Investigating The Obscure Yeller Finned Minner, by Don Orth

Let’s call it the Clinch Dace.  It’s a small minnow, which the locals call “yeller finned minners.”  When Freshwater Fishes of Virginia was first published in 1994, this minnow was not known, at least to scientists.   It’s referred to as Chrosomus sp. cf. saylori.   This means we are sure it is a member of the genus Chrosomus, the fine-scale daces.  The sp. is an abbreviation for species, meaning we are not sure what the species really is.   The cf. is an abbreviation for the Latin verb conferre.   This tells one to consult with or compare with the species saylori, because it is most similar to the Laurel Dace Chrosomus saylori.  The Laurel Dace was described by Dr. Christopher Skelton (2001) and was listed as endangered by the U.S. Fish and Wildlife Service in 2011.  The Clinch Dace was encountered in surveys associated with gas pipeline planning and construction.  The fish was considered a unique species due to differences in morphological and meristic traits (White and Orth 2013).  Because it has not yet been described as a species it has no federal protection. In Virginia, it is a Tier I species (very high conservation need) in the Virginia Wildlife Action Plan.

 

A,  Laurel Dace Chrosomus saylori Photo by Chris Skelton, B. Clinch Dace Chrosomus sp. cf. saylori Photo by Dave Neely

Michael J. Moore recently defended his master’s research which focused on this species. The thesis “Distribution and Population Characterization of Clinch Dace (Chrosomus sp. cf. saylori) in the Upper Clinch River System, Virginia” confirms the rarity and isolation of this fish within its putative range.  Clinch Dace occurred at only 13 of 70 sites sampled (18.6%).   The occupied sites were in small streams of low gradient and low conductivity in watersheds that were largely  (>80%) forested.  They rarely occurred with sculpin (Cottus spp.), but usually coexisted with Blacknose Dace, Creek Chub, Stoneroller, and Fantail Darter.  Both backpack electrofishing and minnow trapping were deemed to be feasible methods for capture and long-term monitoring. Although the Clinch Dace was found at two new locations, it was absent from two locations that previously had Clinch Dace.   The species occurs at low densities, in only 31.5 of the 351 km of headwater streams, making the global population size quite low (below 7,000 adults).  

Dashed line shows range of all collections of Clinch Dace.

Coal mining, logging, gas wells, cattle pastures, roads and culverts occur throughout the highly dissected landscape where the Clinch Dace may be found.  Here, the impacts of surface mining outweigh current mitigation actions, which have been largely criticized (Bernhardt et al. 2012).  The surface mine impacts can have long-lasting and significant effects on aquatic life.  For example, one isolated population of Clinch Dace exists upstream from a large surface mine in Left Fork Coal Creek (see photo).  Here the conductivity is less than 200 μS/cm.   However, downstream of the discharge from the surface mine, conductivity values increase to over 1,000 μS/cm.  Different ionic constituents are part of the dissolved solids loading, though these are not regulated. Of further concern, is that the community of Fork Ridge, Virginia, is one of 50 communities at highest risk of mountaintop mining. 

Aerial photo of Fork Ridge surface mine and isolated Clinch Dace habitat. Photo by D.J. Orth

The landscapes where the Clinch Dace reside provide a microcosm of what is occurring throughout the coal-mining region of Appalachia.  Coal is removed by a method known as contour highwall mining or mountaintop removal and valleys are filled with mine spoil.  Drainage from these surface mines and valley fills have high levels of dissolved solids, which remain elevated for long distances downstream and for 2 decades or more after the mine is “reclaimed”  (Evans et al. 2014). Aquatic macroinvertebrate communities are impaired by high ionic concentrations; these same small creatures are part of the food base for many fishes, including the Clinch Dace. It is unlikely that eggs and larvae can survive the elevated ionic concentrations.  Others have also detected a conductivity threshold for stream fishes. A threshold of conductivity likely exists, above which Clinch Dace and other fishes cannot persist.   With the small, and isolated pattern of the Clinch Dace populations, any further losses in habitat are troublesome.  At present, four of the largest populations in the least disturbed watersheds are the hope for the future of the species. 

We still need to quantify the levels of genetic diversity remaining in these small populations. Habitats that are important for Clinch Dace spawning  need to be identified and protected.  With cooperative landowners we need to identify and remove barriers to population expansion and monitor responses.  These yeller finned minners belong in the small streams that drain these hollers.  There are no alternative habitats once a valley is filled in.   

