Counting Sturgeon Just Got a Little Easier, by Don Orth

I am a fisheries biologist, which means I count fish.  Sound easy?  It’s not!   John Shepherd, a fisheries biologist, once said “Managing fisheries is hard: it’s like managing a forest, in which the trees are invisible and keep moving around.”  This post is about counting sturgeon; their life history (long generation time, high fertility) is more similar to a tree than a fish -- except they move around at all life stages.  

 

Illustration of Atlantic Sturgeon by Hugh Chrisp Source  

Counting sturgeon is a critical issue because many sturgeon are endangered.  Our local Atlantic sturgeon Acipenser oxyrinchus was listed as an endangered species in 2012 when all the counting pointed to severely depleted populations.  'Endangered' status means that the interaction between sturgeon and fishing, shipping, dredging, water quality, dam removal cannot continue to be ignored. “Take” of an endangered species is reviewed and regulated; no one can “harass, harm, pursue, hunt, shoot, wound, kill, trap, capture or collect" and endangered species.  

Atlantic Sturgeon is a large sturgeon that can reach 14 feet and live for 60 years.  Males do not mature until they reach about 4 feet and females mature later at about 6 feet.  Females do not spawn every year and the time between spawns may be anywhere between 2 and 5 years (Smith 1985).  The Shortnose Sturgeon Acipenser brevirostrum is a smaller fish that has been listed as endangered since 1967. For many years fisheries managers held out false hope that the actions in place to protect Shortnose Sturgeon would also protect Atlantic Sturgeon.   

 

A 400 pound sturgeon being carried into a fish store. (Photo taken April 11, 1947 by Reg Speller/Fox Photos/Getty Images) 

Fish die, it’s a fact of life.  But only by counting fish can we decipher how many die and perhaps reduced the avoidable deaths. Atlantic Sturgeon are endangered because they are bycatch in other fisheries, killed by ship strikes, blocked from historic breeding grounds by dams, and unable to use historic habitat due to poor water quality.  The significance of any take of sturgeon will depend on population counts.   Sturgeon are anadromous, which means they spawn in freshwater rivers but spend most of their lives migrating in coastal waters before returning to spawn in their river of origin.  Consequently, the sturgeon are “invisible and keep moving around.”     So it is difficult to ascertain the 'take' of endangered sturgeon.  Yet recovery actions are evaluated based on counts.  

Large Atlantic Sturgeon killed by a ship strike.  Photo by Jared Jacobini, Delaware Department of Natural Resources and Environmental Control, Division of Fish and Wildlife.  (Brown and Murphy 2010) 

Atlantic Sturgeon were once so abundant in Atlantic coastal rivers that no one thought to count populations.  Native Americans harvested sturgeons for food.  Early colonists harvested the sturgeon, which were considered royal fish back in England. Sturgeon from the Hudson River were called ‘Albany Beef.’  Even George Washington fished for sturgeon in the Potomac River in the late 1700s.  The demand for Atlantic Sturgeon for flesh and caviar led to decline in all coastal populations that began soon after the Civil War.  Harvest along with the damming coastal rivers and degrading river and coastal water quality kept Atlantic Sturgeon populations at low levels.  It was 100 years after peak sturgeon harvest that the Atlantic States Marine Fisheries Commission (ASMFC) finally placed a moratorium on coastal sturgeon harvest (ASMFC 1998).

No one knows for certain how many Atlantic Sturgeon once existed.  One estimate, derived by Secor (2002), indicates that there were 180,000 adult females just prior to 1890, the year of peak harvest. In the Chesapeake Bay there may have been 20,000 adult females.  Counts today are far below that target, though population counts are few and far between. 

Tag and recapture methods have been deployed on many coastal rivers. Population estimates indicate that Shortnose Sturgeon have increased in the Kennebec River, whereas Atlantic Sturgeon decreased in the Hudson River (Peterson et al. 2000; Wippelhauser and Squiers 2015).  Population counts are rare. Therefore,  one can only assume these populations are gone or are at early stages of recovery.   Repeated population estimates are needed (Peterson et al. 2011).  Spawning has been documented in the James River and Pamunkey River, which are the only known recent spawning areas in the Chesapeake Bay distinct population segment (Balazik et al. 2012; Kahn et al. 2014).

