STOCKING STRATEGIES FOR WARMWATER FISHES IN LENTIC ENVIRONMENTS
Richard O. Anderson, Missouri Cooperative Fishery Unit.
Proceedings of North Central Warmwater Fish Culture-Management Workshop, 1971 Robert J. Muncy and Ross V. Bulkley, editors. p. 37-48.
Strategy as used in the title of this paper is defined as artful or skillful planning and management. Strategy is an important aspect of fish production in both the hatchery and in the field. Fishery management in its advanced form is an art and good management creates something that is recognized by the critics as worthwhile. I define fishery management as the manipulation of the physical, chemical and biotic factors in aquatic environments to achieve the most satisfactory sustained production and yield of desired species of fish in a program that is regulated by sound biological, political, and economic principles and concepts.
This definition infers the maximization of values over a period of time by the modifiers, "most satisfactory sustained." The optimum yield value may vary between biomass yield, economic gain, or sport and esthetic value. All administrators and biologists should study the discussion of values and management decisions by McFadden (1969). Policy should determine the objectives of where and when to maximize what values. Objectives should have an important influence on management programs including stocking.
A sound economic concept to be considered in management is a favorable benefit-cost ratio. Consideration of the spectrum of desires of the public and the needs of society are important political concepts. Since I am not an economist or sociologist, I will only discuss some of the biological considerations related to stocking. The considerations include productivity, trophic structure, species diversity, vulnerability, growth, recruitment of young, and environmental characteristics.
Ecosystem and population concepts are the biological basis of sound stocking programs. Each body of water is an ecosystem with complex yet predictable relationships. Productivity or the capacity to elaborate organic substance is a characteristic of all ecosystems. Rates of production or elaboration of tissue are real and measurable characteristics of each ecosystems that are related to productivity. Trophic structure is another characteristic of ecosystems whether or not you think of it as a trophic level, trophic link, or trophic web.
Fishery management attempts to create or maintain fish populations which have the capacity to produce a sustained yield of satisfactory fish in proportion to the productive capacity of the water. You should recognize this as the definition of balanced populations of H.S. Swingle (1950). He determined biomass characteristics of satisfactory bass and bluegill populations in Alabama ponds. This empirical approach has led to a recommended steady-state model for these systems (F/C, 3.0 to 6.0; A , 60 to 85; Y , 1.0 to 3.0). In time it should be possible to create models of more complex systems in other latitudes. Such models could be an important part of stocking strategies.
Diversity is a characteristic of ecosystems that is attracting considerable attention of ecological theorists. They suggest that increased species diversity results in greater stability and production. Diversity of fish species with limited competition for food should be considered in the strategy of stocking programs. In food-fish production, mixed culture or polyculture is practiced to utilize available forage or niches (Yoshouv, 1966; Tang, 1970). Redear sunfish and channel catfish are now frequently added to the largemouth bass-bluegill combination in ponds. Diversity in sport fish stocking programs may increase potential sustained biomass yield, increase the extent and type of angling effort and increase esthetic and sporting value of ecosystems. Variety tends to increase angler satisfaction.
Vulnerability must be considered in stocking strategy since this may have an important influence on the transfer of energy and production and yield efficiencies. Controlled experiments demonstrate how the species and size of prey can influence vulnerability (Ivlev, 1961; Mauck, 1970). Vulnerability is important in stocking strategy since a vulnerable prey of relatively small adult size can be drastically reduced or eliminated (e.g. largemouth bass-golden shiner, Swingle, 1949; Regier, 1963). If the prey species has a relatively large adult size and rapid growth, only a small percentage of the production as young of the year could be utilized by the predator (e.g. carp-bass). Size of prey consumed by large predators is an important consideration if the available prey are sport fish. An abundance of large predators may utilize catchable-sized fish and reduce potential biomass harvest (flathead catfish-black bullhead, Kendle, personal communication; muskellunge-yellow perch, Gammon and Hasler, 1965; Schmitz and Hetfield, 1965).
