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Bay Blog: American eel

May
30
2014

Photo Essay: Monitoring American eels with the U.S. Fish and Wildlife Service

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.



Nov
19
2012

Six things the Chesapeake Bay is thankful for

Thanksgiving is the perfect time to express gratitude for the good in life. We have much to be thankful for—and so does the Chesapeake Bay! Here is a look at six moments from the past year that signaled good news for the watershed.

6. A sustainable blue crab population. The most recent report on the Bay’s blue crab stock reveals a population that has reached sustainable levels and is not overfished. Winter estimates place the adult female blue crab population at 97 million, based on a dredge survey taken at almost 1,500 sites throughout the Bay. The survey also measured more juveniles than have been counted in the past two decades. A stable blue crab population means a more stable Bay economy, with watermen employed, restaurants stocked and recreational crabbers (and crab-eaters!) happy.

Image courtesy Erickson Smith/Flickr

5. Additional American eels. American eel numbers are up in the headwater streams of Shenandoah National Park, following the removal of a large dam that once blocked eels from moving upstream. Other anadromous swimmers like shad, herring and striped bass—which must migrate from the ocean into rivers to spawn—are also using this reopened habitat. Our rivers are thankful to see the return of these important residents.

4. A huge boost in oyster restoration. This year, restoration partners in Maryland put more than 600 million oyster spat into the Chesapeake Bay in the largest targeted restoration effort the watershed has ever seen. While some of the oyster larvae went into the Upper Bay, most went into Harris Creek, a tributary of the Choptank River that was declared an oyster sanctuary in 2010. While habitat loss, disease and historic overfishing have contributed to a dramatic decline in native oyster populations, planting “spat on shell” onto harvest-safe sanctuaries is one way to bring the water-filtering bivalves back.

3. A lot of living shorelines. When shorelines wash away, fish, crabs and other wildlife lose valuable habitat, and coastal landowners lose their lawns. To curb shoreline erosion, coastal property owners are turning toward living shorelines, which replace hardened bulkhead and riprap with grasses and trees. This summer, the Chesapeake Bay Trust’s Living Shorelines program awarded $800,000 to 16 homeowner associations, non-profit organizations and towns to install more than 6,800 feet of living shoreline and wetland habitat in the Chesapeake Bay watershed.

2. Greater green infrastructure. With the implementation of green infrastructure, cities can use the natural environment to better manage stormwater runoff. Green roofs, rain gardens and pervious pavement, for instance, can absorb stormwater runoff before it flows into local rivers and streams. This year, the U.S. Environmental Protection Agency (EPA) and the National Fish and Wildlife Foundation (NFWF) awarded $4 million to local governments for green infrastructure projects. But the environment is not the only one who will be thankful; green infrastructure can revitalize communities and produce cost benefits that can exceed those of traditional stormwater management methods. We are grateful that more towns will be greener in both color and concept!

1. Long-term improvements in Bay health. A number of Bay monitoring sites have shown long-term improvements in nutrient and sediment levels. According to an August report from the U.S. Geological Survey (USGS), one-third of monitoring sites have shown improvement in sediment concentrations since 1985, two-thirds have shown improvement in nitrogen concentrations and almost all have shown improvement in phosphorous concentrations. These improvements in long-term trends indicate pollution-reduction efforts—from upgrades to wastewater treatment plants to cuts in fertilizer use on farms and suburban lawns—are working.

Caitlin Finnerty's avatar
About Caitlin Finnerty - Caitlin Finnerty is the Communications Staffer at the Chesapeake Research Consortium and Chesapeake Bay Program. Caitlin grew up digging for dinosaur bones and making mud pies in Harrisburg, Pa. Her fine arts degree landed her environmental field work jobs everywhere from Oregon to Maryland. Now settled in Baltimore, she is eagerly expecting her first child while creating an urban garden oasis on her cement patio.



Aug
06
2012

American eel numbers rise after dam removal

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.



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