Lakes and streams have the capacity to produce a certain number of fish. This capability is based on the amount of water, water quality, food sources, and conditions of the habitat. Natural aquatic systems can maintain a given number of adult fish by recruiting young fish into the population as the older fish die. In a system that is not fished, this balanced state is called carrying capacity.
Most ecosystems have some ability to compensate for increased adult mortality due to fishing by increasing the survival of younger fish. This process of compensatory mortality is sufficient to produce a sustainable harvest when a limited number of anglers are present. As reservoirs and streams are subject to higher fishing pressure, even restrictive harvest limits may not be enough to maintain a sustainable population as too many adult fish are removed.
This problem was noted along the eastern seaboard of the United States’ over 150 years ago. The solution was to raise fish in hatcheries and stock systems with additional fish for anglers to harvest. These early efforts started with species that anglers loved to catch, such as trout and striped bass. Fisheries biologists now have the ability to raise nearly every game and non-game species. The desire to raise fish was so important a century ago that the first professional society studying fish on this continent was named the American Fish Culturists’ Association. Currently, over 40% of all the fish consumed worldwide are the product of aquaculture rather than being caught in the wild.
Reviewing the Utah Division of Wildlife Resources stocking records, it appears the state has released 8 to 10 million fish each of the last several years. In the 1970s, when I first started fishing in Utah, nearly all the stocked fish were rainbow trout. Nowadays, the number of species raised and released in Utah is closer to 20. Some of these species are bred specifically for fishing opportunities such as tiger muskies, splake, tiger trout, and wipers. These designer fish provide opportunities and experiences not available 40 years ago.
Many fishing opportunities in western states occur behind dams. In the absence of stocking, these systems would provide few opportunities for anglers to catch and keep fish. Warm water species like bass, yellow perch, and crappie, have long been stocked in low numbers in reservoirs. Without these efforts, there would be few warm water gamefish in the West.
The number of fish stocked for anglers doesn’t even include the millions of fish, such as Colorado pikeminnow and bonytail sucker, that are released to enhance endangered fish populations. Idaho pursued a large-scale stocking effort to augment endangered Snake River Chinook salmon populations in the 1990s. Because of these efforts, the number of fall Chinook were high enough last year that anglers were allowed to keep six fish a day.
It must be noted that stocking is not always beneficial. Stocked fish can spread disease, affect genetic integrity, and cause competition with, or predation of, native species.
Hatchery-reared trout were the primary vector that spread whirling disease throughout the West. Long-term selective breeding, which historically occurred in some hatcheries, affects how stocked fish carry out their lives in the wild. For example, because hatchery managers spawned the first fish they captured, it is common to see rainbow trout constructing redds (nest of gravel that hold eggs) in late winter, months before their native cousins would start laying eggs in California.
Stocked fish also cause conflicts with native species. In some historically fishless high mountain lakes, stocked trout altered macroinvertebrate communities and reduced amphibian populations. The stocking of brook trout across the West led to hybridization with the endangered bull trout and competition with cutthroat trout. Management agencies are now more adept in their use of hatchery fish. Many stocked trout now have three copies of their chromosomes rather than two. The hatchery technique of using triploid fish, which are sterile, reduces some of the risks to native trout.
The combination of stocked and native fish makes it a great time to be an angler in Utah and Idaho. Nearly every inland gamefish in this country can be caught in these states. Without stocking programs, I would have never caught a smallmouth bass, crappie, or wipers. Most the region’s rivers have non-native brown trout, brook trout, and rainbow trout. While these fish do pose a threat to the native cutthroat trout, my personal solution to this conundrum has been to catch-and-keep non-native species (where legal) and release the native fish. This seems to be a win-win strategy as I have fish for the table and this action also protects native fish.