A school of alewife spawn in the calm shallows where Deer Creek meets the Susquehanna River in Susquehanna State Park in Havre de Grace, Maryland, on April 16, 2015.
Alewife (Alosa pseudoharengus) and their close relative blueback herring (Alosa aestivalis) are collectively known as "river herring." The two can be difficult to distinguish from one another—both are thin, silver-sided fish, each with a single dark spot located behind its head. Alewife, however, can be distinguished by their bronze-green backs, whereas the aptly named blueback has a blue-colored back.
River herring are anadromous: they spend their adult lives at sea, returning to freshwater areas only to spawn in the spring. The small fish serve as important prey for larger predators like striped bass and bluefish. They also once served as one of the largest fisheries in the Chesapeake Bay; in 1931, over 25 million pounds of river herring were harvested from the estuary.
But the destruction of spawning habitat, the constructions of dams restricting migration and increased fishing pressure led to a major decline in river herring abundance. In 2006, commercial catch of river herring for the entire Atlantic coast totaled just 823,000 pounds. By 2012, Maryland, Virginia and the Potomac River had harvest moratoriums for river herring in place, as did many other states along the East Coast.
To restore herring to the Chesapeake Bay, experts like the Chesapeake Bay Program’s Fish Passage Workgroup are helping to remove barriers such as dams and culverts where they block waterways and prevent river herring from migrating. Where structures are unable to be removed, fish ladders and lifts help fish get over or around larger barriers.
Image by Will Parson
American shad larvae start to hatch from eggs collected from the Potomac River at the Van Dyke Research Station for Anadromous Fishes in Port Royal, Pennsylvania. Anadromous fish, like shad, live their adult lives in the ocean, but migrate back to freshwater rivers and streams to spawn.
Shad are an iconic species of the Chesapeake Bay region, but a combination of pollution, overfishing and the blocking of their migratory paths has led to a decline in their populations. To help boost shad numbers, federal, state and tribal governments have raised young shad in hatcheries and released them in rivers across the region.
But in order to sustain a stable population, shad need to be able to reproduce for themselves. As migratory fish, they require clear passage from the ocean to where they spawn in the Chesapeake’s freshwater tributaries, but barriers such as dams and culverts block waterways and separate shad from their spawning areas. The Chesapeake Bay Program’s Fish Passage Workgroup works with state agencies, local governments and nonprofits to remove these barriers where possible.
There are some places where barriers can’t be removed, such as the Conowingo Dam on the Susquehanna River, so the dam’s owner, Exelon Corporation, built a fish lift to help transport shad upstream. Unfortunately, despite some early success with the lift—transporting as many as 193,000 shad in 2001—annual catches have been steadily declining, with only 8,341 shad transported in 2015.
In an attempt to increase those numbers, in April 2016, the U.S. Fish and Wildlife Service announced a 50-year agreement with Exelon to help American shad migrate up the Susquehanna River to spawn. Exelon agreed to make structural changes, including improvements to the fish lift, to help attract shad to the lift and create enough room so they aren’t crowded out by other fish. The company also pledged to truck up to 100,000 shad upstream.
Learn more about the important role shad play in the Chesapeake Bay ecosystem and the work being done to restore them.
Image by Will Parson
Though they spend most of their lives at sea, American shad are nonetheless dependent on the tributaries of the Chesapeake Bay every spring. They are the largest of five species of river herring that swim upstream to spawn in freshwater, a fact that once made them easy pickings for nearby residents. Native Americans and European colonists—tipped off to the shad’s return by the blooming of the aptly-named shadbush—would use baskets, nets and traps to catch the fish.
But population growth put more pressure on the species, and the construction of dams and other structures blocked migrations to shad habitat. The 1980s and 90s saw the closure of commercial shad fisheries in Maryland and Virginia.
To see the efforts of shad restoration today, one can simply follow the shad as they make the same upstream migration they always have. First efforts tap into the same seasonal migration. Adult shad are caught just before spawning, and their fertilized eggs are sent to hatcheries to help restock tributaries. Some dams have been removed, while others, like Conowingo Dam on the Susquehanna River, have implemented fish lifts or other measures to allow shad and other anadromous species to pass. Between 1989 and 2015, more than 3,300 miles of fish passage were opened in the Chesapeake Bay watershed.