Landscape in the region occupied by Clinch Dace. Photo by D.J. Orth.

References

Bernhardt, E.S., et al. 2012.  How many mountains can we mine? Assessing the regional degradation of central Appalachian rivers by surface coal mining. Environmental Science and Technology 46(15):8115-8122.

Evans, D.M., C.E. Zipper, P.F. Donovan, and W.L. Daniels. 2014.  Long-term trends of specific conductance in waters discharged by coal-mine valley fills in central Appalachia, USA.  Journal of the American Water Resources Association  50(6):1449-1460.

Skelton, C.E. 2001.  New dace of the genus Phoxinus (Cyprinidae: Cypriniformes) from the Tennessee River drainage, Tennessee. Copeia 2001:118-128.   

White, S.L, and D.J. Orth. 2013. Ontogenetic and comparative morphology of Clinch Dace (Chrosomus sp. cf. saylori).  Copeia 2013(4):750-756.

Why we fish? It’s more complicated than you think. By Don Orth

Humans have fished for sustenance and subsistence for a long time.  One study suggests that freshwater fish were a part of the diet of early humans in Eurasia 40,000 years ago (Hu et al. 2009).   Probably many of these fishes were the same Asian carp we know today as Cyprinus carpio, and Ctenopharyngodon.   Eating fish is the oldest motivation for why we fish.   Over time, methods of capture diversified so more types of fishes were captured from many different places.  Fish hooks have been used for over 10,000 years and continued to be used today.  Early fish hooks were carved from wood, animal bone and antlers, thorns, and shells since the late Pleistocene.

But our human motivations to fish, to angle with hook and line, gradually changed from pure subsistence to a more complicated web of motivations. When did it go beyond fresh fish to eat?   Probably the moment when individuals have just enough protein to eat, fishing continues in order to be outdoors, relax, and experience the thrill of catching fish.  These are the big three motivators: Outdoors, Relaxation, and Thrill of the Catch. 

The thrill of the catch.  Photo by Bryan Hanson.

Izaak Walton, in The Compleat Angler, first published in 1653, wrote “God never did make a more calm, quiet, innocent recreation than angling.”  Scientists have since explored the motivations of sport anglers in many studies in many situations. The take-home message from all these studies is that there is no such thing as an average angler.   Rather, for any region or any type of fishing pursuit, there exists a spectrum of sport anglers that range from the occasional angler to the specialist angler.   The other surprising finding is the relatively low importance placed on catching and keeping fish in many studies.

Anthony Fedler and Robert Ditton examined seventeen separate studies that explored what an angler seeks in an angling experience.   Anglers were so highly variable that Fedler and Ditton (1994) categorized the most important factors into five types of motivations:  (1) psychological and physiological; (2) natural environment; (3) social; (4) fisheries resource; and (5) skill and equipment.  The most important motivation varied depending on the type of fishing.  For example, drum anglers rated eating fish high, while tournament billfish anglers rated catching fish to eat lower.  Other motivations were common across angler groups. Most studies reported on motivations related to the high importance of natural environment. Motivations for fishing are far more complex than providing for daily protein.

The motivations to fish are different among regions, cultures, and social and economic levels.   In a nationwide study of members of US fishing clubs, investigators found that some motivating factors changed between 1987 and 1997 (Schramm and Gerard 2004).    Being with friends or family was less important, and “escape” became more important.   Further, for those with higher income, catching fish to eat was less important, even as they spent more time and money in pursuit of fishing.  Recreational fishing is a very affordable activity to provide fresh fish to eat. Young et al. (2016) compared motivation of subsistence fishermen with recreational anglers.  Surprisingly, 75% of motivation categories of subsistence fishermen were similar to recreational anglers.  But as the world changes, people will find other motivations to either fish or choose alternative activities. 

 

A cynical view of the effects of teaching a man to fish.

