Antarctic fish set to survive warmer seas

By SIMON COLLINS

A former optometrist has shattered a long-held belief that Antarctic fish will not be able to adapt to global warming.

Cara Lowe, who switched to studying Antarctic fish because optometry "really wasn't challenging enough", found that the cold-adapted Pagothenia borchgrevinki could keep swimming long distances in water up to 9C warmer than their current conditions.

Her findings mean that this fish could survive even if global warming completely melts the Antarctic icecap.

"I was very surprised," she said.

All previous research has suggested that, because the water temperature in Antarctic waters has been stable at minus 1.9C for the past 14 million years and varies by less than 0.3C during each year, the fish in the region are probably unable to tolerate any big increase in temperature.

Researchers in the Arctic have found that some cold-adapted cod species have disappeared from parts of the Greenland coast in the past 10 years because of global warming.

But Ms Lowe, who is writing her doctoral thesis on the subject, told the New Zealand Antarctic Conference at Waikato University yesterday that those previous studies looked only at the effects of temperature on short bursts of fast swimming, which fish can do without taking in extra oxygen.

She has done longer-term research on the effects of warming on prolonged swimming, which requires oxygen.

She and her supervisor, Canterbury University's Dr Bill Davison, caught borchgrevinki through a hole in the ice, then kept them for five weeks in tanks at New Zealand's Scott Base at water temperatures of either minus 1C or plus 4C. They then tested the fish in a "swim tunnel" at various temperatures.

As expected, they found that the swimming performance of the fish that had been kept at minus 1C declined rapidly at higher temperatures. Their heart rates jumped simply to cope with the heat, so they had no energy left for swimming.

But unexpectedly, the fish that had been habituated to 4C for five weeks coped well when they were put in the swim tunnel at even higher temperatures. They had adjusted their heart rates during those five weeks to pump at a slow rate at 4C, so they still had energy to swim.

"The 4C-acclimated fish have a 9C thermal tolerance range - three times the fish acclimated to minus 1C. So it does look as though these fish have not lost the ability to acclimate when things warm up," Ms Lowe said.

Educated at Waikato Diocesan School, she studied optometry at Auckland University and worked as an optometrist for six years in Palmerston North and Christchurch before switching to biology. "I'm fascinated by physiology," she said.

She had not planned on studying fish, but people recommended Dr Davison to her. "It involved visits to Antarctica. It was hard to resist," she said.

Another speaker at the conference, Dr Nancy Bertler from Victoria University, reported that the Lower Victoria Glacier, which runs from the Trans-Antarctic Mountains down to the Ross Sea, was retreating by 12cm a year - confirming that the region was getting warmer.

Previous US research had found that the Ross Sea area below New Zealand was actually getting colder, even though there was clear evidence of global warming on the other side of Antarctica below South America.