Global warming negatively affects fish

Rapidly warming ocean temperatures are pushing some fish species to the limit by stunting their growth, increasing stress and raising the risk of death.

An Australian study, published in the journal Nature Climate Change, focused on the long-lived fish species called the banded morwong in the Tasman Sea, between Australia and New Zealand.

Scientists, using long-term and current data, found that the morwong’s growth in some areas has been slowed by a spike in sea surface temperatures of nearly 2°C over the past 60 years in the Tasman Sea, one of the most rapid increases in the southern hemisphere’s oceans.

The results extend to commercial fisheries, as seas heat up and become more acidic, affecting coral reefs and multi-billion dollar fisheries dependent on them.

Generally, cold-blooded animals respond to warming conditions by boosting growth rates as temperatures rise, said marine ecologist Ron Thresher of Australia’s state-backed research body the CSIRO. But there was a limit.

Some species, though, such as tuna, are far more mobile and are moving further south into cooler waters.

Thresher and his colleagues used data on the morwong going back to 1910 that focused on bony structures called otoliths. These have annual growth rings that are similar to growth rings in trees.

Studying data from samples of the species in the Tasman Sea, they found increased growth for populations in the middle of the species’ range in Australian waters where temperatures have increased, but are still relatively cool.

But growth slowed with rising temperatures at the warmer northern edge of the range around New Zealand.

The scientists found that the drop in growth could be related to higher stress levels from rising temperatures, increased oxygen consumption and a drop in the ability to swim for long periods.

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