Why we need to know?  Fedler and Ditton (1994) emphasized the importance of examining motivation to aid in decision-making.  They wrote “By ignoring angler motivations, managers might not be providing an appropriate balance of angling opportunities to meet public needs fully.”    This is a fundamental principle of fisheries management.  With the many types of anglers, the fisheries manager has many opportunities to improve fishing opportunities.  Angler behavior is tied to their motivations. In one recent example, restrictive angling regulations, while allowing bull trout numbers and catch rates to increase dramatically, resulted in dramatic declines in traditional anglers who did not favor the new regulation (Johnston et al. 2011).   In addition to considering motivations of anglers, I would add that managers must also examine motivations and interests of the non-participating anglers and consider lost opportunities, or what economists call opportunity costs. Only 16% of US population fishes in any given year.  What can be done to engage the other 84%?

Why we don’t fish?  This is a critical question that influences the future of sport fishing.  Sport fish management depends on license sales and taxes on boating fuels and fishing equipment for revenues.  Fewer anglers translate to fewer dollars for fish conservation and management.  The “lapsed angler” is a mystery to be solved.  Anglers may quit fishing due to one of three factors: (1) shifting priorities in work, family, or choice of recreation; (2) health or age; and (3) altered fishing access or opportunities.  Only fishing access and opportunities can be actively managed by fisheries agencies.  The future of fishing requires a holistic view of managing aquatic environments to provide both traditional and novel recreational activities that depend on fish.  

“As no man is born an artist, so no man is born an angler.” – Izaak Walton

 Her first fish was a bluegill.  Source Iowa DNR.

Future fish enthusiasts will not emerge without mentors who introduce youth to these varied and healthy outdoor opportunities.  We need programs, such as Take Me Fishing, to actively combat the nature deficit disorder, All it takes is one experience -- the experience of catching that first fish -- to create a new lifelong angler.  Just watch this (click here) awesome reaction to catching a first fish. Iowa Department of Natural Resources and other agencies have programs to recognize a new angler’s first fish. 

Attracting new “users” (I detest the term) may mean changing the definitions of what it means to “fish” or rethinking archaic definitions of “game” and “non-game” fish.  New fishy-related activities that are growing in popularity in North America include bowfishing, microfishing, “rough”fish, eating invasive fish, native fish aquaria, seine fishing, snorkeling, fish watching, and Japanese Tenkara. Other fishy related activities haven't been imagined yet.  Consider the notion of aquarium therapy,  which eases mental health issues via aquarium viewing.  Each of these and more novel activities will compete for priority in our finite leisure time.   Finally, some segments of US population are under-represented in the 16% that fish.  In particular, Hispanic and  African American communities are less likely to fish and also have different motivations.   Consequently, the Take Me Fishing program has a Spanish language program, Vamos A Pescar., in order to encourage participation.

There are many reasons to go fishing.  Here are ten reasons (if you need an excuse to fish): 

1.     Contribute to conservation.

2.     Stress relief.

3.     Social bonding.

4.     Support wildlife and fisheries management.

5.     Improve health.

6.     Fun recreation.

7.     Self fulfillment.

8.     Boost the local economy.

9.     Fish for food.

10.  Thrill of the catch.

The question for you to ponder is how you will best enjoy your fishing. Don’t become a lapsed angler.  Get your fishing license today!  

References

Fedler, A.J., and R.B. Ditton, 1994.  Understanding angler motivations in fisheries management.  Fisheries 19(4):6-13. 

Hu, Y.  et al. 2009. Stable isotope dietary analysis of the Tianyuan 1 early modern human. Proceedings of the National Academy of Sciences 106:10971-10974. 

Johnston, F.D., R.Arlinghaus, J. Stelfox, and J.R. Post. 2011. Decline in angler use despite increased catch rates: Anglers’ response to the implementation of a total catch-and-release regulation.  Fisheries Research 110:189-197. 

Responsive Management and Southwick Associates.  2012.  Understanding the factors that compete with recreational fishing.  American Sportfishing Association, Alexandria, Virginia. 59 pp.

Schramm, H. L., and P.D. Gerard, P. D. 2004. Temporal changes in fishing motivation among fishing club anglers in the United States.  Fisheries Management and Ecology 11:313.

Walton, I. 1653. The Compleat Angler.  Stackpole Co., Harrisburg, PA (1953) 

Young, M.A.L, S. Foale, and D.R. Bellwood. 2016. Why do fishers fish? Across-cultural examination of the motivations for fishing. Marine Policy 66:114-123.

