Kategorie: News
Round-headed dolphins form their own population
About 9,000 Risso’s dolphins (Grampus griseus), also known as round-headed dolphins, live in British waters - significantly more than the estimated 2,000 animals in the western Mediterranean. A new genetic study now shows that British dolphins rarely interbreed with their counterparts from the Azores, the Mediterranean, or the rest of the North Atlantic.
A team led by Nicola Hodgins of the Maritime Area Regulatory Authority (MARA) and the University of Exeter examined tissue samples from animals that had stranded along the coasts of England, Scotland, and Wales between 1992 and 2016. Analysis of nuclear and mitochondrial DNA revealed that British Risso’s dolphins form a distinct genetic unit, clearly separated from the nearest populations. “The results support the hypothesis that Risso’s dolphins in British waters have been isolated from other populations for some time,” Hodgins explained. She added, however, that not every neighboring region of the Atlantic had been sampled - so the exact boundaries of this unit have not yet been conclusively determined.
It is also striking that genetic diversity within the British population is comparatively low - lower than in populations in the North Pacific, the Azores, or the Mediterranean. This suggests a small founder population or a long period of isolation.
A Distinct Subpopulation in the Future
Within British waters themselves, the researchers found no clear genetic subdivision - the dolphins form a single, mixed gene pool. At first glance, this contradicts photo-identification studies from Scottish waters, which showed that fewer than three percent of individually identified dolphins were sighted on both the west and north coasts - the animals thus appear to remain loyal to specific regions throughout their lives. How this apparent site fidelity of individual animals can be reconciled with the genetic mixing of the overall population is one of the open questions the researchers identify for future studies.
This is certainly significant for conservation. The International Union for Conservation of Nature (IUCN) has already classified the Mediterranean population of Risso’s dolphins separately as “Endangered.” The study authors consider it possible that the British population could also be recognized as a distinct subpopulation in the future - with the result that it would need to be protected and managed in a more targeted manner than before. Currently, British Risso’s dolphins are treated as a single management unit, even though individual groups may be exposed to different pressures and use habitats differently.
The researchers emphasize that further studies are needed that integrate data on the animals’ behavior, appearance, migration patterns, vocalizations, and genetics. Only in this way will it be possible in the future to understand more precisely how Risso’s dolphins around the British Isles are actually interconnected, which habitats they prefer - and how their conservation can be most effectively managed.
Source: University of Exeter, phys.org, Journal of the Marine Biological Association of the United Kingdom