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Rationale for
Warmwater/Coolwater (WW/CW) Stocking
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It is important for anglers and persons interested in Pennsylvania’s aquatic resources to understand that most warmwater and coolwater fishes stocked by the Pennsylvania Fish and Boat Commission are stocked as juveniles, these juveniles must then survive and grow to desirable size or legal size before they can be harvested.

Warmwater and coolwater fishes are typically stocked in “modified or altered” aquatic habitats such as flood control and multiple use reservoirs (ex. Raystown Lake) or impounded rivers (for navigation or hydropower generation, ex. Monongahela River and Susquehanna River). Characteristics of these altered habitats do not yield the levels of natural production for some species these waters have the potential to support.

For example, Raystown Lake does not possess tributaries that accommodate sufficient spawning for striped bass to adequately populate the entire reservoir, consequently, striped bass are stocked as juveniles into Raystown Lake. Raystown Lake possesses the necessary forage fishes and habitat elements to sustain large number of juvenile striped bass to adulthood. Striped bass are, or were, native to the Raystown Branch of the Juniata River before it was impounded for flood control.

A similar statement could be made for many other fish species maintained by stocking across the state, although in some cases warmwater and coolwater fish are stocked because an altered habitat yields conditions capable of supporting popular sport fish not originally indigenous to the watershed. It should be noted that most sportfish typically maintenance-stocked (stocked annually) into a watershed where they did not originally occur, have been shown to have minimal or no ecological impact upon native fauna. Further, in many cases habitats into which stocking takes place have been dramatically altered as noted above. Consider, for example, a situation where a medium size stream is impounded to create a very large reservoir. Fish inhabiting a shallow stream now find themselves in a deep-water habitat and those stream fishes do not create the types of fishing recreation the reservoir has potential to support. Consequently, fishes not indigenous to the stream, but very capable of surviving in a deep reservoir are stocked. Ecological impacts on native species are considered in making such stocking decisions. Frequently, species stocked would not survive in appreciable numbers or at all without stocking and would certainly not survive in a small stream if the reservoir were drained, the dam removed, and original habitats restored.

The Pennsylvania Fish and Boat Commission is devoting significant resources to restoring and improving aquatic habitats such that need for stocking is kept at minimum. However some alterations have become socially acceptable and viewed as economically necessary, not only at the state level, but also at the national and international level. Restoring some natural aquatic habitats will require significant social change and renewed appreciation for original natural habitats, before stocking will no longer be required to support levels of recreational fishing anglers in Pennsylvania have come to expect. Balancing limited resources to accomplish needed habitat protection and restoration while providing exceptional fishing recreation is a challenge our Executive Director has vigorously embraced. All employees take pride in rising to that important challenge and accomplishing habitat restoration goals that lead to an improved aquatic environment and improve economies that have their basis in healthy aquatic resources.

Waters stocked, species stocked and size or Life-stage stocked

Stocking is necessary to support many warmwater and cool water sport fisheries anglers have come to enjoy across the Commonwealth. A wide variety of species are cultured and stocked by the Pennsylvania Fish and Boat Commission, these include walleye, muskellunge, tiger muskellunge, striped bass, and channel catfish. These species are typically stocked annually or maintenance stocked to sustain good fishing opportunities through time. Lesser quantities of largemouth bass, smallmouth bass, bluegill, yellow perch, rock bass and the like are cultured and stocked since these species are stocked only once or twice into a water; thereafter natural reproduction is typically sufficient to sustain healthy populations that yield good fishing. Finally, some fish, American shad and paddlefish are annually stocked, not for immediate creation of fishing opportunities, but to build populations sufficient to naturally sustain themselves. This is termed restoration stocking, and in Pennsylvania, in the future with sustained aquatic habitat improvements it is anticipated that stocking these species will not longer be required.

The period of time necessary for warmwater and coolwater fishes to attain desirable size or legal size typically spans several years (3 to 4 years depending upon the species). Consequently it would be extremely inefficient and very time consuming to attempt to rear these fish to adult size. Most studies show that warmwater and coolwater fish grow faster in the wild as opposed to in a culture setting so it might take even longer for cultured fish to attain adult size. Stocking juveniles into natural, albeit altered habitats leads to the greatest gains in growth. As might be expected, fish stocked as juveniles endure the rigors of life in the wild (ex. predation) much as their wild produced counterparts, and all do not survive. The Pennsylvania Fish and Boat Commission has evaluated survival of a variety of sizes (life stages) stocked at a variety of times, at a variety of density levels, in a variety of water bodies and uses data from these evaluations to guide rearing and stocking procedures such that survival and resulting population levels are maximized. The number of warmwater and coolwater fishes reared and stocked is very large, much larger than the number of adults that would be stocked. Since smaller size fish require much less rearing space, the Fish and Boat Commission can rear very large numbers of a wide variety of warmwater and cool waters fish for stocking in numerous waters.

