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September 25, 2023

Science takes time.

Research can often take years before findings are published and practical applications of science sometimes take even longer to implement. But the time-consuming efforts of scientists to analyze real-world problems to find solutions can pay dividends.

For instance, a U.S. Geological Survey study published in 2019 has since changed the way fish passages across the northeast are built to help the migratory fish and increase the dwindling population of a fish prized by anglers across the U.S.: the American shad.

Once described as “the fish that fed the nation’s founders,” American shad were a common fish found across the northeast U.S. and Atlantic coast. Native Americans valued shad as both food and fertilizer for crops and even taught early settlers various methods to catch shad using nets and traps.

Their abundance made them a staple of the region’s culture and political landscape with them even having a starring role in Virginia’s Shad Planking, an annual bipartisan event which brings communities together with political candidates, reporters, campaign workers and others to drink beer, play games and smoke shad over wood planks on an open fire.

American shad were such a crucial part of the essence of the eastern coast of the U.S., that it was even designated as the official fish of the nation’s capital.

But over the past 100 years, a decrease in their numbers led many Atlantic coastal towns and regions to implement limits or outright bans on fishing them. A key reason for the decrease in shad population: human-made dams and barriers blocking shad migration routes.

While beneficial to the human population of an area for water storage, recreation, hydroelectric power and other uses, damming rivers and streams native to shad can cut them off from their natural spawning areas, which can lead to a drop in their overall population. According to a 2003 study, damming rivers and streams had become so prevalent in the U.S., it has led to a loss of 36% of the original spawning habitat for shad over the last 100 years.

Two people pass nets of fish over a chain fence.
Sam Parker and Kevin Molongoski, USGS scientists, transfer American shad from the study area to a tank on a fish truck before being released in the Connecticut River following a shad fishway entrance gate study at the S.O. Conte Research Laboratory in Turners Falls, Massachusetts, June 1, 2018. USGS photo by Andrea Miehls.

However, a two-year study by the U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, helped to identify how dams and shad can exist together. Researchers found by making water-based facilities, like dams or power plants, more shad friendly with the use of specially designed equipment, called fish ladder entrance gates, they helped shad stay on track and overcome those barriers during their migration.

A fish ladder, a common type of fishway, is a structure built on or around natural and manmade barriers to help fish maintain their natural migration patterns. Most fish ladders are built with steps to allow fish to swim or leap from one to the next to make it around or over barriers.  Fish ladders are equipped with an entrance gate which allows fish to enter the fish ladder, controls the velocity of water coming through, as well as other hydraulic characteristics to make the fishes’ passage through it as optimized as possible. 

“The entrance gate to a fishway is located on the downstream end of the ladder, so this is the point where upstream migrating fish first enter the ladder each spring,” said Kevin Mulligan, research hydraulic engineer with the USGS Eastern Ecological Science Center and the study’s lead author. “The flow of water coming from the fishway is often moving at a relatively slow rate, so the entrance gate constricts the flow, thereby speeding it up, and creating what we refer to as the attraction jet.”

“Fish sense that faster moving water and try to swim up through it,” added Mulligan, a native of Easthampton, Massachusetts. “Once they get over the entrance gate, they are in the fishway and they will typically attempt to ascend the ladder.”

The USGS studied different types of fish ladder entrance gates in various depths of water to examine how different styles of gates influenced the numbers of upstream‐migrating, adult American shad entering the waterways.

“There are many factors contributing to a fishway’s efficiency,” said Brett Towler, the center’s Fish Passage Design & Analysis Team Manager, study coauthor and former USFWS regional fish passage engineer.

One of the contributing factors is entry rate, said Towler. Many existing fishways have a poor entry rate, so practitioners, agencies and dam owners are always on the lookout for ways to improve this factor.

To determine the best entrance gate for shad, the USGS used the only facility on the East Coast up to the challenge: it’s very own indoor 125-ft. long, 19-ft. wide and 20-ft. tall rectangular open water channel, also known as the “flume”, located at the S.O. Conte Research Laboratory, or Conte Lab, located in Turners Falls, Massachusetts.

