{"id":8428,"date":"2016-09-01T15:22:00","date_gmt":"2016-09-01T19:22:00","guid":{"rendered":"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/?page_id=8428"},"modified":"2024-08-21T15:20:11","modified_gmt":"2024-08-21T19:20:11","slug":"naturalists-notebook-the-quiet-decline-of-the-humble-eel","status":"publish","type":"post","link":"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/naturalists-notebook-the-quiet-decline-of-the-humble-eel\/","title":{"rendered":"NATURALIST’S NOTEBOOK: The Quiet Decline of the Humble Eel"},"content":{"rendered":"\n\n\n\n\n

Janna Sasser recently graduated from North Carolina State University with a degree in communication and a minor in journalism.<\/em><\/p>\n\n\n\n

\"American
This close-up photo shows a larval American eel, which hatches in the eerily calm Sargasso Sea near Bermuda. Photo courtesy NOAA teacher at Sea Program.<\/figcaption><\/figure>\n\n\n\n

Standing at the end of a dock on the Neuse River, a young John Fear would cast, wait for a bite, and soon feel the thrilling tug at the end of the line.<\/p>\n\n\n\n

Reeling in the olive, snake-like body \u2014 its skin thick and slimy \u2014 he\u2019d plop the young eel in a bucket, and cast again.<\/p>\n\n\n\n

\u201cI could catch them left and right,\u201d he recalls. \u201cI had no idea what they were, but I knew they had teeth.\u201d<\/p>\n\n\n\n

Today, Fear is an estuarine biogeochemist and North Carolina Sea Grant deputy director \u2014 and the chances of catching an American eel, Anguilla rostrata<\/em>, are slim. The rivers and streams of eastern North America, once coursing with spring runs of eels, now are nearing historically low levels of these fish.<\/p>\n\n\n\n

\u201cThe decline of American eel populations raises a concern about the health of our tidal creek habitats,\u201d Fear adds.<\/p>\n\n\n\n

The most recent stock assessment by the Atlantic States Marine Fisheries Commission, or ASMFC, in 2012 noted that the American eel stock was depleted in United States waters after drastic declines in recent decades.<\/p>\n\n\n\n

\u201cDespite population declines along the Atlantic Coast, there are no demographic rates and surprisingly little basic demographic data on American eel populations for the southeast United States,\u201d notes Paul Rudershausen, a doctoral candidate at North Carolina State University\u2019s Center for Marine Sciences and Technology, or CMAST.<\/p>\n\n\n\n

With funding from Sea Grant, Rudershausen is working with project lead Jeffrey Buckel, a fisheries biologist at CMAST, to study the stock status of eels in North Carolina tidal creeks.<\/p>\n\n\n\n

Juvenile American eels are commonly found in estuarine regions, some moving inland to settle in freshwater streams, and others making homes in brackish or saltwater habitats.<\/p>\n\n\n\n

Once establishing a home range, they may live undisturbed in forgotten pools for decades. Rudershausen is interested in the demographic trends of eels \u2014 changes in the eel population over time.<\/p>\n\n\n\n

\u201cThere seems to be a lot of disagreement about the status of this species,\u201d he explains. \u201cA literature search on the demographics of American eels along the Atlantic Coast reveals almost no information on a species that\u2019s historically been very important \u2014 and now, by most accounts, on a dramatic decline.\u201d<\/p>\n\n\n\n

The goal of the project, Buckel notes, is to relate demographic rates with different attributes of urbanization. \u201cFor example, if one creek is more urbanized than another, we can compare abundance and survival rates.\u201d<\/p>\n\n\n\n

In 2015, the team began sampling for juvenile eels in the tidal creeks of Carteret County. Using six different sites, they are studying habitat factors that may affect the survival rate of American eels.<\/p>\n\n\n\n

SLIPPERY BUSINESS<\/h2>\n\n\n\n

In an era when the chromosomes of many organisms are mapped and sequenced, much about the biology and behaviors of American eels remains a mystery.<\/p>\n\n\n\n

\"Sargasso
The Sargasso Sea has a reputation for being the demise of sailors. With little wind, vessels lay stagnant for days, leading to historical accounts of ships found drifting and derelict with no crew on board. Photo courtesy NOAA Freshwater and Marine Image Bank.<\/figcaption><\/figure>\n\n\n\n

