**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

A Decision Analysis to Reduce Uncertainty in the Implementation and Operation of Sea Lamprey Barriers

R. L. McLaughlin ^1, L. A. Vélez-Espino ^1,2, M. Jones³, A. Hallett ⁴, T. Pratt⁵ and D. G. McDonald¹

 ¹Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1

 ² Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada, 867 Lakeshore Road, Burlington, ON, Canada, L7R 4A6

 ³Department of Fisheries and Wildlife, Michigan State University, Eastb Lansing, MI, USA, 48824-1222

 ⁴41 Caddy Ave, Sault Ste. Marie, ON, Canada, P6A 6H6

 ⁵Fisheries and Oceans Canada, Great Lakes Laboratory for Fisheries and Aquatic Sciences, 1 Canal Drive, Sault Ste. Marie, ON, P6A 6W4

Abstract

Decision analysis was employed to evaluate the effectiveness of barrier and fishway options used for sea lamprey (Petromyzon marinus) control in the Laurentian Great Lakes. Within the Great Lakes, tension surrounding barriers and fishways is emerging over a broad geographic scale of ecological and economic importance. Barriers are a valuable control tool for restricting the movements and reproduction of sea lamprey, but they can also have similar, unwanted effects on non-target fishes that migrate between a lake and its tributaries. Conversely, fishways and dam removals can reduce habitat fragmentation and facilitate broader movement of native fishes, but also expansion of invasive species. For the decision analysis, management objectives, barrier and fishway options, and key uncertainties influencing the expected performance of the options were specified in workshops with control agents and resource managers. The management objective specified was to maximize the difference between reducing the population growth rate of sea lamprey and the mean reduction in population growth rates for non-target fishes likely to be affected by barriers and fishways. Management options specified were permanent barriers with and without a trap-and-sort fishway and seasonally operated barriers with and without a trap-and-sort fishway. Key uncertainties were addressed using syntheses of agency and literature data and mathematical models to (i) quantify the effectiveness of different barrier and fishway options in terms of blocking sea lamprey and passing non-target fishes, (ii) test, as appropriate, spatial, temporal, and sampling hypotheses regarding the effectiveness of barriers at blocking sea lamprey and the effect of barriers on the diversity of non-target fishes, and (iii) project how the different management options, and, for seasonal barriers, different periods of operation, would affect the population growth rates of sea lamprey and migratory non-target fishes. Six key conclusions emerged from our analyses. First, permanent barriers are highly effective at blocking spawning-run sea lamprey. Their effectiveness is higher on tributaries where flow is more variable than on tributaries where flow is less variable, contrary to what we expected and for reasons that are currently unclear. Effectiveness is not related with water temperature during the sea lamprey spawning migration, which can influence the swimming capacity of the sea lamprey, or with the trapping efficiency, which can influence the number of sea lamprey free to pass the barrier. Second, the most reliable and least-biased estimate of how a permanent crest barrier decreases the richness of non-target species above a barrier is -2.5 species on average with 95% of effect size estimates predicted to be between -7.9 and 3.1, based on the field survey of Dodd et al. (2003; J. Great Lakes Res. 29(Suppl. 1):386). The greater uncertainty estimated by Dodd et al. was due largely to imprecision in the design of the field survey, and less to variation in landscape features of the watersheds examined. Third, seasonally operated barriers without a fishway are unlikely to balance sea lamprey control and free movement of migratory non-target fishes satisfactorily. The migration phenologies of non-target fishes overlap considerably with the migration phenology for sea lamprey and the population growth rates of migratory non-target fishes are projected to be as or more sensitive to blocking by a barrier than is the population growth rate of sea lamprey. Fourth, barriers can be effective for controlling sea lamprey, but their efficacy is likely to be lower in general than that of lampricides, because population growth rates of sea lamprey are less sensitive to control options targeting adults (e.g. barriers) than they are to control options targeting larval life stages (e.g. lampricides). As such, barriers are best considered as a complement to lampricides, rather than an alternative for reducing lampricide use in the short-term. Fifth, over a variety of circumstances, a permanent barrier with a trap-and-sort fishway is projected to provide the best balance between sea lamprey control and non-target effects, but other options ranked higher in specific circumstances. Performance of the management options was most sensitive to how fishery managers weight the importance of sea lamprey control versus non-target effects. Sixth, adaptive management involving future barrier and fishway decisions could be used to reduce uncertainty in the performance of the different management options. However, reducing uncertainty will be of greatest value when fishery managers weight passage of non-target fishes over sea lamprey control, a situation where the commission and the control agents would be less inclined to use a barrier and fishway under the new barrier strategy. Our project represents the first application of decision analysis to consider barriers and fishways in light of both control of invasive species and reduction of habitat fragmentation for native species. It provides fishery managers with a logical and scientifically defensible framework for selecting the best barrier and fishway option for a tributary within the Great Lakes and for communicating the rationale behind the selection of that option.