Sturgeons are fascinating and ancient fish that have been around since the time of the dinosaurs. More than 85% of sturgeon species are at risk of extinction, making them one of the most threatened animal groups on the IUCN Red List. Major threats include overfishing, habitat loss, and pollution.
Sturgeons are among the oldest fish species in the world, having been around for over 200 million years. They’re often called living fossils because their appearance and body structure have changed very little since they first appeared in the fossil record. This is quite remarkable, considering they have survived several mass extinctions throughout the history of Earth.
Sturgeons’ long evolutionary history can be seen in some of their unique characteristics, such as their cartilaginous skeletons like sharks, their bony plates or scutes for protection, and their heterocercal tail, the upper lobe is longer than the lower one, which is a feature shared with sharks and some other ancient fish.
Their longevity, slow growth, late sexual maturity, and spawning habits also set them apart from many other fish. All these characteristics make sturgeons a fascinating group to study for scientists interested in fish evolution and biology.
The size of sturgeons can greatly vary depending on the species. They range from the rather small sterlet sturgeon, which grows to about 2-3 feet, to the enormous beluga sturgeon.
The beluga sturgeon, which is native to the Caspian and Black Seas, is not only the largest sturgeon but also the largest freshwater fish in the world. It has been known to reach lengths of more than 20 feet and weigh up to 1,500 pounds, with some unconfirmed reports of even larger specimens.
It’s worth noting that these fish grow very slowly and can live for many decades, or even over a century in some cases. This long lifespan and slow growth contribute to their large size. The size of the beluga sturgeon, along with its prized roe, which is used to make beluga caviar, has unfortunately also made it a target for overfishing. This has led to a significant decline in beluga sturgeon populations, and the species is now considered critically endangered.
Sturgeons have sensory organs called barbels located near their mouths. These barbels resemble whiskers, and there are usually four of them hanging down in front of the sturgeon’s mouth.
Sturgeons use these barbels to navigate their surroundings and find food in murky water. The barbels are highly sensitive and are able to detect vibrations and chemical changes in the water. When they come into contact with potential food, such as small fish, invertebrates, or plant material on the river or sea floor, the sturgeon will open its mouth and suck the food in.
Because sturgeons don’t have teeth and are primarily bottom feeders, these barbels are a crucial part of their feeding strategy. It’s a great example of how species adapt to their environments. In the case of the sturgeon, having to find food in murky, low-visibility waters has led to the development of these unique and effective sensory organs.
Sturgeons have a distinctive appearance because they don’t have traditional scales like most fish. Instead, they have rows of bony plates known as scutes. These scutes run along their bodies and provide a protective armor-like covering.
Scutes are composed of bone and covered by a layer of skin, making them harder and more durable than scales. They help protect sturgeons from predators and injuries, which is particularly important given their habitat and bottom-dwelling lifestyle.
The number, size, and arrangement of these scutes can vary between different species of sturgeon. Some have larger, more prominent scutes, while others have smaller, more streamlined ones. This variation is one of the features that scientists use to differentiate between different species of sturgeon.
Despite their large size and imposing appearance, sturgeons do not have teeth. Instead, they have a unique method of feeding that doesn’t require them to bite or chew their food.
Sturgeons are primarily bottom-feeders. They have a long, extendable, tube-like mouth that they use to vacuum up small animals and plant matter from the river or sea bed. As they swim along the bottom, they use their barbels — the whisker-like sensory organs near their mouth — to detect food in the sediment. Once they find something to eat, they extend their mouth and suck the food in, along with some of the surrounding sediment.
The food is then passed back to the pharynx, where any inedible material like small stones or shells is filtered out and expelled, while the edible material is swallowed and digested. This method of feeding is highly effective for finding food in the low-visibility environments where sturgeons often live. It’s yet another example of the unique adaptations that have allowed these ancient fish to survive and thrive for so many millions of years.
Some sturgeon species, such as the Atlantic sturgeon and the shortnose sturgeon, are anadromous. This means they are born in freshwater rivers, migrate to the sea where they live most of their lives, and then return to the freshwater environments of their birth to spawn.
This lifecycle is similar to that of salmon, another well-known anadromous fish species. The benefit of this type of lifecycle is that it allows sturgeons to exploit the rich feeding grounds of the sea while also taking advantage of the relative safety of freshwater rivers for spawning and the early stages of life.
Interestingly, not all sturgeons are anadromous. Some species, like the lake sturgeon found in North America, spend their entire lives in freshwater environments. Others, like the beluga sturgeon, are primarily found in saltwater environments but will migrate into freshwater to spawn.
This ability to adapt to both fresh and saltwater environments is another factor that has helped sturgeons to survive for so long in a variety of different habitats across the world. Sturgeons are indeed one of the most threatened groups of animals in the world. As of my knowledge cutoff in September 2021, more than 85% of sturgeon species were classified as at risk of extinction, according to the International Union for Conservation of Nature.
Overfishing is a major threat to sturgeons, driven largely by the high demand for their eggs, which are processed into caviar. Because sturgeons take many years to reach sexual maturity and reproduce relatively infrequently, their populations can’t quickly rebound from heavy fishing pressure.
Habitat loss is another significant threat to sturgeons. Many sturgeons rely on specific freshwater habitats to spawn, and these can be disrupted by activities such as dam construction, river channelization, and dredging. Pollution, including chemical contaminants, can also negatively impact sturgeon populations by affecting water quality and food availability.
Conservation efforts are ongoing to try to protect and recover sturgeon populations. These include measures like fishing restrictions, the creation of protected areas, restocking programs, and initiatives to improve water quality and restore natural habitats. Despite these efforts, sturgeons still face considerable challenges, and their future survival is far from guaranteed.
