Tracking the Natal Origin of Parasitic Sea Lamprey Using Statolith Microchemistry

Parasitism of fishes by sea lamprey is a major threat to Great Lakes fisheries. Sea lamprey spawn in lake tributaries and control programs target their larval phase in these tributaries. Information about tributary contribution to the sea lamprey parasitic phase is critical for an appropriate allocation of efforts to control sea lamprey populations. Larvae from different streams can be discriminated based on the chemistry of their statoliths, calcified structures located in the inner ear. So, larval statoliths have been used to establish natal stream chemical signatures. However, statolith microchemistry does not successfully track the natal origin of parasitic lampreys. Lampreys undergo a drastic metamorphosis from the larval non-parasitic stage to the parasitic juvenile stage. The objective of this study is to test if this metamorphosis affects statolith microchemistry and our ability to assign a natal origin to the parasitic juvenile stage. Both pre- metamorphic lampreys (larvae) and newly-metamorphosed lampreys were collected from seven streams: five Lake Champlain tributaries, one Lake Huron tributary and one Lake Michigan tributary. Nine elements were measured in 240 statoliths using a laser-ICP-MS. Our results suggest that an increase in rubidium concentration is associated with metamorphosis. This is problematic because rubidium is a crucial element to discriminate among larvae from different origins. Using newly-metamorphosed lampreys to characterize natal stream chemical signature may improve the accuracy of natal origin identification for parasitic lampreys.