"Gulf sturgeon, also known as the Gulf of Mexico sturgeon, are "anadromous" fish, inhabiting coastal rivers from Louisiana to Florida during the warmer months, and the Gulf of Mexico and its estuaries and bays in the cooler months. Sturgeon are primitive fish characterized by bony plates, or "scutes," and a hard, extended snout; they have a heterocercal caudal fin (their tail is distinctly asymmetrical with the upper lobe longer than the lower). Adults range from 4-8 feet (1-2.5 m) in length, females attain larger sizes than males. They can live for about 60 years; usually 20-25 years."
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm)
The Atlantic sturgeon is a long-lived, estuarine dependent, anadromous fish. Atlantic sturgeon can grow to approximately 14 feet (4.3 m) long and can weigh up to 800 lbs (370 kg). They are bluish-black or olive brown dorsally (on their back) with paler sides and a white belly. They have five major rows of dermal "scutes".
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm)
Following spawning, male Atlantic Sturgeon may remain in the river or lower estuary until the fall; females typically exit the rivers within four to six weeks. Juveniles move downstream and inhabit brackish waters for a few months and when they reach a size of about 30 to 36 inches (76-92 cm) they move into nearshore coastal waters. Tagging data indicate that these immature Atlantic sturgeon travel widely once they emigrate from their natal (birth) rivers.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm).
Gulf sturgeon are found in river systems from Louisiana to Florida, in nearshore bays and estuaries and in the Gulf of Mexico.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm)
Historically, Atlantic sturgeon were present in approximately 38 rivers in the United States from St. Croix, ME to the Saint Johns River, FL, of which 35 rivers have been confirmed to have had a historical spawning population. Atlantic sturgeon are currently present in approximately 32 of these rivers, and spawning occurs in at least 20 of them.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm).
"Gulf sturgeon are anadromous: adults spawn in freshwater and migrate into marine waters in the fall to forage and overwinter. Juvenile Gulf sturgeon stay in the river for about the first 2-3 years. Gulf sturgeon return to their natal stream to spawn. Riverine habitats where the healthiest populations of Gulf sturgeon are found include long, spring-fed, free-flowing rivers, typically with steep banks, a hard bottom, and an average water temperature of 60-72° F. Gulf sturgeon initiate movement up to the rivers between February and April and migrate back out to the Gulf of Mexico between September and November."
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm)
Atlantic sturgeon are "anadromous"; adults spawn in freshwater in the spring and early summer and migrate into "estuarine" and marine waters where they spend most of their lives. In some southern rivers a fall spawning migration may also occur. They spawn in moderately flowing water (46-76 cm/s) in deep parts of large rivers. Sturgeon eggs are highly adhesive and are deposited on bottom substrate, usually on hard surfaces (e.g., cobble). It is likely that cold, clean water is important for proper larval development. Once larvae begin migrating downstream they use benthic structure (especially gravel matrices) as refuges. Juveniles usually reside in estuarine waters for months to years. Subadults and adults live in coastal waters and estuaries when not spawning, generally in shallow (10-50 m depth) nearshore areas dominated by gravel and sand substrates. Long distance migrations away from spawning rivers are common.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm).
Atlantic sturgeon have been aged to 60 years. There is generally faster growth and earlier age at maturation in more southern populations. For example, Atlantic sturgeon mature in South Carolina rivers at 5 to 19 years of age, in the Hudson River at 11 to 21 years, and in the Saint Lawrence River at 22 to 34 years.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm).
Atlantic sturgeon are similar in appearance to shortnose sturgeon (Acipenser brevirostrum), but can be distinguished by their larger size, smaller mouth, different snout shape, and scutes.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm).
