The U.S. Fish and Wildlife Service recently directed Costa Mesa to remove two unpermitted trails in Fairview Park that have damaged sensitive habitat and affected the San Diego fairy shrimp, an endangered species. One of the trails, pictured here, runs along the fence between the park and Estancia High School's Jim Scott Stadium. The entire area is also roped off to prevent further damage or intrusion upon the sensitive habitat and fairy shrimp. (DON LEACH, Daily Pilot / November 26, 2013)

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The U.S. Fish and Wildlife Service has directed the city of Costa Mesa to remove two man-made trails threatening a tiny endangered species that breeds in the seasonal ponds at Fairview Park.

Both trails, located along the 208-acre park's southeastern edge next to Parsons Field and Estancia High School, were topped in the summer with decomposed granite, which the federal agency fears will harm the San Diego fairy shrimp this winter.

The work was done without the city's permission, possibly by volunteers unaware of the area's biological significance. No one has taken responsibility for the work.

According to a city-issued environmental study from September, the two trails meet upon and have damaged a small corner of one of the park's vernal pools, a once-common but now rare temporary wetland that hosts the fairy shrimp and other species.

The FWS issued its "emergency" directive in a letter dated Nov. 14. The Daily Pilot obtained a copy of the letter Tuesday.

FWS Field Supervisor Jim Bartel wrote that the decomposed granite, or chemicals on it, could wash into the two nearby vernal pools, preventing the fairy shrimp from hatching.

It could also limit their productivity, he wrote.

"[FWS] considers the removal activity to be an emergency action necessitated by the unauthorized construction and is intended to prevent [a] take of the listed species anticipated to occur during the upcoming storm season," Bartel wrote.

The city is choosing a firm to do the removal work, which must be done by hand, said Public Services Director Ernesto Munoz.

The cost of the project has not been determined.

"Once we select a firm, we will submit that firm to the U.S. Fish and Wildlife Service for their approval," Munoz said. "Once they approve that firm, then they'll get to work."

In September, the city's environmental study gave some mitigation recommendations, including restoring only the damaged portion of the vernal pool or relocating the entire pool.

Bartel gave some specific instructions for how the removal should be done. Under the supervision of a FWS-approved "biological monitor," the decomposed granite must be carefully scraped from the surface "to prevent impacts to the clay soil crust within the pool basins and to prevent any changes in topography that may alter the vernal pool hydrology."

Within 30 days of the project's completion, the city must also give FWS a report that includes photos.

In the interim, the city has also improved a temporary boundary that goes around the trails and nearby habitat. Steel posts and nylon ropes have replaced the wood stakes and tape placed by city staff in September.

One of the trails, about 400 feet long and running east-west along the Parsons fence, was built and topped with decomposed granite sometime in June without city permission.

The second trail runs north-south — though it was built years ago with permission — and is about 120 feet long. It was also topped and widened, possibly at the same time as the longer trail.

The shorter trail has wooden logs running alongside it. FWS has directed that the logs be removed.

Before being roped off, both trails were commonly used by children going to the nearby schools and athletic fields.

In 2007, the city received federal authority to protect the fairy shrimp, a majority of which are located in a roughly 3-acre vernal pool elsewhere in the park, away from the unapproved trails. That pool is bordered by steel posts and cables to deter access and disturbance.

Who did the trail work has remained a mystery since first being reported in a Pilot investigation in August. The trails and their potential effects on the fairy shrimp garnered FWS' attention soon after.

Some local activists have offered a $500 reward for information leading to their identity.