Wednesday, October 26, 2016

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. 

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 sonarMarine 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

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