Ancient Fish Gets Techno Boost

In 1999, the U.S. Navy approached the University of Washington's Applied Physics lab with a mission: develop a tool that could help harbor surveillance teams detect "swimming intruders" as well as underwater mines and IEDs in essentially zero-visibility conditions.

DIDSON was the lab's techno-fabulous answer. The advanced sonar technology works much like an ultrasound—converting reflected sound waves into visual images—but relies on a special acoustic lens that creates real-time, highly-detailed movies. The resolution blows regular sonar imaging out of the water (Imagine watching "Lord of the Rings" on VHS and then suddenly switching to Blue Ray: pretty sweet).

But what began as James Bond-worthy surveillance technology used to secure the homeland, is now being applied to fisheries research.

Wildlife biologists are wielding DIDSON as a powerful new weapon in their fight to recover the pallid sturgeon, one of the most endangered species in North America. Pallid sturgeon are freshwater giants; fish so wonderfully bizarre and remarkably old (172 million years) they are often referred to as "dinosaurs of the Missouri."

Pallids once thrived in the deep, turbid waters of the Yellowstone, Missouri and Mississippi Rivers. But 100 years of damming and channelization has transformed the waterways from dynamic, natural systems braided with sand bars, gravel flats, and side channels to little more than homogenous chutes along much of their lengths. In the last 40 years, pallid sturgeon have dwindled so dramatically that today there are fewer than 200 wild adults left in the Missouri's upper reaches.

Video 1) In April, as part of pallid recovery teams' long-term telemetry efforts on the Missouri River, CERC  used DIDSON to survey the Osage River in Missouri state, a tributary of the Missouri River, to determine if pallid sturgeon are using the river for refuge, overwintering habitat, feeding grounds, or spawning. They discovered a few sturgeon aggregating below Lock and Dam 1, which suggests the fish are indeed using the Osage and that the lock and dam structure may be obstructing the sturgeon's upstream migration. Video courtesy of USGS Columbia Environmental Research Center

In the past few years, biologists have focused in on a key issue: Something is preventing embryonic and larval pallids from surviving in the wild, a significant barrier to pallid recovery.

"Things are working on the reproduction side but we are just not getting any babies," says Pat Braaten, Research Fish Biologist for the U.S. Geological Survey's Columbia Environmental Research Center (CERC). "There has been no evidence of any [pallid] recruitment for several decades," he says. "Little sturgeon just aren't found, no larvae and no wild sturgeon aged one, two or three years. There is a bottleneck somewhere or something going on between reproduction and the rest of their lifespan."

Tracking and monitoring larval and adult pallids in the Missouri is critical to understanding the species' historical decline and current status. But pallids live 15 feet beneath the surface of the Missouri, obscured by a sunless sweep of clouded current that stretches for a thousand miles to the river's confluence with the Mississippi. That's where DIDSON comes in.

Video 2) In late June, CERC, in collaboration with Mont. Fish, Wildlife and Parks, used DIDSON and acoustic Doppler current profiler (another cool technology) to track a large female sturgeon known as "female code 79" on the Yellowstone River, one of the species' last best habitats. DIDSON captured a striking image of the female pallid swimming with two smaller, unidentified sturgeon, and provided visual clues as to the swift, turbid nature of the species' underwater abode. Video courtesy of USGS Columbia Environmental Research Center

DIDSON is "a spectacular device" that provides "tremendous context," says Aaron DeLonay, an ecologist also with CERC. It produces clear, detailed videos of pallids in their near lightless habitat, helping "[us] tell where [pallids] are spawning, what paths they are selecting to swim upstream, how much energy they are using to swim upstream," what their spawning habitat looks like and when they are using that habitat, says DeLonay (see videos 1 and 2).

Pallid sturgeon recovery spans 11 states, three major rivers, and includes the cooperation and resources of dozens of federal agencies, scientists, and private interests. It's a massive effort. But, thanks to the development and application of advanced technologies like DIDSON, scientists know more than ever about this magnificent and mysterious beast. "It takes a large recovery program to do the work and a lot of expertise from different types of scientists," says DeLonay. Pulling pallids from the brink will "take the best tools that we have."

Marian Lyman Kirst is an intern at High Country News.

Image courtesy the U.S. Fish and Wildlife Service.