In the forum posts many anglers posed similar questions about Miramonte and what Colorado Parks and Wildlife is planning to do. Following is a compilation of those questions -- with answers. This is a longer post than usual. Agency staff know this is controversial. I hope you'll take the time to read this and understand that the decisions about Miramonte were not made lightly.
Why do all the fish in the reservoir have to be poisoned? Isn't there another method to remove the smallmouth bass?
Miramonte has always been managed as a trout fishery and that will continue. Bass are not suited to a high-elevation reservoir that maintains cold water temperatures.
Chemical treatment with Rotenone is the best method to assure complete removal of SMB. Mechanical removal of bass using electro-fishing gear or gillnets is labor intensive, expensive and would never be effective in completely removing all the SMB.
Lots of people say that Rotenone is not really effective for killing off fish.
Rotenone is an EPA registered and approved piscicide that has been used for years throughout North America and Colorado with great success. There have been instances when a second application of Rotenone was required to completely remove the target pest. Those, however, are usually situations where complex tributary or spring habitat prevents the effective application of Rotenone to all occupied fish habitat. Lake treatments are generally very effective and there have been many lake reclamation projects in Colorado where complete removal was achieved with one or two treatments. To help with the efficacy of the application the reservoir will be drawn down substantially.
The press release said that 44 percent of the fish in the lake are now small mouth bass. That just seems way too high. Please, explain.
Yes, that number also surprised the biologists and led to this action. Bass are prolific spawners and can quickly invade suitable habitat. Biologists conduct surveys on lakes and reservoirs to examine fish population trends. Boat electro-fishing is utilized to survey Miramonte Reservoir. The same locations are sampled each year to ensure that data is reliable and unbiased. This method is a proven technique for estimating fish abundance trends and has been used for decades by biologists throughout North America.
In 2010, biologists found that 5 percent of the fish netted during the surveys were SMB. In 2011 (and likely 2010 as well) almost all of the bass in the reservoir were juveniles with just a few mature fish. Many of those have matured and spawned during the last two years. SMB spawning has been very successful and many juvenile bass were present in the 2012 sample.
Female SMB can produce in the range of 8,000 eggs each, depending on the size of the fish. So it doesn’t take many years of successful spawning to produce almost exponential population growth. As an example, let's say there were 100 bass in the lake in 2011 and 25 percent were mature females that produced an average of 4,000 fry with a 50 percent survival rate the first year. That would lead to an increase of over 50,000 bass in only one season.
In June 2012 the number of SMB totaled 44 percent of all the fish netted. Numerous young of year SMB were observed but not netted in the shallow margins of the reservoir, so the number could actually be higher. Biologists have found at least three year classes of SMB at Miramonte.
The latest sampling survey showed that rainbow trout make up 32 percent of the fishery, and brown trout account for 24 percent.
Other reservoirs in Colorado hold trout and bass. Why can't Miramonte be the same?
Miramonte was built specifically for fishing recreation. As a high altitude reservoir (7,800 feet) with a very clean inflow of cold water, it is ideally suited for trout. The reservoir has an outstanding prey base that includes aquatic invertebrates, crayfish, minnows and trout. That forage helps the 60,000 fingerling trout stocked each year to grow fast and reach quality size in less than three years.
Because the water is cold, the growing season is much shorter than productive bass reservoirs in the state. There simply are not enough temperature-degree days in Miramonte needed to produce good bass growth on the available forage.
SMB are highly-effective predators that consume crayfish, minnows and young trout. That robs trout of forage. If SMB stay in the lake, trout will be marginalized; and because of the cold water and a declining prey base, bass will become stunted. Miramonte would quickly lose its status as a high-quality fishery. SMB will also lead to a decline of crayfish at Miramonte.
Because of its location, there is also a risk that SMB will escape the reservoir and reach the San Miguel River and the Dolores River where they pose a threat to three native fish – the roundtail chub, the bluehead sucker and the flannelmouth sucker. Because of native and endangered fish concerns, reservoir fisheries on the Western Slope must be managed differently than East Slope reservoirs.
Ridgway Reservoir and McPhee Reservoir hold SMB, why not treat those reservoirs?
Those reservoirs are much too large to treat. They could only be treated if they were drawn down to a small pool.
There are SMB in the Dolores River that entered the river when the dam at McPhee Reservoir spilled several years ago. That is a concern and biologists monitor the river and are formulating plans for removal of the fish from that waterway.
SMB have not been found during surveys conducted below Ridgway Reservoir in the Uncompahgre River. There is concern, however, that if SMB escaped they could reach the Gunnison River which provides critical habitat for native fish species.
Naturita Creek, which exits Miramonte, is close to the San Miguel and the Dolores rivers, so SMB could survive the short trip downstream.
Brown trout and rainbow trout are not native species to Colorado, why stock them?
That's correct, they are not native. But brown and rainbow trout are adapted to this environment so they are used in Colorado’s coldwater reservoirs to provide sportfish recreation. The habitat in Miramonte is manmade and provides the ideal environment for coldwater sportfish like rainbow and brown trout. Less altered aquatic habitat that is suitable for native species like cutthroat trout or roundtail chubs is managed for those species.
But brown trout eat native fish in the Dolores River.
Browns do live in the Dolores River in the cold water reaches below the McPhee Reservoir dam for about 12 miles, after which they rapidly decline in abundance. Browns will eat native fish, but few are present in the area where native fish are abundant, they have different habitat and temperature preferences.The abundance of SMB is farther downriver.