The Conte Lab’s flume replicates a body of water flowing downhill. It is filled with flowing water from a higher elevation power canal which branches off the nearby Connecticut River. The flume has customizable features to adjust the water flow, circulation and direction, and has electronic sensors and video cameras installed throughout which allows scientists to test different scenarios, track fish progress and monitor environmental situations to see how fish will react and adapt while trying to pass through the flume.

To begin the entrance gate study, American shad were collected from the Connecticut River and transported to the Conte Lab where they were measured, identified by sex, examined for injuries and fitted with glass covered passive integrated transponder, or PIT, tags. 

PIT tags are unpowered tracking tags that can be detected using special antennas installed throughout the flume and, along with underwater video cameras, allowed the researchers to monitor fish movements as they passed the different entrance gates and progressed through the study area.

After being tagged, the fish were held in a rectangular pond for 24 hours before each trial where the water was continuously being circulated with fresh river water from the canal.

Following the 24-hour waiting period, 30 fish were guided from the pond into a staging area and given 30 minutes to acclimate to the new water flow conditions.

Once acclimated, the trial began when researchers lifted a screen that separated the staging area from the entry zone. For the next 2.5 hours, the fish were free to swim upstream toward the entrance gate and into the fishway.

Fish movements during the trials were monitored using PIT antennas installed before the entrance gate and at intervals along the flume which detected each shad when they were within one meter of each antenna. Overhead and underwater cameras also monitored their progress as they made their way to and through each of the different types of entrance gates.

Three different types of entrance gates were studied: the common vertical gate currently in use in many fishways, a less common overshot gate and one even less common type known as a reverse overshot gate. The gates are all located at the same place in the fishway with the difference being the angles they are installed with the vertical gate at a 90-degree angle, the overshot gate at a 45-degree angle with the base facing upstream and the reversed overshot gate at a 45-degree angle with the base facing downstream.

Three people use a net to guide fish in the water of a large cement building
Sam Parker, Kevin Molongoski and Steve Walk, USGS scientists, use nets to guide American shad into a study area during a shad fishway entrance gate study at the S.O. Conte Research Laboratory in Turners Falls, Massachusetts, June 1, 2018. USGS photo by Andrea Miehls.

Three different water depths were tested with each gate resulting in nine different trials, or treatments. Additionally, water temperature, turbulence and flow were also closely monitored and controlled as well to see if those were factors in shad entering the gates during the trials. 

Following the trials, the scientists found the entrance gate most used in the industry, the vertical gate, was actually the least effective for fish passage. The overshot and reversed overshot gates saw significant improvements compared to the vertical gate.

The scientists discovered differences in water turbulence and velocity caused by the different gates were a contributing factor in the attractiveness to shad, as well. Also, the attraction jet of the reversed overshot gate gave the shad a much clearer directional signal which led to higher numbers passing through.

Additionally, water depth played a key role in the results with the scientists finding the deeper the water, the better the performance and the greater the entry rates.

Following the study’s release, the results were included in the USFWS Fish Passage Engineering Design Criteria, a manual which provides technical guidance in the form of accepted criteria, recommendations and best practices for the design of technical fishways, nature-like fishways, dam removals, culvert replacements and other fish protection technologies.

Since being included in the manual, the overshot gate is now the preferred gate type at shad fishways.

“The results obtained from the fishway entrance gate study performed at the Conte Lab were incredibly insightful and integrated immediately into the USFWS Fish Passage Engineering Design Criteria manual,” said Bryan Sojkowski, study coauthor and USFWS Fish Passage Engineering hydraulic engineer. “The information was especially critical when informing fish passage design for American shad, a species that has been historically very difficult to pass in a timely, and effective manner. 

“Since the completion and publication of the entrance gate study, new fishway designs all across the northeast region made sure to meet the new standard and existing fishways were re-assessed to see how the standard could potentially be met through changes to operational protocols or gate type,” Sojkowski said. 

“The Conte Lab continues to play a key role in moving the science of fish passage forward,” added Sojkowski. “Our relationship with Conte allows us to relay issues or research gaps we see in the field and obtain scientifically proven results to aid in more successful fishways being constructed as well as remaining at the forefront of the science.”      

Due to the success of the shad fishway entrance gate study, the methods and techniques developed for it are planned to be used in future fishway entrance research including an upcoming three-year study with river herring beginning in the spring of 2024.

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