A sample of heart tissue from a Yukon king salmon infected with ichthyophonus sits under a microscope at the Alaska Department of Fish and Game laboratory in Anchorage on Aug. 17, 2023.
Scientists think many of these threats are connected to climate change. Ferguson studies one of them, a parasite named ichthyophonus, at the Alaska Department of Fish and Game lab in Anchorage. Often, infected fish look completely normal from the outside, but their flesh will have a spotted or patchy white pattern where the parasite is growing inside. Importantly, infected fish aren’t good to eat.
Salmon are cold-blooded, meaning they can’t regulate their internal temperature. When the river gets above 65 degrees Fahrenheit, that’s a problem. Jim Murphy is a NOAA fisheries biologist who has studied salmon at sea for 20 years. He said marine heat waves are disrupting the availability of salmon prey species. It’s not totally clear what’s happening at sea, Murphy said, but when he examines fish, one thing is clear: all salmon — but especially chum — are not getting enough to eat.