**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for this completion report are provided below.  For a copy of the full completion report, please contact the author via e-mail at rlmclaug@uoguelph.ca. Questions? Contact the GLFC via email at frp@glfc.org or via telephone at 734-662-3209.**

An Evaluation of Statistical Methods for Estimating Abundances of Adult Sea Lamprey From Stratified Mark Recapture Data

Robert L. McLaughlin¹, Dustin Harper², Julie Horrocks², Jessica Barber³, Gale Bravener⁴ and Carl Schwarz⁵

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

²Department of Mathematics & Statistics, University of Guelph, Guelph, ON, N1G 2W1 Canada

³US Fish & Wildlife Service, Marquette Biological Station, 1924 Industrial Pkwy, Marquette, MI 49855

USA

⁴Fisheries and Oceans Canada, Sea Lamprey Control Centre, 1219 Queen Street East, Sault Ste. Marie, ON P6A 2E5 Canada

⁵Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, BC, V5A 1S6 Canada

December 2016

ABSTRACT:

We evaluated the performance of mark-recapture methods appropriate for estimating abundances of adult Sea Lamprey (Petromyzon marinus) migrating upstream in Great Lakes tributaries. In the Great Lakes, the Sea Lamprey is the target of a basin-wide, bi-national control program. Abundance estimates from mark-recapture methods are used to evaluate program success and the efficiency of sea lamprey trapping, but recent tracking studies have raised concerns that mark-recapture estimates of abundance could be biased. We compared four estimators of abundance using stratified (weekly) mark-recapture data collected over 19 years of Sea Lamprey trapping in the St. Marys River connecting Lakes Huron and Superior. Abundances from the pooled Petersen estimator were highly similar to abundances estimated from the currently used stratified Schaefer estimator and the stratified Petersen estimator, but substantially lower than abundances estimated from a stratified Bayesian P-spline estimator. Simulations comparing the pooled Petersen and Bayesian P-spline estimators using virtual lamprey populations revealed that the two estimators provided similar abundance estimates across a range of conditions where catchability differed between marked and unmarked lamprey and changed over the trapping season, with one exception. Abundances from the Bayesian P-spline estimator were strongly positively biased when the catchability of marked lamprey was assumed to increase over the season, while the catchability of unmarked lamprey was not. Abundance estimates from both estimators were negatively biased when lamprey were assumed to display consistent individual differences in catchability and positively biased when a proportion of marked lamprey fell back. Sea Lamprey managers could switch from the stratified Schaefer to the pooled Petersen estimator to simplify field operations without losing accuracy and precision; however, discrepancies in trapping efficiency between mark-recapture and tracking studies suggest that mark-recapture estimates could be biased by individual differences in catchability.