University of British Columbia scientist William Cheung has documented a gradual shifting of some fish species further north than their typical ranges. Some tropical commercial species are being found by fishing boats in waters near New England. Ocean water in the tropics is becoming too warm due to climate change, so they are seeking cooler places.
If tropical waters continue to increase in temperature, habitat for local fish will shrink and they may not be able to inhabit their customary ranges. If more tropical commercial fish move away, local economies could be damaged because there will be reduced catches. (In addition, damage from rising seas will undoubtedly have some negative impacts in coastal areas and island communities.)
Northern areas actually may benefit somewhat, at least in terms of an influx of fish, but what will happen to their native fish populations? If ocean water is increasing in temperature by almost two degrees per decade, many fish species may be unable to live in their normal habitats.
A separate study in 2012 found that even a two-degree increase in Antarctic waters could cause the extinction of local fish species.
“The development of polar climatic conditions that shaped the [evolution] of Antarctic fish is now reversing. The increasing temperature of the Southern Ocean, with the potential for the arrival of invasive species and disruption of food webs, is the greatest threat to the survival of this unparalleled [diversity], explained Yale Associate Professor Thomas Near. (Source: Yale University)
Of course, these fish species did not evolve independently of other animals in their habitats. If there is a sudden die-off of fish species due to increasing water temperatures, many other creatures could be impacted severely throughout the food chain.
Fish are one of the most important food sources for humans, and the collapse of commercial fisheries without an immediate fix, would likely be very damaging to regional and even national economies. At the same time, ocean acidification is damaging reef systems, which also causes fish declines.