Changes in sea lamprey size and fecundity through time in the Great Lakes

Sea lamprey (Petromyzon marinus) are an aquatic nuisance species that cause great harm to fishes in the Great Lakes. Control of sea lamprey is vital to protecting the Great Lakes fishery, and designing an effective control program depends on accurate knowledge of their demographics. This study compared historical and current data on female sea lamprey length, weight, fecundity, gonadosomatic index (GSI) and egg weight in the Great Lakes. Female sea lamprey captured in 2011 were compared with studies conducted in 1960 and 1981 on Lake Superior and in 1981 and 1999 on Lake Ontario, as well as available data from Lakes Huron, Michigan and Erie. In Lake Superior, mean length and weight of female sea lamprey increased by approximately 13% and 45%, respectively, while mean fecundity increased 17% and individual egg weights increased 43%. There was no difference in mean sea lamprey GSI in Lake Superior. In Lake Ontario, female sea lamprey length increased by 7%, but there were no differences in the other metrics. Across the Great Lakes, there was a general increase in fecundity from the period before the 1980s to more recent years. An increased population of larger parasitic sea lamprey will have higher feeding rates and thus a higher impact on commercially and ecologically important fishes. Managers may need to reconsider control targets and lampricide treatment frequency for lakes where sea lamprey growth and fecundity have increased.