Prehistoric sturgeon still call Mississippi home
The Mississippi waters of the Mississippi River are home to pallid sturgeon and shovelnose sturgeon. Unlike many other sturgeon in North America and worldwide that migrate between the ocean and freshwater to complete their life cycle, the pallid and shovelnose sturgeon complete their life cycles entirely in rivers.
These fish descended from a common ancestor 80 million years ago and have changed little. They swam in the rivers when Tyranosaurus Rex walked on land. If sturgeon could talk, they may put to rest the debates about why dinosaurs went extinct.
Two other freshwater sturgeons are known from the United States. Lake sturgeon are native to the Great Lakes and the Mississippi River basin. They occur as far south as Tennessee, and it is likely that lake sturgeon will be captured in the Mississippi waters of the Mississippi River.
The Alabama sturgeon is native to the Alabama River basin, including the Tombigbee River. The last Alabama sturgeon was captured in 2007, and it died in captivity. Alabama sturgeon DNA was detected in Alabama River water samples in 2014 and 2015, suggesting the species may not be extinct as feared.
Pallid sturgeon: an endangered species
The pallid sturgeon once ranged from the upper Missouri River and Yellowstone River in Montana to the Gulf of Mexico outlet of the Mississippi River. Although the creation of large impoundments in the middle Missouri River system stopped successful spawning and recruitment, pallid sturgeon populations in the lower Missouri and Mississippi rivers remain viable, but individuals are rare. Pallid sturgeon are the only federally endangered fish species in the lower Mississippi River.
Pallid sturgeon grow to almost 6 feet, but individuals this large are probably more than 40 years old and extremely rare. Only a few of than 300 pallid sturgeon we have collected in the Mississippi River were more than 3 feet long.
Many questions remain to be answered, but research conducted by the Mississippi Department of Wildlife, Fisheries and Parks, Mississippi State University, the U.S. Army Corps of Engineers, the U.S. Fish and Wildlife Service, and the U.S. Geological Survey has determined that adult pallid sturgeon in the lower Mississippi River prefer current velocities of about 1.6 to 2.7 miles per hour and water depths of about 20 to 50 feet. Pallid sturgeon select sandbars, natural banks, rock revetment banks and downstream island tips and tend to avoid the main channel except during low river stages. Secondary channels are channels separated from the main channel by an island. These island-secondary channel complexes appear to be important habitat for pallid sturgeon, and activities are ongoing to restore flow through selected secondary channels.
Although the spawning habitat of pallid sturgeon has been documented in the Yellowstone River, where they spawn the Mississippi River remains a mystery. U.S. Geological Survey scientists have recorded presumptive spawning on a rock-revetted bank in the lower Missouri River using DIDSON sonar.
Shovelnose: a threatened species
In many years of fishing the Mississippi River with various nets and electrofishing, we captured fewer than a dozen shovelnose sturgeon. We learned that the most effective way to catch sturgeon in the lower Mississippi is to use trotlines baited with nightcrawlers; our catch with trotlines indicates that shovelnose sturgeon are at least as abundant as the plentiful blue catfish.
The shovelnose sturgeon is threatened, not because it is scarce but because it is targeted by commercial fishers for roe (caviar) and is very similar in appearance to the endangered pallid sturgeon. To avoid harvest of the endangered pallid sturgeon, the fishery for both river sturgeon has been closed.
The shovelnose sturgeon occurs throughout the Mississippi River basin, which includes the Mississippi, Missouri, and Ohio rivers and their tributaries. Shovelnose sturgeon grow to about 3 feet.
Like pallid sturgeon, they are riverine and prefer moderate currents and relatively deep water. They occupy a wide range of habitats and appear to orient to steep bottom slopes.
Wanton waste or expensive taste?
The finest caviar is made from sturgeon eggs. All sturgeon are slow growing, and many species, particularly the larger species most valued for their roe, do not reach sexual maturity and develop egg-bearing ovaries for 15 or more years. Harvest of sturgeon for their high-value roe has depleted populations worldwide. With depletion of sturgeon traditionally supplying roe, caviar producers have turned their attention to North American sturgeon, including the pallid and shovelnose sturgeon.
Pallid sturgeon females mature at ages nine or 10 and can spawn at least 40,000 eggs. The smaller shovelnose sturgeon females mature at seven or eight and can spawn approximately 10,000 eggs. The females are thought to develop egg-bearing ovaries every three years. Lifetime fecundity — the eggs an individual female can spawn in a lifetime — might range from 50,000 eggs for a shovelnose sturgeon to at least a quarter million eggs for a pallid sturgeon.
Although sturgeon are sold for meat, usually smoked; the real money is made by the sale of the roe, appropriately called “black gold.” A lot of sturgeon eggs are never spawned, fertilized or developed into young sturgeon so somebody can put them on a cracker.
Enterprises are developing to rear sturgeon in tanks, detect when the females have mature ovaries using ultrasound, kill the fish and harvest the roe. These operations will help our ancient fish persist.
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