Hatching a plan to save salmon
This is the third feature in a five-part series that follows an Atlantic salmon on its journey upstream to spawn in a tributary of Lake Champlain driven by its instincts (and a pickup truck). Learn why this species disappeared from the lake in the 19th century, and how it is making a comeback today thanks to collaboration by partners in the basin.
“You have to step on this footpad to come in and out of this area,” cautioned Scott Frost as we crossed into a roped-off section of the White River National Fish Hatchery. “It has a disinfectant to make sure we don’t drag any contaminants in on our boots.”
Once our boots were clean, Frost, who is the assistant hatchery manager, led me over a row of rectangular structures and rolled up a black curtain to reveal racks of trays alternately labeled with plus and minus signs. Each tray contained hundreds of recently hatched larval salmon.
“These eggs were spawned from fish caught migrating from the lake to spawn in Hatchery Brook last fall,” he said. “We incubate the eggs until they get to the ‘eyed’ stage, where you can see the eyes inside the eggs,” he explained. “They are very fragile up to that stage.”
When I visited, the eyes had appeared, but the young salmon still warranted special treatment. They weren’t just stock for the lake; they were research subjects.
“They are all from the same parents, but half of them have been treated with Vitamin B1, and half of them have not,” he explained. “We are trying to determine if treatment is effective in stopping the Thiamine deficiency problem.” Hence the labels, and the precautions.
The study at White River is just one of many research projects being undertaken by partners in the Lake Champlain Basin to get a handle on a growing challenge for the collective effort to restore salmon: alewife.
Quick recap: Introduced in 2003, alewife gradually crowded out rainbow smelt, the primary native food source for salmon, and salmon began eating alewife instead. That’s bad because alewife carry an enzyme called Thiaminase that digests the Vitamin B1 inside salmon, which suffer the consequences of losing an essential compound used to metabolize energy. For perspective, a deficiency of Vitamin B1 in humans leads to a disease called beriberi that interferes with the nervous system and causes heart failure.
For Lake Champlain salmon, the Vitamin B1 deficiency seems to be interfering with the entire reproductive cycle. It is known to make eggs inviable and inhibit the development of juveniles, and it may be interfering even earlier in the process by having physiological impacts on adults.
This week we’ll look at a snapshot of the research taking place in the basin to ensure that salmon have a future in the face of a threat that is likely here to stay. “We’ll never get rid of alewife,” said U.S. Fish and Wildlife Service Fish Biologist Nicholas Staats. “We just have to manage around them.”
So how do you manage around a problem that affects salmon throughout its life cycle? You start by assessing it at every stage.
The question: In 2014, Concordia University doctoral student Andrew Harbicht noticed that very few salmon were being tallied at the counting station at the fish ladder in the Willsboro Dam (which was removed the following year) even though fishermen in the Boquet River were seeing large numbers of salmon in the pool at the base of cascades below the dam.
“We knew fish were in the river, but they weren’t making it up the rapids: Is that because they couldn’t?” he asked. “Since we know the Thiaminase can cause motor dysfunction among juveniles, we wondered if it might be affecting adults too.”
The approach: Harbicht and his colleagues set up a trap about a mile downriver from the cascades to intercept salmon on their way upstream. They gave half of them an injection of saltwater and Vitamin B1, and the other half a placebo injection of salt water.
Before the researchers released the fish back into the river to continue their upstream migration, they tagged them with transponders that could be detected by a series of six antennae set up at different points within the cascades to monitor their progress. In other words, the salmon were being timed.
Who won? It appears that the treated fish took much less time to reach the top of the rapids, compared to untreated fish, and that they spent less time in the pools within the rapids before continuing their ascent. Although Harbicht cautioned that the results are only preliminary, the study suggests that the Vitamin B1 deficiency is keeping adults from performing their best. “Either because they are less motivated, or need more time to recover.”
The implications: The findings could support a short-term workaround for the alewife problem: Vitamin B doping. “If we can strategically intercept fish as they enter tributaries, not only will it help adults reach stream habitat, it puts Vitamin B in their system that they can pass down to their offspring, giving them a better chance of survival.”
The question: Although scientists have been finding lots of salmon nests, called redds, in rivers in the fall, they have not been finding as many juveniles emerging in the spring as would be expected. Bill Ardren, Senior Fish Scientist for the Lake Champlain Fish and Wildlife Conservation Office,said that has led to them to wonder: “Is it due to a lack of Vitamin B1 in the eggs, or is due to the quality of the habitat?”
