Thursday, June 21, 2018

Why Alligator Gar Need Floodwaters, by Don Orth

Can we save one of the largest fish in North America with floodwaters?  The Alligator Gar Atractosteus spatula is the largest of seven species of Gar found in Central America, Cuba, and North America.  The IGFA world record is 279 pounds, but larger ones have been reported indicating that that can grow up to ten feet and and 350 pounds. An 8 ft. Alligator Gar weighed 254 pounds with a girth of 44 inches was snagged in Lake Texoma and is the largest fish ever caught in Oklahoma waters. Alligator Gar are imperiled due to reduced abundance and diminished range.  In the past, little attention was paid to management or conservation of Alligator Gar. However, Alligator Gar are vulnerable to overfishing and rivers in its range are highly altered due to dams, dikes, dredging, and other forms of habitat and flow alteration.  A recent investigation reported by Robertson et al. (2018), confirmed suspicions that the Alligator Gar are dependent on seasonal flooding in large floodplain rivers.

The gar family (Lepisosteidae) have been around since the Cretaceous Period (~100 million years  ago.  Gars and bowfin are the sister group to other teleost fishes and, therefore, of interest to evolutionary biologists. The largest gars are in the genus Atractosteus, the three extant species are Alligator Gar (or Catan in Mexico), the Cuban Gar A. tristoechus or Manjuari from western Cuba, and the Tropical Gar A. tropicus (or Pejelagarto) from southern Mexico and Central America. Among these three, the Alligator Gar is most imperiled. Gar are fascinating and misunderstood creatures, and unfortunately, the influence of habitat restoration for gars has not yet been fully explored.  Efforts are now underway to restore these magnificent creatures via supplemental stocking.  It will take many years, up to 50 years, for stocked Alligator Gar to reach the potential maximum sizes.  Supplemental stocking is an uncertain and expensive short-term strategy.  Until natural spawning and rearing habitats can be restored, supplemental stocking is necessary.
Alligator Gar that weighed 108 pounds was sampled May 27, 2015 by Florida Fish and Wildlife Research Institute. Creative Commons by NC-ND-2.0. Source.
Ten-foot long Alligator Gar photographed in 1920 from Mhoon Landing, Mississippi River. Public Domain
Managers need to understand what drives populations of Alligator Gar if the species has any chance to be restored throughout its range (O'Connell et al. 2007; Buckmeier et al. 2017).  Although the effects of hydrologic modification of rivers is well document, the prevailing questions related to re-establishing ecologically sustainable flows, such as "How much?" and "How often?" remain unanswered (McManamay et al. 2013).  Fully mature Alligator Gar may produce 157,000 large eggs (2-4 mm in diameter).  These BOFFFF (= big old fat fecund female fish) need do be protected and we also need to provide habitat so that they will spawn naturally.  What is suitable habitat?  The life history of Alligator Gar is tuned to life in floodplain rivers where spawning is synchronized with the high flow pulse events (Buckmeier et al. 2017).  The Robertson et al. (2018) study examined the extent of potential spawning habitat in the Trinity River, downstream from Dallas, Texas. Trinity River is supports guided fishing for trophy size Alligator Gar and is becoming a model for Alligator Gar management elsewhere. 
Map of Spawning Habitat in Floodplains of Trinity River, Texas.  Robertson et al. (2018)
This research used hydraulic models to predict water surface elevations and digital elevation models from LIDar (Light detection and ranging) data. These fine scale models quantified the extent to which floodwaters inundated large expanses of vegetated habitats in low lying floodwaters.  Alligator Gar spawning habitat was mapped as floodwaters between 0.2 and 2 meters deep over woody vegetation and open canopy vegetation types. The plot below shows a dramatic increase in total spawning habitat available as the river flow increases enough to spill onto the floodplains. 