There are a few things known about eels. All eels found in eastern North America and in Europe hatch in the Sargasso Sea. They are carried by ocean currents to the mouths of rivers, where they begin their journey upstream. Most of their life is spent inhabiting creeks and rivers until eventually returning to the Sargasso, where they lay eggs and die.<\/p>\n\n\n\n

This is the consensus among biologists and naturalists today, although no adult eel had ever been found swimming, reproducing or dying in the Sargasso Sea until 2015. That year, a team of researchers in Canada successfully tracked one adult eel from the coast of Nova Scotia to the northern limit of the spawning area in the Sargasso, near Bermuda.<\/p>\n\n\n\n

\u201cThat\u2019s the first actual documentation of an adult eel making the trip,\u201d Buckel notes. \u201cUntil then, everyone just speculated that\u2019s what happened because that\u2019s where you find American eel larvae, so they knew adults had to be there.\u201d<\/p>\n\n\n\n

Several dozen others tagged were never documented beyond the Gulf Stream.\u201c<\/p>\n\n\n\n

American eels are catadromous, meaning they hatch in the ocean, mature in fresh water and migrate back to the ocean to spawn,\u201d explains Thomas Fenske, curator of fish and invertebrates at the North Carolina Museum of Natural Sciences.<\/p>\n\n\n\n

The species extends from Greenland to northern South America, Rudershausen notes. \u201cAll adult eels from those freshwater rivers go to the Sargasso Sea to spawn,\u201d he says. Because of this unique cycle \u2014 with every American eel coming from the same grounds, and returning there to spawn \u2014 American eels are considered to be one \u201cstock.\u201d<\/p>\n\n\n\n

The Sargasso Sea is strange and unique in itself. Lying deep within the Atlantic near Bermuda, it\u2019s the only sea with no land border. Instead, its body of encircling currents is defined by other major ocean currents, such as the Gulf Stream to the west.<\/p>\n\n\n\n

With no coastline, the waters are uncannily calm, and remain warmer and saltier than surrounding waters. And it is vast. The Sargasso Sea stretches approximately 700 miles east to west and 2,000 miles north to south, and is canopied by large, floating mats of golden Sargassum<\/em> seaweed.<\/p>\n\n\n\n

American eels journey thousands of miles to spawn in these waters, retracing the route they took as larvae. In preparation for the return journey, sexually mature females gorge  themselves, Fenske notes, changing color from muddy yellow-green to dark green on top and snow white on their bellies.<\/p>\n\n\n\n

\"eel
Eels are anesthetized, measured, weighed and tagged before being released at the same location as capture. Photo by Gloria Putnam.<\/figcaption><\/figure>\n\n\n\n

Once reaching estuarine waters, the first leg of their journey completed, they never eat again. Their pupils expand and turn blue, adapting to new sight for the depths of the sea.<\/p>\n\n\n\n

\u201cThey follow the Gulf Stream to the Sargasso,\u201d Fenske explains. \u201cOnce there, they release thousands of eggs for the males to fertilize, and then die from exhaustion and starvation.\u201d<\/p>\n\n\n\n

Though spawning activity remains undocumented, larval eels \u2014 flat, transparent and the shape of a willow leaf \u2014 are found floating and swimming in these waters for months before passively drifting with the ocean currents, riding the Gulf Stream to the eastern coast of the Americas.<\/p>\n\n\n\n

At this stage, the leptocephali, or larval eels, are barely more than a thin layer of muscle housing a clear, jelly-like substance. They have a simple tube gut and a small, pointed head with teeth.<\/p>\n\n\n\n

\u201cWhen they sense fresh water close by, the eels metamorphose and begin actively swimming toward the coast,\u201d Fenske explains.<\/p>\n\n\n\n

Juvenile glass eels \u2014 sinuous ribbons merely inches long and clear as glass \u2014 reach the coast after approximately a year, swarming into the mouths of estuaries by the millions.<\/p>\n\n\n\n

Upon arriving, they develop brown pigmentation, a camouflage in the murky water, and are known as elvers. \u201cThey continue to develop slowly, their changes occurring as salinity decreases,\u201d Fenske explains.<\/p>\n\n\n\n