The approach: This fall scientists collected eggs from adult salmon migrating from the lake during spawning season to serve as the research cohort for a study on Vitamin B1 deficiency, much like those Frost showed me at the White River hatchery. Except that after the Vitamin B1 treatment was applied (or not applied) to these eggs, they were returned to the wild.
Concordia University graduate students Nicole Hill and Ashlee Prevost constructed artificial redds in the Winooski River and Huntington River and placed the eggs in boxes to track their survival. “The eggs are incubating right now,” said Ardren. Who will survive? Tune in this spring to find out.
The implications: The findings could confirm suspicions. If none of the eggs hatch, it’s possible habitat conditions are to blame. If only the treated eggs hatch, all signs point to Thiaminase.
It Runs in the Family
The question: As reported last week, scientists found a natural-born salmon fry in the Winooski River last summer for the first time in 200 years. “That gives us hope that at least there are some females out there that did have enough Vitamin B1 to pass onto their offspring for them to survive,” said Ardren. “We want to know: Are some fish through natural selection, or some other means, able to combat this enzyme?”
The approach: Graduate student Avril Harder from Purdue University is conducting a genetic study looking at the response of different salmon families to Thiaminase. “She is taking eggs from the same salmon families that Nicole and Ashlee planted in the wild, rearing the eggs in tanks on a Thiaminase diet, and looking at response that different families have to the deficiency,” explained Ardren. It may be that some families are more tolerant to Thiaminase, giving them the ability to digest and still maintain good Vitamin B1 levels.
The implications: The findings could be game changing. Let me back up a bit. Last fall, scientists took eggs from salmon caught returning from Lake Champlain to Hatchery Brook at Vermont’s Ed Weed Fish Culture Station and transported them to White River Hatchery. Some of those eggs are the research subjects that Frost showed me when I visited the hatchery. The rest of them represent an exciting new future for the Lake Champlain salmon restoration effort.
How so? First, it’s important to know a little more about where these eggs came from. The Ed Weed hatchery is located on the shores of Lake Champlain in the town of Grand Isle, Vt. Salmon are reared in water from the lake which drains out of the hatchery in a man-made brook. When young salmon at Ed Weed become “smolts” — the developmental stage when hormonal changes cue them to migrate to the lake to feed — they are released to the lake.
Guess where these salmon will turn up in about a year and a half when hormonal changes cue them to migrate back upstream to spawn. Hatchery Brook, where the water from the hatchery where they were raised drains into the lake.
The salmon that return to Ed Weed thus are prime specimens for breeding: We know they have what it takes to survive in the lake, and we know their homing ability is spot on. Not to mention, they’re easy targets. Check out this footage of salmon crowding into the brook in 2015. It’s like natural selection on demand.
“The idea is to produce eggs from salmon that have adapted to the lake and shown themselves to be successful in returning to their natal stream,” said Frost. “We will grow those eggs all the way to mature adults that are ready to spawn, and those salmon will be become the production fish for stocking the lake.”
What does have to do with the project at Purdue? If scientists can identify salmon families that are genetically equipped to resist Thiaminase, they can fortify the broodstock by selecting eggs from those parents.
“We have done a lot of work in the hatchery program to improve on the quality of fish across the basin, looking at differences in water temperature regimes, growth rates, and timing of stocking,” said Henry Bouchard, manager of the Dwight D. Eisenhower National Fish Hatchery, where my salmon was born. “Now there may be opportunity for us to use wild eggs to develop a broodstock that is more tolerant to the alewife situation.”
You can probably see where this is going: Future generations of salmon raised in hatcheries to have a natural resistance to Thiaminase are stocked in the Boquet River at the smolt stage, and then swim out into the lake to mature, and when nature beckons them to spawn, they will have the endurance and/or motivation to ascend the cascades, find the pristine spawning grounds, and pass on those desirable genes to their offspring.
And that may have implications beyond Lake Champlain: a salmon that is resistant to Thiaminase could provide a new strain to support conservation of at-risk landlocked salmon populations in other systems, like Lake Ontario, where alewife have also become a problem.
But there’s still work to be done to make sure this system can support future generations of salmon partners hope to see returning to natal streams on their own. For one, ensuring that the streams they return to are in good enough condition for them to spawn. It might help to figure out exactly what leads salmon back to these streams in the first place. My salmon is evidence that we are making progress on that front. Learn why next time.