Northern pike, a non-native predatory sport-fish, captured from the Colorado River near Grand Junction, 1987. This species is relatively rare in the upper Colorado River but has become common in the Yampa River where it has contributed to the decline of the native fish community. Photo by D. Osmundson
In the San Juan River, management efforts to control non-native fish numbers over the past ten years have focused on removing common carp and channel catfish with some success. As a result, populations of native fish have responded with increased survival, and for one species, the bluehead sucker, an expansion of range. In the Colorado River, introduced centrarchids (basses and sunfish) appear to pose the greatest threat to the native fish fauna. Smallmouth and largemouth bass, rare in the 1980s, are now common in the river near Grand Junction, Colorado. These popular sportfish are voracious predators on other fishes, particularly the native fishes, which lack spines or other means of protection. The CRFP and its partner, the Colorado Division of Parks and Wildlife, are working to determine the source of these fish and the best means to control their numbers. Because bass are popular with the sportfishing public, the Colorado Division of Parks and Wildlife works to develop warm-water angling opportunities in nearby off-channel ponds and lakes.
Non-native smallmouth bass captured from the Colorado River in Ruby Canyon, 2003. These invasive sportfish were extremely rare in the upper Colorado River prior to 2000 but have increased in number dramatically in recent years. They prey on native fishes and threaten endangered fish recovery efforts. Photo by B. Burdick
Largemouth bass, a predatory sportfish native to eastern U.S. has become established in the Colorado River near Grand Junction, threatening recovery efforts for the endangered fish. Photo by R. Krueger.
Low-head dams were constructed early in the 20th century to provide irrigation water for farms in Colorado’s Grand Valley. Although important to agriculture, these dams blocked upstream fish movement and eliminated many miles of habitat once suited to the endangered fish. Working with its partners, the CRFP helped restore fish passage on the lower Gunnison River near Grand Junction in 1996 with the completion of a fish ladder around the Redlands Diversion Dam. From 1996 to 2012, some 115,000 native fish have ascended the Redlands Fish Ladder including 122 endangered Colorado pikeminnow, 28 razorback sucker, eight bonytail, and one humpback chub. Fish passage was also provided on the Colorado River upstream of Palisade, Colorado with the completion of fish ladders at the Grand Valley Project Diversion Dam in 2005 and the Price-Stubb Diversion Dam in 2008. Through 2012, 58,000 native fish have passed the more upstream dam, including two razorback sucker, six humpback chub, and 22 bonytail.
The fish ladder installed in 1996 at the Redlands Diversion Dam near the mouth of the Gunnison River allows upstream passage of native fishes and aids in recovery of endangered Colorado pikeminnow and razorback sucker populations. USBR file photo.
Fish captured in the trap at the Grand Valley Project fish ladder. Fish are sorted by hand, counted by species and natives are released to the river upstream of the diversion. USFWS file photo.
Fish ladder at the site of the old Price-Stubb Dam. The dam was removed and concrete chevrons placed in a constructed side channel in 2008. The former 10-foot-high Price-Stubb Dam had blocked fish from moving upstream since its construction in 1911, and acted as the upstream terminus of the distributional range of the Colorado pikeminnow in the upper Colorado River. The dam was no longer used to divert water for irrigation, its function having been replaced by the more upstream Grand Valley Project Diversion Dam. With dam removal, fish now move freely both up and downstream in the main channel at most flow levels. However, when water levels get low, fish must use the adjacent fish ladder to ascend the river. Tagged fish migrating through the fish ladder are monitored with an on-site antennae. Photo by B. Burdick.
Fish ladder at the Grand Valley Project Diversion Dam on the Colorado River in DeBeque Canyon near Cameo, Colorado. The 14-foot-high Grand Valley Project Diversion Dam was built in 1916 and diverts water to the Government Highline Canal and the Orchard Mesa Power Canal. It blocks upstream fish movement at all flow levels. The fish ladder, built in 2005, has a trap at the upper end allowing biologists to monitor all fish that use the ladder to ascend the river. USBR file photo.
Canal diversions that entrapped thousands of native riverine fish each year since the turn of the century are now being retrofitted with state-of-the-art mechanical fish screens designed to safely return fish to the river. Until these are operated continuously throughout the irrigation season, the CRFP crews will manually remove native fish that are trapped when the canals drain in the fall. These fish are then trucked to the river and released.
Fish screen installed on the Redlands canal near Grand Junction. The screen is designed to return fish to the Gunnison River and reduce fish losses to the canal. USBR file photo.
Fish screen at the Redlands canal. Screens prevent fish from entering the canal and direct fish to a pipe that returns them to the river. Photo by B. Burdick.
CRFP personnel capture fish stranded in Grand Valley canals when the irrigation season ends. Captured fish are transported back to the river and released. Photo by C. McAda.
Prior to the building of dams and diversions on the Colorado River and its tributaries, spring snowmelt in the mountains resulted in the river topping its banks in many if not most years. Razorback sucker and Colorado pikeminnow used the flooded, off-channel habitats created during this time. For razorback sucker, these sites were critical as first-year nursery areas because of the warm and food-rich conditions there. Due to reduced flows and levees built by landowners, these seasonal floodplain habitats are reduced in area and infrequently available. Restoring some of these sites so that they flood more frequently is one of the key elements of the strategy to recover razorback sucker populations. The CRFP has worked to inventory floodplain areas along the Colorado and Gunnison rivers, and along with its partners, has entered into various agreements with landowners so that these sites can be managed to benefit the endangered fish.
The Colorado River near 29 Road in Grand Junction during high water of May 1986. Old gravel-pit ponds were reclaimed by the river during the flood years of 1983 & 1984, diversifying the channel and creating flooded bottomland habitat important to native fish. Photo by D. Osmundson.
This dike along the Gunnison River was notched at upstream and downstream ends of a large pond (left of photo) so water can flow into and out of the pond during spring when river waters rise from spring runoff. Larval razorback sucker drifting in the river current can now enter the pond where it is hoped that warm, low-velocity conditions will mimic those of historic flooded bottomlands. Annually flooded areas once provided critical nursery habitat for young razorback suckers before upstream dams were constructed that reduced spring flows. Photo by P. S. Gelatt.
Old Jarvis property near the confluence of the Gunnison and Colorado rivers near downtown Grand Junction. The City of Grand Junction worked with the USFWS to convert this property from an auto salvage yard to a marsh that floods during high river flows. USFWS file photo.