As oceans warm across the planet, one species of fish is escaping the heat by swimming deeper underwater.
For up to a year, scientists at James Cook University monitored the behavior of Redthroat emperor fish (Lethrinus miniatus) around Heron Island in the Great Barrier Reef. After being tagged with transmitters, the fish have been shown diving beyond the reef slope they normally inhabit.
After considering such factors as changes in temperature, rainfall, wind and moon phases, the researchers concluded that the only significant correlation in the species’ deeper-than-normal diving was to days that were significantly warmer.
“Individuals occurred more often on the reef slop during days of cooler temperatures,” according to the study, “suggesting a thermal tolerance threshold may exist.”
While some US politicians debate the science of global warming, scientists have consistently shown that the globe’s temperature is not only increasing, its ocean temperatures are increasing even faster.
According to Dr. John Abraham, professor of thermal sciences at the University of St. Thomas, oceans are in fact warming so quickly that they are “breaking scientists’ charts.”
In July, NASA published a study that shows much of the Earth’s excess heat is accumulating in the Pacific and Indian Oceans, which are effectively functioning as thermal absorbers.
Thus it’s not surprising that the Redthroat emperors are “shifting their position in the water column to remain at a preferred temperature,” as the JCU scientists write.
Lead researcher Dr. Leanne Currey told Phys.org that this is an important area of research, as previous studies on the effect of ocean warming on fish has largely focused on their biology, not how species are redistributing themselves to adapt to the new normal.
“This is a commercially important fish and we are looking at a significant depth shift,” she said.
In 2013, JCU researchers noted that warming waters may also affect overall fish behavior. As the water warms, fish become more lethargic, reducing their ability to swim, grow and reproduce.
“The loss of swimming performance and reduced ability to maintain important activities, like moving to a spawning site to reproduce, could have major implications for the future distribution and abundance of these species,” researcher Dr. Jacob Johansen told Phys.org.
As waters continue to warm, various marine species may end up in very different regions than they’ve historically been found. Some Redthroat emperor have been caught off the coast of Perth, which is south of their traditional region. In her interview, Dr. Currey noted that, though the Redthroat emperor can survive at a depth of 160 meters, it may migrate south in lieu of permanently inhabiting the deeper water column.