Global warming

is killing eelpouts by heating the ocean. They cannot breathe.
"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."
[snip]

"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. "