Ecological Impacts of Lampricide Treatments on Sea Lamprey (Petromyzon marinus) Ammocoetes and Metamorphosed Individuals

Sea lamprey (Petromyzon marinus) ammocoetes are found in fewer locations now than before lampricide treatments began. Posttreatment reinfestation does not always occur in those tributaries previously infested. Abundance of ammocoetes and transformed individuals has declined in most watersheds with a few exceptions where density-dependent factors may have been influential. Increased growth was related to reduced density. Sex compositions of larval and metamorphosing populations were highly variable during initial lampricide treatments. Females predominated in some streams, males in others. Streams once dominated by males now favor females in residual and reestablished populations of larvae. The shift to femaleness in the larval populations has precipitated a similar shift in adult sea lamprey populations of the upper Great Lakes.Key words: sea lamprey, ammocoetes, transformed, distribution, abundance, growth, sex composition