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Sardine, anchovy and mackerel migrate north due to ocean warming

Sardine school. (Photo: Stock File)

Wednesday, February 18, 2015, 23:10 (GMT + 9)
The continuous increase in water temperature is altering the structure and function of marine ecosystems worldwide. In the North Atlantic Sea, the effect is even greater, since the average temperature increased up to 1.3°C over the last 30 years.
The warming of ocean water is causing the appearance of fish species, peculiar to the Iberian Coast, in theoretically colder latitudes, as in waters close to Norway, the North or the Baltic Sea.
In early September, experts from the International Council for the Exploration of the Sea(ICES) said they had detected a spike in recruitment of hake near Norway, where its presence was testimonial before. Now a research, which has analyzed 57,000 fish census for 40 years, has just revealed that the warming of ocean water causes pelagic species such as sardines, anchovies, mackerel (or xarda) and horse mackerel to migrate to northern latitudes, as the North Sea or the Baltic Sea.
Until now, researchers had not been able to test whether the observed changes in the physiology of these species were the result of variations in plankton communities, their main prey - which global warming have changed their distribution and abundance - or whether they were direct consequence of the rise in water temperature.
The new study, published in Global Change Biology, highlights the importance of the second hypothesis as ultimately responsible for catch sub-tropicalization in the North and the Baltic Seas. This explanation is because sardines and anchovies have been caught "even entering the Baltic Sea," where herring and sprat are moving back, Ignasi Montero-Serra, researcher in the Department of Ecology at the University of Barcelona and study’s lead author, said to SINC scientific news agency.
The research, which is the first to be conducted at broader spatial and temporal scale, makes it possible to understand the dynamics of these species in relation to the rapid warming of the oceans that has been occurring since the 80s.
The results reveal that sardines and other fish - which have rapid life cycles, planktonic larval phase and low habitat dependence - are highly vulnerable to changes in ocean temperature, and therefore represent "an outstanding biomarker for measuring the direction and rate of climate change expected in the near future,” Montero-Serra explained.
These pelagic species, besides having a high commercial value, play an important role in marine ecosystems and, according to the researchers, changes in this important ecological group “will impact on the structure and functioning of the entire ecosystem."

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