The White Sturgeon (Acipenser transmontanus, Richardson 1836) is the largest freshwater fish species in North America. It can reach lengths of 6.1 m and weigh up to 816 kg. Like many Acipenseridae, White Sturgeon are long-lived and commonly reach ages of 60-70 years. White Sturgeon older than 100 years have been collected on both the Columbia and Fraser Rivers.
As its species name implies (transmontanus = beyond the mountains), white sturgeon are found west of the Rocky Mountains and spawning populations are found in three major drainages along the west coast; the Fraser (British Columbia), the Columbia (Canada and the U.S.), and the Sacramento-San Joaquin (California) river systems. They are a potadromous species, spending the majority of their time in freshwater, but are capable of undertaking marine movements and have been recorded off the Pacific Coast of North America from the Aleutians, Alaska to northern Baja California, Mexico. Some populations spend their entire lives in freshwater as they have become landlocked, either from human development and dam implementation, like the Upper Columbia and Snake River populations, or from geographic constraints that arose during the last ice age, like the Kootenai River population which has been isolated for approximately 10,000 years.
Spawning typically occurs in the spring between May to July when water temperatures reach 14-18°C. Males become sexually mature around 12-18 years of age (90-120 cm in length), while females usually mature around 15-30 years (160 – 170 cm in length). White Sturgeon are broadcast spawners and deposit milt and eggs into fast moving waters, typically over coarse substrates. Fecundity is high, with younger females less than 200 cm in length, spawning around 400,000 eggs while older females, greater than 200 cm in length, can spawn more than 4,000,000 eggs. Spawning frequency differs between sex and age of the fish. Male white sturgeon can spawn every year, while female White Sturgeon spawn less frequently every 2-6 years. In water temperature around 15°C, embryos will incubate for approximately 7 days before hatching. The diet of young White Sturgeon includes small fish and macroinvertebrates, specifically mollusks, crustaceans, and chironomids. Adult white sturgeon feed on a diverse diet of macroinvertebrates and several fish species including shad and salmon species for example.
White Sturgeon are listed as stable and a species of Least Concern by the IUCN, but the Kootenai River population is considered federally endangered in the U.S. and Canada. Additionally, other listed populations exist in Canada in the Fraser and Columbia Rivers. Like many sturgeon species, White Sturgeon face threats from overexploitation and habitat alteration, specifically dam construction, water diversion, landscape development, and hydrograph alteration. Historically, overexploitation of White Sturgeon for caviar, meat, and isinglass was very common, and in the late 1800’s, the annual harvest of White Sturgeon in the lower Columbia River peaked around 2.7 million kg. Harvest regulations, habitat restoration, and repopulation efforts have helped stabilize White Sturgeon populations in some systems, but limited to no recruitment in areas like the Upper Columbia River system indicate the species are at risk and require continued management efforts to help them persist.