Short-nosed sturgeon
| Short-nosed sturgeon | ||||||||||||
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Short-nosed sturgeon |
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| Acipenser brevirostrum | ||||||||||||
| Lesueur , 1818 |
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The Shortnose ( Acipenser brevirostrum ) is a small North American sturgeon , the great in 16 to 19 rivers and estuarine systems along the Atlantic coast from the Saint John River in New Brunswick , Canada , to the St. Johns River in Florida , United States occurs, . The populations may be disjoint , which is difficult to prove due to the lack of data on migratory behavior. In addition, there are seldom catches of tagged individuals outside of the rivers in which they were tagged.
The species is often confused with juveniles of the Atlantic sturgeon , as the adult specimens of the short-nosed sturgeon are similar in size to the juveniles of the Atlantic sturgeon. Before 1973, there was no distinction between the two species in the US Commercial Fishing Records records . Both were referred to as "common sturgeon", although based on the size information it can be assumed that even then the main mass was Atlantic sturgeon .
features
The animals have the typical physique of the sturgeon with an elongated body, an under-lying proboscis mouth , heterocercial caudal fin and five rows of bone plates along the trunk. Usually the animals reach a length of up to 1.43 m and a weight of 23 kilograms. The body is dark brown with a yellowish to whitish belly and dark bone plates. The snout is always long and V-shaped. Two pairs of short, slender barbels sit halfway from the tip of the snout to the mouth. There is a bone ridge above the eye. The iris is bronze, gold or copper in color. The back row has 7 to 13 bone plates, the side rows have 22 to 34. Between the anus and anal fin, there are 6 to 11 small plates in pairs. There are numerous tiny, diamond-shaped plates between the large bone plates. The dorsal fin has 33 to 42 soft rays.
Reproduction
The animals spawn in fresh water near the tidal limit, in flowing water over gravelly grounds with little mud or organic waste. Spawning time varies depending on the latitude and is likely to depend on the water temperature, which must be between 9 and 12 ° C, but successful spawning can also be observed at temperatures of 6.5–15 ° C; accordingly, spawning season begins in January in South Carolina or Georgia , while it does not begin until May in Maine and New Brunswick . Additional factors are the day length of 13.9-14.9 hours and a water speed at the bottom of 30-120 cm / s. The fry hatch after 13 days. They are 7–11 mm long and carry a large yolk sac . The larvae have minimal vision and swimming ability and a strong instinct to hide. After a further 9–12 days, the larvae mature into young fish of approx. 15 mm and resemble the adult animals from a length of 20 mm. During this time they drift downstream in the river depths, but remain in fresh water for the first year of life. Juvenile animals over 45 cm in length tend to swim in areas where fresh and salt water mix and move with the tidal cycle .
Adult animals live in both fresh and salt water. They become sexually mature from a size of 45 to 55 cm, regardless of age. Usually males reach sexual maturity in Georgia after 2-3 years and after 10-14 years in New Brunswick, and females reach sexual maturity between 6 and 17 years. The animals grow up to 1.2 m. Males can spawn annually, but rarely live longer than 30 years. Females usually spawn every three to five years and produce between 40,000 and 200,000 eggs. They will be 67 years old. They spend many years with less food intake and reduced growth to produce the spawn. It is believed that the maximum age will be reached in the northern regions.
ecology
The highest salinity in which specimens have been found is 3.0 to 3.1%, only slightly below the salinity of sea water. The species was able to survive as a freshwater population in three biotopes ( Connecticut River in Massachusetts, Santee River in South Carolina, Saint John River in New Brunswick) after dams interrupted the migration there. Obviously, the species does not depend on salt water. Fish farmed sturgeons seem to survive best in salt-free fresh water. Northern populations generally spend more time in salt water than southern populations.
Sturgeons are bottom fish that feed mainly on insects and small crustaceans . Young animals were observed that had more than 90% unusable substances in their stomachs, from which one can conclude that they "suck off" the reason more by chance. Adult animals in freshwater live mainly on molluscs and polychaetes , as well as on small benthic fish in the estuaries or crustaceans and insects.
The largest population, estimated at around 60,000 adults in 2007, occurs in the Hudson River . The second largest with an estimated 18,000 adults and approx. 100,000 specimens of all ages can be found in the Saint John River.
There are few non-human predators. American perch fatten up with the fry, and sharks and seals occasionally catch adult specimens. Parasites don't seem to play a role. There are no observations of disease in wild short-nosed sturgeon. In fish farms there are occasional symptoms of illness.
Genetically, short-nosed sturgeons are hexaploid , i.e. they have a six-fold set of chromosomes instead of the usual two-fold set of chromosomes.
Protection status
Since 1967 the species has been considered endangered species in the United States . Maine has created a conservation breeding program.
Individual evidence
- ↑ a b c d e f National Marine Fisheries Service. Recovery Plan for the Shortnose Sturgeon ( Acipenser brevirostrum ) . Prepared by the Shortnose Sturgeon Recovery Team for the National Marine Fisheries Service, Silver Spring, Maryland 1998.
- ↑ a b c Rachel Anderson: Shortnose Sturgeon. ( Memento of the original from October 24, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. McGill University 2004.
- ↑ a b c d e f g C. R. Gilbert: Species profile: life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic Bight) - Atlantic and shortnose sturgeons. ( Memento of the original from October 3, 2006 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. US Fish and Wildlife Service Biological Report 82 (11.122). US Army Corps of Engineers TR EL-82-4, 1989.
- ↑ Acipenser brevirostrum on Fishbase .
- ↑ Species Fact Sheet of FAO
- ↑ Shortnose Sturgeon on the Red List of Threatened Species page .
- ↑ Peter L. Jarvis; James S. Ballantyne; William E. Hogans: The Influence of Salinity on the Growth of Juvenile Shortnose Sturgeon. In: North American Journal of Aquaculture. American Fisheries Society vol. 63, 2001: 272-276.
- ↑ Peter L. Jarvis; James S. Ballantyne: Metabolic responses to salinity acclimation in juvenile shortnose sturgeon Acipenser brevirostrum . In: Aquaculture vol. 219, 1-4: 891-909, April 2, 2003.
- ↑ Mason Inman: Once Endangered Sturgeon Rebounding in Hudson River, St . News.nationalgeographic.com. February 7, 2007.
- ↑ M. Havelka; M. Hulák; DA Bailie; PA Prodöhl; M. Flajšhans: Extensive genome duplications in sturgeons: New evidence from microsatellite data. In: Journal of Applied Ichthyology. vol. 29, 4: 704, 2013