 

Whither Goest the Burbot? By Don Orth

Burbot, Lota lota (Linnaeus, 1758) is the only freshwater member of the Gadidae family. It is also one of the most widely distributed freshwater fish species in the world, but that range is contracting.   Burbot is an elongate, cylindrically shaped fish with two dorsal fins, a long anal fin, and pelvic fins in front of the pectoral fins.   Adults are yellow or light brown, with dark brown or black mottled pattern on back, sides and fins.  They have a single, taste-sensitive barbel on the lower jaw that they use when hunting in the darkness for a meal.  Burbot are well-adapted benthic predators that live in either large, cold rivers or deep lakes. They are primarily piscivores as adults, but have been known to eat frogs, snakes, even birds. Burbot are not a very charismatic fish, although they have a small loyal following.

Burbot.  Illustration by Joshua Knuth

The name, Burbot, is derived from the Latin word barba, meaning beard.  Many other names refer to the Burbot, these include the coney-fish, cusk, eelpout, la lotte, lush, loche, ling, lingcod, mariah, methy, mizay,  mudblows, and mud shark. However, my favorite name for the Burbot is lawyers. Here is a great photo from a fish market, the sign in the window advertising “fresh lawyers” for sale.   Most open-water anglers catch Burbot as incidental catch when fishing for Walleye. Fishing exclusively for Burbot often means ice-fishing.  The all-tackle record is over 25 pounds, though the typical Burbot is much smaller.   

A twenty-five pound burbot by Uncut Angling.

There is a visceral reaction the first time you handle a Burbot.  Burbot have fine, embedded scales and they produce mucho mucous.  The body tapers, so finding a handle on the Burbot is nearly impossible.  Hence, everyone struggles making awkward attempts to handle this slimy fish.  The Burbot spawns in the middle of winter and attracts the hardiest of cold-weather ice-fishermen. The Burbot is not popular as a sport or food fish in much of North America.  However, in some localities, Burbot fishermen eat the flesh, roe and liver.  The large liver is rich in vitamin A and D, but seldom used in North America. The liver is delicacy for some indigenous peoples, as well as people in Finland and France. The roe includes millions of small eggs in a large female.  Even the testes are unusually large.   Some fisheries agencies promote the underutilized Burbot and provide fishing tips and recipes. 

Sergei Aksacov (1997, pp. 142-144), the Russian version of Izaak Walton, described fishing for the Burbot in Russia.  He also described making Burbot soup with the flesh and liver.  Other recipes are available.  Burbot soup was a dish for royalty in Leo Tolstoy's Anna Karenina.  One hundred years ago, the US Department of Commerce, Bureau of Fisheries promoted the Burbot as a food fish.  In a pamphlet from 1917, they wrote “… for the burbot is coming on the markets at a price which will place it within the reach of modest means…. It has long been esteemed a great luxury… its flesh is white and delicate, while its liver is its most delicious morsel.”  It never lived up to its cousin, the cod, due to large-scale preservation issues. 

Looking down into the mouth of a Burbot. Photo by Angelo Viola

Burbot are on the move in winter to shallower waters in search of mates.  They deposit eggs over mixtures of sand to coarse gravel and cobble.    Imagine a large ball of Burbot with a few females in the center, surrounded by many males.  That’s what happens in winter spawning aggregations (Cahn 1936). It is dark under the ice.  Burbot, like other cods, make sound by rapidly contracting drumming mussels associated with their swim bladder.   Peter Cott and associates first recorded vocalizations of the Burbot in Yellowknife Bay, Great Slave Lake, Northwest Territories, Canada.   Burbot vocalizations peaked under-ice at the onset of the spawning period.  Sound signatures were stereotypical of swim-bladder generated calls, almost identical to those of the Haddock (Melanogrammus aeglefinus).  The mating system of the cods and haddock involves large aggregations; spawning calls assist in formation of the spawning aggregation.  Naturalist Sigurd F. Olson observed spawning and wrote:

It was February and the mercury was down far below zero. We had come in the middle of the night to watch the spawning of the eelpout, those brownish, eel-like deep water fish that thrive in the coldest lakes of the north ... As we neared the upper reaches of the Burntside River, we could hear the rapids murmuring through the dark. It was at this spot we would see them for they need shallow water, gravel and sand for their breeding. Not until we were within ten feet of the bank did we shine our lights, and then saw such a sight as few have ever seen—a struggling, squirming mass of fish, the long brownish snaky bodies twisted around each other, the entire contorted mass turning over and over beating the water into foam ... I had seen that night a primitive picture that I could never forget, a picture of what might have taken place in some cold primeval pool millions of years ago. There was life in the raw obeying the great urge to reproduce, the one implacable law of creation."

