Statolith chemical analysis as a means of identifying stream origins of lampreys in Lake Huron

Management of the sea lamprey Petromyzon marinas in the North American Great Lakes would be facilitated by a technique that linked parasitic-phase adults to their natal rivers. We hypothesized that the elemental composition of statoliths in ammocoetes differed among river systems and could be used as a natural tag in the adults. To test this hypothesis we compared the composition of statoliths from three rivers in Michigan's lower peninsula with those from two sites in the St. Marys River, a major spawning area for lampreys in Lake Huron. Probe microanalysis indicated that five elements could be measured accurately and reliably in the statoliths and differed significantly among sites. Strontium and rubidium differences among specimens alone were sufficient to correctly assign most specimens to their natal rivers and almost perfectly distinguished between specimens from the St. Marys River and those from the drainages of Michigan's lower peninsula. The limited environmental data available suggest that these differences reflect the ambient concentrations of Sr and Rb in the river systems and, in particular, reflect regional differences in the geochemistry of the Canadian Shield and Michigan Basin. These regional signatures are likely to provide a means of assessing gross population structure of lampreys in the Great Lakes; however, the geographic resolution achievable by means of statolith analysis may be limited to regions rather than specific rivers.