The young eels spend the majority of their life inhabiting inland streams, ponds and rivers as they mature. They continue upstream \u2014 sometimes moving as far inland as the Mississippi River \u2014 until something tells them they\u2019ve reached home. They may live there up to 30 years, Buckel notes, burrowed under stones and logs by day, and surfacing to roam and feed at night.<\/p>\n\n\n\n

This period spent in freshwater and estuarine environments is crucial for the maturing eel. It will transform from an elver \u2014 merely inches long and barely pigmented \u2014 to a yellow eel, growing up to 3 feet and becoming mottled yellow and olive. It will stay here, feeding, growing, swelling and darkening until reaching sexual maturity. Then it heads downstream, ready to return to its spawning grounds.<\/p>\n\n\n\n

GETTING TO THE BOTTOM OF TIDAL CREEKS<\/h2>\n\n\n\n

The research in Carteret County\u2019s tidal creeks stems from Sea Grant\u2019s 2014 Research Symposium, titled Investments and Opportunities.<\/p>\n\n\n\n

\u201cOur stakeholders identified particular areas of the state\u2019s coastal needs,\u201d Fear recalls. \u201cThis project ranked high and fit into one of those categories \u2014 tidal creek systems.\u201d<\/p>\n\n\n\n

These creeks provide pathways for American eels as they journey from their natal ocean waters. For some, the creeks are home until making their return trip.<\/p>\n\n\n\n

Tidal creeks begin in upland areas and drain into larger creeks, which connect to estuaries and the ocean. They are links between land and estuary, transporting organisms and nutrients with flooding and ebbing tides. They also transport pollutants.<\/p>\n\n\n\n

\u201cOften, upper portions on headwaters of tidal creeks are underappreciated, but important to consider,\u201d notes Gloria Putnam, Sea Grant coastal resources and communities specialist. \u201cThey are complex, ever-changing systems, and on low tides, can be a harsh place for humans,\u201d she adds, \u201cyet they provide homes to unique species that are becoming scarce.\u201d<\/p>\n\n\n\n

\"eel
Baited minnow traps were set in several locations throughout each creek for 24-hour cycles to target nocturnal, yellow-phase eels. Photo by Gloria Putnam.<\/figcaption><\/figure>\n\n\n\n

These landscapes are highly prone to degradation due to their proximity to the uplands they drain. \u201cPeople want to develop on or around the water, so these systems are often moderately to highly impacted,\u201d Putnam explains.<\/p>\n\n\n\n

Putnam joined Rudershausen and Buckel during a sampling trip in April. \u201cI was surprised to learn eels would migrate up to and live in these shallow, narrow portions of creeks \u2014 areas that many might consider useless,\u201d she recalls.<\/p>\n\n\n\n

Twice monthly, the team deploys baited minnow traps in each of the creeks. Captured eels are anesthetized, measured and weighed before being tagged with a transponder device. Transceiver systems installed within the creeks detect the tags, and from the data, the researchers can estimate daily survival rates of the tagged eels.<\/p>\n\n\n\n

Several of the creeks run through residential neighborhoods, or hide behind busy, developed highways. These creeks, found in the midst of Morehead City\u2019s industrialized areas, are particularly vulnerable to habitat degradation, with minimal vegetation to buffer the effects of runoff from nearby development.<\/p>\n\n\n\n

A few sites, however, have relatively natural habitats, bounded by salt marsh with nearby vegetated areas.<\/p>\n\n\n\n

\u201cWe\u2019re sampling across a range of development impacts that are being experienced along the Carolina coastline,\u201d Rudershausen says.<\/p>\n\n\n\n

And that\u2019s by design, Buckel adds. \u201cOur sampling sites provide a determination of what habitat types are important to yellow-phase eels,\u201d he notes.<\/p>\n\n\n\n

\u201cAt the end of the project, we\u2019ll be able to test what habitat factors are important to juvenile eels\u2019 presence or absence at each site.\u201d<\/p>\n\n\n\n

RELATED EEL RESEARCH<\/h3>\n\n\n\n

North Carolina Sea Grant has supported other eel research, including:<\/p>\n\n\n\n