Valley Creek’s Crayfish Corps: volunteers keeping an invasive crayfish in check

In Valley Creek, volunteers wade in with nets to catch an invader. Valley Forge National Historical Park's Crayfish Corps, led by Natural Resource staff, tries to hold the invasive rusty crayfish (Faxonius rusticus) to no more than 20 percent of the crayfish in the creek. The park's 2021 resource brief reports where that effort stands.

The problem

Valley Creek is an Exceptional Value Waterway and a Class A wild trout fishery. Rusty crayfish were first documented there in 2008, and staff set up the volunteer Crayfish Corps in response. The species is native to parts of Ohio, Indiana and Kentucky. It is larger and more aggressive than the park's native crayfish, so it can out-compete them for food and shelter. It may also harm the trout fishery by eating trout eggs and most of the prey the fish depend on. Wherever rusty crayfish have been introduced and left unmanaged, all other crayfish have been greatly reduced or eliminated.

A rusty crayfish. NPS Photo.

The goal

The program has two objectives: suppress rusty crayfish while keeping a ratio of native to rusty crayfish of 4 to 1 (80 percent native, 20 percent rusty), and offer a meaningful volunteer opportunity. Complete eradication is not feasible. The target applies to Valley Creek upstream of the dam along Route 252. The creek is divided into four sections, defined by dams and bridges as well as changing stream conditions.

Sections of Valley Creek. NPS Image.

Who does the work

From May through September, volunteers from AmeriCorps, scout troops, families, schools, community organizations, corporate groups and individuals help park staff catch and remove rusty crayfish. Native crayfish that are caught are documented and returned. The brief's running totals are 27,505 rusty crayfish removed and 72,065 native crayfish documented and returned.

In most years the majority of volunteers and volunteer hours were young people under 18.

Chart of native and rusty crayfish captured by Crayfish Corps per year. NPS Graphic.

What the numbers show

Because group size, time in the water and stream conditions vary, the park standardizes its data as crayfish caught per person-hour. That lets biologists judge which sections need the most work and whether the goal is being met. Rusty crayfish catch totals and catches per person-hour were higher in 2021 than in the two preceding years, but the trend since 2009 is downward.

Percent rusty crayfish captured per creek section over the four most recent years, with the 20 percent goal marked. NPS Graphic.

The share of rusty crayfish is consistently higher in Section 1 than in Sections 2 through 4. The brief suggests the dam between Sections 1 and 2 probably slows upstream movement from the Schuylkill River. Apart from Section 1, below the dam, rusty crayfish have been kept at or near the 20 percent threshold or below in recent years. In 2021 the share rose slightly above 20 percent in Section 2, so the park planned to focus on that section in 2022.

Average number of crayfish captured per person-hour per year, with the trend for rusty crayfish. NPS Graphic.

The brief reads the falling catch per person-hour, together with rusty crayfish staying under 20 percent above the dam, as evidence that the program works, and credits that success to the volunteers. People who want to join can contact the park's Natural Resource Management staff.

Sources

• National Park Service, Valley Forge National Historical Park, Crayfish Corps Resource Brief 2021, prepared by a 2021-22 Natural Resource Management intern; rewritten in hubnx's own words.