Natural movements of Burbot are disrupted by human efforts to change natural waterways. In particular, hydropower developments, warm discharges, blocked migration, and reservoir fluctuation have caused declines in some Burbot populations around the world (Stepanian et al. 2009).  Burbot populations collapsed in Lakes Michigan, Huron and Ontario concurrently with Sea Lamprey (Petromyzon marinus) population increases in the 1940s to 1960s.  Burbot populations have since recovered in all but Lake Ontario, where the introduced Alewife is still too abundant. 

Harrison et al. (2016) reviewed the many threats of hydropower facilities to Burbot populations.  High winter discharges may delay migration and spawning of Burbot.  Often reservoirs release warmer water in winter, which may reduce hatching or survival of Burbot eggs. Some dams release hypolimnetic waters, which are cold and may benefit Burbot populations. Burbot are not strong swimmers and are incapable of passing through large fishways with high current velocities.  The larval and juveniles passively drift and are vulnerable to entrainment into hydro turbines, though few entrainments studies have been done on Burbot.   Dams disrupt migrations of riverine Burbot populations. Despite these potential influences, Burbot populations are not consistently monitored.  The Kootenai River Burbot population collapsed after increased temperatures and high winter discharges commenced below Libby Dam in Idaho (Hardy and Paragamian 2013).  Many other Burbot populations are in need of monitoring and assessment. 

Once a popular food fish in Great Britain, the Burbot disappeared from British waters in the 1960s. Today there are no British champions for the Burbot.  Burbot declines may be occurring in other northern waters influenced by climate warming.  Burbot in Oneida Lake, near the southern edge of the Burbot’s range, have declined significantly since the 1960s (Jackson et al. 2008). 

Burbot caught at the International Eelpout Festival.

If you want to catch Burbot, then you should consider the attending the International Eelpout Festival.   Every year over 10,000 Burbot catchers gather sometime in February on Leech Lake, Minnesota, to celebrate this coldwater specialist.  

Whither goest the Burbot?   Burbot goest to many fewer places than in the past!

References

Aksacov S.  1997.  Notes on fishing and selective fishing prose and poetry. Northwestern University Press, Evanston, Illinois. 232 pp.

Cahn, A.R. 1936. Observations on the breeding of the lawyer, Lota maculosa.  Copeia 1936:163–165

Cott, P.A. et al.  2014.  Song of the burbot: under-ice acoustic signaling by a freshwater gadoid fish.  Journal of Great Lakes Research 40(2):435-440.

Hardy, R., and V.L. Paragamian. 2013. A synthesis of Kootenai River Burbot stock history and future management goals.  Transactions of the American Fisheries Society 142:1662-1670.

Harrison, P.M., L.F.G. Gutowsky, E.G. Martins, D.A. Pattterson, S.J. Cooke, and M. Power.  2016.  Burbot and large hydropower in North America: benefits, threats and research needs for mitigation.  Fisheries Management and Ecology  doi: 10.1111/fme.12178

Jackson, J.R., A.J. VanDeValk, J.L. Forney, B.F. Lantry, T.E. Brooking, and L.R. Rudstam. 2008.  Long-term trends in burbot abundance in Oneida Lake, New York: life at the southern edge of the range in an era of climate change.  Pages 131-152 in V.L. Paragamian and D.H. Bennett, editors.  Burbot: ecology, management, and culture.  American Fisheries Society, Symposium 59, Bethesda, Maryland.

Paragamian, V.L., and D.H. Bennett, editors. 2008.  Burbot: Ecology, management and culture.  American Fisheries Society Symposium 59.  Bethesda, Maryland. 270 pp.

Paragamian, V.L., B.J. Pyper, M.J. Daigneault, R.P. Beamesderfer, and S.C. Ireland. 2008. Population dynamics and extinction risk of burbot in the Kootenai River, Idaho, USA and British Columbia, Canada. Pages 213-234 in V.L. Paragamian and D.H. Bennett, Editors.  Burbot: Ecology, Management, and Culture. American Fisheries Society, Symposium 59, Bethesda, Maryland.

