Global warming makes seal pups go hungry

Retreating ice in the Southern Ocean is making it harder for elephant seal mothers to feed their babies, say Australian researchers.Environmental scientists Dr Clive McMahon and Harry Burton of the Australian Antarctic Division in Tasmania say a warming climate is changing the ecology of the ocean, where the seals forage.They say this changing ecology, which has led to a drop in available seal food, is interfering with mothers' ability to feed their young to a healthy weight.And this has contributed to a dramatic decrease in the seal population over recent decades.The researchers report their findings online in the Royal Society journal Proceedings: Biological Sciences."Seals are acting as a very clear biological indicator of ocean health," says Burton, a senior research scientist who has been studying the southern elephant seals (Mirounga leonina) at Macquarie Island for decades.Burton says he first noticed a drop in numbers in 1985 when he found the population was half that of the 1950s. This, he says, is quite a significant drop for a long-lived marine mammal. The researchers have been following the seals every year during pup season, which is when the pregnant cows, or adult female seals, come ashore to have their pups and feed them.

For three weeks, the mothers lie on the beach while the pups suckle until they weigh three times as much as when they were born, says Burton."It's a remarkable phenomenon," says Burton. "You can see that nature has totally focussed itself on those mothers giving a huge investment into their pup."The researchers have found the heavier a seal pup is when it weans, the better its chances are of surviving.The researchers have mapped the decline in seal numbers against what is known about climate in the Southern Ocean and believe the decline is due to a fall in the amount of squid and fish available for the seals to eat.Burton says the fall in the seals' food supply appears to be linked to an overall decline in the amount of pack-ice covering the oceans in Antarctica as the climate warms.Less pack-ice changes the ecology of the ocean beneath, decreasing the amount of algae, plankton and krill that are the base of the food chain. And the researchers say that if the mothers don't get enough food themselves, they have less to give their pups.