The Pacific Northwest is known for its aquatic life and biodiversity. Unfortunately, invasive crayfish are threatening that biodiversity in the rich freshwater biomes. Crayfish can have a huge impact on the environment. Non-native species can alter the very structure of wetland regions by reducing vegetation, altering the integrity of the bank and causing changes in turbidity. They also compete with native species and cause changes in fish populations. In some parts of the Pacific Northwest the invasion of crayfish is already advanced. The ecological problems may also result in economic ramifications in these areas.
Several species of problematic crayfish have been introduced and adapted quickly. There four main species that have been identified as present, which have also previously caused issues in other parts of the world. Red Swamp Crayfish (Procambarus clarkii) are massively invasive and native to the eastern United States. The other three species, also native to the eastern United States, consist of several members of the Orconectes genus: the Northern Crayfish (Orconectes virilis), Ringed Crayfish (Orconectes neglectus), and Rusty Crayfish (Orconectes rusticus). The US Forest Service lists them all as "Primary Species of Concern." Western Oregon and Washington are being the most impacted. There are three native crayfish species, Signal crayfish (Pacifastacus leniusculus), Snake River Pilos Crayfish (Pacifastacus connectens),and Pilos Crayfish (Pacifastacus gambelii). The two latter crayfish are farther inland.
The Red Swamp Crayfish is commonly used as bait for largemouth bass, which may be how it was introduced to the Pacific Northwest. They are considered to be one of the most invasive species on the planet. They are known to move onto land in search of food if their normal aquatic plant food sources become low. They were intentionally introduced to some regions of Africa in an attempt to control snail populations that were causing a disease known as river blindness. They were successful in that aspect, but had numerous negative consequences that were unforeseen. They ended up feeding on fish eggs and thus damaging native fish populations.
Northern Crayfish are also used as bait and sometimes seen as pets. They are highly competitive with native crayfish species when introduced. They have been documented as causing changes to the structure and composition of littoral zones and increased turbidity. The Ringed Crayfish causes similar ecological changes and is considered a generalist species. They have a wide distribution and are continuing to expand. They are the most abundant species in their native habitats of Arkansas and Oklahoma, and there are no known threats to them. The Rusty Crayfish is again similar with its ecological impacts, but they are additionally aggressive and large. They are known for preying extensively on bivalves, including species that are already endangered.