AGE-DISCRIMINATION AND STATOLITH DIVERSITY IN SEA LAMPREY FROM STREAMS WITH VARYING ALKALINITY

The diversity of statoliths and changes in statolith length were exami ned in larval and metamorphosing sea lampreys Petromyzon marinus from four streams in Ontario. In midsummer, increases in statolith lengths were similarly and positively correlated with larval total lengths in the four streams. Statoliths from larval and metamorphosing lampreys c ollected from Lynde and Farewell creeks in June and September displaye d typical alternating opaque and translucent bands. The number of opaq ue bands, or annuli, provided reliable age estimates when compared wit h length-frequency distributions. In July and September, statoliths fr om some larval and metamorphosing lampreys collected from West Root Ri ver and Cannon Creek were either absent or did not have typical bands, hence they did not always provide reliable ages. The diversity of sta toliths appears to be related to ambient calcium ion concentrations, e specially during periods of rapid larval growth. The use of statoliths is sometimes the only method to age some populations of sea lampreys because of ambiguity in length-frequency distributions. The absence of statoliths, as encountered in this study, has potential management im plications when determining age-at-metamorphosis.