by Scott Van Horn
Most fishing is supported by naturally reproducing populations of fish found in the wild. So how does the N.C Wildlife Resources Commission decide what kinds of fish to stock, where to stock them, and how many to stock? Fishery managers have a checkered history, especially in the profession's early years, of indiscriminant stocking done by trial and error. They lacked even the limited knowledge we now have to understand the effects of fish introductions on the environment and they produced a mix of successes and failures.
Let's quickly review the legacy of indiscriminant stocking. It is easy to identify some good things. Brown trout and rainbow trout are two newcomers that have given pleasure to trout anglers. Largemouth bass were only present in a portion of our state historically. Expanding the largemouth's range has created additional opportunities for bass anglers. Striped bass have been a successful addition to reservoir fisheries.
But these successes have another side. For example, browns and rainbows have forced the native brook trout into remnant populations high in mountain headwater streams. Some biologists worry that stocked largemouth and stripers may move downstream and contaminate the genetic information in native bass and striper populations with unknown effects.
Then there are the obvious stocking mistakes. If we could turn the clock back, would we stock the common carp again? What about tilapia? They're now found in reproducing populations in several power supply reservoirs with heated water discharges. There are others and it matters. Nationwide, estimates are 400 of the 958 federally listed endangered and threaten species are in competition with or must contend with predation by invasive or introduced species.
Many of our aquatic communities have been altered forever by moving fish deemed desirable in one part of the state to new homes in other parts of the state. Flathead and blue catfish have decimated redbreast sunfish and non-game fish populations in our coastal streams. White perch rarely reach their potential when added to upland reservoirs and may reduce the numbers of more desirable game fish such as crappie. Introduced spotted bass have displaced largemouth and smallmouth bass at several locations in North Carolina. The newcomer is often found in stunted populations leaving us with a smaller less desirable fish. Fishery managers have played an early role in many of these transfers, but anglers are now making more new species introductions than biologists.
How Does The Commission Identify Suitable Fish For Stocking?
Biologists try to follow several rules when deciding what fish to stock. A candidate for introduction must have high angler interest or prospects for improving the sport fishery. It must be a good fit for the habitat. Stocking a warmwater lake fish in a coldwater stream is not a good fit. Most importantly, the proposed introduction should not harm the environment, particularly if that harm is irreversible. The best way to meet the last two criteria is to use fish that are, or have been, native to the waters where they will be stocked. For example, adding muskellunge to the French Broad River is simply restoring a fish to its historical range.
Non-native introductions can occur safely under certain conditions. For example striped bass in reservoirs are popular with many anglers and generate lots of hours of fishing pleasure. The fish adapt well to the open water in reservoirs. They feed almost exclusively on shad that are usually abundant in reservoirs. There appear to be few negative impacts on the rest of the reservoir biological communities. Even if negative consequences are identified, stripers don't reproduce in most reservoirs so stocking rates can control their numbers. Ultimately, they can be removed from the lake by not stocking.
How Does The Commission Identify Locations For Fish Stocking?
A common place to stock fish is where they don't reproduce in the wild. Stripers do not reproduce in most reservoirs, so if a striper fishery is desirable, they must be stocked. When the stocked fish are gone, there will be no others unless they are stocked again. Many streams in our trout program will not support trout reproduction but will support adult trout. The Commission can create a fishery by stocking trout, but sustaining the fishery requires repeated hatchery truck trips. Channel catfish and muskellunge are additional examples of fish the Commission stocks because in some locations the fish won't reproduce in the wild.
Other Reasons For Stocking Fish
The Commission may stock where fish reproduction is present but insufficient to meet some fishery management purpose. Biologists call this "supplemental stocking." Trout and walleye are examples of fish that are occasionally stocked on top of existing naturally reproducing populations to make sure there are enough fish for anglers to catch. Coolwater fish lay fewer eggs, so the practice of supplemental stocking is more common in the mountains. Supplemental stocking has been largely unsuccessful for warmwater fish like bass, bream, and crappie. Female warmwater fish have such a high egg capacity, they flood their environment with surpluses of eggs making stocked fingerlings unnecessary.
Fish are also stocked to create a new reproducing population or to restore a population damaged by habitat abuse or over fishing. A new pond is usually stocked with bass and bream to establish its fish population. New reservoirs may be stocked initially with bass to get the bass population off to a good start. The Commission stocks striped bass and American shad in some coastal rivers to restore or strengthen existing populations. We hope we can eventually discontinue such stockings as the newly created fish populations reach their full potential through natural reproduction.
The Numbers Game: How Many To Stock?
How many fish to stock is controlled by several factors. Biologists have an overriding responsibility to refrain from stocking too many fish to the detriment of other parts of the aquatic community. Additionally, fish that are stocked as fingerlings must have enough resources to thrive. Striped bass and walleyes, for example, are stocked when no larger than your thumbnail. They require sufficient room, food, and shelter to grow. If too many fish are stocked, there may not be enough of these resources to go round. Survival of overcrowded fish becomes poor or the fish are thin and slow growing. Each stream or lake has a different capacity to support fish. Like rich ground growing more corn, rich water can support more stocked fish.
In contrast, some of our trout fisheries are managed by putting catchable sized fish (adults) into the stream with the expectation they will be caught within a short period of time. If the fish only survive a few weeks before being caught, available food resources in the stream don't matter much. Without important biological limits to stocking rates, other factors may control how many fish are stocked. Stocking rates might be dictated by fishing pressure. A stream next to a populated area with lots of anglers might get more fish than a remote location with few anglers. Ultimately, stocking rates might be limited by the amount of fish hatchery space available.
Protect and Enhance, Rather Than Imperil, Our Aquatic Natural Resources
Developing a stocking plan for inland fisheries in North Carolina requires carefully considering the wishes of anglers, understanding fish life histories, anticipating impacts on the environment and associated biological communities, and providing resources to grow fish in a hatchery environment or capture and move wild fish. The rivers and streams of North Carolina are a precious resource deserving of our protection.
Decisions on introducing fish to our waters must be made wisely. There are always consequences from stocking fish or introducing new fish species. Those consequences are often irreversible. Please don't stock fish in any of North Carolina's public waters and discourage others from doing the same. Despite good intentions, to improve fishing in a local lake or river, anglers who take it upon themselves to stock fish may be changing the biological communities in our great river systems forever. Choose not to move fish from place to place when you are angling.
Scott Van Horn is the Fishery Research Coordinator for the Piedmont Region.