Tag-recapture studies are expensive and time-consuming, whether populations are large or small.  Furthermore, tag-recapture methods require knowing something about how the tagged sturgeon are “moving around” between the time of tagging and the recapture. Finally, tagging methods require capture and handling of sturgeons, which stresses the fish.  A recent study by Jared Flowers and Joseph Hightower, North Carolina State University and the US Geological Survey, may have solved the problem of how to count sturgeon numbers. The solution involved adoption of side-scan sonar technology to counting the sturgeon.  They estimated sturgeon densities from counts based on side-scan images and the length and width of the survey transects.  With the side-scan images and a smidgen of statistics, Flowers and Hightower provided the first estimates of Atlantic Sturgeon in Carolina coastal rivers.  If their techniques are widely applicable, we can more accurately estimate population sizes as well as count the deaths and project future population sizes.

Edgetech 4125-P side-scan sonar unit used by Flowers and Hightower (2015). Source 

The application of side-scan sonar has also allowed sturgeon scientists to better locate aggregations of sturgeon in their coastal migrations.   Breece et al. (2016) were able to demonstrate that Atlantic Sturgeon form aggregations during coastal migrations.   That’s the good news.  The bad news is the locations of these shallow marine aggregations overlap with coastal trawl and gill-net fisheries based in New York and New Jersey.   Sturgeon researchers should adopt side-scan sonar to identify these areas of overlap between large-mesh gill net fisheries and manage fishing using traditional time, area, and gear restrictions to limit take of Atlantic Sturgeon.     

In the future, sonar will be standard issue for all fisheries biologist charged with counting sturgeon.  More frequent, more precise population estimates are needed in more places. With these counts we can begin to estimate mortality and mortality sources and regulate the take more effectively.  Sonar units can also be employed via autonomous underwater vehicles  (Grothues et al. 2016).  All of us who count fish should be hopeful. Sonar has turned some invisible fish into visible fish.  Despite multiple stressors in the Hudson River, the Shortnose Sturgeon population increased in the decades following protection (Bain et al. 2007).  Access to sonar techniques for more frequent and widespread counting of sturgeon will make the job of the fisheries biologist just a little bit easier. 

References

Atlantic States Marine Fisheries Commission.  1998.  Amendment I to Atlantic States Marine Fisheries Commission Fisheries Management Plan for Atlantic Sturgeon. Fishery Management Report No. 31 of ASMFC, Washington, DC.

Bain, M.B., N. Haley, D.L. Peterson, K.K. Arend, K.E. Mills, and P.J. Sullivan.  2007. Recovery of a US endangered fish. PLoS ONE 2(1): e168.    

Bain, M. B. 1997. Atlantic and shortnose sturgeons of the Hudson River: Common and divergent life history attributes.  Environmental Biology of Fishes 48(1-4): 347-358

Balazik, M.T., K.J. Reine, A.J. Spells, C.A. Fredrickson, M.L. Fine, G.C. Garman, and S.P. McIninch. 2012.  The potential for vessel interactions with adult Atlantic Sturgeon in the James River. North American Journal of Fisheries Management 32:1062-1069.

Breece, M.W.,  D. A. Fox, K.J. Dunton, M. G. Frisk, A. Jordaan, M. J. Oliver. 2016. Dynamic seascapes predict the marine occurrence of an endangered species: Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus. Methods in Ecology and Evolution 

Brown, J.J.  and G.W. Murphy. 2010. Atlantic Sturgeon vessel-strike mortalities in the Delaware Estuary.  Fisheries 35(2):72-83.

