SouSA - Whale and Dolphin Research

June 05, 2017 Meredith Thornton

As the winter chills set upon us in the Southern Hemisphere we celebrate two important days this week - today is World Environment Day, which is all about getting outdoors and into nature, to appreciate its beauty and to be fully conscious of its importance; Thursday is World Oceans Day which is a global day of ocean celebration and collaboration for a better future for us all.  This year’s theme is Our Oceans, Our Future and the conservation action focus is Encouraging solutions to plastic pollution and preventing marine litter for a healthier ocean and a better future.

Grab your friends and colleagues, kick off your shoes and hit the coastline this week, preferably with a garbage bag in hand to do your bit for the planet today!  Let us know what you decided to do, and how it went. Remember Your Choice makes a Difference #WithNature #worldoceansday

Over the last two weeks the Dyer Island Conservation Trust joined forces with a team of researchers from Sea Search Research and Conservation, the Mammal Research Institute’s Whale Unit (University of Pretoria) and Center for Statistics in Ecology, Environment and Conservation (University of Cape Town) to collect acoustic and behavioural data, photo ID’s and biopsy samples from dolphins and whales in the Overstrand area.

The main focus of our study was Indian Ocean humpback dolphins, but these animals are very shy and can be particularly elusive, so we also spent time sampling bottlenose and common dolphins, as well as Brydes’, humpback and southern right whales.

Humpback dolphins utilise exactly the same areas of the coast that we do, so besides for shark predation, threats are usually as a result of man’s activities.  Power boats and jetskis disturb their behaviour, shark nets put up to protect bathers indiscriminately catch dolphins too and because they like estuarine areas they are especially vulnerable to exposure to pesticides and other pollutants that make their way from agricultural areas down the river system and into the sea – often being accumulated in the prey that humpback (and other dolphins) consume.

Two rigid inflatable boats were used for the work, covering different areas at the same time, so that we could maximise the amount of work.  One vessel was set up primarily for acoustic work and the other for biopsying, while both vessels collected both behavioural and photo ID data.

Acoustic monitoring is used in conjunction with the behavioural sampling and allows us to describe the dolphins’ vocalisations, measure the frequency thereof and to infer what sounds are made during certain behaviours or as a result of natural or man-induced stressors.

Biopsy samples are used for genetic and isotope work, answering questions about how populations may be different from other populations within one species, and how these things can change over time, while isotope analysis gives us information about what the dolphins have been feeding on.

Photo ID helps us to determine who’s who in the population and gives us answers on population size, calving intervals and success.  Previous data collected by the Dyer Island Conservation Trust and Dyer Island Cruises has already allowed us to identify about 30 different humpback dolphins from the Dyer Island area!

The team had 8 encounters of humpback dolphins, 16 of bottlenose dolphin and over 20 whale encounters of three species (Bryde’s, southern right and humpback). They managed to get six recordings from humpback dolphins, and identify individuals which were previously seen off Strandfontein in False Bay. They also obtained biopsy samples from bottlenose, common and humpback dolphins. One individual dolphin was photographically identified in Walker Bay, Kleinbaai and Struisbaai during the trip covering a distance of at least 120 km in just a few days.

Future plans are to continue with these fieldtrips every couple of months as they provide valuable information that can aid conservationists and environmental managers in decision making on marine spatial planning in order to help to protect whales and dolphins and preserve important habitats for them in the long term.

The research team members were: Dr Simon Elwen, Dr Tess Gridley, Sandra Hoerbst, Bridget James, Monique Laubscher, Barry McGovern, Meredith Thornton, Dr Els Vermeulen and Chris Wilkinson.  All work was conducted under permit from CapeNature and the Department of Environment Affairs in terms of Section 83 of the Marine Living Resources Act.

Meredith Thornton
Dyer Island Conservation Trust
Mammal Research Institute (University of Pretoria)