UP Whale Unit conducts boat-based research on ‘data deficient’ and ‘vulnerable’ Bryde’s whales off SW Cape coast

Posted on March 12, 2021

The Whale Unit at the University of Pretoria’s Mammal Research Institute (MRI) is currently conducting boat-based field research on Bryde’s whales in Walker Bay on the south-western Cape coast under permit conditions of the South African government. This includes boat approaches to the whales in order to obtain photographs for subsequent individual identification (using the marks in the dorsal fins) as well as skin biopsy samples for subsequent genetic analysis.

At an estimated 600 individuals, the inshore population of Bryde’s whales has the smallest population size of any large whale species occurring in South African waters, with its current international conservation status listed as ‘Data Deficient’ and nationally as ‘Vulnerable’ under the International Union for Conservation of Nature’s criteria.

Bryde’s whales will be photo-identified by the Whale Unit’s research team using the marks on their dorsal fins at various sites along the South African coast to find possible movement patterns of individual whales.

The two research projects underway on the whales are as follows:

Conservation genetics: The South African inshore Bryde’s whales do not make extensive North-South migrations as other baleen whale species (such as the southern right whale), but are known to exhibit a year-round residency in South African coastal waters, the only baleen whale species identified as such. As they need to forage frequently to meet their daily energetic needs, they are subject to following their seasonally moving prey. Therefore, they have a seasonal movement coinciding with the movement of their main prey species (sardines and anchovies), with a northward movement along the east and west coast during autumn and winter, and a return to the central Agulhas bank during spring.

However, it is not fully understood if the movement of inshore Bryde’s whales is geographically restricted to either the west or east coast, or if they all form one random mating and moving population. Nonetheless, knowledge on possible population structure has strong implications in conservation management of the species. In order to address this question, the research team aims to obtain skin biopsy samples of Bryde’s whales for subsequent genetic analysis. Additionally, Bryde’s whales will be photo-identified through the marks on their dorsal fins at various sites along the South African coast to find possible movement patterns of individual whales.

Foraging ecology: Despite the basic knowledge on primary prey and seasonal movements, the feeding and tropic ecology of South Africa’s inshore Bryde’s whales remains understudied. Due to their year-round residency on the Agulhas Bank and dependency on economically important pelagic fish (mainly sardine and anchovy) as their primary food source, they are extremely vulnerable to the effects of overfishing and environmental change. As a result, the team aims to investigate past and present dietary contributions, to evaluate possible changes in foraging strategies and assess the effects of pelagic fish exploitation on the trophic level at which these whales feed. This will be done through the analysis of stable isotope profiles in the baleen plates of stranded animals, as well as from skin biopsy samples. Additionally, the researchers will be flying drones to evaluate the temporal changes in body condition as a proxy of foraging success.

For further enquiries please contact Dr Els Vermeulen (Research Manager at the Whale Unit) on 060 971 4301 or Chris Wilkinson (Technical Manager at the Whale Unit) on 083 580 8247.

- Author Primarashni Gower
Published by Hlengiwe Mnguni

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