The Fight to Recover the Gulf Dinosaur

by Kayla DiBenedetto Kimmel and Glenn Constant

Federally endangered Gulf sturgeon.

Photo Credit: Kayla Kimmel, USFWS

The fight for recovery can be a difficult one. For the Gulf sturgeon (Acipenser oxyrinchus desoto) in the Pearl and Pascagoula Rivers, recovery has been an uphill battle for decades. The species, which inhabits coastal rivers, bays, and estuaries from Louisiana to Florida and the Gulf of Mexico, was listed as threatened under the Endangered Species Act in 1991. Although there are indications that Gulf sturgeon population numbers are increasing in some rivers along the coast, the most western Pearl and Pascagoula River populations have not experienced population increases. Sturgeon in these two rivers have suffered from what recovery biologists are calling a “triple whammy”—a series of stochastic, or random, events including Hurricanes Katrina and Rita; the British Petroleum’s (BP) Deepwater Horizon oil spill; and, most recently, the release of toxic wastewater into the Pearl River.

Considering the complex life history of Gulf sturgeon, the gains made towards the species’ recovery have been impressive. Gulf sturgeon are anadromous fish, spending winter months in the warm waters of the Gulf of Mexico where they grow and increase their condition by feeding on tiny, bottom-dwelling invertebrates. Each spring, these fish migrate to inland rivers from Louisiana to Florida. This is no insignificant task considering their energy stores will have to see them through this 100 mile (62 kilometer) journey upstream to spawn, and then a 6-month fasting period in river systems that can be inhospitable in the heat and drought of summer. For a fish that can grow up to 8 feet (2.5 meters) in length and weigh over 200 pounds (91 kilograms), rearranging their physiology to live in a freshwater environment and investing in reproduction requires a tremendous amount of energy. Young Gulf sturgeon inhabit their natal river system for the first few years before joining the migration; however, due to their late sexual maturity, sturgeon will not spawn before reaching 8 to10 years of age. Ultimately, the viability of these populations depends on individuals reaching sexual maturity to recruit juveniles and thus contribute to the population.

Sturgeons are an ancient group of fishes that have been around since dinosaurs roamed the earth, so they are obviously resilient to changes in their environment. To show positive population trends in some
rivers—despite decades of harvest by the caviar industry, extensive hydrologic modification, and increasing demands on water resources for municipal and commercial use—indicates a strong, positive potential for recovery across its range. The main challenge is refining our understanding of why recovery has not been uniformly effective in all rivers.

Genetic similarities, mark and recapture netting efforts, and migration patterns observed through telemetry show that there is some intermingling of fish between river systems. However, the majority of individuals show a strong fidelity to specific rivers, requiring research and recovery efforts that focus on individual rivers.

This sill, located on the Bogue Chitto river near Bush, LA, is a permanent concrete structure that impedes Gulf sturgeon attempting to migrate upstream to spawn.

Photo Credit: USFWS

Obstacles for Gulf sturgeon started in the Pearl River in the 1950s when underwater concrete sills were constructed to help maintain water levels for the navigation channel that connected the Bogalusa to the mouth of the West Pearl River. These concrete barriers have hindered sturgeon access to historic upstream spawning areas for the past 60 years, and are still impassable today with normal water levels. Additionally, both the Pearl and Paccagoula Rivers sustained extensive damage when Hurricanes Katrina and Rita made landfall along the Gulf Coast in August and September 2005. Navigation was blocked and flow diverted from the large amount of debris, bottom sediments and marsh vegetation. Numerous fish kills were reported, including adult-sized Gulf sturgeon, although the direct impacts of these two storms on the population remain uncertain.

Uncertainty about recovery for the Pearl and Pascagoula River Gulf sturgeon increased in April 2010 with the British Petroleum’s Deepwater Horizon oil spill, where millions of gallons of crude oil spilled into the Gulf of Mexico. Due to concerns about the effects of the oil on Gulf sturgeon, the Natural Resource Damage Assessment process was implemented and will continue research efforts to determine effects of the oil on any of the Gulf sturgeon populations.

Most recently, in August 2011, a fish kill was documented on the Pearl River. A local paper mill in Bogalusa confirmed that it had released potentially toxic wastewater into the river near that time. Preliminary results indicated hundreds of thousands of freshwater mussels and 26 species of fish were killed, including juvenile and adult Gulf sturgeon.

All of these events have contributed to uncertainty regarding the recovery of Gulf sturgeon in the Pearl and Pascagoula Rivers. Biologists from the U.S. Fish and Wildlife Service and National Marine Fisheries Service have learned much about the life history of this species since its listing, and continue to lead the recovery effort in these river systems. A recent 5-year review of the Gulf Sturgeon Recovery Plan reflects the current state of knowledge for this species. It includes research contributions from other federal and state agencies and universities that have enhanced and updated the recovery objectives to accommodate Gulf sturgeon behavior and habitat needs. This intensive collaborative research effort will provide key information that will be used to promote Gulf sturgeon population growth, even when there are bumps in the road to recovery.

Kayla DiBenedetto Kimmel, a fish and wildlife biologist in the Service’s Baton Rouge Fish and Wildlife Conservation Office, can be reached at kayla_dibenedetto@fws.gov or 225-578-8066. Glenn Constant, Project Leader at the Baton Rouge Fish and Wildlife Conservation Office, can be reached at glenn_constant@fws.gov or 225-578-8066.