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article imageOcean warming affecting inshore fish species

By Kimberley Pollock     Apr 18, 2011 in Environment
Australian scientists have reported the first known detrimental impact of southern hemisphere ocean warming on a fish species, the banded morwong.
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of Tasmania (UTas) have been monitoring the waters off Tasmania’s Maria Island since 1944 and their research shows that the surface water temperatures in the Tasman Sea have risen by nearly 2°C over the past 60 years. In a media release, the CSIRO says this is one of the most rapid warmings in southern oceans.
The scientists have taken a closer look at one particular species, the banded morwong (Cheilodactylus spectabilis), to assess the impacts of this temperature increase. The banded morwong are a sedentary temperate fish common on rocky reefs at 10–50 m depth along the southeastern coast of Australia and off New Zealand. The banded morwong was chosen because it is a particularly long lived species and can live to almost 100 years old.
According to CSIRO marine ecologist Dr Ron Thresher, a co-author of the study, the researchers used a similar process to measuring the growth rings in trees. They measured the bony structures fish use for orientation and detection of movement, called otoliths, which also have annual growth rings. Like the growth rings in trees, the otoliths can be counted to indicate a fish’s age and annual growth rate.
Sectioned banded morwong otolith showing growth rings
Sectioned banded morwong otolith showing growth rings
IMAS, University of Tasmania
The team analysed long-term changes in the growth rates of the banded morwong and the results showed that the growth rates of young adult banded morwong have increased significantly at four sample sites. The research team then compared their results with changes in temperature trends across the species’ distribution.
UTas researcher, Dr Jeremy Lyle, said in the media release, “They observed 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 species’ range in New Zealand waters.”
The researchers say their results indicate that the increase in temperature in waters off northern New Zealand is pushing the banded morwong to what they call its “physiological limits.”
“Warming temperatures tend to cause things to grow faster but there is a limit. If it gets too warm things begin to die. We haven't seen death yet but we're getting to that point. Conditions are getting so warm that the fish physiology just can't keep up," Dr Thresher said on the CSIRO website.
Dr Thresher also says that many of the affected fish species will move further and further south to avoid the warm water and that this will bring about large ecosystem changes.
The research was published last week in the online journal, Nature Climate Change.
More about Global warming, Ocean warming, Warming oceans, banded morwong, Fish decline
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