Transplantation of prespawn adult Sea Lampreys as an important restoration strategy

Abstract Objective Anadromous Sea Lamprey Petromyzon marinus , native to the Atlantic coast of the USA, has declined in numbers since European contact due to the construction of barrier dams. Simply addressing the stream barriers, either by removal or the addition of fishways, has not always resulted in the restoration of runs. An experimental approach of transplanting adult lamprey from existing runs into unoccupied upstream habitat was evaluated as a tool for re‐establishing annual spawning runs of the species. Methods Two coastal watersheds without Sea Lamprey runs but with dams with fishways close to the ocean were selected for testing. Prespawn adult Sea Lamprey captured from another river were released in suitable habitat upstream of the dam in one river but not the other. Counts of adult Sea Lamprey ascending the river via the fishways in subsequent years were made and compared between the two rivers. Data of colonizing adult Sea Lamprey in other rivers were analyzed for further comparison. Result In subsequent years, adult Sea Lamprey only immigrated into the river that received transplanted adults. When adult Sea Lampreys were finally released into the second river years later, an annual run of adult Sea Lamprey was re‐established in that stream as well. Conclusion Prespawn adult Sea Lamprey will not emigrate from the ocean into a stream with no resident larval Sea Lamprey. The release of prespawn adults into a vacant habitat resulted in spawning, which produced a resident population of larval Sea Lamprey. Such larvae produce attractant pheromones, which is necessary to attract adults. If a stream has an extant run of Sea Lamprey, removal of a migratory barrier will result in the run expanding upstream into previously vacant habitat. Transplantation of prespawn adult Sea Lamprey can be an important management tool for restoring lost runs of this important anadromous species.