Collins,M.R., Rogers, S.G., Smith, T.J. and M.L. Moser  2000. Primary factors affecting sturgeon populations in the southeastern United States: fishing mortality and degradation of essential habitats. Bulletin of Marine Science 66:917–928.
Flowers, H.J., and J.E. Hightower.  2010. Estimating sturgeon abundance in the Carolinas using side-scan sonar.  Marine and Coastal Fisheries 7:1-9

Grothues, T.M., A.E. Newell, J.F. Lynch, K.S. Vogel, and G.G. Gawarkiewicz. 2016. High-frequency side-scan sonar fish reconnaissance by autonomous underwater vehicles.  Canadian Journal of Fisheries and Aquatic Sciences 

Kahn, J.E., C. Hager, J.C. Watterson, J. Russo, K. Moore, and K. Hartman. 2014.  Atlantic Sturgeon annual spawning run estimate in the Pamunkey River, Virginia.  Transactions of the American Fisheries Society 143:1508-1514.

Peterson, D.L., M.B. Bain, and N. Haley. 2000. Evidence of declining recruitment of Atlantic Sturgeon in the Hudson River.  North American Journal of Fisheries Management 20:231-238.

Peterson, D.L., P. Schueller, R. DeVries, J. Fleming, C. Grunwald, and I. Wirgin.  2008.   Annual run size and genetic characteristics of Atlantic Sturgeon in the Altamaha River, Georgia.  Transactions of the American Fisheries Society 137:393-401.

Secor, D. H. 2002.  Atlantic Sturgeon fisheries and stock abundances during the late nineteenth century. Pages 89-98in W. Van Winkle, P.J. Anders, D.H. Secor, and D.A. Dixon, editors.  Biology, management, and protection of North American sturgeon.  American Fisheries Society, Symposium 28, Bethesda, Maryland.

Smith, T.I.J. 1985. The fishery, biology, and management of Atlantic Sturgeon, Acipenser oxyrhynchus, in North America. Environmental Biology of Fishes 14(1):61-72. 
Wippelhauser, G.S., and T.S. Squiers Jr. 2015. Shortnose Sturgeon and Atlantic Sturgeon in the Kennebec River System, Maine: a 1977–2001 retrospective of abundance and important habitat, Transactions of the American Fisheries Society 144:591-601, DOI: 10.1080/00028487.2015.1022221

 

The Erratic Crappie Leaves Many Anglers Happy, by Don Orth

Crappies are a great American sport fish that provide food and sport for millions of recreational anglers each year.   There are only two species and they widely distributed;  any recreational angler can locate and catch crappies.   Reservoir construction in the Midwest and Southeastern USA greatly increased habitat for both species.  Crappie remain very popular among anglers, many of whom prefer to catch and eat their catch.     Crappie can be captured by a variety of fishing methods and use of affordable sonar allows for better targeting of deep structures that hold more crappie.   Although many impoundments still suffer from “small crappie syndrome,” management of prey and angler harvest can enhance crappie fisheries.  The International Game Fish Association all tackle records  are 2.35 kg (5 pounds, 3 oz) for White Crappie Pomoxis annularis and 2.26 kg (5 pounds) for Black Crappie Pomoxis nigromaculatus.  Tournament fishing for crappies has emerged with a large following in Crappie Masters.    If you are itching to catch more crappie, view this video.

Illustrations of the White Crappie (left) and Black Crappie (right)

The White Crappie was described in Ichthyologia Ohiensis (1818) by Constantine Samuel Rafinesque during his expedition to the Ohio River valley.   Both species are deep bodied and strongly compressed laterally. This explains their association with the term, panfish, as they are suited for being fried in a pan. The French word, crapet, refers to sunfish, and is the root for the common name, crappie (also spelled croppie or crappé).  Therefore, the crapet vert is French for Green Sunfish.  Some pronounce Crappie so it rhymes with hoppy (ˈkrä-pē) , others say it so it rhymes with happy (ˈkra-pē).  Only a linguist can explain why.     No matter how you pronounce ‘crappie, you will be impressed with the gape of this sunfish relative.  The jaws are large with the upper jaw extending well past the middle of the eye.  The spiny and soft dorsal fins are broadly connected.  The principal difference is the coloration pattern.  White crappie is silver with 5-10 often faint, dark vertical bars. The dorsal fin has 6 spines.   In contrast, Black crappie have irregularly arranged speckles and blotches instead of faint vertical bars as the color pattern. They also have 7 or 8 dorsal fin spines instead of 6.  

