If you want to raise the ire of Alison Hutson and Douglas Tave, each of whom holds a doctorate in aquaculture and has made fish their life’s work, call the Los Lunas Silvery Minnow Refugium, which they manage, a DisneyWorld for fish.
True, the refugium doesn’t look like any fish hatchery you’ve ever seen. In its park-like setting, it has a 458-footlong serpentine concrete channel, ponds, shelves, backwaters, and floodplain that simulates the flow of the Rio Grande. It is landscaped with plants common to the river’s banks. It was designed and constructed, at a cost of $1.7 million, especially to spawn and propagate the endangered silvery minnow.
Since it was the first ever constructed, it’s safe to call the Los Lunas Refugium unique. But not Disneyesque. Its purpose is as serious as the biologists who work here.
This silvery minnow is endemic to the Rio Grande. It was once found along 2,400 miles comprising the river. Now it’s restricted to only 174 miles between Cochiti reservoir and the headwaters of Elephant Butte reservoir.
The fish was listed as endangered in 1994, an act that set off a legal battle ending in 2003 when the U.S. Fish and Wildlife Service issued its Biological Opinion. The battle was between the Middle Rio Grande Conservation District, representing irrigators, and environmental groups, including the Southwest Environmental Center based in Las Cruces, attempting to preserve greater habitat for the fish.
“The refugium was required by the Biological Opinion,” Tave explains. “The term, refugium, was not defined. It was kind of an invented word and no one knew what it entailed. The state was required under law to contribute to saving the fish, so we (New Mexico Interstate Stream Commission) agreed to do the refugium.”
Traditional hatcheries coddle brood stock in aquaria and tanks until females lay eggs, and they maintain the environment until the eggs hatch, producing babies called fry. Fry are raised until they reach prescribed length and weight before being released into lakes and streams. In most cases, they’re not there very long before commercial and recreational fisherfolk pull them out of the water.
“What we’re doing is conservation aquaculture,” Tave says. “It’s different than production aquaculture.” Preserving an endangered species requires a different tact. Hutson adds, “We’re trying to put a farmed animal into the wild, and we asked if there is a better way of doing this. The refugium allows us to produce fish that are more wild so when they’re stocked in the river we have a better chance of recovering the species.”
Because every drop of water in the Rio Grande is appropriated for beneficial use, meaning some human being has the right to the water, scientists at the refugium had to apply to the Office of the State Engineer to acquire rights for the nearly 161,000 gallons of water that flows through and is recycled at the facility. The only “new” water added replaces that lost to evaporation.
The serpentine channel was constructed of concrete to prevent erosion and the necessity of periodically rebuilding banks. Soil and sand bags create five ponds, which act as deepwater offshoots and simulate a braided river channel. Low-lying overbanks can be flooded to produce floodplains, especially to replicate spring snowmelt runoff that stimulates spawning and provides nursery habitat.
But the refugium is much more than just water modeling the river. It’s intent is to raise wild fish. In this replication of its natural habitat, the silvery minnow is allowed to fend for itself. Staff adds fertilizer to water at the exit sump, where it can blend thoroughly as the water is recirculated back to the inlet. The fertilizer facilitates growth of freshwater algae, diatoms, zookplankton, and animals that cling to plants. These constitute the primary food, and the fish are left to forage for it.
Landscaping with plants such as sedges, saltgrass, bulrushes, and yerba mansa provides shade, protection from predators, shelter in which the fish can mature, and their “cafeteria.”
When the refugium was completed in 2009, the Fish and Wildlife Service (USFWS) permitted the staff to introduce 100 silvery minnows to assess survival during a one-month trial. They lost only one fish. Phase II allowed them to culture 1,000 fish for several months. Following the success of that phase, USFWS allowed them to introduce 10,000 fish for a growing season.
Fry are introduced to the refugium in May. The exact number has varied as has their age and size, factors which contribute to their survivability. The older and larger, the more likely the fish will be around for the harvest in October. Water is monitored twice daily for dissolved oxygen, temperature, and other conditions. The fish are observed as they move through the habitat. But they are otherwise left on their own.
Predation could be a problem. Heavy wire cables are strung overhead every eighteen inches feet to discourage herons, cranes, and other fish-eating birds from landing. Tave says, “Herons and cranes could consume every fish in the refugium in a short time if we didn’t keep them out.” A perimeter fence topped with barbed wire along with plastic netting buried several inches at the base of the fence and extending up nearly a yard shield the fish from reptiles, amphibians, and mammals — including people.
“Hopefully, the refugium will enable the fish to develop wild-type behaviors and will also prevent the development of maladaptive hatchery-induced behaviors,” Tave and Hutson wrote in a paper for World Aquaculture.
At the end of the season, sand bags and other obstacles are removed and the refugium is seined. Every silvery minnow is captured and tagged with a unique tattoo. A statistical sample of fish is measured and weighed to determine average length and weight. The fish are held temporarily in tanks until Fish and Wildlife staff transport them for stocking the Rio Grande and in an experimental stretch of the river near Big Bend.
The refugium is then drained and left dry from November until March, when water again begins to flow and this unique facility awaits the arrival of the next season’s fry.
The Los Lunas Silvery Minnow Refugium is a stop-gap measure to keep the fish from becoming extinct. The remaining Rio Grande habitat is just too small for it to survive on its own.
Unless, and until, the river is seen as a legal entity, just like the farmer, industrialist, and consumer, it is unlikely there will ever again be enough habitat along its entire length in which not only the silvery minnow, but also other species, which have found more hospitable territories elsewhere, can thrive.