LABORATORY STUDY OF THE EFFECTS OF SPRING WARMING AND LARVAL DENSITY ON THE METAMORPHOSIS OF SEA LAMPREYS

We tested the hypotheses that the incidence of metamorphosis in sea la mpreys Petromyzon marinus is related to the magnitude of the spring ri se in temperature and that high larval density prior to metamorphosis reduces the number of animals entering metamorphosis. Concurrently, we also tested the accuracy of predicting metamorphosis based on minimum size criteria of 120 mm and 3.0 g and condition factor (CF) of 1.45 f or larval data collected in the fall, where CF = 10(6) (mass, g)/(tota l length, mm)(3). The spring rise in temperature was a critical step i n stimulating metamorphosis, but neither the magnitude of warming in t he spring nor larval density significantly affected the proportion of metamorphosing animals. By using a CF of 1.45 or greater as the criter ion for larval data collected in fall, we predicted 92% of the metamor phosis that occurred the following summer. Predictions of sea lamprey metamorphosis based on fall data were as accurate as predictions made in previous studies that examined spring data and used minimum size cr iteria of 120 mm and 3.0 g and a CF of 1.50 or greater. The equal succ ess of using a CF of 1.45 or greater with fall data and a CF of 1.50 o r greater with spring data might have reflected that some lipid accumu lation occurs between the fall and the onset of metamorphosis the foll owing July.