Behavior edit
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 50 meters. Adults are extremely 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 to five years of age. However, many larvae and juveniles do start to migrate and disperse small distances from their spawning sites.[1]
Migration edit
Sturgeons, with are anadromous, 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 Suwanee River in Florida.[2] 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.[3] 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.[2]
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. [2] 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.[4]
Spawning edit
The maximum level of survival for eggs, embryos, and larvae is 15 to 20°C. Studies have shown that high mortalities are seen at temperatures of 25°C or higher.[2] In order for spawning to occur, water temperature should be above 17°C. Spawning normally lasts between nine and twenty-three days, but can continue past this as long as the water temperature remains below 22C.[5]
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.[6] 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.[6]
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.[5]
Body color edit
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. Reason for this is unclear, but it may be adaptive to migration behavior and camouflage.[6]
Diet edit
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.[7] Sturgeon are most generally known for feeding on crustaceans, worms, and molluscs.[8]
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.[6] Sturgeons may have dominance hierarchies with large fish dominant when competing for foraging space that is limited.[3]
Habitat edit
Sturgeons are widely distributed along the Atlantic coast of the United States. Their wide distribution and tendency to disperse has led to numerous subspecies of sturgeon.[8]
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.[2]
Susceptibility to Anthropogenic Disturbances edit
There are many wide-ranging sub-species 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.[9]
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).[9]
The population of Atlantic sturgeon has decreased dramatically in the past century due to overharvesting. 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.[9]
Effects of Hypoxia edit
Hypoxia in a water body, such as the Chesapeake Bay, which is inhabited by sturgeon, can lead to higher water temperatures. This causes decreased survival rates and low respiration rates. Hypoxia can also lead to particularly low temperatures, which again causes low survival and respiration rates.[10]
Hypoxia causes low ambient oxygen levels, which is very harmful to organisms in a body of water. When surface area access is denied, the situation is lethal to sturgeon. Increased incidences of summertime hypoxia lead to degradation of many sturgeon habitats in the United States.[10]
References edit
- ^ Froese, Rainer. "Acipenser oxyrinchus". Fish Base. Retrieved 24 October 2013.
- ^ a b c d e Chapman, Frank A.; Carr, Stephen H. (1995). "Implications of early life stages in the natural history of the Gulf of Mexico sturgeon, Acipenser oxyrinchus de sotoi". Environmental Biology of Fishes. 43 (4): 407–413. doi:10.1007/BF00001178. S2CID 36638570. Retrieved 24 October 2013.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: date and year (link) - ^ a b Kynard, Boyd; Horgan, Martin (2002). "Ontogenetic Behavior and Migration of Atlantic Sturgeon, Acipenser oxyrinchus oxyrinchus, and Shortnose Sturgeon, A. brevirostrum, with Notes on Social Behavior". Environmental Biology of Fishes. 63 (2): 137–150. doi:10.1023/A:1014270129729. S2CID 23950901. Retrieved 25 October 2013.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: date and year (link) - ^ Carr, S.H. (December 1996). "Observations on the natural history of the Gulf of Mexico sturgeon (Acipenser oxyrinchus de sotoi Vladykov 1955) in the Suwannee River, southeastern United States". Ecology of Freshwater Fish. 5 (4): 169–174. doi:10.1111/j.1600-0633.1996.tb00130.x.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)CS1 maint: date and year (link) - ^ a b Sulak, K. J.; Clugston, J. P. (1999). "Recent advances in life history of Gulf of Mexico sturgeon, Acipenser oxyrinchus desotoi, in the Suwannee river, Florida, USA: a synopsis". Journal of Applied Ichthyology. 15 (4–5): 116–128. doi:10.1111/j.1439-0426.1999.tb00220.x. Retrieved 24 October 2013.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: date and year (link) - ^ a b c d Kynard, Boyd; Parker, Erika (2004). "Ontogenetic Behavior and Migration of Gulf of Mexico Sturgeon, Acipenser oxyrinchus desotoi, with Notes on Body Color and Development". Environmental Biology of Fishes. 70 (1): 43–55. doi:10.1023/B:EBFI.0000022855.96143.95. S2CID 34082533. Retrieved 24 October 2013.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: date and year (link) - ^ Mason, William T.; Clugston, James P. (1993). "Foods of the Gulf Sturgeon in the Suwannee River, Florida". Transactions of the American Fisheries Society. 122 (3): 378–385. doi:10.1577/1548-8659(1993)122<0378:FOTGSI>2.3.CO;2. Retrieved 24 October 2013.
{{cite journal}}: CS1 maint: date and year (link) - ^ a b "Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus)". NOAA Fisheries Office of Protected Resources. Retrieved 24 October 2013.
- ^ a b c Grunwald, Cheryl; MacEda, Lorraine; Waldman, John; Stabile, Joseph; Wirgin, Isaac (2008). "Conservation of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus: delineation of stock structure and distinct population segments". Conservation Genetics. 9 (5): 1111–1124. doi:10.1007/s10592-007-9420-1. S2CID 25059194. Retrieved 24 October 2013.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: date and year (link) - ^ a b Secor, David H. (1998). "Effects of hypoxia and temperature on survival, growth, and respiration of juvenile Atlantic sturgeon, Acipenser oxyrinchus" (PDF). 96 (3): 603–613. Retrieved 24 October 2013.
{{cite journal}}: Cite journal requires|journal=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help)
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