Fish rule the world!! That is, they are one of the oldest animals on this planet. Fish were here long before the dinosaurs – about 500 million years ago — and they still thrive today. In this group, sturgeon are amongst the oldest, having originated from the ray finned fishes some 250 million years ago. Since then, they have undergone remarkably little morphological change, which has earned them the nickname of “living fossils” amongst some scientists. They might look a bit like sharks, but sturgeon are in fact from a completely different family called Acipenseridae.
Atlantic Sturgeon can be found living in fresh and coastal waters along the Atlantic coast of North America, from as far north as Ungava Bay, Labrador, to the Gulf of Mexico. Rather than having true scales, they have five rows of bony plates known as scutes, which serve as body armour. Other distinctive features include a long snout with 4 sensory barbels that help locate bottom-dwelling prey. The upper lobe of the tail fin is longer and more slender than the lower lobe, similar to a shark’s. Another thing sturgeon and sharks have in common is a cartilaginous skeleton. Coloration ranges from bluish-black and olive green on the back, with a white underside.
Sturgeon are really big fish! Animals weighing over 800 lb (362 kg) and nearly 15 ft (4m) in length have been recorded, but a typical fish measures around 6–8 ft (1.8–2.4 m) and weights no more than 300 lb (140 kg). Males mature earlier and are a smaller size than females. The largest sturgeon our lab has tagged measured just over 2 meters!
Atlantic sturgeon are anadromous fish, meaning they spawn in freshwater but spend most of their lives at sea. Sturgeon are generally late-maturing fish, and fish in northern climates tend to spawn even later in life than those at mid latitudes. When they are ready to spawn, adult fish enter coastal rivers and begin migrating upstream. The optimal temperature for spawning is approximately 23 ℃.
After spawning, adults may stay in rivers until fall, when they return to the marine environment. Eggs hatch within a week, and young fish develop in freshwater until their scutes are formed, and fins begin to develop. Juvenile sturgeon begin their first ocean-bound migration between 2- 6 years of age. Before this, they must undergo several morphological changes that allow them to survive saltwater conditions. The rest of their lives will be spent at sea, with the exception of spawning events. However, there are also entirely freshwater species of sturgeon, such as the lake sturgeon.
Atl. Sturgeon usually feed on bottom invertebrates such as insect larvae, amphipods, molluscs, and marine worms, but some also eat fishes. Sturgeon actually don’t have teeth – instead of grasping prey, they feed by extending their syphon-like mouths to suck food from the benthos. They are believed to use a combination of sensors, including olfactory (smell), tactile and chemosensory cues detected by the barbels to hunt. In addition, sturgeon have the ability to perceive natural electrical stimuli in the same way that sharks do, with the help of specialized sensing organs called the ampullae of Lorenzini. They provide fish with an additional sense capable of detecting electric and magnetic fields as well as temperature gradients.
Atlantic Sturgeon were fished by Native North Americans for hundreds of years, and have been fished by European settlers since the early 1600’s. Sturgeon were mainly harvested for their roe, which is made into caviar and is considered a delicacy in many countries. Due to a high demand for these products, Atlantic Sturgeon populations significantly decreased over the last century, and many fisheries were forced to close. Only two sturgeon fisheries are still operating in Canada, one in the Saint John River and one in the St. Lawrence River
Besides fishing, sturgeon are threatened by a number of human activities, such as water pollution, impassable dams, habitat destruction, and bycatch in fisheries targeted at other species. Sturgeon are late-maturing fish (6-25 years) that do not reproduce frequently, which makes them particularly susceptible as they are slow to recover from exploitation. It is estimated that the number of sturgeon in major basins has decreased by 70% over the last century.
Many sturgeon species are currently listed as endangered by the International Union for Conservation of nature (IUCN). In Atlantic Canada, two sturgeon populations – one from the St. Lawrence River, and one in the Saint John River – are currently designated as threatened by the Committee of Status Endangered Wildlife in Canada, and are undergoing a listing evaluation by the Species at Risk Act (SARA). Atlantic sturgeon populations in the United States are either endangered or threatened under the U.S. Endangered Species Act.
Sturgeon are known to display a ‘leaping’ behavior, during which the fish will jump as high as seven feet above the water! The exact reason why sturgeon leap remains unknown, but theories include group communication, catching airborne prey, gulping for or expelling air, escaping predators, helping to shed eggs during spawning, and courtship behavior.