Stepanian, M.A. et al. 2009. Worldwide status of burbot and conservation measures.  Fish and Fisheries.  DOI: 10.1111/j.1467-2979.2009.00340.x

U.S. Department of Commerce, Bureau of Fisheries.  1917.  The Burbot: A freshwater cousin to the cod.  Economic Circular No. 25. 

Mysteries of the American Eel, by Don Orth

No one has ever seen the American Eel spawning.  The leptocephalus stage of this fish is so different it was first described as a different species.  We are not sure how they navigate from freshwaters to the spawning area in the Sargasso Sea.   We do not know what happens to adults after spawning. Numerous investigators, each focusing on a different life stage, have collectively provided the story of the American Eel life cycle.   View more about the life cycle here. There are 16 species of freshwater eels (Genus Anguilla) and many questions remain about each and every one (Arai 2016).  Of current concern is the dramatic decline of the temperate eels, European eel (A. anguilla), American eel (A. rostrata), and Japanese eel (A. japonica). 

Life cycle and range of the American Eel.  Illustration by Melissa Beveridge

How do we know?  The leptocephalus larvae were collected during several marine expeditions that began in 1904 (Miller et al. 2015). By mapping the size of leptocephalus larvae collected, the most probable spawning location was inferred.  Yet, despite numerous trials, no investigator ever directly observed adult silver eels reaching the Sargasso Sea.  There are many logistical challenges to overcome, including how to attach some type of transmitter that will survive during the long migration.  It is likely that the long migration is associated with high mortality and significant metabolic costs.   The process of become a silver eel, or “silvering,” is likened to becoming an “endurance athlete.”   This endurance eel now has a greatly increased heart size and red muscle mass, as well as additional blood vessels that feed the swim bladder for better bouyancy control.  On dark autumn nights the silvering eels cease feeding and move downstream.  They survive the long migration by fueling their red muscles with intramuscular fat.

The red star represents the capture location of this eel during downstream migration. The magenta triangle represents the release location after tagging. Source: Beguer-Pon et al. (2015)

Recently a team of investigators, led by Mélanie Béguer-Pon, provided the first direct evidence of an adult American eel migrating to the Sargasso Sea.  They had to track many individuals and many died or transmitters malfunctioned before they could describe a completed migration of one individual.  This eel migrated 2,400 km to the northern limit of the spawning site in the Sargasso Sea. Migration appears to have two distinct phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area.  It appears to be simple path, travel east into deep waters (>2000 m), then head south.  However, these silver eels have never made this migration before.  As leptocephalus larvae they drifted with the currents to reach coastlines many decades earlier.  How can they remember?

 

The olfactory senses of sexually immature eels are highly developed and olfactory cues may play a role in the initial phase of migration. The American eels travel against ocean currents, an observation also made on the European eels tracked in the North Sea. American eels leave the Scotian Shelf and must cross the Gulf Stream, a strong northeastward current.  Based on the migration pattern and studies of sensory systems of the eel, it is likely that eels possess a magnetic map and true navigation abilities (Durif et al. 2013; Hunt et al. 2013). 

The American eels also displayed well-defined patterns of daily vertical movement, once they entered waters where salinity was greater than 35.  Migrating eels move up and down between the warmer, upper layers during the night, and the cooler, deeper layers during the day time.

Temperature experienced along the way is superimposed to the depth profile. A is the Scotian Shelf, B represents the edge of the Scotian Shelf, C represents the exit of the Laurentian Channel (open ocean), D represents the area after C, which includes the Gulf Stream and E represents the Sargasso Sea. Source: Begeur-Pon et al. (2015)

Vertical migration may be due to a "hypothesized trade-off between predator avoidance and the metabolic requirements of migration."  Predators of American eels during the long migration are also migratory fish. In particular, the Porbeagle sharks (Lamna nasus) and Atlantic bluefin tuna (Thunnus thynnus).

The opposite migration is just as challenging and mysterious.  All American eels start as eggs fertilized in the Sargasso Sea; that’s one large, panmictic population.  After spawning the leptocephalus larvae drift with ocean currents and develop into juvenile glass eels. They may enter and ride different gulf streams to either the Gulf of Mexico or Atlantic coastal estuaries. Those glass eels become elvers, which may live in coastal estuaries or swim upstream.  Elvers grow into yellow eels.  Yellow eels are nocturnal, feeding and swimming upstream at night.  Yellow eels may spend 30-40 years in freshwaters.  Those eels that travel farthest upstream tend to grow the slowest and mature as females. These large females (capable of producing 20-30 million eggs) are essential to perpetuating the next generation and must migrate downriver and out to Sargasso Sea to complete the life cycle. 

