Evaluating Sterile Predators as a Management Tool

Led By

Lake and Reservoir Researchers

Study Area

Select lakes and reservoirs

Project Status

Ongoing

Research Objectives

• Evaluate the relative influence of different physical and biological factors on the post-stocking performance of sterile hybrid predators and responses by undesirable or overabundant prey fishes to inform best stocking practices.
  

Project Description

Hybrid predators such as tiger muskellunge (cross between northern pike and muskellunge) and tiger trout (cross between brook trout and brown trout) are sterile (cannot reproduce) and often stocked to control undesirable or overabundant prey fish species (e.g., suckers) that compete with other valuable sport fish such as rainbow trout and cutthroat trout. Because these hybrids are sterile, managers can keep close tabs on their numbers, and predatory or competitive effects only last over their lifespan. Hybrid predators also provide unique angling opportunities and have the potential to reach trophy sizes.

The ability of hybrid predators to control unwanted or overabundant fishes while providing quality angling opportunities depends on many factors related to the physical and biological attributes of a lake or reservoir.

The Lake and Reservoir Research group has been quantifying the effects of different factors on the post-stocking performance (feeding, growth, survival and responses by prey fish populations) of hybrid predators to inform best stocking practices. Informed stocking translates into the efficient use of the limited number of hybrid predators produced by CPW’s hatchery system, a greater chance of achieving desired outcomes, and more rapid development of quality fishing opportunities for Colorado’s anglers.

Tiger trout research highlight:

A recent study on juvenile tiger trout stocked into subalpine lakes found that growth early in life was sensitive to the numbers of tiger trout stocked; the higher the density, the slower their growth. The study also found that when undesirable prey fishes were numerous and large, tiger trout did not grow as well, and the same was true when other trout species were being stocked simultaneously.

Enhanced growth early in life is linked to improved survival and the ability of juvenile predators to transition to eating larger-bodied prey fish sooner. Results from this study suggest that stocking practices (numbers, sizes and frequency) designed to enhance growth early in life or bypass potential growth bottlenecks may improve the ability of tiger trout to meet multiple fisheries management objectives over the long-term. Information provided in this study helps guide managers in this process.

Tiger muskellunge research highlight:

Tiger muskellunge are a valuable management tool, and a focus for CPW researchers. Tiger muskellunge have been stocked in more than 100 lakes and reservoirs in Colorado since 1983. Similar to tiger trout, tiger muskellunge are stocked to control nuisance or overpopulated fish species. However, tiger muskellunge can achieve large sizes (the Colorado record is over 40 pounds), and can be effective at controlling relatively large nuisance fish species (like white suckers).

With over 100 places to learn from, researchers have an opportunity to use historical survey data collected by CPW biologists to understand where stocking tiger muskellunge has had the desired effects (reducing the number of undesirable fish species), and where stocking has not met management objectives. Researchers can also look at other aspects of different lakes and reservoirs like the forage available, trout stocking, and the presence of competitors (like northern pike) to determine if those factors influence the post-stocking performance of tiger muskellunge.

Previous CPW research combined with the historical data analysis completed thus far, has shown that when tiger muskellunge are large enough, they tend to consume catchable trout when they are available. This means that the impact tiger muskellunge have on undesirable fish species is reduced or buffered against when trout are stocked because they are consumed before the intended species. If the weight of trout stocked in a particular lake or reservoir is enough to feed the tiger muskellunge present, their effect on undesirable species will be highly diminished or absent. Understanding these kinds of variables and looking further into historical data will allow CPW researchers to develop stocking formulas for tiger muskellunge (how many and how often) to increase their post-stocking performance and their success at achieving intended management goals.   

Associated Publications

Hansen, A.G., E.T. Cristan, M.M. Moll, M.W. Miller, E.I. Gardunio, and J.M. Lepak. 2022. Factors influencing early growth of juvenile tiger trout stocked into subalpine lakes as biocontrol and to enhance recreational angling. Fishes 7:342.

Lepak, J.M., C.N. Cathcart, and W.L. Stacy. 2014. Tiger muskellunge predation upon stocked sport fish intended for recreational fisheries. Lake and Reservoir Management 30:250-257.

Lepak, J.M., E.R. Fetherman, W.M. Pate, C.D. Craft, and E.I. Gardunio. 2012. An experimental approach to determine esocid prey preference in replicated pond systems. Lake and Reservoir Management 28:224-231.