Plot of area of Alligator Gar spawning habitat versus river flow.  Robertson et al. (2018).
We now have the making of a 'Field of Dreams' hypothesis.  If you build it, they will come.   If floodwaters are held back in reservoirs for release at another time, Alligator Gar may not receive the cue to initiate the courtship and spawning behavior.  However, if we create large expanses of spawning habitat, will the breeding Alligator Gar come and spawn?   Amount, duration, and timing of spawning habitat appeared to correlate with years of exceptional Alligator Gar recruitment in the Trinity River (Robertson et al. 2018).  Larval Alligator Gar are only about 8 mm long upon hatching.  These fish that may grow to ten feet, yet start off as tiny fragile larvae.  Larvae must attach to substrates with an adhesive organ on the snout.  If the flood pulse is artificially shut off after spawning, recruitment will be reduced.  The longer duration of the flood pulse enhances nursery habitats for young Alligator Gar.

In 2014, Kimmel et al. (2014) witnessed spawning of Alligator Gar in floodplain habitat in the Mississippi river floodplains at St. Catherine Creek National Wildlife Refuge.  A large aggregation of Alligator Gar was observed in a flooded ditch, lined with buttonbush, shrubs, and herbaceous vegetation four miles from the main river channel.   These spawning observations help to validate the habitat suitability criteria used by Robertson et al. (2018). 
Spawning behavior displayed by Alligator Gar observed by Kimmel et al.  (2014) in floodplains of St. Catherine Creek, near Natchez, Mississippi. 
Eggs of Alligator Gar deposited in woody debris and vegetation.  Kimmel et al.(2014).
The lessons from the Trinity River study give us optimism for population restoration here and elsewhere.  The demand for water from the Trinity River is growing from population centers of Dallas-Fort Worth and Houston and flood-pulse management may provide for periodic strong Alligator Gar recruitment.  Gar production in hatcheries may help, but they provide an uncertain number of offspring (Schmidt 2015).  While many are experimenting with spawning Alligator Gar (Mendoza et al. 2002), for example the USFWS does hatchery spawning of Alligator Gar, the restoration of natural habitat when and where it is needed has the best likelihood for long-term sustainable populations. 
Larva of the Spotted Gar Lepisosteus oculatus.  Photo by Konrad P. Schmidt.

Buckmeier, D.L., N.G. Smith, D.J. Daugherty, and D.L. Bennett. 2017. Reproductive ecology of Alligator Gar: Identification of environmental drivers of recruitment success.  Journal of the Southeastern Association of Fish and Wildlife Agencies 4:8-17.

Kimmel, K., Y. Allen, and G. Constant. 2014. Seeing is believing: alligator gar spawning event confirms model predictions.  Website  Accessed June 20, 2018.

McManamay, R. A., D.J. Orth, J. Kauffman, and M.M. Davis. 2013.  A database and meta-analysis of ecological responses to stream flow in the south Atlantic region.  Southeastern Naturalist 12(Monograph):1-36. 

Mendoza, R., C. Aguilera, G. Rodríguez, M. Gonz.lez, and R. Castro. 2002. Morphophysiological studies on alligator gar (Atractosteus spatula) larval development as a basis for their culture and repopulation of their natural habitats. Reviews in Fish Biology and Fisheries 12:133–142.

O’Connell, M. T., T. D. Shepherd, A. M. U. O’Connell, and R. A. Myers. 2007. Long-term declines in two apex predators, bull sharks (Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain, an oligohaline estuary in southeastern Louisiana. Estuaries and Coasts 30:567–574.

Robertson, C.R., K. Aziz, D.L. Buckmeier, N.G. Smith, and N. Raphelt.  2018.  Development of flow-specific floodplain inundation model to assess Alligator Gar recruitment success.  Transactions of the American Fisheries Society DOI: 10.1002/tafs.10045
Schmitt, K.  2015. Gar farming.  American Currents  40(4):3-9

