River herring once swam over Connecticut streams to multiply by the billion, then reversed their journey back to sea. But in recent years, their migration has become increasingly precarious, and their numbers have declined. Obstacles such as dams have been added to many streams and rivers and the population has been heavily overfished.
Although the cards are stacked against populations that are already threatened by river herring, UConn researchers are working to learn more about herring habits, a type of river herring, and the hydrology of streams and rivers that lead to their ancestral breeding grounds, including whether fish can exit lakes and ponds where they breed.
swimming upstream
River herring is an ecologically important component of both the freshwater and saltwater food webs of Connecticut. They’re an important food source for many species, and they recycle an enormous amount of nutrients around the ecosystem,” says Eric Schultz, a professor in the Department of Ecology and Evolutionary Biology whose research group studies herring.
Humans have already made labor-intensive migration much worse. Actions to help restore migratory routes include removing obstacles, such as dams, or building structures to facilitate migration, such as fish ladders or improved canals, in an effort to make systems work more like they should, Schultz says.
These efforts help get adults to freshwater areas where they can breed and efforts are made to stock ponds, but surprisingly little is known about how the young fish return to the sea, Schultz says.
“Now we are putting a lot of effort into monitoring these populations,” he says. “The title of the project is, Can they come out?” We know some sites that are important ways for baby fish to leave the lakes and go into the ocean, and we also know that these streams are drying up and the connection is broken.”
Schultz says that if efforts are made to bring adults to fresh water, there may be no point if rivers dry up, as happened in 2022.
What else can be done? This prompted Schultz to reach out to hydrologists James Knighton, assistant professor in the Department of Natural Resources and the Environment, and Catherine King’s 23 MSc.
“Our aspect of the project is to measure the flow of the stream as the water exits the ponds where these fish spawn and to build models of the systems to simulate how rain falling on the Earth’s surface turns into stream flow,” says Knighton.
Measurements and observations made over the past two years will be used to calibrate the models that will be used to run hypothetical climate scenarios to estimate the risks of flow loss and potential stranding events for fish.
“The project is very fortunate that we currently have this huge drought in 2022 because we ended up seeing exactly what we were worried about,” Knighton says. To answer the big question, for this year, no, fish couldn’t get out at one of these locations. I think the bigger question is, will this become more common and what are the risks in any given year? “
Schultz points out that climate models suggest that droughts like the ones we face will become more frequent. Computer modeling will provide insight into how these interruptions in flow affect the success of larvae born in a given year, called ‘season of the year’.
Data on fish out of water
Mike Burgess MS ’23 took continuous observations and measurements of fish from several field sites across the Connecticut coast from Old Saybrook to Mystic. Time-lapse cameras capture the fish as they leave the sites with a picture taken every minute, 24/7.
Burgess checks the sites and changes memory cards every two days, which also means he can keep a close eye on the sites and take biological samples from the fish that leave.
“We’re assuming that after a drought like this, once they can leave, they’re gone no matter what,” Burgess says. “I’m watching their departure, evaluating the environmental factors that drive them to exit, as well as the internal factors in the fish that might influence them to leave.”
Burgess says the near-nightmare scenario of the 2022 drought, while unfortunate for this year’s category of events, provides important data for the second part of his project — modeling what will happen in the long term.
To do this, Burgess is modifying the existing code architecture that models the life cycle of an alewife from the egg to the age of nine.
“We’ll try to modify the part of the cycle where fish migrate from lake to river, incorporate drought data, and see if we can predict what kind of outcomes might come from different hypothetical drought scenarios.”
early warning
King says the modeling tool the researchers are creating will be important to 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 point to the chances of losing flow, or at least relaying based on flow, at some point in the season. The idea behind this is to let managers know in advance about this opportunity, and if it’s a big opportunity They can modify their water use, quantity or practices, whether they release water from dams at different times during the year, or withdraw water from rivers or reservoirs that have a significant impact on flow rates.”
Knighton says there are other measures that can be taken to help with the flow, such as green infrastructure:
“There are different ways of managing storm water to help rain slowly infiltrate into the soil after rain events and it is better for recharging the water table and will keep the streams flowing. The more rain that can infiltrate and not run off undiluted surfaces, the better.”
Burgess notes that the heavy use of municipal water in some locations has caused severe fish deaths. Large numbers of fish manage to leave their lakes but are then unable to reach the ocean and die stuck in the draining stream. Communication is vital in maintaining residual events.
In addition to short-term interventions such as adjusting the use or amount of water released from dams, there are critical long-term decisions that need to be well informed, Schultz says, that are planning and development.
“For example, we’ve heard that a large condominium complex is planned in the catchment area near one of our vital sites. It baffles us that they can go ahead with this, even when they realize that obviously year after year, this site has water problems.”
King and Knighton point to the biggest culprit – the use of water in homes. The more water people pump from wells fed by groundwater, the less water is available to recharge waterways.
“Problems with water supply relate to people in their individual uses, but we can be more strategic in managing those resources so we don’t have those negative effects,” King says.
This sits at an important point at the heart of this research, Schultz says.
“It is important to understand how we affect life and how we affect humans indirectly because while humans need water, they also need functioning aquatic ecosystems,” he says. “The purpose of such projects is to provide decision makers with the information they need to determine the types of structures needed to sustain life and to do so while also focusing on the components of the ecosystem that are already in trouble.”
With current long-term drought conditions, groundwater levels around CT are less than 10 feet where they should be, Knighton says, and that would take more than a rainy day or two to recharge, but the Northeast US is lucky because the area usually gets enough snow To recharge groundwater levels every winter.
“Winter usually resets everything, but when we start losing mass of snow, I don’t know if that’s something we can count on indefinitely,” Knighton says. “I think, for now, we can assume that this winter we will recover.”
Schultz warns that frequent droughts that lead to repeated failures in the animal’s breeding season can be a problem because populations tend to return to the same areas in which they spawn. If enough mortality occurs, one day the fish may not return to breeding.
“If you exclude individuals that were produced in a given year, and do that for several years in a row, we will definitely see an impact on the local population. I expect the modeling will show us how much we will start to see more of that fish depletion in our area than an already depleted situation.”
Originally published at San Jose News Bulletin
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