A new game fish – the tiger trout – has been stocked in Scofield Reservoir by the Utah Division of Wildlife Resources in an effort to contain the reservoir’s chub population.
Tiger trout are a sterile hybrid, developed by combining the eggs of a female brook trout and the milt of a male brown trout. Because they're sterile, tiger trout grow fast, putting their energy into growth rather than reproduction. Tigers are also beautiful fish, renowned by anglers for their fight and their table quality.
About 80,000 fingerling (3-inch) tiger trout were planted by the DWR in Scofield in early September. They could be catchable-size (nine to 10 inches) by next fall.
The DWR has witnessed tremendous growth rates of tigers in other reservoirs. In Duck Fork Reservoir, for example, some fingerling tigers grew 12 or more inches in a single year. That's about double the rate rainbow trout will grow in a year.
The reason the DWR introduced another trout to Scofield is not entirely for sporting reasons.
During surveys at the reservoir in the spring of 2005, DWR biologists discovered Utah chubs in their gill nets. That was the first time Utah chubs have shown up in surveys since the reservoir was treated in the early 1990s to remove undesirable fish populations, including Utah chubs. Apparently, the chubs were brought to Scofield by anglers who were using them as live bait. The practice of using live fish as bait is illegal.
The discovery of chubs in Scofield could be catastrophic for the fishery. Utah chubs are extremely prolific. They reproduce rapidly and can outcompete game fish in a flat-water fishery.
Joes Valley is a good example of this. Anglers, illegally fishing with live chubs, introduced this nuisance species to Joes Valley years ago. The number of chubs in the reservoir has prevented the Joe's Valley fishery from reaching its full potential. While trophy splake are still readily available, much of the reservoir's productivity is tied up in chubs. Fisheries managers are faced with trying to return this fishery to its full potential within financial and bureaucratic constraints that eliminate many options.
Scofield Reservoir is among the four top fisheries in Utah. Losing Scofield's fishery to an invasion of chubs would be devastating.
Chemically treating the reservoir again to eliminate chubs would be very costly. In today's dollars, a treatment would cost a staggering $1 million. In addition, it takes years to satisfy the environmental and bureaucratic requirements that must be met before a treatment can take place. Hopefully, the tiger trout will be the answer fisheries biologists need to control the reservoir's chub population.
Chubs are commonly found in shallow water and shoreline zones, where they consume the food and occupy the space needed by young trout.
As the trout grow, they often move to deeper, cooler water and lose contact with the chubs. This helps the chubs, because they're less vulnerable to attack from fish that are large enough to eat them.
Tiger trout, however, are piscivorous (fish eaters) from an early age. They seem to be more willing to hunt for prey in shallower waters than many other trout subspecies. Fisheries managers hope that tigers will keep Utah chubs from outcompeting and overrunning other game fish in the reservoir.