City seeks trout to ease caddisfly infestation

November 21, 2017 GMT

BULLHEAD CITY — Bullhead City Pest Abatement Manager Joe Iburg is working with state and federal agencies to add an additional 110,000 rainbow trout to the Colorado River below Davis Dam in 2018.

At Iburg’s request, City Council members will consider making the formal request to Arizona Game and Fish Department at tonight’s regular council meeting.

The formal council communication would ask AZGFD to allow an additional 30,000 catchable rainbow trout to be stocked into the Colorado River between April and May and another 80,000 sub-catchable trout to be stocked in August.

“We’re trying to get everything in order with the assessments and anything that needs to be done to get the additional 30,000 catchable fish and an additional 80,000 fish through AZGFD,” Iburg said.

The request for the additional 110,000 fish is above the already approved 35,000 trout being stocked by AZGFD with funds from Pest Abatement District and 45,000 trout being stocked by U.S. Fish and Wildlife Service.

USFWS is stocking 20,000 fish, about 1,700 fish per week (beginning last month) through the end of February, Iburg said. AZGFD is putting 20,000 fish in April and May, the same time the caddisfly emerges in its spring hatch.

“April and May is the time we want to boost the amount of fish,” Iburg said. “It would make 50,000 trout going into the river in just those two months.”

June and July are too hot for the trout so they are not stocked during those months, Iburg said. He wants to add 80,000 sub-catchable trout in August.

“We’re not asking for this every year,” Iburg said. “We’ll see what happens after one year, because we want to make sure we’re not endangering the native species and that we’re having a negative affect on the caddisfly numbers, because this will be far and above any amount of fish that have ever gone into the river.”

Neither AZGFD nor USFWS are involved in pest abatement, Iburg said. Both agencies are concerned with the endangered species, which is where they come into play regarding the caddisfly issue. AZGFD objectives are angler satisfaction and opportunity and sustaining the fish population.

For conservation purposes, USFWS annually stocks 10,000 razorback suckers and bonytail chub into the Lower Colorado River through the Lower Colorado River Multi-Species Conservation Program.

“Stocking after the new construction at Willow Beach Hatchery started January 12, 2017,” said Jeff Humphrey, USFWS spokesman. “Trout have been stocked for about nine months, including during this caddisfly emergence. It is too early to know for sure that more trout will help. We plan to assist AZGFD and Bullhead City Pest Abatement Manager (Iburg) with their current efforts to study this issue. Putting in too many fish could crash the fishery, causing death of fish, and an exacerbation of the caddisfly issue.”

“People need to understand, USFWS is not telling us yes or no on anything,” Iburg said. “They do want to inform all of us of the risk of what all these decisions mean to the endangered species. They aren’t saying no, it’s just we will have to work together to make sure there is no take (of the endangered species).”

The Biological Opinion (Endangered Species Act review and permitting) states that USFWS can stock up to 150,000 rainbow trout river-wide, with 50,000 of those being stocked below Davis Dam, Humphrey said. One hundred and fifty thousand trout was the maximum number of trout realistically considered to ever be available at that time.

“The service is stocking more and larger, catchable rainbow trout below Davis Dam than ever,” Humphrey said. “In the past decade the average annual total was 24,000. Currently Willow Beach hatchery is stocking over 40,000 catchable-sized trout per year below Davis Dam.”

Rainbow trout are pisciviorous — they eat other fish, including the endangered razorback suckers — so USFWS trout stocking is not conducted between January and April, when the endangered species spawn.

AZGFD stocks trout below Davis Dam at three sites — Davis Camp, Community Park and Rotary Park, Iburg said.

“In October and November, USFWS stocks two sites each week, alternating between Rotary and Community Parks, so it is always Davis Camp and Community Park one week and Davis Camp and Rotary Park the next,” Iburg said. “From December through February, USFWS only stocks at Davis Camp and Community Park in order to avoid stocking trout near the razorback sucker spawning beds near Rotary Park.”

Iburg said he had been working on a spring trout stocking even prior to the city-hosted caddisfly forum on Nov. 1.

“Our plan has been to try to put a large amount of fish in prior to one of these major caddisfly hatches,” Iburg said. “We were waiting to see the September and October 2017 numbers because between AZGFD and USFWS, 80,000 fish went in during fiscal year 2017 and it seemed to us that the 2017 spring hatch was very light. It wasn’t until August and September that we saw those numbers spike and we had conversations with AZGFD about trying more fish during those time periods.”