New Web-Based Fish Counter Allows Citizens to Contribute to Rejuvenation of a Downeast River

Pembroke - The Maine Department of Marine Resources (DMR) has launched a new feature on its website that lets citizens contribute to the assessment of river herring on a downeast Maine river.

The feature, located on DMR’s website, allows visitors to watch river herring, which include alewives and blue back herring, as they pass in front of a camera mounted in the Pennamaquan River, located in Pembroke. Viewers can enter the number of river herring swimming in front of the camera into a simple web form.

The data will be used by the department to determine if the Pennamaquan can support a commercial harvest of river herring.

River herring are anadromous (sea-run) fish that spend most of their life at sea but return to freshwater to spawn. They are important to the ecology of freshwater, estuarine, and marine environments, providing forage for osprey, eagles, great blue heron, loons and other fish-eating birds, as well as marine mammals and freshwater and marine fish.

River herring also provide important commercial benefits as revenue for towns that lease their fishing privileges to harvesters, and economic opportunity for the harvesters who catch and sell them as bait for Maine’s valuable lobster fishery.

In addition, river herring offer recreational opportunities for people who want to catch and smoke them for personal consumption.

For several decades the Pennamaquan River provided large quantities of river herring for commercial harvest and served as a local source of fish for personal use. Over the years the ability of sea-run fish to reach spawning habitat on the Pennamaquan deteriorated.

Aging fishways, inability to monitor run size, and obstructed passages led to a decline in river herring populations. Through the hard work and cooperation of state and local governments, Maine Sea Grant, the Passamaquoddy Tribe, Downeast Salmon Federation, and other partners to restore passage, river herring populations are increasing significantly.

However, in order to restore the river herring run for commercial harvest, fish counts must be collected and provided to DMR, which will determine whether the run has a sustainable population before it can be harvested.

“The Pennamaquan River is now returning fish in ever increasing numbers and may once again be able to support commercial catches and increases in recreational fishing opportunities,” said Mike Brown, a scientist with DMR’s Bureau of Sea Run Fisheries and Habitat.

“River herring returns to the river have increased to the point where conventional electronic counting methods can no longer be used due to the numbers of fish returning to the sea after they have spawned in the lake and riverine habitats available in the watershed,” said Brown.

Electronic counting involves a device made of PVC tubes wired with electromagnetic fields which detects and counts fish as they pass upstream. The system performs well when fish are moving upstream, but river herring are reluctant to pass downstream through the tubes as they return to the ocean, which requires that the device be removed to allow for downstream passage, resulting in missed counts of fish moving upstream.

“Video count systems that provide passage for fish moving upstream and downstream are now the best option to continue to monitor the increase in population size on the Pennamaquan River,” said Brown. 

Using the counter is simple and easy. Viewers watch pre-recorded video clips of varying length of river herring as they cross in front of the camera, and then enter the number of fish seen in the video into a form. The video can be paused and started if viewers need time to write the number of fish on paper before entering the total into a web form.

Instructions and frequently asked questions documents are available for users.

The technology for this project was provided by the Mystic River Watershed Association in Mystic Connecticut, which uses similar technology for counting river herring on the Mystic River. Maine Sea Grant installed and monitored the video counting system and provided critical oversight for the project.

"Recording video of migrating river herring allows for unobstructed passage for fish of all sizes, including larger American shad that we have found stranded below the electronic counter in recent years,” Said Chris Bartlett, Senior Extension Program Manager of Maine Sea Grant. “Counting fish on the videos is easy, including the ability to slow down or speed up the footage depending on how many fish are swimming past the camera.  We would greatly appreciate interested volunteers to help us with counting fish on these videos."

“This new counter is a great way for anyone, from students to community members, to participate in citizen science that will help rejuvenate the ecology and economy of a downeast river,” said Brown.

For information or to use DMR's river herring counter, visit