Development of White Crappie 

Drawings from Tabor (1969), not to scale.  Juvenile is 25.5mm.

Crappie are nest spawners and females are very fecund.   Males begin to defend territories and chase intruders by biting, butting or flaring opercles. Males sweep sediments out of the nest depression with fin and body movements; however, the crappie nests are not as well defined as nests built by sunfish Lepomis species. Larval development is fast.  Compared to other centrarchids, crappie have a longer spawning season, large clutch size, and shorter hatching time and time to disperse from the brood.  They often nest in colonies and have less specific habitat requirements for nesting.  Their strategy works well and,  in small ponds, crappie often overpopulate, leaving the pond owner with “small crappie syndrome.” Elsewhere, the duration and magnitude of water-level fluctuations and the development time of early life stages are critical to determining reproductive success.  Recruitment of crappie is highly variable, even erratic (Mitzner 1991; Guy and Willis 1995; Allen and Miranda 1998; Clark et al. 2008).  Bad recruitment years lead to bad years of fishing and unsatisfied crappie anglers.   Many states do supplemental stocking of crappie with variable success, creating many unhappy crappie anglers.  

 

Historic ranges of the White Crappie (left) and Black Crappie (right).  source Lee et al. (1980)

The distribution of the two crappie species violates the notion that closely related species should not overlap in distribution.   The two sister species show broad overlap throughout the native range.  The problem when examining speciation of these two species is that we don’t know what the distributions were when the species diverged in the Miocene.   The overlap means that Black and White Crappie produce natural hybrids in the zone of overlap, in one case as high as 17% (Travnichek et al. 1996; Spier and Heidinger 2003). This may raise the question ‘how rare does hybridization have to be to accept these as distinct species?’   Hybridization appears to be higher in zones where the two species are allopatric.  I could find no research into the olfactory, acoustic, or visual cues that may serve as pre-mating barriers to hybridization in the two crappie species.   There must be species recognition by one or more senses in breeding individuals for speciation to occur.   In the rare cases of hybridization, these premating barriers must break down.   The hybrids are viable and approximately 50% male; therefore, post-mating isolating mechanisms are not important.   Like other hybrid sport fishes, hybrid crappie demonstrate hybrid vigor and accelerated growth.  Naturally produced hybrids in Weiss Reservoir, Alabama, were less vulnerable to angling even though they grew faster (Travnichek et al. 1997). Most hybrid crappie are sold to the sportfish market for stocking ponds and small impoundments (Kelly and Baumhoer 2014).   Hybrids may not solve the “small crappie syndrome,” but a sterile triploid crappie might. 

White Crappie (top), Hybrid crappie (middle), and Black Crappie (bottom). Photo from Tennessee Wildlife Resources Agency.

An orange crappie is a rare find. This is a condition called xanthism or xanthochroism or xanthochromism.   It is a rare condition where all pigments other than yellow and orange are either absent or minimally expressed. It is hard to imagine the xanthic crappie pictured below successfully feeding and avoiding predators to become a full-size adult; however they are rarely encountered in the wild.  The xanthic pigment anomaly has been observed in other vertebrates as either partial or fully xanthic.

Xanthic crappie.  photo by Donnie Lornson

Another variation of the crappie is the “black-striped” variation of the Black Crappie.  This fish has a dark line along the dorsal margin from its nose to its tail.  This black stripe is a recessive trait and fish culturists quickly learned that it breeds true.  In an attempt to solve “small crappie syndrome” Mississippi Department of Wildlife, Fish and Park created a triploid Magnolia Crappie. It’s a cross between a white Crappie female and a black-striped Black Crappie male in which the embryo is pressure treated to create three sets of chromosomes.  The triploid is sterile and will direct energy to growth instead of reproduction (Parsons and Meals 1997). 

 

Black-striped variant of the Black Crappie.  Photo by Jim Negus.

If you are confused about crappie, don’t feel alone.   Just remember it rhymes with ‘hoppy’ -- unless you’re in the south.  No matter where you catch them, eating crappie makes you happy.

References

Allen, M.S., and L.E. Miranda. 1998.  An age-structured model for erratic crappie fisheries.  Ecological Modeling 107:289-303.

