By: Miranda Raaf
Cape Town – Heaviside dolphins along the southern West Coast of Africa are all related and belong to one of two major populations, a genetic study has found.
Before this study in South Africa, little was known about the species, which is only found along a stretch of coastline from Table Bay to southern Angola. Conservation experts did not even have data about its migratory patterns or reproductive habits.
Conservation geneticist Keshni Gopal carried out the research as part of her doctoral thesis in zoology.
“What is currently known about its biology and behaviour comes from opportunistic research rather than long-term studies,” she said.
“Hopefully the results of this study can be incorporated into risk assessments and much-needed conservation management and monitoring strategies for this species, and help towards its long-term survival.”
Gopal conducted sensitivity analyses to see how changes in life history traits or environmental variations could influence the resilience of the Heaviside dolphin population.
Her research found that if even 15 dolphins were removed from a small population of 10 000, it could have a dire effect on the overall population size.
By determining the genetic relationship between the different populations, Gopal helped to identify smaller population units.
“Knowledge of such units is vital to ensure effective conservation management strategies,” the University of Pretoria, where Gopal graduated with a PhD on April 9, said in a statement.
“Her data will also go a long way to update the species’ conservation status.”
Heaviside dolphins are currently classified as “data deficient” by the International Union for Conservation of Nature’s (IUCN) red list of threatened species. This is because little is known about their population size and life history, including direct and indirect threats that may lead to their extinction.
Hondeklipbaai is one of seven areas along the West Coast that Gopal visited during the course of four summers.
She collected biopsy tissue samples from 395 dolphins in Table Bay, St Helena Bay, Lambert’s Bay, Hondeklipbaai, Port Nolloth, and Luderitz and Walvis Bay in Namibia.
“An unexpected but positive experience was the opportunity to share information about my research to local fishermen in some of the fishing villages along the West Coast,” she said.
“The fishing communities in these areas have adopted the dolphins as their own, as I still often receive messages from them informing me about ‘their dolphins’ and of new additions to their area.”
Whale and Dolphin Conservation said not many studies had been done on this species, and more data was needed.
“Few studies have been conducted on Heaviside dolphins and very little information is available on their biology, life history and population parameters,” it said on its website.
MarineBio concurred on its website, saying the species’ overall migratory patterns and reproductive habits were not known.
“More data is needed on… populations to determine the population numbers and range of the Heaviside dolphin,” it said.
“This data may also be used to assess the risk of threats to its sustainability such as overfishing of Heaviside dolphin prey and increased commercial fishing in its range.”
According to its website, Heaviside dolphins have blunt heads and robust bodies. Adults reach an average of 1.7m in length and weigh between 60 and 70kg.
“In terms of human interaction, the Heaviside dolphin is known as a shyer version of its playful counterparts.”
According to the Namibian Dolphin Project (NDP), Heaviside dolphins are among the smallest of all dolphins.
They are endemic to the Benguela ecosystem on the south west coast of Africa and only occur along about 2500km of coastline in the whole world. They tend to stay in water less than 100m deep.
“Their density is highest close to shore, where they can often be seen jumping or playing in the waves,” the NDP says on its website.
“However, their presence inshore varies greatly on a daily basis as they often move offshore to feed in deep water at night.” – Sapa