Environmental conditions such as the amount of cover (rooted vegetation) may also influence predator efficiency (Swingle, 1952; Heman, Campbell, and Redmond, 1969; Michaelson, 1969). Environmental characteristics should also be considered in formulating stocking strategy.
The angler is an important predator with certain preferences. An understanding of variations in vulnerability between species or subspecies and other factors influencing fish vulnerability should influence stocking strategy. For example, the difference in vulnerability between brown trout and brook trout is well recognized and is considered in trout stocking programs.
An important population concept that must be considered in stocking is the relationship between density of fish and growth. The number of fish stocked should be proportional to productivity and at a rate which will allow rapid growth to catchable size and maturity. A practical bluegill in fertilized and unfertilized ponds (Crance, 1969).
Another population concept that may be important is the relationship between adult stock and recruitment of young. Limited data for bluegill and gizzard shad suggest the generalization that a high recruitment of young of forage species may occur at a relativly low adult density. an inverse relationship between number of young bluegill and weight of adults is apparent in Figure 1 from the data of Swingle (1950) for selected ponds which had a standing crop of at least 300 pounds per acre of primarily bass and bluegill when drained in the fall. This may be important when stocking bluegill. If the initial adult stock is low, excessively high numbers of young may increase the probability of excessive intra- and possibly interspecific competition and unbalanced populations in the future (Swingle, 1951). Data from Starrett and Fritz (1965) indicate that a strong year class of gizzard shad was produced in a year with a relatively low adult density (Figure 2). Smith (1958) reports a high recruitment of young gizzard shad following reduction of populations with rotenone. Low adult densities may be desirable for gizzard shad and promote the maximum production of small forage. If a large predator such as northern pike, muskellunge or striped bass could regulate and reduce the average density of adult gizzard shad, a more consistent and higher production of young shad might result which could benefit the production of crappie, white bass and other species that consume small gizzard shad. This may prove to be an important stocking strategy in the future.
Stocking strategies also should consider physical and chemical characteristics of receiving waters. The practical potential of a body of water may be related to size. Turbidity may influence vulnerability and reproduction. Substrate can influence reproduction and benthos production. Alkalinity and nutrients influence productivity. Temperature and oxygen can influence feeding, growth, distribution and survival.
THE FIVE W'S
A sound stocking strategy must determine: what species, strain or hybrid; what quality; what number; when; and where.
It is well recognized in some trout stocking programs that different strains or stocks have different vulnerability, survival and growth (Donaldson, Hansler and Buckridge, 1957; Calhoun, 1966). This concept has been inadequately examined for warmwater fishes. Studies by the Missouri Cooperative Fishery Unit have shown that there are significant differences in growth potential, survival and vulnerability of different stocks of smallmouth bass (Mohler, 1966; Divine, 1968). The Florida largemouth bass appears to have charaacteristics that are different from the northern largemouth bass in California (Calhoun, personal communication). Further research and evaluation is warranted on these and other warmwater species such as bluegill, walleye and muskellunge.
The potential of hybrids in a stocking program is a relatively active area of research. Some of these hybrids include crosses of several sunfishes, largemouth bass-warmouth bass, muskellunge-northern pike, striped bass-white bass, and a super predator in Michigan, the coho-walleye-muskellunge named Kowalsky. Careful evaluation should reveal the feasibility, practicality and value of these fishes.
Exotic and transplanted species can be valuable in stocking programs. In this period of enlightened ecological awareness, new species should be introduced only after deliberate study and planning and a knowledge of the requirements and characteristics of the species and the biotic and abiotic characteristics of the receiving water. Potential costs to unique or valued endemic species should be considered. Important political considerations include reaction of the public and other interested and involved agencies. Publication and distribution of reports and plans can be an important method of communication. A good example of study and planning is the report by Tody and Tanner (1966).
