Warmer waters and climate change - a challenge to fisheries
Friday 9 November 2018
The world is warming – by an average one degree Celsius since the late 19th century – and the oceans are feeling it.
Ocean temperatures are rising more rapidly than previously calculated, according to Princeton University geoscientist Laure Resplandy in a study published in Nature journal.
More than 90 percent of the excess energy trapped within the world’s atmosphere is absorbed by the oceans.
Scientists have found that ocean heat has increased at all depths since the 1960s, while surface waters have also warmed.
There was certainly evidence of that in our waters last summer to an unusual degree.
Parts of the Tasman sea were like a bath. Warmer water species like snapper and kingfish extended their range well south, as far as Fiordland and Southland.
In Australia, increasing drought on land (except in Melbourne on Cup day) is impacting on the oceans as well.
Catches of popular species like prawns, bream, swimmer crabs and mud crabs which spend part of their life in estuaries, which in turn rely on good rains and flushes of freshwater, are down in NSW.
“Drought and climate change also impact the ocean; it’s just not as visible when it’s at sea,” Seafood Industry Australia (SIA) chief executive Jane Lovell said.
The SIA has called on the Federal Government to extend financial support available to land-based farmers to wild catch fishers.
In the US, dramatic shifts in some species’ distribution are having a profound impact on livelihoods and cultures.
The summer flounder fishery in North Carolina has all but disappeared, not as a result of overfishing but of the fish moving north to cooler waters.
Long established fishing communities have become ghost towns as a result.
An epic dislocation appears to be under way.
In the US North Atlantic, at least 85 percent of the nearly 70 species tracked by federal authorities have shifted north or deeper, according to a Reuters analysis of fisheries data.
Striped bass have disappeared too from North Carolina but are now routinely found in Canadian waters, which was unheard of a generation ago.
So what to expect for our climate this summer?
The National Institute of Water and Atmospheric Research (NIWA) is predicting the slow emergence of a moderate to weak El Nino climate system, which could persist through autumn and even into the following year.
El Nino typically produces more rain in the west of the country, more westerly wind and drier conditions on the east coast. In winter, colder southerlies tend to prevail.
The last such pattern was in 2015-16.
Last year’s unprecedented marine heatwave is not expected to be repeated.
Even so, seas are up to a degree above average along our coastlines, with December ocean temperatures expected to be near where they would typically be in January.
Over the past month, sea surface temperatures in the central Pacific have warmed notably, increasing from 0.25C warmer than normal in September to 0.75C above normal.
Such fluctuations can have a marked impact on fish spawning and distribution.
NIWA has some powerful new tools to help assess climate changes in the form of three new supercomputers capable of assessing massive amounts of data in seconds.
A $23 million high performance computing facility was opened this week, with two supercomputers at NIWA in Wellington and a third at the University of Auckland.
Whether the fisheries management system is nimble enough to respond to ocean changes and possible resultant altered distribution of stocks is another matter.
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