Vulnerability, stability, and coherence of the fish community in Lake Superior

In the 1950s the Ontario fisheries of Lake Superior experienced a major perturbation due to invasion by sea lamprey Petromyzon marinus. This invasion and the consequent shifting of the fisheries to more intensive fishing on lower trophic level species resulted in higher vulnerability of the predatory fish species, ie likelihood of extinction increased. Spectrum analysis was applied to the yield series of 5 fish species from Lake Superior. Analysis of data before and after invasion by sea lamprey indicated major structural changes in the fishery: 1) except for lake trout Salvelinus namaycush either the dominant amplitude, the dominant frequency, or both decreased; 2) partial coherencies between pairs of yield series changed after the invasion; 3) lake whitefish Coregonus clupeaformis and lake trout replaced lake herring C. artedii as the species whose fuctuations in commercial yield were most highly synchronized with those of other species of commercial importance. -from Authors