Tuesday, June 12, 2018

Sargassum: Essential Habitat or Beach Nuisance, by Don Orth

A vacation at a beach resort near white sandy beaches and aqua blue waters was the plan.  However, the white sandy beaches and surf were covered with a thick mats of Sargassum, a brown macroalgae or 'seaweed.'  As I waded out beyond the floating seaweed, I could not see my feet in the sand, the water was that murky. The resort was along the Caribbean coastline known as the Riviera Maya, Mexico. This coastal zone is famous for its beaches and reef dependent recreation.  Tourism contributes 8.6% to the national GDP of Mexico and 45% of tourists choose the coastal zone as their destination (UNWTO 2016). Pristine beaches and associated recreational amenities are key attractions to coastal tourism worldwide (Onofrio and Nunes 2013). Hotel room prices are positively correlated to the beauty of the beach and recreation (Mendoza-González et al. 2018).  However,  'seaweed' is not part of the marketing plan for resorts.
Sargassum on the beach.
I know only a little about Sargassum, and that is about its role as offshore habitat for fish and invertebrates.  There are many species of Sargassum, bu  two species, Sargassum fluitans and Sargassum natans, dominate the floating mats. When trolling for pelagic fish the boat captain will seek out rafts of Sargassum, which attract numerous species (Dooley 1972). Some fishes will complete their entire lives in Sargassum, others use it for breeding, and others use it only for larval and juvenile habitats.  The Sargassumfish Histrio histrio is a frogfish (Antennariidae) that lives its entire life amidst the Sargassum (Pietsch and Grobecker 1987).  Sargassumfish are camouflaged with colors that change and weedy projections so that it blends into the floating seaweed. It dangles its esca as a fishing lure to attract small fish, shrimp and other invertebrates close enough to capture them.  
Floating raft of Sargassum photographed June 3, 2018 near Playa del Carmen, Mexico.
Sampling fishes in and around the floating Sargassum mats is a complicated process.  Therefore, I was not surprised by how few studies investigated the association of Sargassum and fishes. The studies I reviewed showed that small individuals from four or five fish families (Antenariidae, Carangidae, Monacanthidae, Syngnatidae, Tetraodontidae) typically made up over 90% of the sampled catch.  Depending the study duration and lcoation, between 36 to 110 fish species were identified (Dooley 1972; Bortone et al. 1977; Moser et al. 1998; Wells and Rooker 2004; Cassaza and Ross 2008; Moritz 2015).   Larger fishes, such as dolphinfishes, jacks, wahoo, and billfishes aggregated below the weedlines using the Sargassum for feeding habitat.  In addition to the fishes, Sargassum habitat provides feeding habitat for marine mammals, sea birds, and sea turtles (Cassaza and Ross 2008).
Fishes along Sargassum weed line near Cape Hatteras, North Carolina.  A. small planehead filefish; B. larger jacks below weed line; C. large predators, dolphinfish; D. schooling unicorn filefish; E. planehead filefish feeding on ctenophore;  and F. edge of Sagarssum weed line.  (Cassaza and Ross 2008).  
Realizing the importance of Sargassum to recruitment of many marine animals, NOAA approved a Sargassum Management Plan in 2003.  See the final rule here.  Development of this management plan was controversial over the interpretation of Sargassum as an essential habitat versus a harvestable product.  Larval and juvenile fishes of many species will be taken by Sargassum harvesters and effects of harvesting are unstudied. However, the current estimated harvest is miniscule compared with the estimated biomass of Sargassum.
Sargassum underwater near beach at Playa del Carmen, Mexico, photographed June 5, 2018. 
The Saragassum is widely distributed but the occurrence of Sargassum strandings on Caribbean beaches has become more common since 2011 (Franks et al. 2016).  Warming climate and changes in oceanic currents influence the spatial distribution and some researchers believe increases in nutrient loading may be stimulating an increase in Sargassum.  A forecast system based on satellite measurements shows promise for predicting the distribution and timing of Saragassum blooms, thereby providing localities with advance warnings of beaching events (Wang and Hu 2017).   