The Atlantic sturgeon is managed under a Fishery Management Plan implemented by the Atlantic States Marine Fisheries Commission (ASMFC). In 1998, the ASFMC instituted a coast-wide moratorium on the harvest of Atlantic sturgeon, which is to remain in effect until there are at least 20 protected age classes in each spawning stock (anticipated to take up to 40 or more years). NMFS followed the ASMFC moratorium with a similar moratorium for Federal waters. Amendment 1 to ASMFC's Atlantic sturgeon Fishery Management Plan also includes measures for preservation of existing habitat, habitat restoration and improvement, monitoring of bycatch and stock recovery, and breeding/stocking protocols.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm)
"Gulf sturgeon migrate into rivers to spawn in the spring; spawning occurs in areas of clean substrate comprised of rock and rubble. Their eggs are sticky, negatively buoyant and adhere in clumps to snags, outcroppings, or other clean surfaces."
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm)
Spawning adult Atlantic Sturgeon migrate upriver in spring, beginning in February-March in the south, April-May in the mid-Atlantic, and May-June in Canadian waters. In some areas, a small spawning migration may also occur in the fall. Spawning occurs in flowing water between the salt front and fall line of large rivers. Atlantic sturgeon spawning intervals range from 1 to 5 years for males and 2 to 5 years for females. "Fecundity" of female Atlantic sturgeon is correlated with age and body size and ranges from 400,000 to 8 million eggs. The average age at which 50% of maximum lifetime egg production is achieved is estimated to be 29 years, which is approximately 3 to 10 times older than for other bony fish species.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm)
Gulf sturgeon number initially declined due to overfishing throughout most of the 20th century. Habitat loss was exacerbated by the construction of water control structures, such as dams and "sills", mostly after 1950. Other habitat disturbances such as dredging, groundwater extraction, irrigation, and flow alterations also threaten the Gulf sturgeon. Poor water quality and contaminants, primarily from industrial sources, also contribute to population declines.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm)
Historical overharvest led to wide-spread declines in Atlantic sturgeon abundance. A large U.S. commercial fishery (100,000 - 250,000 lbs/yr) existed for Atlantic sturgeon from the 1950s through the mid-1990s; the origin of the fishery dates back to colonial times. Since a 1998 harvest moratorium there have been few surveys to assess status and abundance. "Bycatch" of sturgeon in fisheries targeting other species is a current threat in the ocean environment.
In their estuarine and freshwater habitats, Atlantic sturgeon face additional threats, including habitat degradation and loss from various human activities such as dredging, dams, water withdrawals, and other development. Some populations are being impacted habitat impediments including locks and dams (e.g., Cape Fear and Santee-Cooper Rivers ) and ship strikes (e.g., Delaware and James Rivers). Although there are no known diseases threatening Atlantic sturgeon populations, there is concern that non-indigenous sturgeon pathogens could be introduced through aquaculture operations.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm)
Total number of mature individuals throughout their range is unknown. However, among coastal rivers of the Gulf of Mexico, the Suwannee River supports the most viable subpopulation, which was estimated at 7,650 adults. The subpopulation estimate for mature Gulf sturgeon in the Choctawhatchee River ranges from 1,700-3,000 fish; estimates in the Apalachicola, Pascagoula and Pearl rivers range between 50-350 fish.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm and references cited)
Studies have consistently found Atlantic Sturgeon populations to be genetically diverse and indicate that there are between 7 and 10 populations that can be statistically differentiated. However, there is some disagreement among studies, and results do not include samples from all rivers inhabited by Atlantic sturgeon. There are only two Atlantic sturgeon populations for which size estimates are available - the Hudson River and the Altamaha River populations. In 1995, sampling crews on the Hudson River estimated that there were 9,500 juvenile Atlantic sturgeon in the estuary. Since 4,900 of these were stocked hatchery-raised fish, about 4,600 fish were thought to be of wild origin. The mean annual spawning stock size (spawning adults) was estimated at 870 (600 males and 270 females). The Altamaha River supports one of the healthiest Atlantic sturgeon populations in the Southeast, with over 2,000 subadults captured in research surveys in the past few years, 800 of which were 1 to 2 years of age. The population appears to be stable.
