BEIJING, Jan. 5 (Xinhuanet) -- Recently completed research reveals warmer oceans caused by global warming is making it more difficult for eelpouts to breath and survive.
Biologists have known for years declining fish stocks are connected to global warming, but a new study of eelpouts -- big-headed fish that resemble eels -- is the first to go deeper and see how warmer seas are connected to how fishes take in oxygen.
Scientists at the Alfred Wegener Institute for Polar and Marine Research in Germany studied the relationship between sea temperature and eelpouts counts in the Southern North Sea, combining data from the field with lab investigations of eelpout physiology.
The researchers not only found the oxygen levels in the waters of the North and Baltic seas have dropped because of increasing temperatures over the past 50 years -- a factor that reduces fish populations -- they also discovered eelpouts need more oxygen in warmer waters, a second factor that is reducing their numbers.
A key factor in the diminishing size of fish stock is increased difficulty in absorbing oxygen via respiration and blood circulation caused by the warming waters.
The study, published in the Jan. 5 issue of the journal Science, also noted the population of eelpouts dropped as average summer temperatures increased. The impact was also observed in the short term such that eelpout numbers decreased the year immediately after a warm summer.
Animals tolerate a limited range of environmental conditions. Anything out of their tolerance window can cause damage. Fish in the North Sea have evolved to tolerate a wider range of temperatures than fish elsewhere because of the large seasonal fluctuations there.
However, warming waters and their impact on oxygen supply can stress fish to the point their thermal tolerance range is thrown off and they perish, the scientists said.
In the future, eelpouts could prove to be important bioindicators that would help experts assess what might happen to other marine species in the region, the scientists explained.
Worldwide, warming waters can be expected to strain species that require lots of oxygen, forcing them to either relocate to cooler waters or face extinction, the authors write.
(Agencies)
