Gulf sturgeon

Gulf sturgeon
Gulf sturgeon on side
Conservation status
Vulnerable  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Acipenseriformes
Family:	Acipenseridae
Genus:	Acipenser
Species:	A. oxyrhynchus
Subspecies:	A. o. desotoi
Trinomial name
Acipenser oxyrhynchus desotoi Vladykov, 1955[2]

Critical habitat map for the gulf sturgeon, as of 2003

Gulf sturgeon jumping near Rock Bluff, Suwannee River, Florida; July 2007.

The Gulf sturgeon, Acipenser oxyrinchus desotoi is a subspecies of sturgeon that lives in the Gulf of Mexico and some rivers draining into it. The gulf sturgeon was first recognized as a separate subspecies in 1955. The nominate subspecies is the Atlantic sturgeon, Acipenser oxyrhynchus oxyrinchus.^[3] The gulf sturgeon is listed as threatened under the United States Endangered Species Act, having been listed in 1991. Critical habitat, reflecting the current range of the subspecies, has been designated (see map). The historical range is thought to have been from the Suwanee River on the western coast of Florida to the Mississippi River, and marine waters of the central and eastern portions of the Gulf of Mexico. Three sturgeon species in genus Scaphirhynchus share river territory with the Gulf sturgeon; none of these are anadromous.^[4]

Physical appearance

Visually, Gulf sturgeon are almost impossible to differentiate from Atlantic sturgeon, as the most significant morphological difference is the spleen length, which is internal. Gulf sturgeon have a spleen length averaging 12.3% of their fork length, while Atlantic sturgeon have a spleen length averaging 5.7% of their fork length. Lesser morphological differences include relative head length, shape of dorsal scutes, and pectoral fin length. Genetic differences between the subspecies have been studied, and tend to indicate that reproductive isolation occurred in the Pleistocene period. Behavioral differences are more clear, especially the dietary habits. Adult Gulf sturgeon eat primarily, or possibly only, during the winter months when they are in marine or brackish water, and eat little to nothing during the remainder of the year when they are in rivers. ^{[citation needed]} Their weights vary in accordance with this eating pattern, with significant weight gains in the winter and smaller weight losses in the summers. Because their diet consists of mollusks that can cause paralytic shellfish poisoning (PSP), in addition to other bottom-dwelling organisms such as grass shrimp, marine worms, isopods and amphipods, it is possible that their unique feeding pattern reflects an adaptation to prevent PSP that coincides with higher rates of algal blooms in summer months. ^[3][4]

Life cycle

Juvenile Gulf sturgeon remain in the spawning river until roughly two years of age, eating there. Thereafter, they join the adults in their anadromous migrations and eating habits. The upriver migration normally occurs between February and April, as river temperatures rise to between 16 and 23 degrees Celsius. Downriver migration normally begins in late September or October when water temperatures drop to 23 degrees Celsius. Males reach sexual maturity between seven and twelve years of age, females between eight and seventeen years of age. Spawning almost always occurs in the natal river, generally over a hard bottom just downstream of a spring on the river bottom feeding groundwater into the river. After spawning, the adults and older juveniles collect in regions of cooler, deeper, slower flowing water, generally downstream of springs.^{[3] [5][4]}

Jumping

All species of sturgeon will jump at times. The Gulf sturgeon does at two times; in the rivers during July and August and early in the offshore feeding period. It is conjectured that they jump in order to communicate and maintain group cohesion.^[5] Since at least 2002, boaters on the Suwannee River have accidentally run into jumping sturgeon every summer, leading to serious injuries.^[6][7]

Population controls

Predators of the sturgeon, other than humans, are unknown but thought to have limited impact upon the species. Parasites include the fish louse Argulus stizostehi, nematodes, trematodes, and leeches. No detrimental impacts from these parasites have been observed. The species also serves as host to the glochidia (larva) of three freshwater mussel species. Overfishing and dam construction probably contributed to the historical decline in populations.^[4]

See also

• Sturgeon
• Atlantic sturgeon, Acipenser oxyrhynchus oxyrinchus, the other subspecies

References

• Froese, Rainer, and Daniel Pauly, eds. (2009). "Acipenser oxyrinchus desotoi" in FishBase. February 2009 version.

External links

• NOAA Fisheries gulf sturgeon web page