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm)
"Gulf sturgeon are bottom feeders, and eat primarily macroinvertebrates, including brachiopods, mollusks, worms, and crustaceans. All foraging occurs in brackish or marine waters of the Gulf of Mexico and its estuaries; sturgeon do not forage in riverine habitat."
(Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/gulfsturgeon.htm)
Atlantic sturgeon are benthic feeders and typically forage on "benthic" invertebrates (e.g. crustaceans, worms, mollusks) (Office of Protected Resources, http://www.nmfs.noaa.gov/pr/species/fish/atlanticsturgeon.htm).
Acipenser oxyrinchus is a species of sturgeon.
Acipenser oxyrinchus is a species with two subspecies:
Their main diet includes crustaceans, worms, and mollusks. This species is also known to migrate up the river when it is spawning.[5] This species is recorded to be near threatened and at risk of becoming an endangered species due to dam construction, dredging, dredge spoil disposal, groundwater extraction, irrigation, flow alterations, and other surface water withdrawals. Acipenser oxyrinchus is mostly native to the countries of Canada and the United States, with a smaller population in northern Europe (essentially the Baltic region).[3][6] They can be found in temperate and subtropical climates and in marine or freshwater environments.[3]
Acipenser oxyrinchus can grow to a length of 14 ft (4.3 m) and a weight of 800 lb (360 kg). The lifespan of this species can be around 60 years. The color of Acipenser oxyrinchus is bluish-black or olive brown with lighter sides and a white belly.
Sturgeon are an anadromous species that live solitarily or in small groups. They migrate upriver in the spring to spawn. Sturgeons tend to inhabit the shallow waters of coastal shelves, coastal and estuarine areas on soft bottom in the sea, and can live down to a depth of 160 ft (49 m). Adults are migratory while at sea and will make long migrations to coastal areas, while juveniles will stay in fresh or brackish water until they are between two and five years of age. However, many larvae and juveniles do start to migrate and disperse small distances from their spawning sites.[3]
Sturgeons will migrate upriver to spawn. Sturgeons from the Gulf of Mexico will naturally exhibit spawning migration in the spring. Peak numbers have been observed in March and April, which is when the fish will migrate into the Suwannee River in Florida.[7] Sturgeon will migrate downstream for twelve days, peaking within the first six days. Atlantic sturgeons only need to move a short distance to reach rearing areas. Early sturgeon migrants tend to be nocturnal while later migrants are diurnal.[8] During summer months, sturgeon will remain in localized bottom areas of the rivers. In the late fall, the sturgeon migrate out of spawning rivers and into the Gulf of Mexico.[7]
For all populations and subspecies of sturgeon, there are spawning migrations into freshwater in early spring and movement into salt water in the fall. Timing and the unusual migratory behavior of sturgeon is a result of temporal water temperature changes.[7] Studies have also shown that amongst sturgeon in Gulf of Mexico and Suwannee River in Florida, fish gained 20% of their body weight while in Gulf of Mexico and lost 12% of their body weight during their time in the river.[9]
The maximum level of survival for eggs, embryos, and larvae is at 15 to 20 °C (59 to 68 °F). Studies have shown that high mortalities are seen at temperatures of 25 °C (77 °F) or higher.[7] In order for spawning to occur, water temperature should be above 17 °C (63 °F). Spawning normally lasts between nine and twenty-three days, but can continue past this as long as the water temperature remains below 22 °C (72 °F).[10]
Free sturgeon embryos (the first interval of sturgeon after hatching) hide under rocks and do not migrate. They are found in the freshwater spawning areas. Larvae and some juveniles start to migrate slowly for about five months downstream. This leads to a wide dispersal of the fish.[11] Typically, the entire freshwater reach of the river downstream from the actual spawning site is so filled with larva-juvenile individuals that it is considered to be a nursery habitat.[11]
Sturgeon populations will use the same spawning reefs from year to year. Habitat factors that can help determine spawning sites include the presence of gravel substrate, presence of eddy fields, slightly basic pH, and a range in calcium ion content. Eggs are usually deposited in a small area and scatter very little. It is not until larvae and juveniles start to migrate that the fish disperse widely.[10]
