Lamprey captured in weir
Invasive non-native species, including both plant and animal species, are major threats to lakeshore resources. Invasive aquatic species such as the sea lamprey (Petromyzon marinus), zebra mussel (Dreissena polymorpha), river ruffe (Gymnocephalus cernuus), and spiny water flea (bythetrepes cederstroemi) have been found in Lake Superior, most likely transported via ballast water or migration through manmade waterways.
The parasitic sea lamprey reached Lake Superior by the 1940's and quickly devastated the commercial fishery (Smith et al., 1974). The U.S. Fish and Wildlife Service has conducted research and control efforts for over 20 years as part of a joint U.S./Canada effort, including annual assessments and treatments of Pictured Rocks National lakeshore streams and lakes.
The zebra mussel and ruffe are more recent invaders whose full ecological impacts are not yet known. At this time neither species has been found within the lakeshore, but could possibly find suitable habitat in Pictured Rocks National Lakeshore waters. The spiny water flea has been found in Beaver Lake.
Other invasive species -- most notably the gypsy moth (Lymantria dispar) and spotted knapweed (Centaurea maculosa) -- are relatively recent terrestrial invaders. The gypsy moth has defoliated vast amounts eastern hardwood forest, up to 12 million acres in a single year (McManus et al., 1989). The NPS at Pictured Rocks cooperates with the U.S. Forest Service State and Private Forestry program in monitoring gypsy moths via traps with pheromone baits. Moths have been trapped in the lakeshore since 1990, but not in large numbers. The Lakeshore is currently located at the western front of the moth invasion moving through the Upper Peninsula. The State of Michigan supplements the USFS monitoring effort with a more intensive trapping program called "Slow the Spread".
Spotted knapweed quickly overtakes dry and open or disturbed plant habitats, reducing species diversity. It is a serious threat to lakeshore resources, particularly dunes systems. Sand Point, the Miners Beach area, and the Grand Sable Dunes all have significant populations. Initial control efforts have begun at Sand Point, where the population is small enough to control via mechanical means (hand pulling) and there is no easy access for seed recolonization. More aggressive control efforts would require sustained chemical treatment and substantial investigation of treatments on native plant communities, as well as follow-up monitoring. Such efforts are beyond lakeshore budget and staff means at this time. The invasion of dunes plant communities, many of which contain threatened, endangered and rare species, is of particular interest and concern.
One purple loosestrife (Lythrum salicaria) plant was found within the Lakeshore along the Mosquito River Trail in the early 1990's and was quickly removed. Plants were found and removed in the same area in later years. One plant was found at the Little Beaver boat ramp in 1996 and removed. This species has tremendous potential to overtake wetland habitats, replacing native species, but has yet to invade PRNL. The abundance of wetlands in the lakeshore subject to invasion make monitoring for this species particularly important.