Dolphin whistles used to estimate population size

AN INTERNATIONAL team of scientists has successfully used the whistles of bottlenose dolphins living off the coast of Namibia to estimate the size of their population and track their movement, Stellenbosch University and the University of Plymouth said yesterday.

In a joint statement, the two institutions said the research marks the first time acoustic monitoring has replaced the traditional photographic mark-recapture method in estimating dolphin numbers.

Researchers now want to see if they can refine the technique so it can be used to track other species such as the endangered humpback dolphins.

“The capture-recapture of individually distinctive signature whistles has not been attempted before,” said Dr Tess Gridley, co-director of Sea Search, a non-profit scientific organisation that conducts research in the marine realm, and the Namibian Dolphin Project. Gridley is also a post-doctoral fellow at Stellenbosch.

“The dolphins use these sounds throughout life and each has its own unique whistle. Therefore, by recording signature whistles over time and in different places we can calculate where animals are moving to and how many animals there are in a population,” she said.

The Namibian Dolphin Project has been researching the country’s bottlenose dolphins for the past 12 years, compiling a catalogue of more than 55 signature whistles.

From the day they are born, bottlenose dolphins produce high frequency whistles and in the first year of life these develop into individually distinct signature sounds, with each animal having its own unique call throughout life. Signature whistles act like a name and help animals stay in contact and communicate under water.

The Namibia Dolphin Project operates in the towns of Walvis Bay and Luderitz and is managed as part of Sea Search. It involves scientists and specialists from various South African and international universities and institutes. |