Locations of pelagic Sargassum and current vectors.  Franks et al. 2016. 
While, we were beach combing, my wife, Valerie, noted a small dead fish in the surf.  We began searching the recently beached Sargassum and found many others, all about 2-3 cm long.  She thought it was a pufferfish and my initial identification was incorrect.   After posting on All Fish Species Identification Group on Facebook, Pete Liptrot and Roy Hemdel identified it as Sharpose Puffer Canthigaster rostrata

Sharpnose Puffer Canthigaster rostrata and one puffer Sphoeroides sp. (bottom left) from beached Sargassum.
Sharpnose Puffer Canthigaster rostrata
Tourists in the region quickly learn that Sargassum is a common occurrence, but the quantity that reaches Caribbean beaches has increased.   The Caribbean Alliance for Sustainable Tourism and the Caribbean Hotel and Tourism Association created Sargassum: A Resource Guide for the Caribbean.   This guide examines possible impacts on beach tourism, uses of Sargassum, and management practices for beach resorts. Sargassum is an excellent medium for plant and crop growth and may become a new source of revenue.   Beach cleaning machines are available, but many resorts use manual removal in order to save costs and avoid issues with sea turtles. 

Gabriel raking Sargassum on beach.  Burying the Sargassum provides some relief to the problem.
Sargassum is a living renewable marine resource, a primary producer, and an essential habitat for many marine organisms, including highly migratory species.  For that reason, Sargassum should be managed and protected as essential habitat.  However, tourists expecting the picturesque sandy beaches will be dismayed to walk amidst the decaying Sargassum on the beaches. In the future, Caribbean beach resorts will need to adapt to changing climate conditions and the delivery of excessive amounts of Sargassum to pristine beaches. 


Casazzarro, T.L., and S.W. Ross. 2008. Fishes associated with pelagic Sargassum and open water lacking Sargassum in the Gulf Stream off North Carolina.  Fisheries Bulletin 106:348-363.
Dooley, J. K. 1972. Fishes associated with the pelagic Sargassum complex, with a discussion of the Sargassum community. Contributions in Marine Science 16:1–32.
Franks, J.S., D.R. Johnson, and D.S. Ko. 2016. Pelagic Sargassum in the tropical North Atlantic.   Gulf and Caribbean Research 27: SC6-11.
Mendoza-González, G., M.L. Martínez, R. Guevara, O. Pérez-Maqueo, M.C. Garza-Lagler, abd A. Howard, 2018. Towards a sustainable sun, sea, and sand tourism: The value of ocean view and proximity to the coast. Sustainability 10:1012-1026.
Moritz, T. 2015. Fishes of a stranded Sargassum meadow at Punta Cana, Dominican Republic. Bulletin of Fish Biology 15:141-146.
Moser, M.L., P.J. Auster, P.J., and J.B. Bichy. 1998. Effects of mat morphology on large Sargassum-associated fishes: observations from a remotely operated vehicle (ROV) and free-floating video cameras.    Environmental Biology of Fishes 51: 391-398.  
Onofri, L., and P.A.L.D Nunes. 2013. Beach ‘lovers’ and ‘greens’: A worldwide empirical analysis of coastal tourism. Ecological Economics 88:49–56.
Pietsch, T.W., and D.B. Grobecker.  1987. Frogfishes of the world. Stanford University Press, Stanford, CA, p 420
United Nations World Tourism Organization (UNWTO). Tourism Highlights. 2016. Available online: (accessed on 11 June 2018).
Wang, M. and  C. Hu. 2017. Predicting Sargassum blooms in the Caribbean Sea from MODIS observations. Geophysical Research Letters 44:3265-3273.
Wells, R.J.D., and J.R. Rooker. 2004. Spatial and temporal patterns of habitat use by fishes associated with Sargassum mats in the northwestern Gulf of Mexico.  Bulletin of Marine Sciences 74:81-99.