Clark, M.E., K.A. Rose, J. A. Chandler, T.J. Richter, D.J. Orth, and W. VanWinkle. 2008. Water-level fluctuation effects on centrarchid reproductive success in reservoirs: a modeling analysis.  North American Journal of Fisheries Management 28:1138-1156. 

Guy, C.S., and D.W. Willis.  1995.  Population characteristics of black crappie in South Dakota waters: a case for ecosystem-specific management.  North American Journal of Fisheries Management 15:754-765.

Kelly, A.M. and B. Baumhoer.  2014.  Species profile: hybrid crappie.  Southern Regional Aquaculture Center Publication No. 7212. 5 pp.  

Lee, D.S., C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E. McAllister, J.R Stauffer, Jr. 1980.  Atlas of North American freshwater fishes.  Publication #1980-12 of the North Carolina Biological Survey.  854 pp.

Mitzner, L. 1991.  Effect of environmental variablesupon crappie young, year-class strength, and the sport fishery.  North American Journal of Fisheries Management 11:534-542. 

Parsons, G.R., and K. Meals. 1997.  Comparison of triploid hybrid crappie and diploid white crappie in experimental ponds.  North American Journal of Fisheries Management 17:803-806.

Spier, T.W., and R.C. Heidinger. 2003.  Hybridization between black crappie and white crappie in southern Illinois.  Transactions of the Illinois State Academy of Science 96:119-133.

Tabor, C.A. 1969.  The distribution and identification of larval fishes in the Buncombe Creek arm of Lake Texoma with observations on spawning habits and relative abundance.   Doctoral dissertation, University of Oklahoma.  120 pp. 

Travnichek, V. H., M. J. Maceina, S. M. Smith, and R. A. Dunham. 1996. Natural Hybridization Between Black and White Crappies (Pomoxis) in 10 Alabama Reservoirs. American Midland Naturalist 135: 310-316.

Travnichek, V. H., M. J. Maceina, and R. A. Dunham. 1997.  Angling vulnerability of black crappies, white crappies, and their naturally produced hybrid in Weiss Reservoir, Alabama Fisheries Research 29:185-191. 

Plight of the Paddlefish, by Don Orth

If we were able to travel back in time to the Cretaceous period, the world would appear very different to us.  We would not recognize any of the first flowering plants that appeared in the early Cretaceous period.  We would not recognize our continental boundaries -- the supercontinent of Pangea was breaking apart.  A broad shallow sea covered central North America at the time.   We might recognize some of the dinosaurs, pterosaurs, and ichthyosaurs of the period, but only from museums or the Jurassic Park movie.   However, we would recognize the Paddlefish.   Paddlefish fossils appeared in Cretaceous and Paleocene formations and are clearly Paddlefish.  The American Paddlefish Polyodon spathula is as distinctive as its fossilized ancestors. It can reach 2.1 m (7 feet) and weigh as much as 74 kg (163 pounds).  Only one species of Paddlefish exists in North America.  The only other paddlefish in the world, the Chinese Paddlefish Psephurus gladius, is most likely extinct; no Chinese Paddlefish has been captured since 2003 (Dudgeon 2011).  Therefore, the plight of this unique large freshwater fish must be dealt with effectively. 

 Historical drawing of the Paddlefish from the U.S. National Museum.

Johann Julius Walbaum, a German physician and naturalist, described the Paddlefish in 1792.  Because of the cartilaginous skeleton, the paddlefish was first classified as a shark.  Walbaum named it Squalus spathula, thinking it was closely related to dogfish sharks.  Later the French naturalist Bernard Germain de Lacépède would name the genus, Polyodon.  Polyodon, is derived from the Greek root words meaning “many teeth.”  The basic body form is common to ancestral acipenseriform fishes since the Jurrasic.    The body is fusiform and tapers in the tail region to an asymmetric heterocercal tail.  The skeleton is mostly cartilaginous with minimal calicification.  Only small modified scales appear on the caudal fin base.

