Warming oceans moving fish south

A landmark report on the impact of climate change on Australia’s oceans has found more tropical fish species are likely to be seen in the Capes region as ocean temperatures rise and extreme climate events become more frequent.

Compiled by an author team representing 34 universities and organisations and funded by the Federal Government, the Marine Climate Change Report Card 2012 suggests climate change is already having an impact on Australia’s oceans and marine ecosystems.

Co-author Nick Caputi from the Department of Fisheries invertebrate branch said one of the report’s observations was tropical fish species had been found further south in WA as a result of the strengthening of the warm, southflowing Leeuwin current.

“What we’ve had over the last 20 years is a gradual strengthening brought about by a couple of strong La Nina events in 2008 and 2010/ 2011 resulting in a strong flow south and as a result of this a lot of tropical species came south,” Dr Caputi said.

“The Spanish mackerel is a good example. It was strongly counted in Rottnest and even down in (Busselton).”

The strengthening of the current was partially responsible for a two to four degree temperature increase off the WA coast in early 2011, described in the report as an “unprecedented marine heat wave”, which affected the local abundance and distribution of marine life.

Dr Caputi said it was hard to predict whether the strengthening of the Leeuwin Current and the resulting heat wave were caused by climate change, but they fitted with predictions of more frequent extreme climate events.

He said an example of how rising sea temperatures affected marine species could be found in the western rock lobster population, which was experiencing smaller sizes of migrating immature lobsters.

“The size of the breeding female has (also) been smaller in recent years and we believe this is linked to water temperature,” he said.

However, Dr Caputi said climate change may also positively affect marine life and should not be viewed on wholly negative terms.

“Climate change is not all negative impacts on fish. It’s a case of trying to identify possible winners and losers and managing them accordingly,” he said.