Bringing Fishways into the 21st Century
The first European settlers in Plymouth, Massachusetts were probably familiar with Town Brook, a freshwater stream flowing into Plymouth Harbor. In the late 1700s, people began damming the brook in order to capture the stream’s power for industry, and the nation’s first fish ladder was installed.
Over the years, six dams have been constructed along Town Brook. These modifications impede the upstream movement of anadromous fish, those marine species that travel inland in order to spawn. Similar scenarios exist today in many streams along New England shorelines.
In recent years, a National Marine Fisheries Service-funded project has been underway to restore Town Brook and remove or modify the blockages to increase upstream movement of local species, including alewife, shad, sea lamprey, striped bass, and blueback herring. The forward-looking project involves a new fishway design and electronic monitoring devices that continuously collect data.
Traditionally, fishways are flat-bottomed concrete, metal, or wood structures that are stepped or “laddered” so that fish can work their way upstream (commonly called “technical” fishways). They are limited by the volume of water flowing downstream; if flow is too low, the water is too shallow for the fish to swim in, and many species are unable to swim up them.
The new structure installed at Town Brook, called a nature-like fishway, is made of natural materials that mimic the natural habitat. “It’s basically a series of pools with boulders in between,” explains the head of the monitoring project, Alex Haro, an ecologist at the U.S. Geological Survey’s Silvio O. Conte Anadromous Fish Research Center in Turners Falls, MA. In contrast with the more traditional “technical” designs, nature-like fishways have a v-shaped cross-section, which is more likely to ensure sufficient water depth for fish movement. “Such fishways are becoming popular in Europe,” Haro explains, “and people wanted to try them in the Northeast. They’re relatively inexpensive, and theoretically allow more fish species to pass upstream. However, nobody had done the testing with our northeastern species, so that was our project.”
Once the 75-meter-long fishway was in place, the three-month monitoring project began. Haro’s group needed to collect two kinds of data: numbers of fish traveling upstream through the fishway, and water flow. Ideally, each would be monitored constantly.
The species the group chose to monitor was alewife. In the past, fish were counted for such projects by people watching for fish passing the technical fishways, which is difficult to do for long periods of time and is subject to human error. For this study, the researchers captured and implanted Passive Integrated Transponder (PIT) tags into about 400 fish; the tags act just like electronic tags used at highway toll booths, and are detected by telemetry antennas and receivers located every 10 meters or so along the fishway.
Monitoring water flow through the fishway was also crucial to the study. Haro’s team chose to use HOBO® Water Level Loggers manufactured by Onset, and used data from those to calculate flow. The cigar-shaped, stainless steel loggers run for many years on a single battery, and allow the user to easily designate the logging interval. They monitor water level 24 hours a day, and the data values are time-stamped so they can be correlated to other data.
Haro’s group found the data loggers easy to use. He said, “I handed the box to a grad student, and within an hour, she figured it out and was ready to go.” The logger’s point-and-click configuration makes it easy to set up the desired sampling interval and start time, as well as download and graph data with a few clicks of a mouse.
The researchers only needed two water level loggers. They deployed three, however - one above the fishway, one below for data verification, and a third 50 meters away in a telemetry receiver housing, for barometric compensation. The field site was in a highly visible and heavily visited area, but there were no problems with vandalism, as the researchers housed the loggers inside sections of two-inch steel pipe anchored to 60-pound boulders that were placed in the stream. The data were downloaded weekly to a laptop computer for graphing and analysis using Onset’s HOBOware® Pro software, and the time-stamped data were easily matched with the fish count data.
Haro is pleased with the HOBO loggers’ performance, and appreciates that they are relatively inexpensive and reusable. He has used them again for a similar project in Connecticut, and hopes to deploy them in another river next spring. He also uses several water level loggers in the lab, a flume facility where full-scale fishways are built and tested. “They are simple to set up, and are much easier than hooking up wired sensors and cables and dedicating a computer to data logging,” he said.
Overall, the performance results of the new nature-like fishway at Town Brook were good. About 95% of the alewives that tried to make it up the fishway during the study period succeeded, which suggests that nature-like fishways may be acceptable structures in future river and stream restoration projects.