Researchers conducting a population estimate of shortnose sturgeon in the Hudson River caught one on Nov. 19 that had been tagged 26 years ago, during the last such count, and is likely more than 40 years old.
The 33.5 inch shortnose sturgeon was tagged in 1995 in the same overwintering area near Staatsburg, New York, by the late Mark Bain, professor of systems ecology in Cornell's Department of Natural Resources (DNR) in the College of Agriculture and Life Sciences (CALS). Records from 1995 show that the fish was already 25.5 inches and possibly 15 years old, based on its size.
While it’s not uncommon for researchers to recapture fish, the length of time between captures in this case was a surprise.
“That’s a long time to be at large and still alive,” said Amanda Higgs, a research support specialist in the DNR in CALS, who is based in New Paltz, New York, and is part of the current shortnose sturgeon population count.
Recapturing the same sturgeon provides information on its growth rate and confirms that the fish are using the same overwintering area that they did in the 1970s.
“This overwintering area was important back then, and it’s still important,” Higgs said.
Working with colleagues from the U.S. Geological Survey Eastern Ecological Science Center in Kearneysville, West Virginia, the University of Delaware and Delaware State University, Higgs along with Rich Pendleton, who is also a research support specialist in the DNR in CALS, and based in New Paltz, began this third sturgeon count in the spring. They are taking advantage of new technologies such as acoustic telemetry – which employs a riverwide array of stationary receivers to detect signals from species tagged with transmitters – and side-scan sonar – which uses sound to image the river floor and objects in the water column.
Fish were caught and fitted with transmitters in the spring so the researchers could follow them using telemetry, which is used in tandem with side-scan sonar to locate and count other fish. The data is used to mathematically estimate population numbers in overwintering areas and in the overall Hudson River.
In order to provide validation for the technologies, to make sure the objects imaged are indeed shortnose sturgeon, the researchers used panels of netting that snag fish, called gill-nets, which was how they landed the sturgeon Bain tagged in the 1990s.
The team expects to complete the current survey in July 2023 and hopes to secure additional funding for more frequent counts. The side-scan transmitters are long-lived and should continue providing signals into the 2030s.
Shortnose sturgeon are much smaller than Atlantic Sturgeon, also found in the Hudson River, and reach maturity at around seven to 10 years and then grow very slowly. They rarely exceed 4 feet long and 18 pounds in weight. The oldest known female reached 67 years of age and the oldest known male was 32 years.
The shortnose was the first species listed as endangered when the 1973 Endangered Species Act was enacted. An initial population estimate took place soon in the 1970s in the Hudson River, with the second count occurring in the 1990s, which showed a 400% increase in numbers due to improved fishery management.
Funding for the project comes from the Hudson River Foundation and the Hudson River Estuary Program. The researchers received a permit from the National Marine Fisheries Service to catch, scan for previous tags, measure and release fish for the population estimate.