**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**

Micro-elemental analysis of statoliths as a tool for tracking tributary origins of sea lamprey

S.A. Ludsin^2, C.H. Hand³, J.E. Marsden⁴, B.J. Fryer³, and E.A. Howe⁴

 ² National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105-2945, USA

³ Great Lakes Institute for Environmental Research, University of Windsor, 406 Sunset, Windsor, ON, Canada N9B 3P4

 ⁴ University of Vermont, Aiken Center, 81 Carrigan Drive, Burlington, VT, USA 05405

Abstract

The analysis of otolith micro-elemental composition has been a valuable tool for differentiating among local spawning populations, and identifying origins of recruits to the fishery. Herein, we explored whether the analysis of sea lamprey (Petromyzon marinus) statolith micro-elemental composition by laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS) could be used as a tool to 1) discriminate among sea lamprey larvae collected from Lake Huron tributaries, and 2) classify a mixed-sample of unknown-origin parasites or spawners back to their natal source. By providing the GLFC with an alternate means, to labor-intensive tagging studies, to determine relative contributions of parasites and spawners from various spawning tributaries, we sought to enhance the GLFC’s ability to prioritize sea lamprey control efforts. As part of this effort, we analyzed statoliths of larvae collected in 45 Lake Huron tributaries during 2004 and 2005, as well as 72 female spawners collected in the Thessalon and Opequeoc rivers during 2005. Our analyses were conducted at three different classification scales: by geologic zone (n = 4 zones), by watershed (n = 9 watersheds), and by individual stream (n = 45 streams). Similar to a previous GLFC pilot study conducted using Proton Induced X-ray Emission (PIXE), we found that LA-ICP-MS analysis of statolith micro-elemental composition could be used to reliably differentiate among individuals produced in different regions (i.e., geologic zones, watersheds, streams), with the level of successful discrimination varying with classification scale. Regardless of the scale of classification, rubidium (Rb), strontium (Sr), manganese (Mn), and barium (Ba) were always most important for discrimination, with zinc (Zn), magnesium (Mg), and lead (Pb) being less useful. Analysis of water and sediment samples from 31 Lake Huron and Lake Champlain tributaries helps to understand these differences in utility for discrimination in that concentrations of Rb, Sr, Mn, and Ba in larval statoliths and ambient water were correlated, whereas concentrations of Zn, Mg, and Pb were not. Analysis of left-right statolith pairs also demonstrate that Zn, Mg, and Pb were not analytically stable in our analyses for reasons that are not entirely clear. Ultimately, using Rb, Sr, Mn, and Ba in maximum-likelihood estimation analyses conducted on a mixed-stock of adult spawners collected in 2005, we found that the sources contributing the greatest proportion of adults to our mixed sample were: 1) the Southern Lake Superior geologic zone (located north of Lake Huron); 2) the Wanipiti-French watershed; and 3) Beavertail Creek, Mississagi River, Lauzon Creek, Garden River, and Musquash River. However, these results need to be viewed with some caution, given are lack of success in accurately typing a sample of known-origin (tagged) spawners back to their natal streams in parallel study conducted in Lake Champlain. In discussing these results, we identify analytical and research needs that could further support our findings, and advance the use of statolith microchemistry as a means to identify natal origins of parasitic and adult sea lamprey in Lake Huron.