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By Scott Bryan, Senior Biologist

You’ve heard of herding sheep – how about herding fish?

Agua Fria Siphon Fish RemovalIn 2018, CAP tackled the task of inspecting two of our larger siphons – the immense pipes that channel CAP water underneath the Agua Fria and Salt River beds. To facilitate these inspections, the water needed to be completely drained prior to entry, which is an operational challenge given the CAP system moves water 365 days per year.

The method to dry out these siphons involves first placing stop logs at both ends of the siphon to prevent water from entering at either end. Once the logs are in place, as much water as possible is evacuated from the siphon and released into the river. All that remains in the siphon is a small amount of water in the bottom, which is not enough to sustain fish that are trapped. Many of these fish have been stocked by CAP to control aquatic vegetation and nuisance insects, so we were determined to save as many of these valuable fish as possible.

We were determined to save as many fish as possible. At both sites, stop logs were dropped early in the morning, when fish were not seeking the shaded, cooler water of the siphon. Water was removed through the evacuation structure and the use of large pumps. When the water level was down to about two feet, we were ready to salvage the fish. 

Agua Fria Siphon - three-man crews entered the siphon at about 7:30 p.m. and used a bag seine to “herd” the fish to one-end of the siphon. From there, fish were transferred to a custom fish basket with dip nets, then hoisted out through a man-hole. In the end, the fish removal process took less than three hours. We collected nearly 200 fish from the siphon, comprised mostly of catfish (70%), large common carp (25%), and some striped bass and bluegill (5%). Close to 150 catfish and carp were re-released into the canal. Many of the carp weighed between 20 and 40 pounds, while the biggest catfish was estimated to be about 8-10 lbs. 

Fish Remova at Agua Fria SiphonIt was unbearably hot and humid in the siphon, but the six-man fish removal crew rotated frequently to keep everyone fresh and there was plenty of support staff waiting outside with cool drinks and air-conditioned trucks. 

Salt River Siphon – I was assisted by a six-man crew from our contractor Achen Gardner to remove fish from two locations (Shallow Well and Deep Well) in the Salt River siphon. At Shallow Well, the crew entered at 8 a.m. and used dip nets to collect about 70 fish from the small area of remaining water (about 30 feet long and 1.5 feet deep). Common carp (45%), channel catfish (50%) and striped bass (5%) were collected in less than an hour, placed in the fish basket and hoisted to the surface. All of the catfish were placed in a fish hauling tank and released back into the canal downstream of the Salt-Gila Pumping Plant.

At Deep Well, the crew entered at noon and used a bag seine and dip nets to remove about 400 fish from the siphon. Some fish in this section of the siphon were huge! There were several grass carp that exceeded 36” in length and 40-60 lbs. The biggest striped bass were estimated to be nearly 30 lbs and two smallmouth bass were more than 5 lbs.  In addition to those three species, we found common carp (60%), channel catfish (30%), bluegill (1%), threadfin shad (1%) and a single Sonora sucker (stocked in 2017 as part of a native fish tracking study). Because we were able to lower the water level to less than 18”, the removal of the 400 fish took only two hours. 

For both siphon inspections, the upfront planning and the support of so many various work groups helped make this “herding of fish” a huge success!

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