Investigating Our Success in Assessing
Low-Density Larval Sea Lamprey Populations
BY LISA WALTER, MARQUETTE BIOLOGICAL STATION
backpack electrofishing to assess sea lamprey populations after a lampricide treatment.
Since 2008, the US Fish and Wildlife Service-Sea Lamprey Control Program (Program), in partnership with the Canadian Department of Fisheries (Department) and Oceans and the Great Lakes Fishery Commission, has increased lampricide control using a large-scale treatment scenario that treats target streams in two consecutive years to reduce the number of sea lampreys in the Great Lakes. During 2009-11, the Program and its Department counterparts treated the majority of sea lamprey producing streams around and including the St. Marys River as part of this treatment scenario. In general, lampricide treatments remove about 95% of larval sea lampreys from a stream, and a second treatment should remove over 99% of the total sea lamprey population.
One concern of fish biologists within the Program was whether current electrofishing gear and sampling protocols would adequately monitor larval populations if new control actions were successful at dramatically reducing larval densities in tributaries. Biologists hypothesized that additional survey effort might be needed to adequately assess streams with extremely low density sea lamprey populations.
Relative stream treatment success is assessed using AbP-2 backpack electrofishers. Surveys are generally conducted at least two months after treatment, giving larval lampreys a chance to disperse. This study was conducted on 20 stream reaches in Michigan’s eastern Upper Peninsula and Ontario. US streams included the Carp, Little Munuscong and Pine rivers and Albany, Beavertail, Prentiss and Trout creeks. These streams were surveyed with electrofishers after the first treatment, and staff placed fyke nets throughout the rivers during the second treatment to collect larvae that emerged from their burrows and were swept downstream. The latter is a common method of collecting larvae during a treatment and can provide a more thorough estimate of stream density.
Larval sea lampreys were captured in electrofishing surveys in 14 stream reaches and in fyke netting surveys in 16 stream reaches. Thus far, the consecutive treatment strategy does not appear to reduce larval densities to undetectable levels, but an ongoing analysis is examining the optimal amount of effort to expend when assessing low density populations.
Program biologists concluded that current methods for assessment are effective at surveying low density populations, but are concerned that factors contributing to poor visibility such as water depth and turbidity can lead to a missed infestation. Alternative survey tools, such as a deep-water electrofishers or application of granular Bayluscide are used to assess streams where poor visibility is a concern. Continued investigations into alternative sampling methods, such as the University of Manitoba’s development of an eDNA assay to assess and quantify larval sea lamprey presence, continue to be a high priority.