For a given water body numbers and species of fish to be stocked are very carefully defined. After a biologist (Area Fishery Manager) samples or inventories the water body and carefully evaluates fish abundance and condition, including forage fish abundance, a Fishery Management plan is developed which details the species and life-stage of fish to stock as well as the regulation (harvest) program to be applied to the water body.

Some fish are stocked as fry just a few days old; others are stocked as fingerlings and are several months to many months old. The rearing duration of a fingerling is (1) frequently a function of timing release such that forage organisms are abundantly available in the receiving water (for example if it is known that a particular minnow species or forage species produces an abundance of young in June, fingerlings of a size capable of consuming those young are released at that time), (2) a function of the size defined by Area fishery managers for stocking to avoid predation, and/or, (3) a function of the availability of natural food resources in a rearing pond, regularly checked by fish culturists. On rare occasions small numbers of adult size warmwater and coolwater fishes are stocked in association with re-establishing fish populations in newly constructed or newly re-filled reservoirs. Here the adult fishes are stocked as brood fish that will produce numerous young, and not stocked to be caught as adults by anglers although some capture occurs. Combinations of adult and young fish in an initial stocking can affect the ultimate size structure of adult fishes some years after stocking, great care is exercised in stocking adults in combination with juveniles. For example adult size largemouth bass are stocked in combination with fingerling bluegill to produce a balanced size structure. To simplify it has been shown that this combination yields sizes of bass and panfish that are desirable by anglers without one species predominating or small size fish of either species predominating.

Natural Variation in Annual Fish Production and Survival

Warmwater and coolwater fish production typically takes place outdoors and in many instances food supply is dependent upon natural production of zooplankton in rearing ponds. Ponds are precisely fertilized by Fish Culturists to produce a plankton “bloom” prior to introduction of fry. Despite the utmost care and control, the pond environment can change in association with prevailing weather conditions, which influences the development of the food supply, consequently the number of young fish produced each year varies. Variation is similar to the variation in the number of ears of corn a farmer produces each year based upon weather. Consequently the numbers of fish to be stocked in a water in the current year are not listed in the Pennsylvania Fish and Boat Commission tables for the current year because the number stocked not precisely known. The planned number to be stocked is precisely known and supplies culturists with a precise goal. Generally speaking, a water destined to receive a particular species is regularly stocked with that species and anglers can expect to find adult size fish in the waterway even though there is year to year variation in number stocked.

Anglers interested in specific numbers stocked can view our historic stocking record listed by county for various waters. The historic stocking record is available, beginning the year after stocking takes and includes the actual number of fish stocked in the water body. Historic data are of interest to anglers since the number of young stocked three or four years prior to a fishing trip are those that will be of legal or desirable size and available for capture during the trip. Although numbers stocked are important, conditions at the time of stocking and circumstances fish encounter after stocking influence survival and abundance as well. In some large scale studies evaluating walleye fingerling stocking it was found that number stocked explained only 28% of the variation in subsequent yearling indices (Fayram et al. 2005). Predator fish density, availability of forage fish, and conditions of the year (drought, flood, above average temperatures, below average temperatures) substantially influence survival and ultimate density of fish stocked.

Variation in outdoor production and variation in survival after stocking leads to fluctuations in warmwater and coolwater fish populations maintained by stocking. These variations are similar to natural variations that occur among naturally produced populations. Remember stocking warmwater and coolwater fish takes place because one or more critical habitat elements or water quality components, essential to spawning, incubation and early life, is typically lacking. That early phase in the life of a stocked fish occurs in the protected setting of Pennsylvania Fish and Boat Commission hatcheries where artificial habitats and water quality are maintained at optimal levels for growth and survival. The bottom line is that given optimal receiving water conditions, numbers stocked will exert some influence upon subsequent adult abundance but will not be the sole determinant of abundance. Consequently variation in numbers stocked from year to year in a water should not cause concern among anglers.

Numbers stocked provided in the historical stocking pages are listed by county and often include flowing water sections (river or stream sections) that span two or more counties. Flowing waters often form borders between counties. To accurately portray numbers stocked in these waters the total number stocked was divided proportionally by the percentage of the surface area for the section attributable to each county. The total number stocked in a river section requires the addition of stocked fish from each county the section encompasses. In most cases lakes or reservoirs do not form borders between counties and for reservoirs and lakes the total number of fish stocked into the reservoir is listed for the entire water regardless of county border although some reservoirs are listed in more than one county.

Warmwater and coolwater fishing opportunities maintained by Pennsylvania Fish and Boat Commission stocking programs and those maintained by natural production provide for some exceptional recreation. Enjoy some great fishing in Pennsylvania today!

References

Andrew H. Fayram, Michael J. Hansen, Nancy A. Nate (2005). Determining Optimal Stocking Rates Using a Stock–Recruitment Model: An Example Using Walleye in Northern Wisconsin. North American Journal of Fisheries Management Volume 25, Issue 4 (November 2005) pp. 1215–1225

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