The effects of experimental bait collection and trampling on a<Emphasis Type="Italic"> Mytilus californianus</Emphasis> mussel bed in southern California

Rocky shores in southern California are heavily visited by humans. At sites used by recreational fishers, the effects of foot traffic combined with the collection of mussels for bait may reduce mussel cover and create mussel-free gaps. To test this hypothesis, the effects of trampling and bait-removal on mussel populations were experimentally examined. Plots in a mussel bed were subjected to monthly combinations of trampling (0, 150, or 300 steps) and simulated bait-removal (0 or 2 removed mussels). Although the experiment was done during a period of high natural disturbance associated with the 1997–1998 ENSO, plots receiving treatments experienced significantly greater reductions in mussel cover, mass, and density than controls. These results indicate that visitor foot traffic and bait-removal by fishers can significantly reduce mussel cover, density, biomass, and sizes.Communicated by P.W. Sammarco, Chauvin