By 2014, shad numbers in some tributaries had improved significantly. Shad were above targets in the Potomac and Rappahannock rivers, though they were less established in the lower James and York and negligible in the upper James and Susquehanna.
To view more photos, visit the Chesapeake Bay Program’s Flickr page
Photos and text by Will Parson
Each spring, migratory fish use the rivers and streams of the Chesapeake Bay watershed to move between fresh water and the saltier ocean. Anadromous species—like American shad, hickory shad and blueback herring—return from the ocean to lay their eggs in fresh water, while catadromous species—like the American eel—move from streams to the ocean to spawn. While dams and culverts can block the movement of these fish, dam removal and fish passage construction projects have reopened thousands of area stream miles to fish migration.
According to the Maryland Department of Natural Resources, 33 fish species have ascended a fish lift, ladder or other structure in the state. While this indicates the value of fish ladders, lifts and other structures that help move fish over dams, it’s important to note the shift that new research has brought to fish passage restoration.
“Our [fish passage] program has changed over the years,” said Nancy Butowski, who manages fish passage in Maryland and serves as a member of the Chesapeake Bay Program’s Fish Passage Workgroup. “In the 1990s, it was focused on providing fish passage through ladders. But…fish passages are not 100 percent efficient. Now, we prefer dam removal.”
Dam removal can benefit a wider range of species—like the resident fish who also move up and downstream at different times of year—and the stream itself, Butowski said. Depending on the dam, its removal can even benefit human health: there have been several deaths at the Patapsco River’s Bloede Dam, which is slated for removal.
Maryland has worked with Pennsylvania, Virginia and the Nature Conservancy to develop a tool that will prioritize fish passage restoration projects. It takes close to 40 different characteristics into account, including how many miles a project would open, how much a project would cost and whether there are migratory fish currently using the waterway. Through the Chesapeake Bay Watershed Agreement, the Bay Program has committed to reopening 1,000 more stream miles to migratory fish by 2025. Learn more about our work to reopen fish passage.
A habitat is the natural environment in which plants, animals and other organisms live, feed and breed. Many habitats are shared by numerous living things, forming what is called an ecosystem. Ecosystems range in size and can be as tiny as a patch of dirt or as large as the Chesapeake Bay watershed.
Sometimes, different species within the same ecosystem are forced to compete for resources like food, water and shelter. Dominant species and environmental stressors can take their toll on lesser plants and animals.
Rapidly increasing human development contributes to this environmental stress: as our population rises, so does our demand for the same resources that many plants and animals also depend on to survive. We build dams to control stream flow and capture energy, develop wilderness into urban hubs and use our finite freshwater resources at an alarming rate.
Migratory fish are particularly sensitive to ecosystem changes because they rely on certain migration routes between connected habitats to reach their breeding grounds. Dams, road culverts and other blockages that fragment waterways can act as barriers to fish passage.
In an effort to better understand the effect that dams and other manmade structures have on fish passage, Steve Minkkinen, project leader at the U.S. Fish and Wildlife Service (USFWS) Maryland Fisheries Office, has teamed up with the U.S. Geological Survey (USGS) and the U.S. Army Corps of Engineers to conduct a 10-year survey of American eel populations in the Susquehanna River.
“We learned quite a bit in 2013. We collected 300,000 juveniles [eels] and transported them above the [Conowingo] Dam. The dam has been blocking the [eels’] migration up the Susquehanna River,” Minkkinen explained. “There has been a lot of work [to open] upstream passage for shad and river herring,” Minkkinen continued. But that work has only focused on adult fish, and as Minkkinen pointed out, the dam’s flow is too fast for younger eels to travel through.
Monitoring American eels is important: at historic levels, they made up 20 percent of the freshwater biomass along the Eastern seaboard. However, the introduction of dams and other structures has blocked eel populations from important migration routes, changing eel populations.
Researchers capture and inject chips known as passive integrated transponders, or PIT tags, into the eels. These tags can be detected in future surveys and help the team track eel populations by letting them know if they are encountering a new eel or one that was caught during a previous survey.