The American eel has multiple values.  It is harvested at every life stage (elvers, glass eels, yellow, and silver) for either bait, food, export, or aquaculture.  Because of its life cycle, all harvest is pre-spawn harvest.  For example, Maine licensed fishermen caught nearly $38 million worth of elvers in 2012, making the elver fishery second only in value to the lobster industry. Recent declines in the Asian and European eels have increased demand of elvers, driving prices up to over $1,000 per pound.   

 

Glass eels in small net.  Photo by Samuel J. Baldwin.

There are declines in several measures of American eel abundance, yet no consistent, range-wide monitoring of young elvers exists in US waters.  Yet there are many obstacles to the American eels reaching upland freshwater growth habitats.  Busch et al. (1998) estimated that diadromous fish, dependent on access to Atlantic coastal watersheds, may be hindered from reaching up to 84% of upstream habitats!   American eels are listed as Endangered by the IUCN and threatened in Canada. In the USA, the Fish and Wildlife Service reviewed the status of the American eel in 2007 and in 2015.  In each review the Service found that Endangered Species Act protection for the American eel was not warranted.  They acknowledged declines in yellow eels, but specifically concluded that “no range-wide decline in elvers and glass eels or in marine harvest.” The listing of the American Eel would create significant new constraints for many industries, including hydropower and the fledging aquaculture industry.  For example, ESA listing the American eel could impact 32,719 MW of production capacity at 939 US hydropower plants (Jager et al. 2013). 

Many restrictions need to be imposed to protect the American eel from further declines.   A fishery management plan for American eel was approved in 2000 (ASMFC 2000).  Is the American eel population overfished?   Yes!  The ASMFC (2012) stock assessment concluded that the American eels stock was depleted. Is overfishing occurring?  Time will tell.  Addendum III established a 9” minimum size limit for recreational and commercial yellow eel fisheries, trip-level reporting for the commercial yellow eel fishery, a seasonal closure of silver eel fisheries, a 25 recreational fish per day creel limit, and measures to restrict the development of fisheries on pigmented eels. It also called for the implementation of state-specific monitoring programs and provides recommendations for habitat improvements.   Addendum IV imposed additional harvest restrictions on yellow, silver, and glass eels.   Recently, the ASFMC approved the aquaculture plan for North Carolina and set harvest quotas, so future monitoring will continue.

Total commercial landings of American eels in Atlantic. Source:  ASFMC (2012) American Eel benchmark stock assessment.

Future questions  -- Some mysteries of the eel will persist for a long time.  The eel doesn’t have a sex chromosome; rather, the sex of the eel is environmentally determined by conditions in freshwater in the yellow eel stage.  In terms of life history strategies, the females are referred to as "size maximizers" and males are "age minimizers."  We don’t understand the role sex determination plays in American eel population dynamics.   The European eel and the American eel spawn in partially overlapping parts of the North Atlantic, yet we don’t understand how they maintain reproductive isolation.   Most of the freshwater growth habitat in North America has been altered and no measures of future female spawning biomass are developed for forecasting future glass eel population size.   Further, not all American eel enter freshwaters. Their migration pattern may be more accurately labeled as facultative catadromy.  What effect does this have on the characteristics of the spawning population?   Declines in American eel are less debated today; however, the influences of habitat destruction, pollution, overfishing, and global climate change cannot be readily quantified.   

Only Japanese researchers have developed the technology to complete the life cycle of the eel in captivity (Tanaka 2015).  With this mystery solved we no longer believe that eels emerged from the mud (as Aristotle thought) or  that they multiplied by rubbing themselves on rocks (as Pliny believed).   One mystery solved leads to other questions.  For those interested in producing more eels, the mass production of glass eels remains an unrealized goal, fueling current demand for harvest of glass eels. 

References

Arai, T. Editor.   2016. Biology and Ecology of Anguillid Eels.  CRC Press, Taylor & Francis Group, Boca Raton, USA.

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