Ohio’s Living Fossils
Sturgeon are a group of around twenty-five fish species that are in the family Acipenseridae. They are found all over the world, from Europe to Asia to right here in North America. In the United States, they are native to the Great Lakes, the St. Lawrence, Missouri, and Mississippi Rivers, and can be found on both the east and west coast and in the Gulf of Mexico. Interestingly enough, there are no known native populations of sturgeon that exist south of the Equator (Fishbase 2017). This group of fish has been found in the fossil record as early as 245 million years ago, making them the oldest of the ray-finned fishes. However, what makes them “living fossils” is that they have not evolved much in the last 240 million years; the sturgeons that exist today are very similar to the sturgeons that lived during the same time of the dinosaurs (Gardiner 1984). The image below shows a tree of the relationships between modern fish groups. The placement of the sturgeon in relation to the teleosts (which contains 96% of all modern fish diversity) demonstrates its status as a “relict” fish, a living fossil, along with the gar, bowfins, and birchirs.
Image taken from the lectures of Dr. Suzanne Gray, The Ohio State University
The Life of a Sturgeon
Sturgeon primarily are benthic feeders, which means that they feed on the bottom of rivers and lakes. They usually feed on snails and mussels, but have also been known to eat fish and plants (ODNR Lake 2012). To have babies, sturgeon move into rivers to spawn. When this happens, females can lay thousands of eggs at a time into the water column that are then fertilized by the males’ sperm. This process is called “broadcast spawning.” However, very few of these eggs to adulthood. The baby sturgeon are slow-growing and can take a long time to reach sexual maturity (20-25 years in the case of Ohio’s own lake sturgeon). Unlike salmon, sturgeon can spawn multiple times throughout their life, but do not spawn every year, sometimes going multiple years between spawning events (lake sturgeon typically spawn every four to seven years). While they may take a long time to mature, sturgeon are incredibly long-lived. Their average life-span is 60 years, but some species, like the lake sturgeon, can live longer than a century (ODNR Lake 2012).
Now that you know a little bit more about sturgeon in general, let’s take a look at the two species that call the waters of Ohio home:
Lake Sturgeon (Acipenser fulvescens)
Photo by the Tennessee Aquarium
The lake sturgeon is native to the waters of Lake Erie and the Ohio River, as well as in some of the larger inland rivers that feed into these water bodies. A large fish, this sturgeon measures 6-8 feet in length and usually weighs around 100 pounds (Trautman 1981). The largest specimen recorded was caught in 1929, weighing 216 pounds (ODNR Lake 2012) The Lake Sturgeon is “sharply bicolored” meaning that the dorsal (top) half of its body is one color (in this case olive-yellow, grey, or bluish), and its underside is a different color (in this case milky/yellow-white). These fish have a series of bony plates that run along their back and sides, forming ridges on their body. While these plates are sharp in juveniles, they dull as the sturgeon ages, becoming blunt by the time they reach adulthood (Trautman 1981).
Shovelnose Sturgeon (Scaphirhynchus platorynchus)
Photo by Ohio Division of Wildlife
The other native Ohio species of sturgeon, the shovelnose sturgeon, is the smallest sturgeon species in North America, reaching lengths of about 2.5 feet long and weighing usually 1-5 pounds. However, the largest specimen recorded in Ohio was 32 inches long and weighed 10 pounds. The shovelnose can be easily distinguished from the lake sturgeon by its wide, flat snout that gives this species its name. It also is bicolored like the lake sturgeon, but the shovelnose is usually brown, olive, or grey dorsally, and whitish underneath. The shovelnose has a long, thin caudal peduncle completely covered in bony plates, whereas the lake sturgeon’s is much wider and only has plates on the side. The bony plates covering the caudal peduncle are also sharp in both juveniles and adults, and do not dull over time like the Lake Sturgeon. In Ohio, the shovelnose sturgeon is native to the waters of the Ohio River and its tributaries, having also been caught in the Scioto and Muskingum Rivers (Trautman 1981). Interestingly, while lake sturgeons have been reportedly able to live to be 150 years old, shovelnose sturgeon live much shorter lives, rarely living past the age of 12, and spawn fewer times in their lifetime (ODNR Shovelnose 2012).
Conservation
While sturgeon are incredibly interesting as living fossils, populations of sturgeon species worldwide have been in decline. Both the lake sturgeon and shovelnose sturgeon are listed as “Endangered” in the state of Ohio. Information from the International Union for Conservation of Nature (IUCN) suggests that sturgeon are one of the most imperiled groups on the planet, with 85% of the species worldwide at risk for extinction (IUCN 2010). Two important human-induced factors leading to their declines are shown below: dams and caviar.
Left image from AS Food Studio, Right image from Popular Mechanics
While dams may be beneficial to us, they play havoc with a sturgeon’s life cycle. Many sturgeon species have migration routes and preferred spawning grounds. The construction of dams blocks a sturgeon’s ability to follow these routes or get to their spawning grounds, affecting their reproduction. Sturgeon are also harvested for their eggs, which are sold as caviar at high prices. In recent years, the market for this product has grown considerably, so more and more sturgeon have been harvested, both legally and illegally, to meet this demand (WWF 2017). Because it takes so long for sturgeon to reach maturity, and because they do not spawn every year, they are incredibly susceptible to overfishing, which has been shown in their species declines over the last few decades. Although they have been around for millions of years, unless action is taken to reduce sturgeon population declines, these living relics could potentially disappear into the fossil record for good.
Works Cited
Fishbase. 2016. Family: Acipenseridae. Fishbase. Online. Retrieved November 2nd, 2017 from http://www.fishbase.us/identification/SpeciesList.php?famcode=32&areacode=&spines=&fins=.
IUCN. 2010. Sturgeon more critically endangered than any other group of species. IUCN. Online. Retrieved November 2nd, 2017 from https://www.iucn.org/content/sturgeon-more-critically-endangered-any-other-group-species.
Gardiner, B.G. 1984. Sturgeons as living fossils. Pg. 148-152 in Living Fossils, Eldredge, N., and Stanley, S.M. Springer-Verlag, New York.
ODNR. 2012. Lake Sturgeon. ODNR Division of Wildlife. Online. Retrieved on November 2nd, 2017 from http://wildlife.ohiodnr.gov/species-and-habitats/species-guide-index/fish/lake-sturgeon.
ODNR. 2012. Shovelnose Sturgeon. ODNR Division of Wildlife. Online. Retrieved on November 2nd, 2017 from http://wildlife.ohiodnr.gov/species-and-habitats/species-guide-index/fish/lake-sturgeon.
Trautman, M.B. 1981. The Fishes of Ohio. Ohio State University Press, Columbus, OH.
WWF. 2017. Sturgeon. World Wildlife Foundation. Online. Retrieved November 2nd, 2017 from http://wwf.panda.org/what_we_do/endangered_species/sturgeon/.