The American eel is the only catadromous fish in the Bay region, which means they spend most of their lives in fresh water but migrate to the ocean to spawn. Spawning takes place in late January when the fish swim out of the Bay and into the Sargasso Sea, a portion of the Atlantic Ocean east of the Bahamas.
Eel larvae drift in ocean currents for nine to 12 months before reaching fresh water and swimming upstream. Monitoring allows scientists to study the migration habits of juvenile eels and learn how to aid their upstream journey.
Minkkinen and his team believe that if fish passage to the upper Susquehanna opens, both American eels and freshwater mussels would thrive. This bivalve relies on fish to store their eggs in their gills until the mussels turn into microscopic juveniles and drop off. Mussel populations in the upper Susquehanna are, for the most part, comprised of older, larger individuals. Because mussels are natural filter feeders, Minkkinen’s team believes that a rise in freshwater mussels will lead to cleaner water and a healthier ecosystem.
“Our hopes are that we can develop passage and restore eel and mussel habitat to that [upper Susquehanna] portion of the watershed,” Minkkinen said.
To view more photos, visit the Chesapeake Bay Program Flickr page.
Images by Steve Droter. Captions by Jenna Valente.
More than 40 miles of the Patapsco River will be opened to the annual migrations of herring, alewife and American shad once the waterway’s lowermost dam is removed.
Bloede Dam has blocked the passage of migratory fish for close to a century. It has also posed a public safety hazard, creating strong currents that have killed a number of swimmers. Its removal is the next step in the Patapsco River Restoration Project, and will be funded by a $3.57 million grant from the National Oceanic and Atmospheric Administration (NOAA)’s Restoration Center to American Rivers.
American Rivers has worked on the Patapsco project for the past five years with NOAA, the Maryland Department of Natural Resources (DNR) and the Friends of the Patapsco Valley State Park. The river’s Union and Simkins dams were removed in 2010 and 2011 in order to create better habitat for fish and a safer swimming hole for people.
“Removing one dam can make a major difference in the health of a river and its fisheries. But removing multiple dams… is really a game-changer,” said Serena McClain, director of river restoration at American Rivers, in a media release.
The Chesapeake Bay Program tracks the opening of fish passage as an indicator of Chesapeake Bay health, and has achieved 91 percent of its goal to open more than 2,800 miles of fish passage by 2014. Because dams, culverts and other barriers can disrupt the natural flow of rivers, their removal can mean a boost in habitat, a drop in pollution and improved protection from flooding.
Learn more about the removal of Bloede Dam.
American eel numbers are up in the headwater streams of Shenandoah National Park, following the 2004 removal of a large downstream dam.
Significant increases in upstream American eel populations began two years after the Rappahannock River's Embrey Dam was removed and have continued nearly every year since, according to a report released last week by the U.S. Geological Survey (USGS), U.S. Fish and Wildlife Service (USFWS) and National Park Service (NPS) researchers.
Image courtesy EricksonSmith/Flickr.
Dams can act as travel barriers to American eels, which undertake long-distance migrations from their ocean spawning grounds to freshwater streams along the Atlantic coast. While American eels can surpass substantial natural barriers--like the rapids of the Potomac River's Great Falls, for instance--dams pose a more difficult obstacle and have contributed to the widespread decline in American eel populations. Dam removal, therefore, could have long-term benefits for eel conservation.
"Our study shows that the benefits of dam removal can extend far upstream," said USGS biologist Nathanial Hitt. "American eels have been in decline for decades and so we're delighted to see them begin to return in abundance to their native streams."
Embrey Dam, which once provided hydroelectric power to Fredericksburg, Va., was breached in 2004 following years of work by nonprofit organizations and city, state and federal government agencies. Its removal was intended to benefit more than the American eel, however, as dams can impact a number of fish that must migrate up rivers to spawn.
"Shad, herring and striped bass are also using reopened habitat on the Rappahannock River," said Alan Weaver, fish passage coordinator for the Virginia Department of Game and Inland Fisheries. "It's exciting to see a growing number of species benefiting from dam removal in Virginia."
Learn more about American eel abundance in Shenandoah National Park.