Changes in the Distribution of Native Lampreys in Lake Superior Tributaries in Response to Sea Lamprey (Petromyzon marinus) Control, 1953–77

Abstract

Populations of three species of lampreys, American brook lamprey (Lampetra lamottei), northern brook lamprey (Ichthyomyzon fossor), and silver lamprey (I. unicuspis), endemic to the Lake Superior drainage basin have declined since chemical control of the sea lamprey (Petromyzon marinus) was begun; 64% (103 of 162) of the streams inhabited by endemic species have required treatment. The parasitic silver lamprey was most adversely affected by lampricide applications. Though 4278 were captured at 35 of 55 Lake Superior barriers in 1959, a total of 91 were reported in only nine tributaries and the St. Marys River from 1973 to 1977. American brook lampreys were least affected by chemical control and have disappeared from 6 of 42 treated streams which they inhabited. Ichthyomyzon larvae are no longer found in 41 of 81 treated streams they once inhabited, though few larvae were found in many of these streams. Several factors affected the vulnerability of native lampreys to chemicals. Nonparasitic lampreys, especially American brook lampreys, inhabited headwater areas which were often not invaded by sea lampreys, but silver lampreys spawned in lower reaches and their entire stream distribution was exposed to the effects of the lampricide. Differences in fecundity of lampreys also affected their recovery after chemical treatments.Key words: Ichthyomyzon fossor, ichthyomyzon unicuspis, Lampetra lamottei, streams, distribution, habitat, temperature, fecundity, survival, TFM