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Global warming threatens Atlantic cod stocks

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Atlantic cod are facing climate change pressure.

New study to take close look at climate impacts to commercially important cod fishery

By Summit Voice

FRISCO — With Atlantic cod already moving into waters around Spitsbergen — into Arctic cod territory — fisheries biologists are keeping a close eye the commercially important species to determine the consequences of climate-related migrations. Specifically, researchers want to how how the fish are responding to warmer and more acidic water, and at which stages of life the changes are most dangerous to them.

In the next two and a half years, biologists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, together with scientists from Kiel, Bremen, Düsseldorf and Münster, will study all life stages of the fish and their genetic patterns: from spawn and the development of the larvae, through the juvenile fish and their favorite food, the copepod, to the mature parent fish.

“ … Atlantic cod and Arctic cod feel the most comfortable in a specific temperature range. During the spawning season, for example, … Atlantic cod prefers temperatures of between three and seven degrees Celsius. By contrast, the Arctic cod breeds at temperatures of between zero to four degrees Celsius,” said Alfred Wegener Institute biologist Dr. Daniela Storch.

“If the temperature of the sea now increases due to climate change, the animals become stressed, a condition which is greatly exacerbated by the increasing ocean acidification. We suspect that these new environmental conditions will lead to the comfort ranges of both species becoming smaller and that the habitat of the fish will increasingly overlap. This means that the Atlantic cod can be expected to seriously compete with the Arctic cod,” Storch said.

Just which fish species has the best chances of survival will be investigated by the project members in complex behavioral experiments and during a four-week expedition.

“From mid August to mid September this year we will be fishing the fjords of the north, west and south coasts of Spitsbergen on the research vessel Heincke. We firstly wish to document where we find which species at this time of year. Secondly, we are interested in catching a great deal of fish which we will bring back alive to Bremerhaven and can then study in the over 100 new basins of our aquarium facility”, explained researcher Felix Mark.

The planned experiments include performance analyses in the ultra-modern flow channel and the two MRI scanners of the Alfred Wegener Institute in Bremerhaven.

“Using this apparatus we can not only look into the brain of the fish but even into its individual cells. We are able to recognize, for example, how its metabolism alters within the cells, how heart and blood circulation of the fish react to the rise in water temperature, at which pH value of the water the fish reaches its performance limits or in which way temperature and degree of acidification affect its senses”, Mark said.

Researchers know from investigations of tropical fish, for example, that their offspring have a reduced sense of smell as ocean acidification rises. As a result, young fish find it more difficult to return home and are more likely to become prey.

So are heat-shy Atlantic cod and its Arctic cousin facing a similar fate in view of climate change? Early lab results suggest the consequences could be serious.

“There are many signs that the water temperature plays an important role in the breeding of the cod. There was as virtually no life in those eggs fertilized in sea water at a temperature of twelve degrees”, said  graduate student Flemming Dahlke, reporting some of the earliest research results conducted at the Swedish research station of Kristineberg.

 

 

 

The researchers know from investigations of tropical fish, for example, that their offspring have a reduced sense of smell as ocean acidification rises. The consequence: the young fish find it more difficult to return home and are more likely to fall prey to others. So are heat-shy Atlantic cod and its Arctic cousin facing a similar fate in view of climate change? Flemming Dahlke’s first results are at least interesting: “There are many signs that the water temperature plays an important role in the breeding of the cod. There was as virtually no life in those eggs fertilised in sea water at a temperature of twelve degrees”, reports the phd student.

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