Erie, Pa. — A follow-up round of water sampling in Presque Isle Bay in Erie County did not reveal any evidence of environmental DNA – often referred to as eDNA – of silver carp or bighead carp.
According to the Pennsylvania Fish and Boat Commission, the samples were collected during October by the U.S. Fish and Wildlife Service.
The tests were conducted at the request of the commission after the federal service reported in July that silver carp eDNA had been detected in a single water sample collected in the bay this past spring.
The feds recommended waiting to conduct follow-up testing until fall 2022, when more favorable environmental conditions were present for eDNA sampling.
Upon learning of the positive detection in July, the commission took immediate precautionary measures by conducting targeted boat electrofishing sampling near the detection location. No silver carp were collected or observed.
Sean Hartzell, aquatic invasive species coordinator with the Fish and Boat Commission, said a positive sample does not necessarily imply the presence of an organism.
“Given that further eDNA sampling by USFWS during fall 2022 did not yield any positive samples for silver carp in Presque Isle Bay, and that no silver carp were collected by commission staff during electrofishing surveys in that area, it seems likely that the positive eDNA sample from spring 2022 was from a secondary vector,” Hartzell said.
“However, regular monitoring should certainly continue in Presque Isle Bay for silver carp as well as other invasive carp species.”
The U.S. Fish and Wildlife Service samples Presque Isle Bay annually in the spring and is planning to complete surveys again in May 2023.
The detection of eDNA is simply that – it indicates that DNA from the target organism is present in the sampling area, which doesn’t necessarily mean the organism itself is there.
Testing for eDNA cannot distinguish DNA associated with a live fish from other DNA sources, such as bird feces, water transported in a recreational boat live well that had been in carp-infested waters, or from melted ice used to store silver carp at fish markets that flowed into storm sewers.
However, repeated detections of eDNA over time increase concerns that the genetic material may have come from fish living in the area where the sample was collected, which is why regular eDNA sampling is recommended.
According to Hartzell, the U.S. Fish and Wildlife Service has been sampling eDNA for invasive carp species, such as silver carp, annually in Presque Isle Bay since 2015 (with the exception of 2020 when eDNA sampling was not done due to the COVID-19 pandemic).
No samples collected prior to 2022 have been positive for silver carp eDNA or other invasive carp eDNA.
Invasive carp, including bighead carp and silver carp, pose a significant threat to the Great Lakes ecosystem, the $7 billion-fishery, and other economic interests dependent on the Great Lakes and its tributaries.
Bighead and silver carp compete with native and recreational fish species and are known to quickly reproduce.
Anglers are urged to become familiar with the identification of invasive carp – both adults and juveniles – because the spread of juvenile invasive carp using live bait buckets has been identified as a potential point of entry into Great Lakes waters.
The U.S. Fish and Wildlife Service does environmental DNA sampling for invasive carp species throughout various parts of the Great Lakes basin and Mississippi River basins to better understand the distribution of these invasive species in North America and identify potential range expansions, Hartzell said.
Presque Isle Bay is part of its annual sampling in the Great Lakes basin, and other portions of Lake Erie in Ohio waters are sampled annually as well.
With the exception of grass carp, other invasive carp species (bighead carp, silver carp, and black carp) are not known to occur in the Great Lakes but are anticipated to have potential major economic impacts by displacing the Great Lakes food web if they become established there.
In addition to Presque Isle, eDNA samples are collected by the federal service in parts of Pennsylvania’s Ohio River basin, as bighead carp and silver carp are known from the Ohio River below the Pennsylvania border.