Friday, May 11, 2018

What Limits Recovery of Atlantic Sturgeon, Austin Beaudet

One hundred years ago, a fisherman could fish in any river on the east coast and have a chance to catch a colossal, prehistoric looking monster, Acipenser oxyrinchus, or better known as the Atlantic Sturgeon. This bony plated monster could grow up to 14 feet in length a weigh a whopping 800 pounds (NOAA). This creature’s huge size and bizarre features made it a target to fisherman all along the east coast. They began to catch these fish at an at a frantic pace to get in on the short lived goldmine that sturgeon provided. Then it all just stopped. Humans kept hunting them until they had completely decimated their numbers. In areas like the Chesapeake Bay which had an estimated 20,000 sturgeon at one point were brought down to roughly 300 alive in the present that are able to reproduce (Dietrich 2017). Since the inclusion of the sturgeon under the endangered species act, many groups and agencies have been desperately trying to bring this population back to a much more stable and healthy size. Certain methods of recovery today include a ban on all capture of Atlantic Sturgeon, hatcheries attempting to provide a boost to the sturgeon population, and other research projects and studies which are trying to learn more about the habitat, life history, and migration patterns of the sturgeon. However, recovery efforts are not going nearly as well as we have hoped and the sturgeon population has failed to comeback in the numbers we wished and many people want to figure out why. According to the research and data that scientists currently have, the main problems limiting the recovery efforts are bycatch mortality, water quality, and dredging activities which all seem to be hugely detrimental in regions inhabited by sturgeon.
Young Atlantic Salmon captured from the Altamaha basin in Georgia.  Photo by Brett Albanese, Georgia DNR.  Creative Commons Flickr
Water quality plays a major role in the development, reproduction, and overall health of the Atlantic Sturgeon. Although there has been multiple laws protecting our waters from pollution, mankind still finds a way to dump harmful chemicals into our river system. One chemical that is particularly damaging to the recovery of sturgeon is polychlorinated biphenyls (PCB). PCB was a very popular form of coolant within many electrical systems in the 1900’s but usage has since declined due to the discovery of it's harmful properties to both humans and wildlife. However, the damage has already been done and will continue to haunt our environment long into the foreseeable future. One estimate has stated that the United States has produced 600,000 tonnes of PCB and a good portion of it has entered our riverways (Cooper 1989, Sinderman 1994). To make things worse, according to the Atlantic Sturgeon Status Review, “Atlantic sturgeon may be particularly susceptible to impacts from environmental contamination due to their benthic foraging behavior and long-life span” (Cooper 1989, Sinderman 1994). Today, PCB sits at the bottom of local rivers and continues to poison the sturgeon population and it seems as though there is very little we can do about it. Studies have now been conducted and have concluded that, “exposure to PCBs reportedly causes a higher incidence of fin erosion, epidermal lesions, blood anemia, and an altered immune response” (Kennish et al. 1992). Until a proper method of removal of PCB from our waterways can be figured out then sturgeon will never stop dealing with the consequences the pollutant causes.
Another major factor that continues to hinder Atlantic Sturgeon recovery efforts is the freshwater dredging that occurs up and down the east coast river systems. This dredging still goes on today and it needs to be run in a much more environmentally conscious manner or be shut down all together. The consequences that sturgeon face due to dredging include, “direct removal/burial of organisms; turbidity/siltation effects; contaminant resuspension; noise/disturbance; alterations to hydrodynamic regime and physical habitat and actual loss of riparian habitat...destruction of benthic feeding areas, disruption of spawning migrations, deposition of resuspended fine sediments in spawning habitat…, and the lethal entrainment of fish up through the dredge drag-arms and impeller pumps” (Chytalo 1996, Winger et al. 2000). To make matters worse, this form of dredging is not nearly regulated enough especially considering the damage is currently is causing. Changes need to start happening as soon as possible if there is still hope to save the Atlantic Sturgeon population from extinction.
A five-foot Atlantic Sturgeon killed by ship strike in the James River, Virginia.  Photo by James River Association. creative commons Flickr
The last major factor preventing the Atlantic Sturgeon from having a stable population size is the damages done through ship strikes and by-catch of the sturgeon (Melnychuk et al. 2016; ASMFC 2017). By-catch is when a certain fish is caught by commercial fisheries that is not the intended target fish. Although intentional hunting of Atlantic Sturgeon is strictly banned, bycatch still remains to be a huge problem. Records show that Atlantic Sturgeon become victims of by-catch through trawls, pound nets, and gill nets. Pound nets seem to be the least damaging to the sturgeon population and don’t have any recorded cases of directly causing death to sturgeon. Trawls have caused some deaths in the sturgeon population but most trawling systems on the southern half of the east coast have mechanisms in place to help prevent the capture of unwanted fish species. Gill nets are the main source of death and accountable for doing the most harm to the sturgeon population. Certain surveys have shown that sturgeon caught in these nets have up to a 70% chance of mortality depending on length of time before the sturgeon are freed (NMFS Observer Database). These nets continue to cause incidents that result in the death of sturgeon every year and if environmental groups and protection/conservation agencies continue to work on the recovery of this species without figuring out a solution to by-catch problems then their fight will most likely be doomed.
             When thinking of limiting factors to the recovery of the Atlantic Sturgeon, things like hunting, global warming, and fecundity come to mind. However, after extensive research it can clearly be seen that the obstacles limiting the Atlantic Sturgeon are quite different. Problems dealing with water quality, by-catch, ship strikcs, and dredging all have become major contributors in the continued decline of this species. Although these threats may not cause as much mortality to sturgeon as ship strikes or dams that block migration routes, they are currently problems that have gone under the radar and need to be fixed just as badly as other, more commonly discussed problems. The good news is that in some rivers, such as the Hudson and Savannah,  biologists are beginning to see an increase in the numbers (Bahr and Peterson 2016; New York State Conservationist 2016).  If protective measures continue, the Atlantic Sturgeon may show signs of recovery in more rivers.


