Warming seas affecting fish size, Trinity scientist warns

There is now concern that the consequences of rapid and variable responses of fish size to climate warming might be potentially greater than if all species were shrinking.

Warming seas are affecting fish sizes in a way that could upset complex ocean food webs, scientists have found.

Co-author of the report, zoologist Nicholas Payne from Trinity College Dublin, said they were surprised by the results.

Prof Payne said that up to now, much of their understanding of the “temperature/size” relationship came from the laboratory.

“Taking our predictions to the wild, shows us there is still a lot we still need to learn about this hugely important phenomena,” he said.

A team of scientists analysed 10m visual survey records of 335 fish species in coastal locations in Australia and spanning multiple decades.

The study, published in Nature Ecology And Evolution, puts a line through the hypothesis that fish sizes would reduce as temperatures increased.

In general, but not universally, larger species tended to get even bigger in warmer waters, while smaller species tended to get smaller.

Around 55% of fish species were smaller in warmer waters, while 45% were bigger.

The research also underlined that fish size changed between 4% and 40% for every one-degree change in temperature.

Ocean temperatures are set to rise between 1.2C and 3.2C by 2100 and the effects are expected to be very significant.

Lead study author, Asta Audzijonyte from the University of Tasmania, said the research would help in forecasting how different species will respond to future warming of the oceans.

There is now concern that the consequences of rapid and variable responses of fish size to climate warming might be potentially greater than if all species were shrinking.

Meanwhile, Australia’s Great Barrier Reef has experienced its most widespread bleaching event on record, with scientists blaming global warming.

The latest bleaching was observed in an aerial analysis conducted by scientists from James Cook University and the Great Barrier Reef Marine Part Authority.

They found that coastal reefs along a stretch of about 2,300km from the Torres Strait in the north to the reef’s southern boundary have been severely bleached.

Director of the ARC Center of Excellence for Coral Reef Studies at James Cook University, Terry Hughes, said that they were shocked at how quickly the bleaching occurred.

“Three severe bleaching events in five years is not something we anticipated happening until the middle of the century,” he said.

Corals become stressed when the water is too warm and expel the algae living in their tissues which is their main energy source, causing them to turn white and die if temperatures remain high.

Earlier this year many reefs experienced temperatures that were 3C above the normal summer maximum.