FOLLOWING extensive study on humpback dolphins conducted at Richards Bay from 1998 to 2006, researcher Shanan Atkins has released a further scientific paper.
Shanan headed the original study done by the Endangered Wildlife Trust (EWT), in collaboration with the University of the Witwatersrand and the University of Pretoria.
Photo-identification data collected was used to assess humpback dolphins’ residency (the amount of time individuals spend in the area), site fidelity (their tendency to return), movement patterns, and to evaluate how emigration, immigration, and mortality rates influenced the use of Richards Bay at various time scales.
‘We identified 109 distinctive individuals that visited the Richards Bay area,’ said Shanan.
‘A clustering technique sorted them into residency categories and we ended up with three categories– residents, intermediates and transients.’
• The resident category was small, only five individuals (photographed in more than four months per year in all eight years). ‘Richards Bay’s human residents may remember the names we gave them: Zipper, LineL, Ivory, Venus and FL (the only male),’ said Shanan.
• The transient category contained the majority of individuals (81), and were photographed less than one month per year in 1–6 years.
• In the intermediate category were 14 individuals (photographed 1-3 months/year in 5-8 years) which did not fit neatly into either of the other categories.
Visiting patterns
‘You may have done the math and noticed this accounts for only 100 of the individuals.
‘The other nine were caught in the shark nets, which meant that placing them in residency categories was a little more complicated but the result was: 3 residents, 1 intermediate and 5 transients.
‘We found that, overall, individual humpback dolphins did not spend much time at Richards Bay but they did tend to return quite often.
‘This resulted in high population turnover in the short-term but low turnover over six months and longer.
‘There was clear indication that individuals varied in their visiting patterns but there was no evidence their visits were seasonal.
‘Analysing these movement patterns showed that there is a net loss of dolphins from the Richards Bay area, which could be due to permanent emigration, mortality or, most likely, a bit of both,’ said Shanan.
Shark net issue
‘While dolphins naturally emigrate from the area, the fact we recognised some individuals caught in the shark nets indicated that mortality in the shark nets contributes to the permanent loss of humpback dolphins from Richards Bay.
‘The finding that many of the dolphins were transients means that what happens at Richards Bay has the potential to affect the wider population of humpback dolphins in KZN and we believe that focusing conservation efforts at Richards Bay would be prudent.’
Shanan said the KZN Sharks Board works hard to minimise the negative impact the shark nets may have on marine biodiversity.
‘During the project the Sharks Board replaced part of the shark net that caught the most dolphins with drumlines and this appears to have reduced the number of accidental entanglements.
‘We’re approaching the local authorities about additional conservation actions that would further the cause of the humpback dolphin, which is now considered endangered.
‘But for any changes that are considered, the potential effect on the safety of bathers remains the highest priority.
‘It is also important to consider the potential effects on sharks. We would like to find a way that will allow bathers, dolphins and sharks to swim safely at Richards Bay.’
Playing our part
Zululand Observer Editor, Dave Savides a frequent visitor to the dolphin lookout point at Alkantstrand, regularly sends photos of humpback dolphins to Shanan Atkins of the EWT as well as to scientists from a new project called SouSA, which has created a citizen science platform looking for photos of humpback dolphins all along the SA coast, for use in identifying individual dolphins and monitoring their locations and movements. They can be found on https://www.sousaproject.org/
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