Saving the American eel

Eels are a very mysterious animal. And even though they can be found virtually everywhere in the globe, in fresh and salt water ecosystems alike, very little is known about them.

I find eels fascinating because they are totally bizarre. They challenge all the paradigms of normality in the biological world—at least as perceived by a humble economist as myself.

This post is a distillation of the weird things I learned about ecology while participating on an economics project looking at ways to protect the declining population of American eels in the Southeast of the U.S.

The American eel is a rare fish—so rare that it even belongs to a rare taxonomy: the catadromus fish. These kind of fish are migrate from fresh water to spawn in the sea—exactly the opposite of salmon. As you would expect from a rare fish, Eels (American and European at least) are born in, of course, in a rather rare place: near the Bermuda Triangle. That’s right, they are born in the middle of the Atlantic Ocean, in what is called the Sargasso Sea.

Immediately after they are born, eels begin to travel—drifting with ocean currents—to the coasts and estuaries of the American continent (recent records report they have been found from the coastlines of Venezuela to those of Greenland and Iceland). Once infant eels (also known as elvers) reach the coastlines, they either stay in the estuaries to become adult males or continue their migration into streams, rivers and lakes where they feed and mature into female eels.

Female eels live in fresh waters for approximately 10 to 25 years. Adult eels typically have a yellow color. However, once they reach sexual maturity, they begin a complicated metamorphosis process to become ready for a long trip back to the Sargasso Sea. To prepare for their migration back to the Sargasso Sea, eels undergo a bizarre host of physiological changes: they acquire a silver color, their eyes enlarge, their skin thickens, their digestive tract degenerates—as they won’t be feeding at all during their journey, their kidneys turn into some sort of air cavities that will allow them to float in the Ocean ad take advantage of Oceanic currents, their pectoral fins adapt to the oceanic environment, and they undergo a multitude of hormonal changes to increase the supply of energy and stamina for the long haul. Long story short, they are no longer well suited for riverine conditions, and being totally uncomfortable as they are, they are terribly anxious to find their way to the Ocean.eels cycle

The trip back to the Sargasso Sea can be as long as 6,000 kilometers for some eels, and it may take years to complete. Once they’ve reached the spawning grounds, each female eel will lay up to 4 million eggs. After such an inconceivable feat of endurance and speed, she, of course, dies—therefore completing her life cycle.

The important points to take away for the remainder of this story are the following:

  1. Once they are sexually mature, female eels change their bodies to such degree that they are absolutely uncomfortable in freshwater ecosystems. They want to reach the Ocean as fast as possible.
  2. Given that the migration to Sargasso can be thousands of kilometers long, it is imperative for eels to conserve as much energy as possible during their migration.

Eels are efficient swimmers. With their hydrodynamic shape and their sturdy completion not only do they exploit the power of water currents but if necessary they can crawl their way through land—eels can survive out of water for ours by exuding a mucus coat over themselves when they jump out. Yet, even with an advantageous physic, anything that reduces their ability to swim efficiently is sure to damage their chances of reaching the Sargasso Sea.

Dams are one such obstacle.

Oh Dam!

 Eel populations across the world have been in sharp decline over the last few decades and multiple efforts have been put forward to recover their populations. To the point that the U.S. Fish and Wildlife Service has been petitioned to list it as a threatened or endangered species under the ESA.

As I described above, the eel’s complex life cycle implies that its reproductive success depends heavily on being able to easily travel downstream during their spawning migration. Dams in run-of-river hydroelectric power plants are one of the many threats obstructing eel passage; depending on the timing, hydrology, and operating characteristics of a given facility, dams can represent a significant risk to eels through migratory delay and turbine mortality—I want to emphasize here, what turbine mortality means. It means that eels get tangled in the turbines while passing through the dam: the hydropower plants become a sushi factory, essentially. (These facilities are especially problematic for eels and not for other fish because of their long shape.)

eels dam

Sushi aside, in an effort to reduce turbine-related mortality of adult American Eels during their downstream migration to the Atlantic Ocean, hydropower dam operation in the Shenandoah River System is regulated following Federal Energy Regulatory Commission’s (FERC) relicensing conditions. For the majority of the facilities that I am aware are regulated, the current policy prescribes a shutdown of turbines from September 15 to December 15 during the hours between dusk and dawn (when the Eels are believed to be moving).

September 15 to December 15. Dawn to dusk. These seem rather arbitrary and aesthetically appealing parameters, don’t they? In fact, the details of the policy are rather authoritative and based on highly uncertain scientific knowledge suggesting that this schedule of operation is a reliable way to minimize eel mortality.

However, the migration of eels from rivers to the spawning grounds in the Sargasso Sea is one of the greatest mysteries in marine biology, and recent tracking studies have shown that downstream migration is not limited to the fall season and may be influenced by non-seasonal ecological cues, such as water flow, in addition to seasonal environmental factors like water temperature and, mysteriously enough, the phase of the moon (Eyler, 2014).

Recent studies show that substantial eel mortality outside of the regulated time period. Since protective policies do not necessarily prevent mortality, they should be revisited to accurately reflect the actual patterns of eel migration. Better yet, why not to just shut them down all year long and this way reduce eel mortality to zero? Furthermore, it is widely known that the damming and development of rivers can permanently impact the visual landscape, interrupt natural river flow and harm aquatic resources and local ecosystems. Complete closure of these power plants seems like a great idea, or… does it?

