Even giants of the oceans deserve gentle care
Whale populations have only recently begun to recover from commercial whaling, but a new factor is already beginning to threaten them: global climate change. And this is not just speculation – the impact is being felt in reproduction and population genetics. Petra Nevečeřalová and Pavel Hulva from the Department of Zoology at the Faculty of Science of Charles University have conducted genetic research on one of the largest mammals on Earth. Together with an international team of scientists, they used non-invasive methods of collecting samples for DNA analysis. Their project aimed to describe the population structure of southern right whales (Eubalaena australis) and the population changes of the species in recent decades.
More than 150,000 individuals of this oceanic megafauna have been killed during the whaling era. Intense whaling has driven some species almost to the brink of extinction. Since the ban on whaling in 1971, the recovery of cetacean populations has been fairly successful. With an approximate annual growth rate of 7% (for about half of all cetacean species), whale populations are slowly returning to their original numbers. Unfortunately, with the new era, often referred to as the Anthropocene, which is characterised by human-induced changes affecting the planet, comes a threat to living organisms. Whales, like numerous other species, will not escape the impact of global climate change.
Cetacean genetic sampling usually involves taking skin biopsies, which is done remotely using a crossbow and is considered a mini-invasive technique (subject to ethics committee approval). However, for this project, the researchers primarily used gentle, non-invasive (i.e. non-intrusive) methods to obtain the samples. Naturally exfoliated skin (epidermis) from whales was used for DNA isolation. Southern right whales spend a substantial amount of time at the surface of the water and often get a tan – consequently the upper part of their skin naturally starts to peel off, just like it does in humans. Also contributing to the flaking is the change in water temperature and salinity as they migrate from the cold waters around Antarctica to the warmer coastal waters of the African continent. The scientists worked with local whale-watching companies, whose boats were used to collect samples to ensure minimal disturbance to the animals. A marginal number of samples were thus collected on commercial cruise ship trips during the Southern Hemisphere winter of 2016–2018, primarily in the Gansbaai, Walker Bay area of South Africa. Skin pieces were collected from the water using a collection net and then transferred with sterile tweezers into a tube containing 96% ethanol. This preserved them safely and prevented contamination before analysis.
Current estimates indicate that South Africa hosts the largest ever population of southern right whales, numbering approximately over 6,100 individuals. However, a recent study reports that despite a population boom in the 1990s, the increase in numbers once again began to decline around 2010 and is currently stagnant. For example, following genetic analysis of the samples obtained, the researchers concluded that inbreeding – which reduces population variability – is almost doubling. This may be due, for example, to changes in feeding ecology. Our scientists are also the first to describe genetic samples from Namibia, where the population has been completely eradicated.
The main outcome of the study is to show that monitoring cetacean populations, essential for conservation, is possible through non-invasive sampling within non-scientific platforms such as commercial whale watching. The researchers encourage the use of the same or similar non-invasive methods in future studies that minimally interfere with the lives of animals. They also stress the importance of future research on whale populations. Unfortunately, the observed population changes coincide with changes in feeding ecology and a decline in reproduction in the South African whale population, which likely reflects a large-scale restructuring of feeding ecology. Indeed, with the Anthropocene era comes changes in zooplankton availability, which is also reflected in changes in migration that probably extend beyond marine mammals.
Tereza Žirovnická
Published:
Apr 17, 2023 10:40 AM
Document Actions
