To biologists, the decline or loss of a species is nothing short of a crime. And fittingly, they’re investigating it like one. Just as the suspect in a crime scene drama gets careless and leaves behind a fingerprint or DNA, fish – and all organisms, for that matter – are constantly leaving evidence. Evidence in the form of environmental DNA (“eDNA”) – that which has left the organism but persists in its surroundings for some time, carrying the unique genetic signature of the species.
In the case of fish, DNA enters the water from scales and slime flushing off or waste and gametes being excreted. Water samples can then be taken and analyzed for DNA to detect the presence of a target species, greatly reducing the amount of effort required to actually capture a potentially elusive critter using more labor-intensive methods.
It’s a process seeing increasing application in both conservation of imperiled fishes and monitoring of invasive species, from confirming the existence of the extremely rare Alabama Sturgeon, feared to be extinct but recently discovered using eDNA, to tracking the spread of destructive Asian carp in the Great Lakes region. And it is particularly useful when trying to find a reclusive, 2-inch-long fish, only a handful of which might live amongst acres of snaggy swamps or miles of meandering blackwater creeks.
In South Carolina and other eastern states, an investigation is underway to find evidence of the Blackbanded Sunfish, a silver dollar-sized boldly barred fish of blackwaters and backwaters in the coastal plain. This fish is getting harder to come by, especially in other portions of its historic range such as Georgia and Maryland, where biologists searching in former locations are coming away empty-handed. Reasons for the fish’s apparent decline are not entirely