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Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability
Dissertation (MSc ((Zoology))--University of Pretoria, 2020.
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University of Pretoria
2021
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| _version_ | 1867613635851845632 |
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| access_status_str | Open Access |
| author2 | Ganswindt, Andre |
| author_browse | Ganswindt, Andre |
| author_facet | Ganswindt, Andre |
| collection | Thesis |
| dc_rights_str_mv | © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Dissertation (MSc ((Zoology))--University of Pretoria, 2020. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/78123 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:39:17.410Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/78123 Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability Ganswindt, Andre vandenberggideon@gmail.com Vermeulen, Els Van den Berg, Gideon Leon Southern right whale (Eubalaena australis) Population dynamics Climate change El Niño– Southern Oscillation Southern Ocean Stable isotopes Foraging ecology UCTD Dissertation (MSc ((Zoology))--University of Pretoria, 2020. South African southern right whales (SRWs; Eubalaena australis) have been studied intensively since 1969, and annual aerial surveys between 1971 and 2006 indicate a predominant 6.9% annual population growth rate – a conservation success story after the species’ legal protection from commercial whaling in 1935. However, the prevalence of South African SRW unaccompanied adults (non-calving adults) and cow-calf pairs dropped sharply after 2009 and 2015, respectively. Additionally, the calving interval of many female South African SRWs has shifted from a three-year cycle to a four- or five-year cycle, since 2010, suggesting calving failure. This has resulted in a decrease in the population growth rate from 6.9% between 1971 and 2006, to 6.5% in 2017. SRWs are capital breeders that meet migratory and reproductive costs through seasonal energy intake, leading to strong links between their calving and foraging success. The anomalous trends in the South African SRW population have therefore raised concern about the ecological status of its broad feeding range in the Southern Ocean and ultimately about its continued population recovery. This necessitated investigation firstly into the influence of large-scale global climate drivers, Antarctic winter sea-ice extent and summer ocean productivity on the calving output of the South African SRW population. Auto-regressive integrated moving average models revealed significant model performance improvement through the inclusion of the Oceanic Niño Index (a key measure of El Niño events), the Antarctic Oscillation (the leading mode of atmospheric variability in the Southern Ocean) and chlorophyll a concentrations. The findings indicate that the South African SRW calving output appears closely influenced by not only the species’ life cycle, but also by foraging ground productivity and global climate. Secondly, the foraging strategies of South African SRWs during the 1990s (i.e. a period of high calving rates) and the late 2010s (i.e. a period of low calving rates), were assessed, through the analyses of stable carbon (δ13C) and nitrogen (δ15N) isotope values in SRW skin biopsy samples (n = 122). Results show that South African SRWs underwent a dramatic northward shift in foraging location, as well as a diversification in foraging strategy, between the 1990s and 2010s. Bayesian mixing models suggest that during the 1990s, the population foraged on prey with isotopic values similar to krill from around South Georgia. By contrast, in the 2010s, it is inferred that the population foraged on prey with isotopic values consistent with prey found in the waters of the Subtropical Convergence, Polar Front, and Marion Island. This shift could represent a new strategy to cope with changes in the availability of preferred prey or changes in habitat productivity. However, the co-occurring reproductive declines show that altering foraging strategies may not be sufficient to successfully adapt to a changing ocean. Overall, the results of this dissertation advocate that South African SRWs have recently been affected by environmental change at their foraging grounds, in turn affecting their reproductive success. Their predictive coastal presence and the existing long-term monitoring suggest that the species should be regarded as an indicator species – illustrative of climate change impacts in Southern Ocean ecosystems. Zoology and Entomology MSc (Zoology) Restricted 2021-01-26T09:07:53Z 2021-01-26T09:07:53Z 2021-04 2020-10 Dissertation * A2021 http://hdl.handle.net/2263/78123 en © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | Southern right whale (Eubalaena australis) Population dynamics Climate change El Niño– Southern Oscillation Southern Ocean Stable isotopes Foraging ecology UCTD Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability |
| title | Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability |
| title_full | Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability |
| title_fullStr | Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability |
| title_full_unstemmed | Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability |
| title_short | Foraging ecology of South Africa’s southern right whales (Eubalaena australis) in relation to calving success and global climate variability |
| title_sort | foraging ecology of south africa s southern right whales eubalaena australis in relation to calving success and global climate variability |
| topic | Southern right whale (Eubalaena australis) Population dynamics Climate change El Niño– Southern Oscillation Southern Ocean Stable isotopes Foraging ecology UCTD |
| url | http://hdl.handle.net/2263/78123 |