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New Jersey Endangered and Threatened Species Field Guide
Species Group: Fish
The shortnose sturgeon is the smallest of three sturgeon species that occur in eastern North America. Sturgeon are sometimes called “living fossils” since they are among the oldest bony fishes and have retained many primitive characteristics. The shortnose sturgeon has a short and rounded snout, subterminal mouth (located on the underside of the head), barbels, numerous scutes (bony or horny plates) along its back, sides, bottom, and a heterocercal tail (the upper lobe of the tail fin is larger and contains the upturned end of the spinal column). The head and snout are fairly short when compared to the Atlantic sturgeon. The body is typically yellowish brown to nearly black on the head, back and upper sides, and whitish to yellowish below. Length at maturity for this species occurs between 18-22 inch fork length, from the snout to the middle of the tail for males and females. Maximum known fork lengths are nearly 49 inches for a female and nearly 39 inches for a male.
Distribution and Habitat
The shortnose sturgeon is a diadramous fish species (migrates between fresh and saltwater). More specifically, it can be called freshwater amphidromous, which means that it spawns and remains in freshwater for most of its life cycle, but spends some time in saline waters. It is found in large estuaries and near-shore waters along the Atlantic Coast from New Brunswick, Canada to the St. John River in Florida. River mouths, tidal rivers, estuaries, and bays serve as prime habitat for the shortnose sturgeon. In addition, individuals occasionally enter the open ocean. A significant portion of New Jersey's shortnose sturgeon occur in the upper tidal Delaware River. They can also be found within the Hudson River.
Sturgeon feed by feeling the substrate with barbels (sensory organs that look like whiskers) and vacuuming the river bottom with a protractile mouth. Young shortnose sturgeon eat bottom-dwelling crustaceans and insects. Adults have been known to feed on insects, freshwater clams and mussels, snails, marine worms, crustaceans, small flounder, and a variety of other organisms.
Most Delaware River shortnose sturgeon overwinter from December to March in the area of Roebling, Bordentown, and Trenton. The channel off Duck Island is used heavily by overwintering sturgeon. Adults of the species become active and move upstream between Trenton Rapids and Scudders Falls in mid- to late March. Spawning occurs in this general location between late March and early May. Once spawning is complete, the fish travel downstream into the tidal portion of the river near Philadelphia and remain in that area through May. By the end of June, the sturgeon may move upstream to the area near Trenton and remain there for the summer and winter. Recent studies suggest that some shortnose sturgeon are using a second overwintering area, located in the lower portion of the river below Wilmington, DE. In addition, tracking data show that at least some juvenile shortnose sturgeon may be overwintering between Philadelphia to below Artificial Island.
Young and adult shortnose sturgeon may also be found within the New Jersey portion of the Hudson River. Larvae and eggs however, will not be encountered in this area. The Hudson River population spawns upstream in upstate New York.
Female shortnose sturgeon will produce anywhere from 40,000 to 200,000 eggs during a spawning event. Eggs are demersal (found on or near the bottom) and adhesive, sticking to rocks and plant material underwater. Eggs hatch about 13 days after fertilization. The hatching larvae look like tadpoles, are about 2.9-4.5 inches long, and have an attached yolk sac. Larvae and juveniles are bottom-dwelling and usually occupy deep channels with strong currents.
Shortnose sturgeon are not considered adults until they are between 3 to 10 years old and are 49.5-60.5 inches in fork length. Males may begin spawning one or two years after maturity, but female spawning may be delayed for five years after maturity.
Shortnose sturgeon will begin migratory behavior once they reach adult size. They will move upstream in spring to spawn and downstream in fall. Female shortnose sturgeon have been known to live as long as 67 years while the oldest known male was 32-years old.
Current Threats, Status, and Conservation
The shortnose sturgeon has been federally listed as endangered since the Endangered Species Act was created in 1973, when it was also considered endangered in New Jersey. This species is afforded protection under both federal and state Endangered Species acts, Clean Water acts, and fishing regulations. This species’ numbers were drastically reduced primarily due to overfishing, both for its meat and for its eggs, which were sold as caviar between 1870 and the early 1900’s. River pollution may have also been a cause for the species’ decline. In 1987, the population of adult shortnose sturgeon in the Delaware River was estimated to be approximately 12,796. A more recent analysis (2006) based on data collected between 1999-2003 estimates the adult population at approximately 12,047 individuals. Despite the similarity between the two population estimates, new information from field collections of tagged fish indicates that older fish comprise a substantial portion of the Delaware River population.
River dredging and water quality degradation related to development are potential threats to shortnose sturgeon. Although water quality in the Delaware River is generally improving, contaminants such as endocrine disrupting chemicals (EDC’s) may pose serious threats to shortnose sturgeon and other fish species. These contaminants include PCDD’s/TCDF’s, DDE, PCB’s and cadmium. EDC’s have been linked in fish to reduced fecundity and egg viability, increased early life stage mortality, anatomical defects in larvae, and other reproductive problems. There is also a potential risk for young sturgeon to be accidentally caught and killed in water intake systems from the area of Scudders Falls in the Delaware River and extending downstream towards the sea. The population is especially at risk during the winter and early spring, when young shortnose sturgeon may occur in dense schools. Other threats to shortnose sturgeon include boat/ship strikes, mortality from commercial and recreational fishing (bycatch), and poaching.
Fisheries experts recently found early life stage shortnose sturgeon (eggs and larvae) over an approximately 11 mile reach of the lower non-tidal Delaware River. Despite the new information, it is unknown whether spawning is occurring upstream of the area, where there is an abundance of suitable substrate and habitat. Though not known, it is theorized that shortnose sturgeon spawn upstream to at least Lambertville. In addition, not much is known about the locations and habits of juvenile sturgeon. This lack of information is a serious problem in determining the impacts of human activities such as river dredging and other instream projects on critical areas for the species.. Additional research on sturgeon movement is also being conducted and should be expanded in order to determine if this species is utilizing more southern portions of the Delaware River. Finally, more research is needed on what role the New Jersey portion of the Hudson River plays in maintaining that river’s population of shortnose sturgeon.
Text derived from the book, Endangered and Threatened Wildlife of New Jersey. 2003. Originally edited by Bruce E. Beans and Larry Niles. Edited and updated Jeanette Bowers-Altman and Michael J. Davenport in 2010.
Species: A. brevirostrum
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