Surveys show healthly bass in Imperial Division Backwaters
The Imperial Division of the Colorado River is a 38-mile stretch extending from Imperial Dam, upstream to Cibola Lake. Imperial Dam was completed in 1938 for the purpose of diverting water for irrigation. The upper 28 miles fall within the boundaries of the Cibola and Imperial National Wildlife Refuges. The lower 10 miles are mostly on land managed by the Bureau of Land Management. Part of the shore on the California side across the river from the Imperial National Wildlife Refuge is managed by the State of California as the Picacho State Recreation Area.
The Imperial Division of the Colorado River is different from the river upstream because it has not been highly channelized. This division includes numerous backwaters on both sides of the river channel. The total surface area of backwaters in this division is approximately 1,325 acres. Within the Imperial Division, backwaters greater than 20 acres comprise approximately 85 percent of the total backwater area. The banks of this division are lined with vegetation compared to upstream divisions that are mostly riprapped. Bankline vegetation mostly includes phragmites (Phragmites spp.), cattail (Typha spp.), and bulrush (Scirpus spp.).
The Arizona Game and Fish Department Region IV Fisheries Program conducted an annual electrofishing survey of the backwaters of the Imperial Division of the Colorado River on November 15 – 17. These annual surveys are performed to gather data on relative abundance, size, growth of fish, and to detect any large scale changes in the fish population. A total of 2,235 fish were sampled at 17 survey stations including 206 Largemouth Bass. Other species collected included Bluegill Sunfish, Redear Sunfish, Black Crappie, Warmouth Sunfish, Threadfin Shad, Gizzard Shad, Blue Tilapia, Common Carp, Striped Bass, Flathead Catfish, and Channel Catfish. All of the fish were collected, weighed, measured, and released unharmed.
The Largemouth Bass population in the Imperial Division backwaters appears to be stable and doing well! The largest bass sampled during the survey was 23.9 inches and 9.5 pounds. Over 20 percent of the Largemouth Bass captured during the survey were 15 inches or larger, so there should be plenty of large fish to catch! We also sampled a large number of young of year Largemouth Bass, which may point to a bright future for the bass population of the backwaters of the Imperial Division of the Colorado River.
