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Jul 28

Antarctic Fur Seal Threatened With Extinction

Fur seals vs Penguins

A King penguin stands his ground against two Antarctic fur seals

Scientists have found Antarctic fur seals, ruthlessly hunted to the brink of extinction more than a century ago, are now facing a new threat from food shortages caused by climate change.

According to a 20 year study, the effects of climate change are so severe that even the genetic make-up of the population in the South Atlantic is being affected and there is a direct link between genetics and krill, the main source of food for the species.

Female fur seals living on South Georgia Island with only a certain combination of genes are surviving long enough to breed. According to scientists, these seals are breeding later in life and less frequently than seals in previous years with a different genetic constitution.

Dr Juame Forcada, the lead author of the study is quoted as saying “Compared with 20 years ago, we can see that female fur seals are now born with a lower weight, those that survive and return to breed tend to be the bigger ones and they have their first pup later in life than they used to,”

“Such changes are typically associated with food stress. An important food source for the seals is Antarctic krill. Decades of data collected at South Georgia show how changes to the seal population have occurred over time with changes in krill availability,”

Genetic testing has shown that female fur seals with a diverse combination of genes from both parents – known as heterozygosity – are surviving longer than females with a low level of genetic diversity, known as homozygosity.

Normally, heterozygosity is associated with evolutionary genetic fitness as individuals are better at surviving, but this is not longlasting as the trait results from the random recombination of genes and is not uniformly passed down the generations like other inherited traits, the scientists said.

Finding an increase in genetic heterozygosity might suggest that the seals are responding well to environmental pressures, but in fact the reverse is probably happening and is a worrying symptom of a population that is once again in decline, they said.

Joe Hoffman of Bielefeld University in Germany, the study’s coauthor said “We found that over the last two decades, the proportion of breeding females that are highly heterozygous has increased, as these individuals are more likely to survive the changing conditions,”

“Strong selection by the environment can drive rapid evolution.” he continued “However, in this case the seals do not appear to be evolving because surviving females do not pass their high heterozygosity on to their offspring,” .

“With each new generation, the process of selection has to start all over again, with only those individuals that happen to be born more heterozygous having a good chance of survival. As the climate continues to change, many fur seal pups are not surviving to adulthood and the population is declining,”

The scientists add that the availability of krill, a shrimp-like crustacean, is becoming more varied as a result of the changing climate in the region. Warmer waters and melting ice.are having a direct impact in the numbers of krill found within the fur seals’ hunting grounds.

“Our results provide compelling evidence that selection due to climate change is intensifying, with far-reaching consequences,” they concluded in their study.

Oxford zoologists Tim Coulson and Sonya Clegg warned in a commentary article that the findings suggest that it may be much harder to arrest the ongoing decline of the Antarctic fur seal in the 21st Century than it was in the last century.