To bring back the salmon population, the DOW is starting a project to remove some lake trout from the reservoir. The goal is to assure sustainability of the kokanee population, and to continue to provide trophy lake trout fishing.

The 2010 update (pdf) contains the most recent information on the Lake Trout removal operation.

The latest fishery survey summary for Blue Mesa Reservoir explains stocking, management strategies and fish survey data.

For frequently asked questions regarding Blue Mesa Reservoir, see FAQs (pdf).

Following is information that explains the project and the unique circumstances of Blue Mesa Reservoir.

At an elevation of 7,520 feet, the water warms up enough to produce large quantities of plankton, which in turn, provide the primary food source for kokanee and rainbow trout. The connection of the reservoir to the Gunnison River also provides a unique environment for kokanee to spawn up river at the Roaring Judy Hatchery, where the DOW can then collect millions of salmon eggs every fall. Blue Mesa is the primary source for kokanee eggs used for producing salmon for more than 20 reservoirs throughout Colorado.

The reservoir also provides ideal conditions for lake trout. It is deep --330 feet at the deepest-- so there is plenty of room for the lake trout to descend to cold water during the summer; and shallow areas provide fall spawning beds. Natural reproduction is increasing steadily. Lake trout are predators, and live primarily by eating kokanee salmon at Blue Mesa.

A critical factor in understanding the Blue Mesa fishery is that the reservoir is a human-made impoundment. The biology of a reservoir is far different than a natural lake and managing a fishery in this type of environment is challenging. The fish are not native to the environment and the species did not evolve together, so the predator-prey relationship is not natural. In Colorado reservoirs some fish can reproduce naturally, others must be stocked and some species (specifically perch at Blue Mesa) have been introduced illegally.

Balancing the fishery at Blue Mesa Reservoir for the benefit of resident and non-resident anglers is the goal of the Colorado Division of Wildlife. The reservoir is managed first and foremost for kokanee salmon. Blue Mesa is also managed for rainbow and brown trout, and lake trout.

To read about scientific research on the kokanee/lake trout issue, see http://welcome.warnercnr.colostate.edu/~brett/lab/coldwater/trophic.html. This paper, produced by the Fisheries Ecology Lab at Colorado State University provides a detailed explanation of cold water reservoir fisheries in Colorado.

Numerous Western States Face the Same Issue

Kokanee Salmon

The location of the reservoir also allowed the DOW to build a highly-efficient and cost-effective kokanee rearing facility at the Roaring Judy hatchery. Eggs hatch in the facility in December, and the young are raised to a length of 2 inches in the hatchery building. In April, they are released directly into a one-half mile long canal which flows into the East River/Gunnison River system. The fingerlings move down the river 21 miles until they arrive at Blue Mesa Reservoir.

After three to four years of living in the reservoir, the fish respond to their natural instincts and make their way back up river seeking the place where they were born. They swim into the fish raceways just below the hatchery where their spawn is collected. Every year the DOW is able to develop a new year-class of fish. 
 
Rainbow trout
Rainbow trout are the most popular game fish in Colorado. For many years, the U.S. Fish and Wildlife Service has stocked 850,000 5-inch rainbows in Blue Mesa. The trout are raised at the federal hatchery in Hotchkiss. These small fish, however, are vulnerable to predation by lake trout. Starting in 2010, the service will stock 10-inch rainbows which are, generally, large enough to avoid predation by small- to medium-sized lake trout. Rainbow trout reproduce naturally in several Blue Mesa tributaries but not in large enough numbers needed to sustain a sport fishery in the reservoir.

Brown trout
Brown trout reproduce naturally in the Gunnison River, the Lake Fork of the Gunnison River and Cebolla Creek. The fish then move into the reservoir as they get older. In 2008, anglers caught about 12,000 brown trout that average 14 inches in length. Brown trout prefer water near the banks of the reservoir and water depths no greater than 65 feet. They are predators and do eat small kokanee; but their predation effect is insignificant compared with lake trout.  

Lake trout
Lake trout - also known as Mackinaw - are natives of northern North America. This predator species is the largest trout in North America and can routinely grow to 25 pounds or more if they have a reliable source of other fish to eat. The largest lake trout taken at Blue Mesa weighed 50 pounds and was caught in 2007. They were first introduced in Blue Mesa in 1968. Biologists knew that the presence of kokanee and rainbows would provide a prey base for the lake trout. Subsequent stocking occurred in the early 1970s, 1980s and 1990s. Lake trout spend most time in open water, the same area favored by kokanee.

