Shortnose sturgeon
(Acipenser brevirostrum)
The shortnose sturgeon (Acipenser brevirostrum) is a small and endangered species of North American sturgeon. The earliest remains of the species are from the Late Cretaceous Period, over 70 million years ago. Shortnose sturgeons are long-lived and slow to sexually mature. Most sturgeons are anadromous bottom-feeders, which means they migrate upstream to spawn but spend most of their lives feeding in rivers, deltas and estuaries. The shortnose sturgeon is often mistaken as a juvenile Atlantic sturgeon, because of their small size. Prior to 1973, U.S. commercial fishing records did not differentiate between the two species, both were reported as common sturgeon, although it is believed based on sizes that the bulk of the catch was Atlantic sturgeon. The shortnose is distinguishable from the Atlantic sturgeon due to its shorter and rounder head.
Conservation status
The history of the shortnose sturgeon exploitation goes back 4,000 years. Native American fishermen harvested shortnose and Atlantic sturgeon for their meat and eggs. This continued with the Jamestown settlers in 1607 who utilized sturgeon as the primary food source for survival. Profitable fishery business using shortnose sturgeon began to grow in the 1800s leading to a rapid decline of the species population and distribution. By the late-1800s, sturgeon were being over-exploited. In 1890, over 7 million pounds of sturgeon were harvested in 1 year and as a result, in 1920, only 23,000 pounds of sturgeon were caught. Today, the shortnose sturgeon is in danger of extinction throughout its range and was listed as endangered under the Endangered Species Act on March 11, 1967. Shortnose sturgeon are protected in accordance with Section 1(c) of the Endangered Species Preservation Act of October 15, 1966 (80 Stat. 926: 16 U.S.C. 668aa(c)) after consulting the States, interested organizations and individual scientists, and finding that it was threatened with extinction. The IUCN has listed the shortnose sturgeon as a vulnerable species in 2004 with increasing action plans needed. NatureServe similarly lists the species as Vulnerable.
Distribution
Historically, shortnose sturgeon were found in the coastal rivers along the East Coast of North America. Living from the Saint John River in New Brunswick all the way to the Indian River in Florida. Currently, shortnose sturgeon can be found in 41 bays and rivers along the East Coast. Their distribution across this range is broken up, with a large gap of about 250 miles separating the northern and mid-Atlantic metapopulations from the southern metapopulation. There has been a shift slightly with lower sturgeon levels in river systems particularly further south. Modern spawning locations for the sturgeon include areas such as the Saint John River, Bay of Fundy, and the Altamaha River with noticeable absences in North Carolina rivers.
The southern metapopulations of shortnose sturgeon are currently found in the Great Pee Dee, Waccamaw, Edisto, Cooper, Santee, Altamaha, Ogeechee, and Savannah rivers. They may also be found in the Black, Sampit, Ashley, Roanoke, and Cape Fear rivers. Shortnose sturgeon were considered extinct in the Satilla, St. Marys, and the St. Johns rivers, but were recently found again in both the Satilla and St. Marys rivers.
In the northern and mid-Atlantic metapopulations, shortnose sturgeon are currently found in Saint John (Canada), Penobscot, Kennebec, Androscoggin, Piscataqua, Merrimack, Connecticut, Hudson, Delaware, and Potomac rivers. They have also been spotted foraging and transiting in the St. George, Medomak, Damariscotta, Sheepscot, Saco, Deerfield, East, and Susquehanna rivers. On rare occasions, they have been seen in the Narraguagus, Presumpscot, Westfield, Housatonic, Schuylkill, Rappahannock, and James rivers.
Habitat
Shortnose sturgeon live in rivers and coastal waters that run from Canada to Florida. Because shortnose sturgeon are amphidromous fish, after spawning most of their time is spent in estuaries and rivers. Shortnose sturgeon rarely spend time in the Atlantic Ocean. However, if the sturgeon do enter marine waters to feed or migrate they stay close to the shore. Shortnose sturgeon are more likely to move through all areas of a river system. Times they remain at sites for an extended period of time include resting and feeding periods.
Critical habitat has not been designated for the shortnose sturgeon. This is an area of the conservation plan that is essential to the conservation of the species. Research needs to be done to identify what habitats are critical to ensure the protection of each life stage.
One area of research for discovering and designating critical habitat of shortnose sturgeon will be the study of foraging ecology and growth of the various life stages, as well as defining the benthic habitats that support preferred prey. To enhance this understanding, results on the mapping of the benthic organisms will be needed to better define both the available and preferred diets of sturgeon. Probabilistic or generalized linear models or similar approaches used to map benthic habitat should be constructed to help identify the distribution of shortnose sturgeon density. Additionally, obtaining information on nursery areas and characterization of nursery habitat is a major priority.
Description
The shortnose sturgeon is the smallest of three sturgeon species that are present in the eastern seaboard of North America. It has a cylindrical body and compared to the Atlantic sturgeon, its head and snout are relatively small. Younger shortnose sturgeons tend to have longer snouts compared to their older counterparts. Adult sturgeons have bony plates along their esophagus that help them crush hard items instead of having teeth.
Shortnose sturgeon are cartilaginous with bones only in the skull, jaw and pectoral girdle. It is a physostome fish, so its swim bladder is connected to the intestinal tract by a special duct. This duct allows for gas pressure regulation through swallowing air or releasing air through the gut. The intestines for shortnose sturgeon are dark and have a spiral valve (important for nutrient absorption), similar to that of sharks and rays. As seen in the image, these sturgeons tend to be generally dark brown to olive/black on the dorsal surface.
Shortnose sturgeon tend to consume small bivalves, gastropods, polychaetes, and small benthic fishes based on studies of their gut contents. The most common prey are amphipods, while Atlantic sturgeon primarily consume polychaetes. Some reports have found that female adult shortnose sturgeon feed throughout the year, but a study from the Saint John River found that pre-spawning females rarely had food in their stomachs and likely stopped feeding about eight months prior to spawning while ripening males generally had full stomachs.
Sturgeon are often called living fossil, due to their ancient lineage and a fossil record that points to a holarctic distribution. With the earliest reported remains of North American sturgeon dating to the late Cretaceous period. Sturgeons have bony plates called scutes that extend from the skull to the caudal peduncle and are divided into five rows on the body: one dorsal row, then two lateral and ventral rows respectively. The fins on the shortnose sturgeon are located far back on the body. The pectoral fins are positioned low, while the pelvic fins are along with the abdominal position. Prominent features of the shortnose sturgeon are the scutes, protractile tube-like mouth, and chemosensory barbels. Sturgeon tend to be long-lived, slow-maturing, and spawn infrequently, which have served the species well through evolutionary time but poorly to anthropogenic impacts like overharvesting, habitat loss, and degradation.
Potential predators of the shortnose sturgeon include alligators, sharks, and other large fish such as catfish. Other known ones include sea lampreys gar, striped bass, common carp, northern pikeminnow, channel catfish, smallmouth bass, yellow perch, walleye, grey seal, fallfish, and sea lions.