The Paddlefish has a very large mouth and a long, paddle-shaped snout that is one-third of its body length.   The paddle, or rostrum, is filled with electrosensory receptors that can detect the weak electrical fields generated by a swarm of zooplankton. The small eyes, numerous slender gill rakers (="many teeth"), and long tapering operculum flap are adaptations for a filter-feeding life in large, often turbid, rivers and oxbow lakes. The electrosensory pores on the rostrum help the Paddlefish orient to abundant zooplankton.  The numerous fine gill rakers help it feed efficiently on numerous small zooplankton, such as cladocerans and copepods. 

Paddlefish rostrum and close-up of electrosensory pores (Helfman et al. 2007)

The Paddlefish swim with its mouth open to filter feed on abundant zooplankton. Their first five years are all about growing to a large body size and they mature late and can live a long life, if not interrupted by fishing.  After five years, Paddlefish increase in body weight rapidly.   Many populations of Paddlefish have been studied to examine individual growth patterns and breeding patterns.  The dentary bone (i.e., lower jaw) can be sectioned to expose annual rings.  The oldest Paddlefish specimen was aged at 56 years old!  

 

Gill rakers of Paddlefish (left), photo by John Lyons.

Transverse sections of dentary bones (right). Photo from Adams (1942).

The Paddlefish is a migratory species that occurs in all large rivers of the Mississippi River as well as large Gulf Coast tributaries.   These are working rivers that have been highly modified for navigation and flood control.  The dams are barriers to migration and modify flow levels that serve as migration cues.  Navigable river channels have been dredged, deepened, and straightened, modifying habitats for Paddlefish.  Pollutants, contaminants, and waterway development continue to constrain populations of Paddlefishes.  The dcline in Paddlefish began in the early 1900s due to unregulated harvest.  Consequently, many states have research and management efforts to regulate harvest of populations. . 

Catch of Paddlefish from Illinois River, circa 1900 ( Forbes and Richardson 1920)

Paddlefish display strong spawning site fidelity and larges shoals of adults gather over clean gravel-cobble stream substrates for spawning.  Females delay spawning until they are between seven and ten years old and do not breed each year. Small eggs (2-3 mm) are produced by a single female and the total fecundity ranges from 9,000 to 26,000 per kg of female body weight.  That is why large female are so important to sustaining productivity of a population. A 20-kg female can produce 520,000 eggs and a 40-kg female produces over one million eggs.   However, these big old fecund female fish (BOFFF) are very rare in exploited populations.   

Fertilized eggs can hatch in 6-10 days while drifting downstream in the river currents; therefore, flow levels determine where larval Paddlefish will end up when they are ready to begin feeding.      Larval Paddlefish hatch at about 8-9 mm and have no paddle.  For a inside look at a Paddlefish larva, view this micro-CT scan.  The paddle begins to appear after larval metamorphosis and juveniles begin to resemble adult Paddlefish at 2 to 3 inches in length.   Recruitment of Paddlefish is usually better during years of high spring flows and recruitment failure is common during drought years.  

Larval Paddlefish SEM (Top)  Photo by William Bemis.  Underside and side views of juvenile Paddlefish, blue stained for cartilage.  Photo by M.C. Davis.

Management of Paddlefish populations is complicated because it requires coordination of efforts from many states that are responsible for this mobile species that does not stay in one state for its entire life cycle. Paddlefish freely move between political jurisdictions subject to differing management strategies and harvest regulations (Prachiel et al. 2012).   The Mississippi Interstate Cooperative Resource Association was organized in 1991 to improve interjurisdictional management.  Paddlefish is a major priority and increased knowledge is needed to manage this highly migratory and valuable planktivore.