Back to the economics

It has been established above, that there are benefits from shutting down the turbines at run-of-river hydroelectric power plants: reduced eel mortality. However, there are also costs. And if you have read my posts, you know I am all about taking both, benefits and costs into account. Not only have I been trained in this discipline as an economist, at the personal level, I just love playing devil’s advocate.

So, what are the costs?

Well, the shutting down of the turbines implies no water will pass through them and no energy will be generated. That no electricity is generated is a direct cost to the utilities company but it is also an indirect cost to society. Let me elaborate on this.

Hydroelectric power is an attractive alternative for energy generation; it is a flexible source of electricity, it has relatively low operational and maintenance costs, and after construction is completed, a hydropower project produces no direct waste and has lower levels of greenhouse gas emissions than fossil-fuel-powered energy plants. Today, hydroelectric power is the most widely used form of renewable energy. Recent estimates suggest it accounts for 16% of global electricity generation and is expected to increase at an annual rate of 3% for the next 25 years (Worldwatch Institute, 2013).

Within the hydropower industry, small and micro-hydropower (plants with an installed capacity of up to 10 MW and 100 KW, respectively) has been postulated as an effective tool to meet renewable energy targets and provide energy to remote, rural communities.[1] Small-scale, well-sited, run-of-river hydropower projects can be developed with minimal environmental impacts and are therefore likely to become increasingly important instruments in the development, energy and environmental debate.[2]

So…. In summary, hydroelectric power plants are in essence a source of green energy. Shutting them down is costly to society as it would encourage utility companies to shift towards more polluting sources of power to make up for their foregone revenues.

But, we already saw that letting the turbines run all year long is literally leading the American eel to extinction. So what to do? Should the current policy be revisited to reduce eel mortality to zero? Perhaps not.

The virtuous middle

It is important to acknowledge both benefits and costs of any action in order to accurately understand what is being sacrificed by taking one decision over the alternatives. It seems clear that to preserve the natural integrity of biological systems in the Shenandoah River, hydroelectric generation regimes should incorporate a consideration for reducing eel mortality based on actual migration patterns.

However, direct restrictions on hydropower operations that are imposed to mitigate environmental impacts and favor consumers of ecosystem services can also inflict additional costs to hydropower producers.

In general, the imposition of environmental constraints reduces the value of a river to power producer by increasing operation and licensing (or relicensing) costs.[3] An increase in costs may be sufficient to encourage a shift towards dirtier sources of power and to discourage private investment in costly environmentally friendly technologies. Thus, it is possible that well-intended environmental constraints may actually have an overall negative impact on the environment via reduced air quality from increased use of dirtier sources of power and unrealized prevention of further environmental damages.

It is evident from this short discussion that to adequately design policies that ameliorate environmental impacts of hydropower generation, policy-makers must take into consideration the direct benefits to natural habitats and users of ecosystem services as well as the costs to producers that result from tightening operation and relicensing requirements and the indirect social costs that result from responses of producer behavior to new environmental regulations.

So… both conservation and hydropower objectives are important. Yet, what is really interesting, is that these values do not necessarily constitute opposing interests. In fact, reducing eel mortality would not only be beneficial for eel populations and ecosystem dynamics (eels are top predators in riverine ecosystems), in fact, protecting eel populations would actually be in the best interest of the hydropower plant operators. Why?

Simple. Money. If the American eel population declines to a threshold point where the US Fish and Wildlife Service enlists it as an endangered species, then, energy generation in any river transited by the American eel will become prohibitly costly—just by virtue of all the legal requirements that are tied to the Endangered Species Act.

So… it seems that there are interests by environmental agencies (together with conservationist groups and the general public concerned with the health of riverine ecosystems) and hydropower generating utilities to protect American eel from turbine mortality and potentially deadly migratory delays.

The next step seems to be to collaborate in a study that addresses the issue of directly linking scientific information with ongoing decisions in a way that explicitly accounts for the inherent trade-off between ecosystem conservation and energy generation. That’s the project I worked in. Stay tuned for its publication.

[1] Although well-sited, small-scale, run-of river hydropower development projects can be designed to have minimal environmental impact, their popularity is in part based on the fact that they are exempt from costly regulations that apply to larger projects.

[2] There are two main types of hydropower plants (ignoring pumped storage facilities): Run-of-river (ROR) and peaking plants. ROR plants typically have limited water storage capability and electricity generation are therefore proportional to natural stream flow and varies little during the day. Peaking plants, on the other hand, often have significant water storage capacity and are designed to maximize flow through the turbines by rapidly change water releases during periods of high demand.

[3] For example, in a study of the Glen Canyon Dam on the Colorado River, Harpman (1999) found a reduction of 8.8% in the short-run economic value of the hydroelectricity generated at the dam after the imposition of new flow regulations in 1996.


  • Welsh, S. A., D. R. Smith, and S. Eyler. 2014. Migration of silver-phase and yellow-phase American eels in relation to hydroelectric dams on the Shenandoah River.  Progress Report to NAES Corporation, PE Hydro Generation, LLC.
  • “American Eel: American Eel Stock Determined to be Depleted.” ASMFC Fisheries Focus, Vol. 21, Issue 3, April/May 2012.
  • Wolf-Dieter N. Busch & David P. Braun. “A Case for Accelerated Reestablishment of American Eel in the Lake Ontario and Champlain Watersheds.” Fisheries 39.7(2014): 298-304


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s