Here are extracts from the conversation with Dr Joe Hoffman of the Department of Animal Behaviour at Bielefeld University, who co-authored the paper with Dr Jaume Forcada of the British Antarctic Survey. 

You’ve been studying the Antarctic fur seals in the South Atlantic Ocean. As I understand it, you’ve been tracking physical changes and behavioural changes in the seals. What’s the significant change in the fur seal population that you’ve monitored? 

“First of all, we’ve monitored the climate, and we’ve monitored a measure called the Southern Annular Mode or SAM [an index which measures climate variation].

“SAM has become progressively more positive with every year [that passes], and since the early 1990s it’s been locked in a positive phase. When SAM is positive, that’s associated with an increase in storms in the South Pacific.”

What is SAM exactly?

“It’s a primary pattern of climate variability. Essentially, when SAM is high, there are more winds, and those winds cause storms in the South Pacific. This locally reduces the sea ice around south Georgia, where the seals are breeding.”

Does that have an effect therefore on the food that is available to the seals – what does it do to them?

 “The Antarctic fur seals feed almost exclusively on Antarctic krill. This is a shrimp-like organism that actually uses the sea ice as a nursery.

“So that means when the sea ice is locally reduced, there’s less food available for the seals. “

And that presumably affects their ability to breed or how likely the pups are to survive?

“Exactly. Over a 30-year period, we’ve shown that the numbers of adult females breeding within this study colony have gone down by 24 percent overall. From year to year, there are also fluctuations in the numbers of breeding females.

“We’ve constructed a statistical model that shows that the numbers of females are very accurately predicted by SAM, and also by the availability of krill. This suggests that the female numbers are responding to climate change via changes in local food availability.”

Krill (Photo: BAS)

If the fur seals are being affected so dramatically by the availability of the krill, which in turn depends on the ice, and if all this links to climate variability, presumably the whole ecosystem must be affected in some way?

“We believe this is probably the case, because Antarctic fur seals are actually a wonderful indicator species for the health of the Southern Ocean ecosystem as a whole. The reason for that is that the fur seals feed on krill. But so do all the other predators. So that includes penguins, albatrosses, whales, and lots of other fish species.”

If you take the fur seals out of the equation, or their numbers are drastically reduced, presumably that may be bad news for the krill, but is it bad news for some other animal?

“It’s unlikely to be good news for any organisms because all of these predators are feeding on the krill. So if krill numbers are going down, then fur seal numbers are going down, but also it’s highly likely that the numbers of other predators will also be going down because their food source is also reduced.”

You’ve also been studying the strengths and weakness of different females within the population. What have you learned there about the females who are most likely to be successful at breeding?

 “What we’ve done is we’ve followed almost 400 individual females that were born within the study colony. They were fitted with a small subcutaneous tag, a bit like the ones that your pet cat or dog has. These allowed us to follow these females through their life histories, to see if they lived long enough to breed within the colony and whether they bred successfully or not.

“We found that females who had higher heterozygosity were more likely to survive and breed than those who had lower heterozygosity. 

“All sexually reproducing organisms inherit two copies of every gene – one from the mother and one from the father.

“If an individual is heterzygous it inherits two different copies from the mother and the father – two different versions of the gene. If an individual is homozygous, it inherits identical copies of the gene.

“In general, an individual who is heterozygous has much higher variability across its genome.

“Heterozygosity tends to be correlate positively with fitness traits such as survival, the ability to resist parasites and disease, and reproductive success in many different species. And that’s exactly what we find in the fur seals.

To hear the full interview please click on the Play button under the main photo