On a golden morning in early October, two graduate students from New Mexico State University plunge into the icy current of Leandro Creek. The small waterway flows through the 550,000 acre Vermejo park ranch, a reserve in the Sangre de Cristo Mountains, and the pair are in search of an unusual fish.
Kelsie Field, 25, from the Department of Wildlife and Conservation Ecology, wears a pair of worn grey waders and carries two eight-gallon buckets, one full of water, the other, of scientific gear: test tubes, an electronic scanner and surgical implements. Michael Miller, 30, shoulders a large, waterproof backpack containing a battery attached to an electrode that resembles a metal detector.
Miller dips the “detector” into the creek, squeezing the handle to send approximately 300 volts through the water. While the team’s rubber boots insulate them from the shock, the resident fish are stunned and drift to the surface just long enough for Miller to net them and deposit them in the bucket. Most measure about 10 inches, though some are no larger than a little finger and a few stretch to 16 inches or more.
There are just two species here. One is an embattled native, the Rio Grande cutthroat trout (Oncorhynchus clarki virginalis), distinguished by its cream-coloured skin, mottling of black spots and a vibrant orange slash under the jaw. Once widely distributed in rivers and streams across northern New Mexico and southern Colorado, it is now found across just 10% of its historical range. Today, it is reeling under the pressures of the climate crisis, habitat loss and – in the case of Leandro Creek – a hardy intruder.
Read Prof. Sandler and other experts discuss the ethics of invasive species in The Guardian.