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Shortnose sturgeon (Acipensor brevirostrum)
Identification:Though a large fish, shortnose sturgeon is a relatively small species of sturgeon. Adults typically grow to three feet long and weigh about 14 pounds. The top half of the fish is typically olive to dark gray in color, while the ventral side is yellowish. Sturgeon are identified by the rows of large bony plates that grow in rows on the sides of their bodies, their ventral protruding mouths surrounded by barbels, and their long noses. The only other sturgeon that is present in the Hudson River is the Atlantic sturgeon, which can grow to over double the size. The two can be distinguished rather easily as adults because of the shortnose sturgeon's short rounded nose and the Atlantic sturgeon's longer more pointed nose. More detailed descriptions would be helpful for distinguishing the two but the nose length is the obvious distinguishing characteristic.
Life History:Shortnose sturgeon are an anadromous species which means they spend their adult life in or near salt water and migrate upstream to spawn in freshwater (just below the Troy dam in the Hudson River in our area). They spawn in moving water in early spring (April to May) in the Hudson River, when water temperatures reach 8oC to 9oC. The spawn consists of a rapid run up river from their feeding grounds to their spawning grounds on various substrates in moderately flowing water. Fertilization is external and a female may discharge 30,000 to 180,000 eggs to be fertilized by a male. Females spawn once every three years, while males spawn once every two years. The adults will return to their feeding grounds within one week of spawning while the fertilized eggs will not hatch for 13 days.
The 7-11 mm long hatchlings have an attached yolk sac and actively seek cover on the river bottom in the deepest parts of the river. Within two weeks the young absorb their yolk sac, grow to 11-15 mm long, and are called larvae. At 20 mm the fish are called juveniles, resembling the adults in appearance, and begin feeding and swimming through the water column. At this stage the sturgeon eats plankton and fly larvae. They will migrate downstream for about two days and reside in fresh water for the remainder of their first year.
In their second summer yearlings will continue their migration downstream to adult feeding grounds in brackish (mixture of salt and fresh) water, in the Hudson this is south of Kingston, NY. There they will feed off the river bottom, eating mollusks, mussels, sludge worms, insect larvae, shrimp, crayfish, and plants. The adults prefer a silty substrate and live in 30 ft to 80 ft of water. Females, the larger of the two genders, can live to 67 years, while a male may live to 32 years.
Range:The Shortnose sturgeon is found in 19 distinct populations in 25 river systems on the east coast of North America ranging from the St. John river in New Brunswick, Canada to the St. Johns river in Florida. Though all populations are the same species, each population is treated as its own species under the endangered species act to promote the survival of each population. This is done because there is very little migration of shortnose sturgeon from one river to another and each population has become genetically unique. This genetic and range diversity may prove critical for the survival of the species. It is possible that many other rivers along the East Coast were populated by this species allowing for easier migration between rivers in the past. The population sizes in each river varies from as few as 30 fish in the Merrimack River in Maine to as many as 55,000 fish in the Hudson River. Dams have blocked the range of the species in most rivers, especially the spawning range. This is evident in the Hudson because the entire population spawns just below the Troy dam.
Status:Both New York State and the Federal Government consider the shortnose sturgeon Endangered. Several factors contributed to the decline of this species:
For most of the 1900's rivers were used as dumping grounds for everything from chemical waste to sewage. The chemical wastes including PCB's, DDT and metals like mercury and lead, bioacculumate through food webs. Shortnose sturgeons are omnivorous but most of their food sources place them near the top of the food chain. Therefore levels of toxins were very high in these fish, primarily affecting their reproductive success.
Dumping of sewage and farm waste in rivers added large amounts of nutrients to the rivers. This results in rapid and large blooms of aquatic plants. When these plants die they decompose along with the decomposing matter in the sewage. This decomposition consumes vast amounts of the oxygen dissolved in the water leaving little to none left for fish. This dissolved oxygen depletion is probably responsible for killing large numbers of shortnose sturgeon in the first half of the 20th century.
During the first half of the 1900's sturgeon were also fished heavily for their meat and eggs (caviar). They were most likely fished out faster than they could reproduce.
A final factor that contributed to their decline was the vast amounts of construction that occurred along rivers in the early to middle 1900's. Construction of bridges, roads, and dams produce a large volume of silt that can cover spawning habitat and juvenile sturgeon. The construction of dams also prevented sturgeon from reaching their upstream spawning habitat.
The Shortnose sturgeon was listed as endangered in 1967. Since then dramatic strides have been made in several populations. The Hudson River population status may be changed to threatened by the end of this decade. Decrease in construction and reducing silt from construction projects has helped, as well as having a fishing ban and the dramatic increase in the regulation of pollution in rivers. Since its listing as endangered, the sturgeon populations have been studied and the knowledge gained from those studies is aiding in the preservation of the species.
Current Threats:Hudson River shortnose sturgeon still face many risks:
Adults are still caught in the gill nets of shad fisheries in the Hudson, especially during the spawn. Unfortunately the shad spawn and sturgeon spawn coincide. Fortunately the numbers of sturgeon killed this way is not significant to the 55,000 fish population on the Hudson. Further study may reveal ways to reduce sturgeon mortality from shad fisheries.
Power plant turbines can impale sturgeon. This was measured at the Albany steam plant, at a rate of 160 per year in the early 1980's. This is prevented by shocking the water around the intakes to keep sturgeon from coming near.
Siltation from construction can still be dangerous to sturgeon especially during their spawn when silt can cover eggs and juveniles. Regulations can be put in place to prevent risky construction during the spawn and existing regulations require contractors to keep silt from leaving construction sites.
Navigational dredging in waters downstream of Troy dam can also hurt the sturgeon population especially if conducted in spawning habitat during the spawn. Benthic (river bottom) ecosystems can recover rapidly after dredging so long-term effects are probably not as significant.
In the long term, it is possible that an introduced species could outcompete the shortnose sturgeon in its own ecosystem. This is not currently the case, but care should always be taken to prevent the introduction of exotic species.
What Can Be Done?Maintaining the current regulations and commerce on the Hudson River will probably be sufficient for continued recovery of its shortnose sturgeon population. Addressing the issues listed above can only benefit. It could be debated what affect dredging PCP's from the upper river would have on the sturgeon population. The dredging itself would probably have little to no immediate effect because the dredging operations are so far from sturgeon spawning and feeding habitat. However, the ultimate decrease PCB concentrations in the Hudson River ecosystem would most likely prove beneficial. It is important that your elected officials know the importance of this species and one thing you can do to insure the shortnose sturgeon's survival is write to your elected officials and educate them about the fish and let them know what you think should be done to protect it.