Nick Dulvy

Biologist Nick Dulvy’s research suggests that fish may be swimming deeper to avoid warmer ocean temperatures.

Climate change driving fish deeper: study

July 24, 2008

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By Stuart Colcleugh

A new study led by SFU biologist Nick Dulvy suggests that fish are responding to warmer ocean temperatures as a result of global warming not by moving northward as many experts predicted but by swimming deeper, to cooler waters.

Dulvy, a recently arrived Canada Research Chair in marine biodiversity and conservation at SFU, worked with colleagues at the Centre for Environment, Fisheries and Aquaculture in Lowestoft, England, to study bottom-dwelling, or “demersal”, species in the North Sea.

The shallow sea’s bottom temperature has increased about 1.6 degrees centigrade in the past 25 years. Dulvy’s team examined annual survey data on 28 demersal species during the same period to see how they responded to the warming water.

Their study, published online June 28 in the Journal of Applied Ecology, found that the fish had descended an average of nine metres to continue living at the same water temperature. Some species such as the megrim or whiff (Lepidorhombus whiffiagonus) flatfish descended as much as 35 metres.

“The deepening of North Sea bottom-dwelling fishes in response to climate change is the marine analogue of the upward movement of terrestrial species to higher altitudes,” Dulvy writes.

“The deepening of the demersal fish … in response to temperature could be used as a (biological) indicator of the effects of climate change in the North Sea and other semi-enclosed seas.”

What the downward migration of these fish means is still unclear, says Dulvy. It could mean they are simply adapting without declining in numbers or it could be a preliminary sign of major extinctions to come.

But over-fishing remains a far greater threat at this stage, says Dulvy. “Fishing has caused a massive decline in the biomass of large predatory fishes, but so far few marine species have been driven to extinction.

“There is still chance to develop, refine and implement sustainable management to minimize marine biodiversity loss while ensuring stable yields to the fishing industry and society.”
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