A photo-identification-based assessment model of southern right whales
Photo-identification data for southern right whale cow–calf pairs on the South African calving grounds provide one of the longest abundance time-series for any whale population worldwide. Following a very steady increase from a heavily depleted state, surveys since 2015 reflect many notably low coun...
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ftjafricanj:oai:ajol.info:article/248440 2023-06-18T03:43:13+02:00 A photo-identification-based assessment model of southern right whales Brandão, A. Ross-Gillespie, A. Vermeulen, E. Butterworth, D.S. 2023-05-29 application/pdf https://www.ajol.info/index.php/ajms/article/view/248440 eng eng NISC https://www.ajol.info/index.php/ajms/article/view/248440/234959 https://www.ajol.info/index.php/ajms/article/view/248440 African Journal of Marine Science; Vol. 45 No. 1 (2023); 15-27 1814-2338 1814-232X calving interval cow–calf pairs demographic parameters population growth rate sightings histories three-year reproductive cycle population model info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Peer-reviewed Article 2023 ftjafricanj 2023-06-04T07:39:14Z Photo-identification data for southern right whale cow–calf pairs on the South African calving grounds provide one of the longest abundance time-series for any whale population worldwide. Following a very steady increase from a heavily depleted state, surveys since 2015 reflect many notably low counts. These data are analysed to investigate whether these low counts can be explained by changes in reproduction-related parameters. This necessitates a modification to an earlier reproduction model for these whales, fit to photo-identification data to allow for early abortions; hence, a whale pregnant one year can again be pregnant the next. This can account for an increase in calving intervals in a way that differs from a whale resting for another year or an increase in late-abortion probability. This modification was able to account for the low number of sightings of cow–calf pairs over the 2015 to 2020 period (excepting for 2018), though the estimated probability of sighting a cow–calf pair in 2018 is somewhat low given a nearly unchanged annual survey effort. Hence, low numbers of sightings of females with calves for five of the years from 2015 to 2020 can be explained by changes in reproduction-related parameters rather than an increased natural mortality which is inconsistent with the photo-identification data. Changing environmental (particularly feeding) conditions seems to be the likely cause, possibly associated with a changed distribution of these whales. The estimated number of all whales in the population in 2020 is 6 470 (SE 285), with the number of parous females estimated to have increased 15-fold over the last four decades. Article in Journal/Newspaper Southern Right Whale AJOL - African Journals Online |
institution |
Open Polar |
collection |
AJOL - African Journals Online |
op_collection_id |
ftjafricanj |
language |
English |
topic |
calving interval cow–calf pairs demographic parameters population growth rate sightings histories three-year reproductive cycle population model |
spellingShingle |
calving interval cow–calf pairs demographic parameters population growth rate sightings histories three-year reproductive cycle population model Brandão, A. Ross-Gillespie, A. Vermeulen, E. Butterworth, D.S. A photo-identification-based assessment model of southern right whales |
topic_facet |
calving interval cow–calf pairs demographic parameters population growth rate sightings histories three-year reproductive cycle population model |
description |
Photo-identification data for southern right whale cow–calf pairs on the South African calving grounds provide one of the longest abundance time-series for any whale population worldwide. Following a very steady increase from a heavily depleted state, surveys since 2015 reflect many notably low counts. These data are analysed to investigate whether these low counts can be explained by changes in reproduction-related parameters. This necessitates a modification to an earlier reproduction model for these whales, fit to photo-identification data to allow for early abortions; hence, a whale pregnant one year can again be pregnant the next. This can account for an increase in calving intervals in a way that differs from a whale resting for another year or an increase in late-abortion probability. This modification was able to account for the low number of sightings of cow–calf pairs over the 2015 to 2020 period (excepting for 2018), though the estimated probability of sighting a cow–calf pair in 2018 is somewhat low given a nearly unchanged annual survey effort. Hence, low numbers of sightings of females with calves for five of the years from 2015 to 2020 can be explained by changes in reproduction-related parameters rather than an increased natural mortality which is inconsistent with the photo-identification data. Changing environmental (particularly feeding) conditions seems to be the likely cause, possibly associated with a changed distribution of these whales. The estimated number of all whales in the population in 2020 is 6 470 (SE 285), with the number of parous females estimated to have increased 15-fold over the last four decades. |
format |
Article in Journal/Newspaper |
author |
Brandão, A. Ross-Gillespie, A. Vermeulen, E. Butterworth, D.S. |
author_facet |
Brandão, A. Ross-Gillespie, A. Vermeulen, E. Butterworth, D.S. |
author_sort |
Brandão, A. |
title |
A photo-identification-based assessment model of southern right whales |
title_short |
A photo-identification-based assessment model of southern right whales |
title_full |
A photo-identification-based assessment model of southern right whales |
title_fullStr |
A photo-identification-based assessment model of southern right whales |
title_full_unstemmed |
A photo-identification-based assessment model of southern right whales |
title_sort |
photo-identification-based assessment model of southern right whales |
publisher |
NISC |
publishDate |
2023 |
url |
https://www.ajol.info/index.php/ajms/article/view/248440 |
genre |
Southern Right Whale |
genre_facet |
Southern Right Whale |
op_source |
African Journal of Marine Science; Vol. 45 No. 1 (2023); 15-27 1814-2338 1814-232X |
op_relation |
https://www.ajol.info/index.php/ajms/article/view/248440/234959 https://www.ajol.info/index.php/ajms/article/view/248440 |
_version_ |
1769009518641938432 |