THERMAL NICHE OF LARVAL SEA LAMPREY, PETROMYZON-MARINUS

We used behavioral and physiological responses of larval sea lamprey, Petromyzon marinus, to temperature to describe the thermal niche and define optimal thermal habitat. Acclimation temperature had a weak direct positive effect on acute preferred temperatures in summer but no effect on acute preferred temperatures in winter tests. Swimming speed, mass, and acclimation temperature accounted for 66% of the variation in the active metabolic rate of larval sea lamprey. When larvae are swimming at their maximum prolonged rate, the relationship between temperature and metabolic rate is a unimodal curve, as has been found for more active fish species. The final preferred temperature in summer, 20.8-degrees-C, is similar to the temperature at which maximum scope for activity occurs, approximately 19-degrees-C. We propose the ''fundamental thermal niche' of larval sea lamprey to be the range of temperatures between 17.8 and 21.8-degrees-C. Some practical applications for the thermal niche are sketched with respect to the integrated management of sea lamprey in the Great Lakes.