  

When Paddlefish caviar sells for $24 per ounce (caviarlover.com), the demand for harvest will remain high even has catches are historical lows. Poaching remains difficult to stop and fraudulent sales of Paddlefish caviar as more expensive black caviar (Sturgeon) will no doubt continue.  Several different management strategies are in play.  One is stocking of juvenile Paddlefish since much is known about raising Paddlefish in captivity (Mims and Shelton 2015).   Some believe that Sturgeon and Paddlefish aquaculture will almost certainly be the major source of caviar in the future. For now, however, regulating harvest to protect females is needed throughout the range.  Some commercial fisheries have been banned to protect small fragmented populations.  Recently Hupfeld et al. (2016) advocated adoption of a basin-wide minimum length limit of at least 810 mm (or 32 inches) on Paddlefish fisheries in the Mississippi River.  Other proposals include a harvest slot and maximum size limits. Many dams serve to concentrate Paddlefish during the spring migration; here they are highly vulnerable to popular recreational snag fisheries.  The Oklahoma Department of Wildlife Conservation (ODWC) piloted a recreational harvest permit for Paddlefish in 2006.  Permit holders can bring their catch for the ODWC staff to clean and fillet.  In exchange for fillets the ODWC retains eggs from the female paddlefish for caviar.    This program has earned approximately $14 million since its inception, while processing 30,000 Paddlefish caught by anglers. 

Commercial harvest of Paddlefish (Pikitch et al. 2005).

McIntire et al. (2016) used “triple jeopardy” to describe the precarious situation faced by migratory fishes, such as the Paddlefish.  Paddlefish need suitable habitats in the feeding and breeding habitats, as well as along the migratory corridors connecting these habitats. Lack of spring high flows means that Paddlefish do not have a strong cue for spawning and recruitment is reduced (Prachiel et al. 2012).   Alterations of large rivers for navigation change the migratory corridors increasing the energy demands for upstream migration.  Construction of dams without fish passage restricts movement to historical breeding grounds.   Loss of oxbows means fewer productive feeding habitats exist.  In addition to the “triple jeopardy,” the Paddlefish now co-occur with large Asian Carp populations.What influence will this abundant non-native planktivore have on the planktivorous Paddlefish?  Without wise management actions, we risk keeping fisheries for Paddlefish trivial compared to their historic potential and we risk the loss of the last Paddlefish species on the planet.  

References

Dudgeon, D. 2011.  Asian river fishes in the Anthropocene: threats and conservation challenges in an era of rapid environmental change.  Journal of Fish Biology 79:1487-1524.

Firehammer, J. A., and D. L. Scarnecchia. 2007. The influence of discharge on duration, ascent distance, and fidelity of the spawning migration for Paddlefish of the Yellowstone- Sakakawea stock, Montana and North Dakota, USA. Environmental Biology of Fishes 78:23–36.

Forbes, S.A., and R. E. Richardson. 1920. The fishes of Illinois.  Illinois Natural History Survey Division.  357 pp.  

Hupfeld, R.N., Q. E. Phelps, S.J. Tripp, and D.P. Herzog. 2016.  Mississippi River basin paddlefish population dynamics: implications for the management of a highly migratory species.  Fisheries 41(10): in press.

McIntyre P.B., C. Reidy Liermann, E. Childress, E.J. Hamann, J.D. Hogan, S.R. Januchowski-Hartley, A.A. Koning, T.M. Neeson, D.L. Oele, and B.M. Pracheil. 2016. Conservation of migratory fishes in freshwater ecosystems. In Closs G, Krkosek M, & Olden JD: Conservation of Freshwater Fishes.

Mims, S.D., and W. L. Shelton.  2015.  Paddlefish aquaculture.  Wiley Blackwell,  Hoboken, New Jersey.  298 pp.

Neely, B.C., B.M. Pracheil, and S.T. Lynott. 2014. Hydrologic variables predict harvest in a recreational paddlefish fishery. Fisheries Management and Ecology 32: 259-263.

Paukert, C. and G. Scholten editors. 2009.  Paddlefish management, propagation, and conservation in the 21st century: building from 20 years of research and management. American Fisheries Society, Symposium 66, Bethesda, Maryland.

Pikitch, E.K. P. Koukakis, L. Lauck, P. Chakrabarty, and D.L. Erickson. 2005.  Status, trends and management of sturgeon and paddlefish fisheries.  Fish and Fisheries 6:233-265.

Pracheil, B.M., L.A. Powell, M.A. Pegg, and G.E. Mestl. 2012. Swimways: protecting paddlefish through movement-centered management. Fisheries 37: 449-457.