Wildlife officials in Colorado are calling it the latest threat to Colorado’s wildlife. They have found rusty crayfish in the West Fork Little Thompson River in Larimer County. That’s the remarkable story of this invasive species, which hails from the Ohio River basin. It is a serious threat to community ecosystems and has become one of the state’s biggest worries over invasive aquatic species. The rust-colored crustaceans, first spotted on April 7, were reported by a user using iNaturalist, a widely used species identification app.
This latest discovery is the first documented presence of rusty crayfish in the agency’s northeastern state region. In addition, this serves as the second record of occurrence of this invasive species discovered east of the Continental Divide in Colorado. The Colorado Parks and Wildlife (CPW) agency, which is generally skeptical of invasive species detections, has thus far confirmed rusty crayfish at five different waterways across the state since 2009. Most recently, they discovered these crayfish at Lake Granby in August 2023.
Characteristics and Impact of Rusty Crayfish
Rusties are much larger and more aggressive than Colorado’s native crayfish species. Males are able to grow up to 5 inches in length, giving them size to aid in competition for resources. That aggressiveness allows them to outcompete native, more timid crayfish for food, a double blow to local aquatic ecosystems.
“Rusty crayfish are much more aggressive than our native crayfish species and are not an ideal food source for our sportfish,” said a spokesperson from Colorado Parks and Wildlife.
Rusty crayfish affect other crayfish and the aquatic ecosystem at large. They eat lots of aquatic vegetation, including the type that are home to native fish spawning and habitat. Invasive crayfish are spreading like wildfire. They compete with native plants to the detriment of fragile local ecosystems that rely on native species for ecosystem health and stability.
Ongoing Monitoring and Research
As a result of this alarming find, Colorado wildlife crews are racing to do more surveys on the Little Thompson River and surrounding waters. Their mission is to determine the abundance and distribution of the rusty crayfish population along Lake Annie’s shoreline. These surveys will help assess what the potential impacts to local wildlife are, and better guide management decisions in the future.
Further diving CPW’s main effort is in assessing if rusty crayfish might alter the behavior or success of other native species in the river ecosystem. This proactive approach is a powerful tool in combatting the harmful effects of invasive species. It gets them before they have a chance to establish a more powerful base.
Historical Context of Invasive Species in Colorado
Since their introduction into different water bodies around the United States, rusty crayfish have presented problems to native wildlife. In Colorado, wildlife managers are taking the initiative to confront the expanding threat of invasive species. They are particularly alarmed by the usurping rusty crayfish.
Rusty crayfish have since been verified at Stillwater, and several other locations. Their presence is alarming and indicative of a pervasive threat to Colorado’s waterways and biodiversity as a whole. The CPW urges that constant vigilance and education is key in the fight against invasive dangers such as this one.