At the time the lake trout were introduced it was believed that they would not naturally reproduce in the reservoir. In the early1990s, water management at Blue Mesa was changed which reduced water level fluctuation in the fall and appear to have made conditions more favorable for lake trout reproduction. Since then the species has reproduced naturally, the population has grown significantly and lake trout have become the major predator fish in the reservoir.

Surveying Fish Populations at Blue Mesa

Methods include: sonar technology to count open water fish; angler surveys -- also known as creel surveys -- to estimate catch, harvest and fishing pressure; live fish surveys using electro-fishing or net sampling to study body condition, growth, diet and abundance; and by tracking how many fish are stocked in a body of water each year.

These methods have revealed that the kokanee population has dropped significantly during the last 10 years. In 1994, the DOW estimated the Blue Mesa kokanee population at about 1 million. Now, the population is estimated to be only about 110,000 -- despite the stocking of more fish whenever possible.

While the catch of kokanee has dropped substantially, angler surveys show that the catch of lake trout has increased significantly -- an indication that the population is growing fast. In the late 1990s, creel surveys showed that anglers caught about 1,700 lake trout per year. In 2008, anglers caught 8,600 lake trout and released more than half of them back into the reservoir.

Creel surveys also show that lake trout predation is taking a large toll on rainbows. In the late 1990s, anglers caught about 70,000 rainbows each year. In 2008, anglers caught only about 10,000 rainbows.

The fishery can be restored to a balance at Blue Mesa Reservoir through sound management practices. Anglers can also assist by keeping the small- to medium-sized lake trout that they catch.

At Blue Mesa Reservoir, lake trout are consuming significant numbers of kokanee and the predator-prey relationship is dangerously out of balance. Lake trout are also adversely impacting the stocked supply of rainbow trout.

To restore a balance in the reservoir between kokanee and lake trout, the DOW is removing lake trout that are 30 inches or less. Fish of that size are being targeted because they make up the bulk of the lake trout population and, consequently, eat the most kokanee.

The removal project will continue indefinitely each spring and fall until DOW aquatic biologists determine that predation on kokanee salmon is declining. That decision will be aided by spring survey research that will be done by the DOW and by researchers from Colorado State University.

By removing fish, the predation on kokanee will decline and trophy-sized lake trout will face less competition for the primary food source. During netting surveys in the past few years, DOW aquatic biologists have found that the plumpness of lake trout is diminishing. Instead of displaying a round shape with substantial girth, lake trout are thin. That is an indication that prey abundance is decreasing.

Anglers targeting trophy lake trout are primarily searching for fish weighing 25 pounds or more. Fish of that size can only be sustained by assuring that adequate numbers of kokanee exist. At lakes and reservoirs throughout the West, no other prey species has been able to replace kokanee as the forage fish for sustaining trophy lake trout.

In the removal operation, small mesh gill nets will be used to collect lake trout. Fish larger than 30 inches will not be as easily entangled in the nets, so most times they will be released safely.

The DOW will also: consider changes to the bag and possession limits for kokanee and lake trout; encourage lake trout anglers to keep the fish that they catch; and develop more law enforcement patrols to enforce the kokanee bag limits.

In 2004, a study estimated that fishing at Blue Mesa generated an economic impact of about $8 million per year. Of that amount, 80 percent of the spending -- about $6.4 million -- came from kokanee anglers. Kokanee fishing is popular and people from throughout Colorado and the United States travel to Blue Mesa to fish for these small salmon.

According to surveys with anglers from 1997-2007, an average of 60 percent of anglers stated that they were satisfied with the number of fish that they caught at Blue Mesa. However, their perception changed radically in 2008: only 18 percent of anglers interviewed said they were satisfied. Their dissatisfaction is attributed primarily to the decline in the number of kokanee salmon and rainbow trout they caught.

Beyond the immediate impacts in Gunnison County, kokanee production at the reservoir is critical to sport fishing throughout Colorado. Blue Mesa provides an average of 60 percent of the eggs needed to stock fingerlings in 26 other lakes and reservoirs in the state. The overall annual economic impact of kokanee salmon fishing in Colorado is estimated to be at least $29 million.