Relation of Sea Lamprey Size and Sex Ratio to Salmonid Availability in Three Great Lakes

Since 1980 the proportion of males appears to have increased to ∼50% in the sea lamprey (Petromyzon marinus) populations of Lakes Superior and Huron following a period (1970–1980) of stability. In Lake Ontario, there has been a shift from an approximately equal sex ratio (1970–1980) to a slight preponderance (∼60%) of males. Multiple regression analysis indicated that prey availability (reflected by salmonid stocking or commercial catch) was significantly related to the observed changes in length, weight, and proportion of males. We also found that, while sea lamprey length and weight may have stabilized in Lake Superior (1960 to present), sea lamprey have generally become larger in both Lakes Huron and Ontario. Again, prey availability was most closely related to weight of sea lamprey. Sex ratio and adult weight in Great Lakes sea lamprey appear to be related to prey availability and therefore may not be adequate indicators of the success of sea lamprey control.