TASMANIA, Australia — A shaded creek winds through fern forest along the Lilydale Falls Trail in northern Tasmania. As hikers pass by, researcher Todd Walsh reaches into the slow-moving water and beneath a rock to pull out a juvenile giant freshwater crayfish caught in one of his live traps. In streams like this one, he says, present day temperatures rarely climb above about 21° Celsius (69.8° Fahrenheit). “The lethal temperature seems to be about 23°[C, or 73.4°F] for these guys,” says Walsh, an independent crayfish expert who has studied the animals for decades and is known locally as the “Lobster Man.” Walsh says he has encountered a few other Tasmanian creeks reaching 25-26°C (77-78.8°F), which would exceed the species’ apparent thermal limits, and he hasn’t found any crayfish in those streams. Crayfish expert Todd Walsh checks a live trap in a shaded stream in northern Tasmania, where cold, forested waterways provide critical habitat for the giant freshwater crayfish. Image by Stefan Lovgren. A juvenile Tasmanian giant freshwater crayfish. Few survive to adulthood, making the loss of habitat for young individuals a major threat to the species. Image by Stefan Lovgren. The Tasmanian giant freshwater crayfish (Astacopsis gouldi), also dubbed the giant freshwater lobster (even though it’s not a lobster), is the largest freshwater invertebrate on Earth, capable of growing up to a meter long (more than 3 feet) and living for decades. It occurs only in northern Tasmania’s cool, forested river watersheds — habitat that has remained colder and wetter…This article was originally published on Mongabay

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