Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics
Elephant seals regularly perform dives during which they spend a large proportion of time drifting passively through the water column. The rate of vertical change in depth during these 'drift' dives is largely a result of the proportion of lipid tissue in the body, with fatter seals having...
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Online Access: | https://doi.org/10.1242/jeb.00583 http://www.ncbi.nlm.nih.gov/pubmed/12939372 http://ecite.utas.edu.au/26806 |
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ftunivtasecite:oai:ecite.utas.edu.au:26806 2023-05-15T16:05:25+02:00 Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics Biuw, M McConnell, B Bradshaw, CJA Burton, H Fedal, M 2003 https://doi.org/10.1242/jeb.00583 http://www.ncbi.nlm.nih.gov/pubmed/12939372 http://ecite.utas.edu.au/26806 en eng Company of Biologists Ltd http://dx.doi.org/10.1242/jeb.00583 Biuw, M and McConnell, B and Bradshaw, CJA and Burton, H and Fedal, M, Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics, Journal of Experimental Biology, 206, (19) pp. 3405-3423. ISSN 0022-0949 (2003) [Refereed Article] http://www.ncbi.nlm.nih.gov/pubmed/12939372 http://ecite.utas.edu.au/26806 Biological Sciences Physiology Physiology not elsewhere classified Refereed Article PeerReviewed 2003 ftunivtasecite https://doi.org/10.1242/jeb.00583 2019-12-13T21:07:35Z Elephant seals regularly perform dives during which they spend a large proportion of time drifting passively through the water column. The rate of vertical change in depth during these 'drift' dives is largely a result of the proportion of lipid tissue in the body, with fatter seals having higher (more positive or less negative) drift rates compared with leaner seals. We examined the temporal changes in drift rates of 24 newly weaned southern elephant seal (Mirounga leonina) pups during their first trip to sea to determine if this easily recorded dive characteristic can be used to continuously monitor changes in body composition of seals throughout their foraging trips. All seals demonstrated a similar trend over time: drift rates were initially positive but decreased steadily over the first 30-50 days after departure (Phase 1), corresponding to seals becoming gradually less buoyant. Over the following 100 days (Phase 2), drift rates again increased gradually, while during the last 20-45 days (Phase 3) drift rates either remained constant or decreased slightly. The daily rate of change in drift rate was negatively related to the daily rate of horizontal displacement (daily travel rate), and daily travel rates of more than 80 km were almost exclusively associated with negative changes in drift rate. We developed a mechanistic model based on body compositions and morphometrics measured in the field, published values for the density of seawater and various body components, and values of drag coefficients for objects of different shapes. We used this model to examine the theoretical relationships between drift rate and body composition and carried out a sensitivity analysis to quantify errors and biases caused by varying model parameters. While variations in seawater density and uncertainties in estimated body surface area and volume are unlikely to result in errors in estimated lipid content of more than 2.5%, variations in drag coefficient can lead to errors of 10%. Finally, we compared the lipid contents predicted by our model with the lipid contents measured using isotopically labelled water and found a strong positive passively is between 0.49 (roughly corresponding to a sphere-shaped object) and 0.69 (a prolate spheroid), and we were able to estimate relative lipid content to within approximately 2% lipid. Our results suggest that this simple method can be used to estimate the changes in lipid content of free-ranging seals while at sea and may help improve our understanding of the foraging strategies of these important marine predators. Article in Journal/Newspaper Elephant Seal Elephant Seals Mirounga leonina Southern Elephant Seal eCite UTAS (University of Tasmania) Journal of Experimental Biology 206 19 3405 3423 |
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Open Polar |
collection |
eCite UTAS (University of Tasmania) |
op_collection_id |
ftunivtasecite |
language |
English |
topic |
Biological Sciences Physiology Physiology not elsewhere classified |
spellingShingle |
Biological Sciences Physiology Physiology not elsewhere classified Biuw, M McConnell, B Bradshaw, CJA Burton, H Fedal, M Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
topic_facet |
Biological Sciences Physiology Physiology not elsewhere classified |
description |
Elephant seals regularly perform dives during which they spend a large proportion of time drifting passively through the water column. The rate of vertical change in depth during these 'drift' dives is largely a result of the proportion of lipid tissue in the body, with fatter seals having higher (more positive or less negative) drift rates compared with leaner seals. We examined the temporal changes in drift rates of 24 newly weaned southern elephant seal (Mirounga leonina) pups during their first trip to sea to determine if this easily recorded dive characteristic can be used to continuously monitor changes in body composition of seals throughout their foraging trips. All seals demonstrated a similar trend over time: drift rates were initially positive but decreased steadily over the first 30-50 days after departure (Phase 1), corresponding to seals becoming gradually less buoyant. Over the following 100 days (Phase 2), drift rates again increased gradually, while during the last 20-45 days (Phase 3) drift rates either remained constant or decreased slightly. The daily rate of change in drift rate was negatively related to the daily rate of horizontal displacement (daily travel rate), and daily travel rates of more than 80 km were almost exclusively associated with negative changes in drift rate. We developed a mechanistic model based on body compositions and morphometrics measured in the field, published values for the density of seawater and various body components, and values of drag coefficients for objects of different shapes. We used this model to examine the theoretical relationships between drift rate and body composition and carried out a sensitivity analysis to quantify errors and biases caused by varying model parameters. While variations in seawater density and uncertainties in estimated body surface area and volume are unlikely to result in errors in estimated lipid content of more than 2.5%, variations in drag coefficient can lead to errors of 10%. Finally, we compared the lipid contents predicted by our model with the lipid contents measured using isotopically labelled water and found a strong positive passively is between 0.49 (roughly corresponding to a sphere-shaped object) and 0.69 (a prolate spheroid), and we were able to estimate relative lipid content to within approximately 2% lipid. Our results suggest that this simple method can be used to estimate the changes in lipid content of free-ranging seals while at sea and may help improve our understanding of the foraging strategies of these important marine predators. |
format |
Article in Journal/Newspaper |
author |
Biuw, M McConnell, B Bradshaw, CJA Burton, H Fedal, M |
author_facet |
Biuw, M McConnell, B Bradshaw, CJA Burton, H Fedal, M |
author_sort |
Biuw, M |
title |
Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
title_short |
Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
title_full |
Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
title_fullStr |
Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
title_full_unstemmed |
Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
title_sort |
blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics |
publisher |
Company of Biologists Ltd |
publishDate |
2003 |
url |
https://doi.org/10.1242/jeb.00583 http://www.ncbi.nlm.nih.gov/pubmed/12939372 http://ecite.utas.edu.au/26806 |
genre |
Elephant Seal Elephant Seals Mirounga leonina Southern Elephant Seal |
genre_facet |
Elephant Seal Elephant Seals Mirounga leonina Southern Elephant Seal |
op_relation |
http://dx.doi.org/10.1242/jeb.00583 Biuw, M and McConnell, B and Bradshaw, CJA and Burton, H and Fedal, M, Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics, Journal of Experimental Biology, 206, (19) pp. 3405-3423. ISSN 0022-0949 (2003) [Refereed Article] http://www.ncbi.nlm.nih.gov/pubmed/12939372 http://ecite.utas.edu.au/26806 |
op_doi |
https://doi.org/10.1242/jeb.00583 |
container_title |
Journal of Experimental Biology |
container_volume |
206 |
container_issue |
19 |
container_start_page |
3405 |
op_container_end_page |
3423 |
_version_ |
1766401317201248256 |