The travails of an alewife: Dams, drought, and climate change

Getting into the streams to take measurements is one of the favorite aspects of this project from UConn researcher Katherine King. Credit: University of Connecticut

River herring once swam up Connecticut’s streams to reproduce by the billions, then returned to sea. However, in recent years their migration has become more and more dangerous and their numbers have fallen sharply. Obstacles such as dams have been added to many of the streams and rivers and the population has been drastically overfished.

While the cards are stacked against the already endangered river herring population, UConn researchers are working to learn more about the habits of eels, a species of river herring, and the hydrology of the streams and rivers leading to their ancestral spawning grounds, including whether the fish from the lakes and ponds can reach where they reproduce.

Swim upstream

River herring is an ecologically important part of both freshwater and saltwater food webs in Connecticut. They serve as an important food source for many species, and they circulate a huge amount of nutrients throughout the ecosystem, said Eric Schultz, a professor in the Department of Ecology and Evolutionary Biology whose research group studies river herring.

Humans have made an already labor-intensive migration much worse. Measures to help restore migratory routes include removing barriers, such as dams, or building structures to facilitate migration, such as fish ladders or improved culverts, in efforts to make the systems function better as they should, Schultz says .

These efforts are helping get the adult fish into freshwater areas where they can reproduce and efforts are being made to resupply ponds, but surprisingly little is known about how the young fish get back to the sea, Schultz says.

“Now we’re putting a lot of effort into monitoring these populations,” he says. “The title of the project is, ‘Can They Get Out?’ We know of some sites that are important pathways for the baby fish to leave the lakes and into the ocean, we also know that those streams are drying up and the connection is broken.”

If effort is made to get adults to freshwater, Schultz says, it may be in vain if streams dry up, as some have done in 2022.

What else can be done? This is why Schultz reached out to hydrologists James Knighton, assistant professor in the Department of Natural Resources and Environment, and Katherine King.

“Our side of the project is measuring the stream flow where water comes out of the ponds where these fish spawn and building models of the systems to simulate how rain falling on the Earth’s surface turns into flow,” Knighton says.

The measurements and observations from the past two years will be used to calibrate models that will be used to run synthetic, hypothetical climate scenarios to estimate the risk of loss of flow and possible strandings for the fish.

“The project is actually very lucky that we are currently having this massive drought in 2022 because we finally saw exactly what we were concerned about,” Knighton says. “To answer the big question, no, the fish couldn’t get out in any of these locations this year. I think the bigger question is, will this be more common and what is the risk in any given year?”

Schultz points out that climate models suggest droughts like the one we have now will become more frequent. The computer modeling will provide insight into the extent to which these interruptions in the flow affect the success of young born in a given year, called a “year class”.

“Some of the unexpected things that have happened is that when we built the structure, a large perch became very interested in just occupying it,” says Schultz. Turtles are also of great interest. Credit: University of Connecticut

Data on fish out of the water

Mike Burgess has continuously observed and measured the fish from various field locations along the Connecticut coast, from Old Saybrook to Mystic. Time-lapse cameras capture the fish leaving the sites and a photo is taken every minute, 24/7.

Burgess checks the locations and changes memory cards every two days, which also allows him to keep a close eye on the locations and take biological samples from departing fish.

“We’re assuming that after a drought like this, once they have access to leave, they’ll go anyway,” Burgess says. “I keep an eye on them as they leave and evaluate the environmental factors that drive them out, as well as the internal factors in the fish that may be influencing them to leave.”

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

To do this, Burgess is working on modifying an existing code structure published in Ecological modelling in 2020 that models the alewife’s life cycle from the egg to age nine.

“We’re going to try to adjust the part of the cycle where the fish migrate from the lake to the river and include the drought data and see if we can predict what kind of results could come from different hypothetical drought scenarios.”

Early warning

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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 are working on this tool is to bring these factors together and indicate the probability of loss of flow at some point in the season, or at least flow-based migration. The idea behind this is to let managers know in advance what that opportunity is, and if the opportunity is high, they can adjust water use, amounts, or practices, whether they run water from dams at different times of the year or water from rivers or reservoirs have a huge impact on flow rates.”

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

“There are several ways to manage stormwater to allow rain to slowly infiltrate the soil after rainfall events, which is better for recharging the water table and maintaining stream flow. The more rain that can infiltrate and not run off the impermeable surfaces , the better.”

One of the area streams that dried up after the summer 2022 drought. Credit: University of Connecticut

Burgess notes that heavy use of municipal water has clearly led to high fish mortality in some locations. Significant numbers of fish have been able to leave their lake, but are then unable to reach the ocean and die, stranded, in the drying stream. Communication is essential to retain the young people who are left behind.

In addition to short-term interventions, such as adjusting use or the amount of water released from dams, there are critical long-term decisions that need to be informed, Schultz says, namely planning and development.

“For example, we’ve heard that a large condominium complex is planned for an area in a catchment area close to one of our critical locations. It baffles us that they can go through with this even if they acknowledge and it’s clear that year after year this one has site water problems.

King and Knighton point to the main culprit: household water consumption. The more water people pump from groundwater-fed wells, the less water is available to replenish streams.

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

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

“It’s critical to understand how we affect life and how we affect people more indirectly, because while humans need water, they also need functioning aquatic ecosystems,” he says. “The goal of these types of projects is to give decision-makers the information they need to determine what types of structures are needed to sustain life and to do so, while also focusing on components of the ecosystem that really in trouble.”

With the current prolonged dry conditions, groundwater levels around CT are 10 feet below where they should be, Knighton says, and that will take more than a rainy day or two to recharge, but the northeastern US is lucky. that the region usually gets enough snow to replenish the groundwater level each winter.

“Usually winter resets everything, but when we start losing snow I don’t know if that’s something we can rely on indefinitely,” Knighton says. “I think for the time being we can assume that this winter will recover us.”

Schultz warns that frequent droughts leading to frequent failures of the reproductive season for the alewife can be a problem, as populations tend to return to the same areas where they hatched. If enough die-offs occur, it is possible that one day no more fish will return to reproduce.

“If you take out the individuals that were produced in a given year, and you 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 far we will start with seeing further depletion of those fish in our area from an already depleted position.”

Fishing passes can reconnect species to habitats blocked by dams. That’s how they work

More information:
Gary A. Nelson et al, A Life Cycle Simulation Model for Investigating Causes of Population Change in Alewife (Alosa pseudoharengus), Ecological modelling (2020). DOI: 10.116/j.ecolmodel.2020.109004

Provided by the University of Connecticut

Quote: The Trials of an Alewife: Dams, Drought, and Climate Change (2022, Oct. 18) Retrieved Oct. 19, 2022 from

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