaticcommons.org/15077/1/tollit1.pdf Tollit, Dominic J. and Heaslip, Susan G. and Zeppelin, Tonya K. and Joy, Ruth and Call, Katherine A. and Trites, Andrew W. (2004) A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats. Fishery Bulletin, 102(3), pp. 498-508. Ecology Fisheries Article PeerReviewed 2004 ftaquaticcommons 2020-02-27T09:26:46Z The lengths of otoliths and other skeletal structures recovered from the scats of pinnipeds, such as Steller sea lions (Eumetopias jubatus), correlate with body size and can be used to estimate the length of prey consumed. Unfortunately, otoliths are often found in too few scats or are too digested to usefully estimate prey size. Alternative diagnostic bones are frequently recovered, but few bone-size to prey-size correlations exist and bones are also reduced in size by various degrees owing to digestion. To prevent underestimates in prey sizes consumed techniques are required to account for the degree of digestion of alternative bones prior to estimating prey size. We developed a method (using defined criteria and photo-reference material) to assign the degree of digestion for key cranial structures of two prey species: walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). The method grades each structure into one of three condition categories; good, fair or poor. We also conducted feeding trials with captive Steller sea lions, feeding both fish species to determine the extent of erosion of each structure and to derive condition-specific digestion correction factors to reconstruct the original sizes of the structures consumed. In general, larger structures were relatively more digested than smaller ones. Mean size reduction varied between different types of structures (3.3−26.3%), but was not influenced by the size of the prey consumed. Results from the observations and experiments were combined to be able to reconstruct the size of prey consumed by sea lions and other pinnipeds. The proposed method has four steps: 1) measure the recovered structures and grade the extent of digestion by using defined criteria and photo-reference collection; 2) exclude structures graded in poor condition; 3) multiply measurements of structures in good and fair condition by their appropriate digestion correction factors to derive their original size; and 4) calculate the size of prey from allometric regressions relating corrected structure measurements to body lengths. This technique can be readily applied to piscivore dietary studies that use hard remains of fish. Article in Journal/Newspaper Theragra chalcogramma International Association of Aquatic and Marine Science Libraries and Information Centers (IAMSLIC): Aquatic Commons Atka ENVELOPE(151.789,151.789,60.835,60.835) |
institution |
Open Polar |
collection |
International Association of Aquatic and Marine Science Libraries and Information Centers (IAMSLIC): Aquatic Commons |
op_collection_id |
ftaquaticcommons |
language |
English |
topic |
Ecology Fisheries |
spellingShingle |
Ecology Fisheries Tollit, Dominic J. Heaslip, Susan G. Zeppelin, Tonya K. Joy, Ruth Call, Katherine A. Trites, Andrew W. A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
topic_facet |
Ecology Fisheries |
description |
The lengths of otoliths and other skeletal structures recovered from the scats of pinnipeds, such as Steller sea lions (Eumetopias jubatus), correlate with body size and can be used to estimate the length of prey consumed. Unfortunately, otoliths are often found in too few scats or are too digested to usefully estimate prey size. Alternative diagnostic bones are frequently recovered, but few bone-size to prey-size correlations exist and bones are also reduced in size by various degrees owing to digestion. To prevent underestimates in prey sizes consumed techniques are required to account for the degree of digestion of alternative bones prior to estimating prey size. We developed a method (using defined criteria and photo-reference material) to assign the degree of digestion for key cranial structures of two prey species: walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). The method grades each structure into one of three condition categories; good, fair or poor. We also conducted feeding trials with captive Steller sea lions, feeding both fish species to determine the extent of erosion of each structure and to derive condition-specific digestion correction factors to reconstruct the original sizes of the structures consumed. In general, larger structures were relatively more digested than smaller ones. Mean size reduction varied between different types of structures (3.3−26.3%), but was not influenced by the size of the prey consumed. Results from the observations and experiments were combined to be able to reconstruct the size of prey consumed by sea lions and other pinnipeds. The proposed method has four steps: 1) measure the recovered structures and grade the extent of digestion by using defined criteria and photo-reference collection; 2) exclude structures graded in poor condition; 3) multiply measurements of structures in good and fair condition by their appropriate digestion correction factors to derive their original size; and 4) calculate the size of prey from allometric regressions relating corrected structure measurements to body lengths. This technique can be readily applied to piscivore dietary studies that use hard remains of fish. |
format |
Article in Journal/Newspaper |
author |
Tollit, Dominic J. Heaslip, Susan G. Zeppelin, Tonya K. Joy, Ruth Call, Katherine A. Trites, Andrew W. |
author_facet |
Tollit, Dominic J. Heaslip, Susan G. Zeppelin, Tonya K. Joy, Ruth Call, Katherine A. Trites, Andrew W. |
author_sort |
Tollit, Dominic J. |
title |
A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
title_short |
A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
title_full |
A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
title_fullStr |
A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
title_full_unstemmed |
A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
title_sort |
method to improve size estimates of walleye pollock (theragra chalcogramma) atka mackerel (pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats |
publishDate |
2004 |
url |
http://aquaticcommons.org/15077/ http://fishbull.noaa.gov/1023/tollit1.pdf http://aquaticcommons.org/15077/1/tollit1.pdf |
long_lat |
ENVELOPE(151.789,151.789,60.835,60.835) |
geographic |
Atka |
geographic_facet |
Atka |
genre |
Theragra chalcogramma |
genre_facet |
Theragra chalcogramma |
op_relation |
http://aquaticcommons.org/15077/1/tollit1.pdf Tollit, Dominic J. and Heaslip, Susan G. and Zeppelin, Tonya K. and Joy, Ruth and Call, Katherine A. and Trites, Andrew W. (2004) A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats. Fishery Bulletin, 102(3), pp. 498-508. |
_version_ |
1766217050908262400 |