Silvery Minnow Refugium makes progress
In the second year of a spawning experiment, the Los Lunas Silvery Minnow Refugium has seen positive results.
The refugium applied for and was awarded a contract from the Bureau of Reclamation in 2010, said refugium Assistant Manager Alison Hutson.
“They wanted to try and define where the minnows preferred to spawn,” Hutson said.
Since the small fish were declared an endangered species and efforts began to try and rebuild their numbers, there has been an ongoing debate of just where they preferred to spawn in the Rio Grande.
Did they prefer the deeper, faster moving water in the river channel or the slower shallows of the over-bank areas?
Answering that question could help find solutions to river flow issues such as those the Rio Grande is experiencing this year.
“If there are years like this year, where the river is very low and there is little over banking, what happens to the fish if they prefer to spawn in the over-bank,” Hutson said.
Not only could the experiment answer questions about how much water the fish wanted and needed in order to spawn, but it could reveal other triggers that caused the event.
“If we are only relying on natural cues, we don’t even know what they all are,” Hutson said.
Refugium Manager Douglas Tave said there were a couple of cues that could safely be assumed.
“They spawn at a certain time of the year, so warmer temperatures seem to be a cue,” Tave said.
And with the warmer temperatures come increased flows in the river from the spring snow run off.
“Other than that, nobody knows, so it could be anything,” he said. “Alison’s project focused on the couple of known cues.”
The uniqueness of the refugium is that is mimics the Rio Grande. There are no chemicals used to treat the water, no food pellets for the fish. Larger predators that could wipe out the population are kept at bay, but if a hungry raccoon wanders in, the minnows are fair game.
Last year, Hutson and Tave put the man-made river at the refugium through its flood cycle, but there was no spawning.
This year, they started the flood on April 24.
Since there was no significant spring melt runoff this year, Tave said they had to rely on historical data to recreate the river flows. The level of the “river” was left high for a week, then brought back down. The next flood began on May 7.
Three days later, Hutson spotted the new fish.
“They must have been produced in response to the flood on April 24,” Huston said. “But we hadn’t found any eggs before we started the second flood.
“There was no reason to see a response from any flood, so we were just going to continue. It was really exciting to see them.”
Because the purpose of the experiment was to get the minnows to spawn, Tave said collectors had been placed in the river, but remained clear of eggs after the first flood cycle. When Hutson designed the study, she decided to give the fish two distinct places to spawn — the deep channel or the shallow over-bank.
Refugium staff spent a day hauling and stacking sand bags in the river to block off the ponds. But the wily minnows snuck in anyway, accessing the deeper, very slow velocity ponds through small areas where the sand bag barricades had settled.
“We set up a scientific study with these parameters and specifics,” Huston said. “But they confounded everything and chose low velocity, deeper areas we weren’t monitoring.”
And while some might say Huston and Tave got lucky with the experiment, Tave said it isn’t all just chance.
“Luck plays into this a bit. But there’s a quote from Louis Pasteur. ‘Luck favors the prepared mind.’ When luck comes along, if you are doing the right things, you know how to exploit it,” he said. “Yes, there was some luck, but Alison set up one hell of an experiment.”
In most commercial hatcheries, and even the facilities that produce the minnows that are used to stock the refugium, getting the fish to spawn is usually a matter of introducing artificial elements, such as hormones and manipulation of sunlight to create spawning cycles twice in one year.
Huston said no artificial elements were introduced into the refugium experiment.
“The concept of the refugium is to raise the minnows as much as possible, as close as we can, to what they would experience in the wild,” she said. “There is very little human interaction and exposure. That creates beneficial traits in the wild. So when they go back to the river, they have the skills to survive on their own.”
Tave said this concept is a new direction aqua culture is taking throughout the country. At the refugium, there are minnows in hatchery tanks that rely on human care. He said when a person approaches the tanks, the minnows approach and swim to the surface.
“The ones in the river, when they see a shadow they scatter,” Tave said. “In the wild, that behavior can make the difference between survival and being a snack.”
By getting the minnows to spawn in the refugium, there is the potential to use the date produced to help direct management of the river.
“There are things we can do here that can’t be done on the river, that we can observe,” he said. “What we do here costs pennies versus dollars on the river. One of the central purposes of the refugium is to learn how to manage the water in the river, so that it benefits both the minnow and local irrigators.”
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