Fish growing faster as seas warm up

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Some species of Australian marine fish are growing larger and faster than ever before as sea temperatures continue to rise, experts have announced.

Scientists from Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) observed changes in growth rates in several coastal and long-lived deep-ocean fish species in the south west Pacific, which they believe are linked to changes in sea temperature rises and wind shifts.

"We have drawn correlations between the growth of fish species related to their environmental conditions - faster growth in waters above a depth of 250 metres and slower rates of growth below 1000 metres", said lead author Dr Ron Thresher.

Thresher says that the observations suggest that climate change has enhanced some elements of productivity in shallower waters, but also reduced the productivity of deep-oceans, as well as potentially making them less resilient.

The results are based on a study of fish earbones, or otoliths, which contain a detailed series of growth rings, like those also seen in trees and fish scales. When examined under a microscope, the rings can be used to age fish with surprising accuracy.

By comparing the date rings on otoliths to historical records of sea temperatures the team were able to determine how fish growth rates have changed as sea temperatures have risen over the past 60 years.

Over 555 fish were examined, which ranged in age from two years to 128 years. The results showed that coastal species, such as Morwong in the mid 1990s were 28.5% faster than they were in the mid 1950s, when they study started.

In deeper waters of 500-1000 m deep, there was little difference in the growth rates of the fish species.

Thresher believes that there's a link between temperature rises and the apparent change in growth rates.

Water temperatures in the south west Pacific east of Tasmania have risen by nearly two degrees. There has also been a southward shift in South Pacific zonal winds, which has strengthened the warm, poleward-flowing East Australian Current.

"Modelling suggests that, with increasing global warming, temperatures at intermediate depths are likely to rise near-globally", said Thresher. "This could mean that over the course of time, the decrease in growth rates for deep-water species could slow or even be reversed."