Here's the thing about extinctions: They are very rarely witnessed. The last members of a species in the wild tend to go quietly into the night with no one to witness their deaths. All too often, humans don't even notice that a species has disappeared until years—if not decades—after the fact. Even then, conservationists tend to hesitate before declaring that a species has gone extinct, preferring to search for signs of life until hope is pretty much exhausted.

Hope has been exhausted for the Scioto madtom (Noturus trautmani). Unseen since 1957, the small catfish has now been listed as "extinct" on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, following decades of fruitless searches. The madtom was the only extinction out of more than 430 species updates published to the Red List last week.

Even when the species was alive, sightings of the Scioto madtom were rare, possibly due to their blink-and-you'll-miss-them size (between 35 and 61 millimeters). Sightings of the species were recorded only 18 times; each happened within a single stretch of Big Darby Creek, a tributary of the Scioto River in central Ohio. Little was ever known about the fish's ecology or behavior.

Its rarity, however, was enough to get the madtom protected under the U.S. Endangered Species Act back in 1975. Biologists then spent years looking for signs of the fish and information on how to protect it. "No other fish has been searched for more persistently by researchers in Ohio than this species," according to the Ohio Department of Nature Resources.

In 2009 the U.S. Fish and Wildlife Service (FWS) published a review of the Scioto madtom's status (pdf), writing that the species—which, like the five other madtom species in Ohio, depended on shallow, fast-moving waters with a lot of gravel and silt substrate—probably disappeared "due to modification of its habitat from siltation, suspended industrial effluents and agricultural runoff," as well as competition from another madtom species that had moved into that region of the stream. The review concluded that the long amount of time since the Scioto madtom has been seen meant it no longer met the definition of an endangered species, "and therefore delisting the species due to extinction is recommended." The FWS has yet to take that step, but the IUCN responded to the recommendation and has now finally declared the species to be extinct.

Of course, who knows—the Scioto madtom could still be out there. A 2003 article in the Darby Creek Advocate characterized the fish as "small, inconspicuous, and nocturnal," making it hard to find. The fact that the fish was only ever observed in fall and early winter has also led to suspicion that it bred (or still breeds) elsewhere. Perhaps the fish found in Big Darby Creek were outliers, caught swimming somewhere they would not normally be found. Another madtom species, the northern madtom (N. stigmosus) went unseen for 31 years until ichthyologist Milton Trautman, who discovered the Scioto madtom, found two of them elsewhere in Big Darby Creek. Maybe the Scioto madtom will follow suit.

Or maybe it won't. People have been looking for the Scioto madtom for years. In all likelihood, it is gone for good—another species that disappeared when we weren't looking.

Scioto madtom photo by M.R. Thomas, via the Florida Museum of Natural History. Big Darby Creek photo by Jinjian Liang via Flickr. Used under Creative Commons license