Current invasive species research being conducted at MSU
Return to MSU Research

Project 7

Project Title: Recruitment variation in Great Lakes sea lamprey populations
Investigators: Heather Dawson, Michael Jones
Contact: Heather Dawson (dawsonhe@msu.edu)

Abstract:
Like many fish species, sea lampreys exhibit large variations in recruitment from year to year. As well, little is known about the stock-recruitment relationship for sea lampreys. Recruitment variation and density dependence (also known as compensation) can have a large influence on the efficacy of sea lamprey control strategies that target reproductive success, such as the release of sterile males into spawning grounds. To gain a better understanding of sea lamprey population dynamics, we measured recruitment at age 1 in contrasting streams by introducing a known number of spawners in barricaded-off sections of streams. We then conducted standardized surveys to estimate larval abundance and recruitment.  Sea lamprey stock-recruitment data combined from streams across the Great Lakes basin indicated both density-dependent survival and a large amount of density-independent recruitment variation.  Streams described by sea lamprey program staff as having a regular and predictable cycle of lampricide treatment experienced significantly higher recruitment than less predictable (irregular) streams. Lakes Superior and Michigan tributaries experienced significantly higher recruitment than streams from Lakes Huron or Ontario. Recruitment was also significantly higher in streams where the number of lamprey competitors (sea lamprey and native lamprey) to age-1 sea lamprey recruits was greater. We incorporated density-independent recruitment variation found from this study, larval assessment uncertainty, and other sea lamprey demographic information into a management model to facilitate a realistic comparison of the effectiveness of different sea lamprey control strategies. Assuming our best estimates of adult control costs and efficacy, results suggest that increasing adult control efforts at the expense of lampricide use will result in an increased abundance of sea lamprey in the Great Lakes.  By simultaneously increasing the efficacy of alternative control and decreasing the initial unit cost of alternative control we found a few hybrid strategies (using both control methods) that perform better than using only lampricide control.

Because estimating the recruitment of sea lamprey involves assessing the larval population in streams and separating the population into age classes, the accuracy of these estimates can be limited by errors in larval age determination. Developing a standard method of age-assessment using both statolith and length-frequency data requires the validation and improvement of both methods of age interpretation. Therefore, we established known-age populations in two contrasting streams by introducing a single cohort of sea lampreys and then compared the age determined by statolith interpretation to the known age using two different methods for statolith preparation and evaluation.  Multiple independent age readings of sea lamprey statoliths indicated that the overall average percent error indicated a higher bias in age estimates using the Crystal Bond method as opposed to the Immersion Oil method. The statolith data were bias-corrected and combined with length-frequency data in the statistical model to determine proportion-at-age in our “known-age” sea lamprey populations, which resulted in a substantial increase in the precision of this estimate. This project has produced insight into the population dynamics of sea lamprey, providing understanding to improve the management of this species and thus, protect many of our Great Lakes fish and fisheries.

For more information:
Michael L. Jones, Ph.D : http://glpd.fw.msu.edu/Mike/
Heather Dawson, Ph.D. : http://glpd.fw.msu.edu/Mike/dawson.htm
Great Lakes Fishery Commission: http://www.glfc.org/lampcon.php