Some evidence has shown that developmental body color is related to migration style. Free embryos are light and are non-migratory, while migratory larvae and adults are dark. This is found to be consistent among many Acipenser species. The reason for this is unclear, but it may be adaptive to migration behavior and camouflage.[11]
The primary foods of sturgeon while in freshwater areas include soft-bodied annelids, arthropods, aquatic insects, and globular mollusks. Adults that have emigrated from estuaries and into the sea will usually feed on epibenthic and hyperbenthic amphipods, grass shrimp, isopods, and worms. Most adult sturgeon will also feed on detritus and biofilm.[12] Sturgeons are most generally known for feeding on crustaceans, worms, and molluscs.[13]
Larvae-juvenile feeding was at the bottom, benthic foraging. However, food in the benthic zone is scarce, so many adapt drift feeding, in which they have holding positions in the water column and wait for food.[11] Sturgeons may have dominance hierarchies with large fish being dominant when competing for limited foraging space.[8]
Sturgeons are widely distributed along the Atlantic coast of the United States. Their wide distribution and tendency to disperse has led to numerous subpopulations of sturgeon.[13]
In general, sturgeons usually inhabit primarily the temperate waters of the northern hemisphere. Gulf of Mexico sturgeons are probably adapted to warmer water temperatures. Due to sturgeons' predilection for cooler waters, when water temperatures rise too high, sturgeon will try to find cool spring waters which serve as thermal refuges until temperatures drop again.[7]
There are many wide-ranging subspecies along the Atlantic Coast of North America. Identification of distinct population segments (DPS) is problematic because of sturgeons' ability to disperse so widely. However, it is possible to do some characterization of genetic differentiation and estimate gene flow. This method has been used to determine possibility for listing under the U.S. Endangered Species Act.[14]
The sturgeon's characteristics and life history make it susceptible to anthropogenic disturbances and make population restoration particularly difficult. They have late sexual maturity, only moderate fecundity, and spawn at low frequencies. Females spawn once every three to five years, and males every one to five years. This is due to their ability to live for an extremely long time (various sub-species can have a lifespan ranging from ten years to sixty years).[14]
The population of Atlantic sturgeons has decreased dramatically due to overharvesting. The late 19th century saw a surge in demand for caviar, which led to overfishing of the Atlantic sturgeon. Today, only 22 out of its 38 original spawning rivers still have viable populations of the species.[15] They are particularly susceptible to bycatch mortality due to the many fisheries that exist within their natal estuaries. Their habitat range, which usually includes coastal spawning sites and coastal migrations, makes sturgeon well within contact of coastal fisheries.[14]
Hypoxia combined with high water temperatures in the summer has been shown to be consistent with decreased survival rates of young of the year sturgeon in Chesapeake Bay.[16]
Hypoxia is defined as low ambient oxygen levels, which may be very harmful to organisms living in the hypoxic body of water. Often, lower regions of the water column will be more hypoxic than upper levels, closer to the surface. When surface access is denied, the situation is lethal to sturgeon. Increased incidences of summertime hypoxia have led, in part, to degradation of many sturgeon nursery habitats in the United States.[16]
Populations have declined dramatically over the last centuries, and even became extinct in Baltic range states in the later 20th century. Channelisation and barriers were part of the causes for declines affecting migration, along with pollution. Since 1996 Baltic sturgeon recovery has been attempted, with American donor populations used due to genetic similarities. Re-introduction with focus on returning these sturgeon to their native spawning grounds.[17] NatureServe considers the species Vulnerable.[18]
In 2012, the Atlantic sturgeon received protection under the Endangered Species Act.[19]
In 2022, the International Union for the Conservation of Nature noted that sturgeon was "the animal group most at risk of extinction in the world."[15]
Acipenser oxyrinchus is a species of sturgeon.
