The Eurasian ruffe, a fish species inadvertently introduced into North America' s Great Lakes in recent years, feeds on the eggs of lake whitefish, a native species, thus threatening the lakes' natural ecosystem  To help track the ruffe' s spread, government agencies have produced wallet-sized cards about the ruffe
The cards contain pictures of the ruffe and explain the danger they pose; the cards also request anglers to report any ruffe they catch
Ruffe generally feed at night, but most recreational fishing on the Great Lakes is done during daytime hours.