Too Hot to Swim: Global Warming Impacts Large Reef Fish

Climate change is impacting species across the globe. Perhaps one of the most drastic effects of this change, though, is warmer temperatures. Now, scientists have discovered that ocean warming may make some large reef fish more sluggish and less likely to swim, which could have drastic impacts on both the environment and fisheries.

Fish rely on swimming for almost all activities necessary for survival, from hunting for food to finding mates. So what happens when it's simply too hot for fish to make the effort? And at what point do fish deem it too hot? In order to find that out, the researchers looked a bit closer at temperature and fish behavior.

The scientists focused on understanding the impact of global warming on the commercially important fish species, coral trout. In the end, they found that increasing ocean temperatures may cause large fish to become lethargic and that they spend more time resting on the bottom and less time swimming in search for food or reproductive activities. Even when individuals do muster up enough energy to swim around, they swim at a much slower rate. This lower activity is likely to directly impact their ability to catch food or visit spawning sites.

"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," said Jacob Johansen, one of the researchers, in a news release.

That's not to say that it's all bad news, though. There was some evidence that coral trout may be able to adapt to increasing temperatures. Populations from the northern region of the Great Barrier Reef were better off than southern populations at tolerating these warmer conditions. Even so, it's important to take these warmer temperatures into account when setting fish catch limits in the future.

"Coral trout is one of the most important fisheries in the South-East Pacific," said Johansen in a news release. "If we want to keep this fishery in the future, it is critical that we understand how global warming may impact the species. This will allow us to develop management plans that will help to keep the species, and its fisheries, healthy."

The findings are published in the journal Global Change Biology.