ASMFC. 2017. Atlantic Sturgeon Benchmark Stock Assessment and Peer Review Report, Arlington, VA. 456p.  Available from

Bahr, D.L., and D.L. Peterson. 2016.  Recruitment of Atlantic Sturgeon in the Savannah River, Georgia.  Transactions of the American Fisheries Society 145:1171-1178.
Chytalo, K. 1996. Summary of Long Island Sound dredging windows strategy workshop. In:    Management of Atlantic Coastal Marine Fish Habitat: Proceedings of a Workshop for Habitat Managers. ASMFC Habitat Management Series #2.
Cooper, K. 1989. Effects of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans on aquatic organisms. Reviews innAquatic Sciences 1(2): 227-242.
Dietrich, Tamara. “Sturgeon Get a Double Boost in the Chesapeake Bay.”, Daily  Press, 17 Aug. 2017,
Kennish, M. J., T. J. Belton, P. Hauge, K. Lockwood, and B. E. Ruppert. 1992. Polychlorinated biphenyls in estuarine and coastal marine waters of New Jersey: a review of contamination problems. Reviews in Aquatic Sciences 6: 275-293.
Melnychuk, M.C., K.J. Dunton, A. Jordaan, K. McKown, and M.G. Frisk. 2016.  Informing conservation strategies for the endangered Atlantic sturgeon using acoustic telemetry and multi-state mark-recapture models.  Journal of Applied Ecology 54:914-925.
New York State Conservationist. 2016.  "Atlantic sturgeon show signs of population recovery." ,  p. 36. Student Resources In Context Accessed 10 May 2018.
Sindermann, C. J. 1994. Quantitative effects of pollution on marine and anadromous fish populations. NOAA Technical Memorandum NMFS-F/NEC-104, National Marine Fisheries Service, Woods Hole, Massachusetts.
Smith, T., and J. Clugston. “Atlantic Sturgeon Recovery Program.” Greater Atlantic Regional Fisheries Office, NOAA Fisheries, 29 Jan. 2014,

Winger, P. V., P. J. Lasier, D. H. White, J. T. Seginak. 2000. Effects of contaminants in dredge material from the lower Savannah River. Archives of Environmental Contamination and Toxicology 38: 128-136.