As a class of fish, sturgeon have existed since the Jurassic Period, but millions of years after their appearance, the blossoming of industrialization and man-made impediments along waterways they navigated drastically impacted their ability to reach their spawning grounds. Lake Sturgeon were once abundant in the Tennessee River, but man-made alterations to the waterway and overharvesting caused their numbers drastically to dwindle in the 20th century. As a result, the species is considered endangered in the state of Tennessee.
Thanks to changes to dam operation by the Tennessee Valley Authority and the work of the Tennessee Aquarium Conservation Institute and organizational partners, however, Lake Sturgeon have been reintroduced to the waterways along their native range. That work continues, and Conservation Institute Science Program Manager and ichthyologist Dr. Bernie Kuhajda took the time to answer a few questions about these living fossils and to provide an update on our efforts to ensure to their seeming timelessness doesn't run out.
Q: How far do Lake Sturgeon typically migrate? Are they long-haulers, or is their migration route pretty short compared to other species?
A: Lake Sturgeon have relatively short migrations averaging 62 miles. This compares to an average migration of 109 miles for another Tennessee species, the Shovelnose Sturgeon, and up to 746 miles for the White Sturgeon of the Pacific Northwest.
Q: When do they typically begin to migrate?
A: Lake Sturgeon do not spawn for the first time until males reach an age of 15-20 years and females are 22-33 years old, but sub-adults and non-spawning adults may accompany spawning adults on migrations. Lake Sturgeon begin their spawning movement in the autumn with a pre-spawning migration from a lake or downstream area of a river to deep holes near spawning sites, where they overwinter. Actual spawning is from April to the end in late June, with southern populations spawning earlier than northern populations. Adults do not spawn every year, with spawning intervals of two to seven years for males and three to 12 years for females.
Q: Do all Lake Sturgeon spawn in the same general location, or do they have many spawning sites?
A: Spawning sites for Lake Sturgeon can be in different tributaries to a lake or at different sites within a tributary, but if there is a dam blocking further upstream migration, Lake Sturgeon often congregate and spawn below the dam. For an individual Lake Sturgeon, they often demonstrate fidelity to certain tributaries and even certain sites within tributaries to spawn.
Q: Until fairly recently, the Lake Sturgeon in this region were suffering as a result of impediments to their migration route. Talk about what some of those obstacles were and why they were — or are — a problem for this species.
A: Lake Sturgeon completely disappeared from the Tennessee River in the 1970s due to commercial fishing, water pollution, and poor water quality and quantity below dams. Because they are so long-lived — up to 150 years — we do not know if Lake Sturgeon were capable of successful spawning, hatching, and survival of early life stages after dams were installed on the Tennessee River in the 1930s. Now that 1) taking a Lake Sturgeon in the State of Tennessee is illegal, 2) our water in much cleaner due the Clean Water Act of 1972, and 3) TVA implemented a dam improvement program, Lake Sturgeon that have been reintroduced in the Tennessee River by the Tennessee Aquarium and our many partners are doing well.
But until both sexes reach maturity (at least another several years for females), we do not know if Lake Sturgeon will be able to reproduce on their own in the Tennessee River. Will there be proper habitat for Lake Sturgeon to overwinter and will there be proper spawning habitat? Dams not only affect upstream migration of adults, but also downstream migration of Lake Sturgeon larvae and juveniles. Lake Sturgeon larvae need to be suspended in river current for, on average, 7-16 miles to successfully transform to a juvenile. Reservoirs behind dams slow the flow of water and may cause larvae to settle to the bottom and die. So it is not only dams that block migration, but they also create inhospitable habitat for early life stages.
Q: Do these kinds of impediments affect many species, or is the Lake Sturgeon an outlier?
A: There are many species that migrate in large-river habitat to spawn and need free-flowing rivers for early life stages to develop. Shovelnose Sturgeon, Shortnose Gar, Goldeye, Alabama Shad, and Mississippi Silvery Minnows have all disappeared from the Tennessee River, and the abundance of American Eels and Blue Suckers have drastically declined.
Q: In all, how many Lake Sturgeon have now been released, as a result of the Conservation Institute's propagation program?
A: A total of over 200,000 Lake Sturgeon juveniles have been released since 2000 by the Tennessee Aquarium and its many partners.
Q: What additional work is needed to ensure the Lake Sturgeon can once again follow its instincts and pursue its natural migration path?
A: Other than removing main stem dams in the Tennessee River to allow adults to migrate upstream and larvae to drift downstream, there are not many good options. While some fishes can utilize locks to move upstream of dams, fishes that live on or near the bottom — benthic fishes — would need to swim up a vertical wall at the upstream end of the lock to exit upstream, which is unlikely. Fish ladders work for some fishes, but once again, not for benthic fishes. A sloping “wheelchair ramp” would potentially work, but it would utilize a great deal of property and would need a large flow to attract Lake Sturgeon to the structure.