The labors of an alewife: dams, drought and climate change

River herring once traveled up Connecticut’s waterways to spawn in the billions, then reversed their journey out to sea. In recent years, however, their migration has become increasingly perilous and their numbers have plummeted. Barriers such as dams were added to many streams and rivers and the population was greatly overexploited.

Although the cards are stacked against the already threatened population of river herring, UConn researchers are scrambling to learn more about the habits of alewife, a type of river herring, and the hydrology of streams and streams. rivers that lead to their ancestral spawning grounds, including whether fish can leave the lakes and ponds where they reproduce.

Swim upstream

River herring are an ecologically important component of Connecticut’s freshwater and saltwater food webs. They serve as an important food source for many species and they recycle a huge amount of nutrients in the ecosystem, says Eric Schultz, a professor in the Department of Ecology and Evolutionary Biology whose research group studies river herring.

Humans have aggravated an already labor-intensive migration. Measures to help restore migration routes include removing barriers, such as dams, or building structures to facilitate migration, such as fish ladders or improved culverts, in an attempt to make the systems work. closer to how they should, says Schultz.

“Some of the unexpected things that happened were when we built the structure, some largemouth bass showed great interest in occupying it,” Schultz says. The turtles also took a keen interest. (photo added)

These efforts help bring adults to freshwater areas where they can breed and efforts are being made to stock ponds, but surprisingly little is known about how young fish return to the sea, says Schultz.

“Now we put a lot of effort into monitoring these populations,” he says. “The title of the project is: ‘Can they come out? We know of certain sites that are important pathways for baby fish to leave the lakes and go to the ocean, we also know that these streams are drying up and the link is broken.

If the effort is to bring adults into fresh water, Schultz says, it could be wasted if streams dry up, as some did in 2022.

What else can we do? That’s what led Schultz to contact hydrologists James Knighton, assistant professor in the Department of Natural Resources and Environment, and Katherine King ’23 MS.

“Our part of the project measures stream flow where water exits the ponds where these fish breed and builds models of the systems to simulate how rain falling on the Earth’s surface changes to flow,” explains Knighton.

Measurements and observations taken over the past two years will be used to calibrate models that will be used to run synthetic and hypothetical climate scenarios to estimate the risk of loss of flow and potential strandings for fish.

“The project is very fortunate actually that we are currently facing this huge drought in 2022, because we ended up seeing exactly what we were worried about,” says Knighton. “To answer the big question, for this year, no, the fish couldn’t come out at any of these sites. I think the big question is will it become more common and what is the risk in any given year? »

Schultz points out that climate models suggest that droughts like the one we are experiencing will become more frequent. Computer modeling will provide insight into the extent to which these flow interruptions will impact the success of fry born in a particular year, referred to as the ‘year class’.

Fish out of water data

Mike Burgess MS ’23 conducted continuous fish observations and measurements from multiple field locations on the Connecticut coast, from Old Saybrook to Mystic. Time-lapse cameras capture fish leaving the scene with a photo taken every minute, 24/7.

Burgess checks locations and changes flashcards every couple of days, which also means he can monitor sites closely and take biological samples from fish that leave.

“We assume that after a drought like this, as soon as they have access to time off, they’re going to leave no matter what,” Burgess says. “I monitor their departure, I assess the environmental factors that push them out, as well as the factors internal to the fish that could encourage them to leave.”

Burgess says the near-nightmarish drought scenario of 2022, while unfortunate for this year’s class of juveniles, provides important data for the second part of his project – modeling what will happen in the long term.

To do this, Burgess is working to modify an existing code structure that models the gaspereau’s life cycle from egg to age nine.

“We’re going to try to change the part of the cycle where fish migrate from lake to lake and incorporate the drought data and see if we can predict what kind of results might come from various hypothetical drought scenarios.”

Early warning

King says the modeling tool the researchers are building will be important for wildlife and resource managers who can make informed decisions.

“Part of the reason we’re working on this tool is to bring these factors together and indicate the risks of flow loss, or at least flow-based migration, at any given time of the season. The idea behind this is to let managers know in advance what that chance is, and if it’s a high chance, they can change the use, quantities, or practices of the water they release. water from dams at different times of the year. or taking water from rivers or reservoirs, which has a huge impact on flows.

There are other measures that can be taken to help with traffic, such as green infrastructure, says Knighton:

“There are different ways to manage stormwater to help rain slowly infiltrate into soils after rain events, which is best for recharging groundwater and maintaining stream flow. The more rain that can seep through and not run off impervious surfaces, the better.

Burgess notes that heavy use of municipal water at some sites has clearly caused high fish kills. A significant number of fish were able to leave their lake but are then unable to reach the ocean and die, stranded, in the dry watercourse. Communication is vital to preserve the remaining juveniles.

In addition to short-term interventions like changing the use or amount of water discharged from dams, there are critical long-term decisions that need to be well-informed, Schultz says, namely planning and design. development.

A dry stream bed.
One of the rivers in the region that dried up after the 2022 summer drought. (Contributing photo)

“For example, we heard that a large condominium complex is planned for an area in a watershed near one of our critical sites. It mystifies us that they can go ahead, even though they recognize and it is obvious that year after year this site has water problems.

King and Knighton point to the big culprit – household water use. The more water people pump from wells fed by groundwater, the less water is available to recharge streams.

“Water supply issues are about people in their own individual use, but we can be more strategic in managing these resources so that we don’t have these negative effects,” King says.

This gets to an important point at the heart of this research, Schultz says.

“Understanding how we affect life and how we affect humans more indirectly is critical because while humans need water, they also need functioning aquatic ecosystems,” he says. “The goal of projects like this is to provide decision makers with the information they need to determine what kinds of structures are needed to sustain life and to do so while also focusing on the components of the ecosystem that are really in trouble.”

With the current and prolonged dry conditions, groundwater levels around CT are 10 feet below where they should be, Knighton says, and it’s going to take more than a rainy day or two to recharge. , but the northeastern United States is fortunate in that the region usually receives enough snow to recharge ground water tables each winter.

“Usually winter resets everything, but as we start to lose snowpack, I don’t know if it’s something we can rely on indefinitely,” Knighton says. “I think, for now, we can assume that this winter will recover us.”

Schultz warns that frequent droughts leading to frequent failures of the alewife’s breeding season could be a problem because populations tend to return to the same areas where they spawned. If enough mass mortalities occur, one day there may be no fish returning to breed.

“If you take out the individuals that were produced in a given year, and you do that several years in a row, we will definitely see an impact on the local populations. I expect the modeling to show us the extent to which we will begin to see further depletion of these fish in our area from an already depleted position.