What species and where should be determined by environmental conditions and by the values to be maximized. Table 1 is presented to suggest how esthetic and sporting values or biomass yield values might be favored in a problem lake with excess rooted vegetation and in an ecosystem with no apparent problems. The table also suggests a variation in diversity as a function of lake size. A small pond need satisfy only the owner or a few friends and can be managed for a narrow set of values. Large waters must be managed to satisfy a broader spectrum of angler interests. Another consideration is that a 10% increase in production in a half-acre pond does not achieve much absolute gain, but in a 1000-acre reservoir it could provide many hours of additional satisfactory recreation.
A diversity of forage species is suggested in the table. Too much forage should not be a problem but a challenge to be efficiently used by piscivorous species. Centrarchids are placed in a separate species category (Fs) from the minnow species and gizzard shad (Ff) in the table to distinguish their potential sport and harvest value.
Some of the species may be suitable only for certain waters in the central portion of the United States. There is little published information to support these combinations. The use of smallmouth bass and minnows is based on observations over a short period in a limited number of small ponds in Missouri (Divine, 1968). Smallmouth bass have produced excellent yields in some Illinois ponds (Bennett and Childers, 1957) but were not considered suitable in Indiana (Krumholz, 1952). The use of minnows as a substitute for bluegill as forage for bass has been recommended in Michigan by Ball (1952) and in New York by Regier (1960,1963). The substitution of redear sunfish for bluegill has been recommended by Krumholz (1952). Evaluation of the combined stocking of largemouth and smallmouth bass and the stocking of gizzard shad and northern pike are in progress at the Missouri Cooperative Fishery Unit. Muskellunge and striped bass are not suggested for stocking in this table. They could be considered for waters larger than 1000 acres.
What number is an important "W." The number of bass and bluegill to be introduced into new waters has been debated for many years. Many states today are stocking ratios of five to ten bluegill to one bass at a rate of 50 to 100 bass per acre. A reasonable stocking rate can be calculated if the biomass, survival and growth rate can be predicted to some future date such as after two growing seasons.
The equation is:
weight of surviving stock / survival % x average size
= number to stock.
Reasonable values for satisfactory Missouri ponds after two growing seasons for largemouth bass may be:
40lb. per acre / 80% x 1.0 lb = 50 per acre
40lb. per acre / 80% x 0.5 lb = 100 per acre
Reasonable values for bluegill may be:
120 lb. per acre / 80% x .25 lb = 600 per acre
The population at this time may also include 90 pounds of small and intermediate-sized fish (10 pounds bass, 80 pounds bluegill) for a total standing crop of 250 pounds per acre. This formula is similar to the method for formulating a trout stocking program in lakes (Borgeson, 1966). Similar calculations may be made for more complex populations if reasonable predictions of biomass, survival and average size can be made. Accurate predictions or models of growth and standing crop are worthless, however, if the quality of the hatchery product is deficient and the stocked fish are too small, diseased or severely stressed in handling or transport.
What quality and when are important but inadequately studied questions. One aspect of quality is length. It is usually assumed that the rate of survival will increase with size, however, exceptions to this generalization have been demonstrated in stocking trout in lakes (Borgeson, 1966).
Survival and growth of stocked fish can be influenced by a number of factors. The most favorable time may be related to seasonal variation in food supply and predator density. Temperature may be important since it will influence the ability of fish to repair damage and recover from stress. The minimum size of fish that will produce predictable and satisfactory results will improve the benefit-cost ratio.
A split stocking of largemouth bass has been tried in Missouri by Mr. Dennis Norman (personal communication). In a large reclaimed impoundment, carryover fingerling largemouth bass (50 per acre) were stocked in the early spring along with bluegill and channel catfish. A second stocking of young-of-the-year bass was made in late fall. This split stocking resulted in excellent growth of the initial stock and a tri-modal size distribution in the second summer after the initial stock had reproduced. This stocking appeared to produce favorable size and structure for the bass population.
Weight, condition factor or fat content are other factors that may influence quality and survival. This is another area of research that has been devoted almost entirely to salmonids.
Parasites and diseases are another aspect of quality. Introduction of a new parasites or diseases to a body of water can be a potential cost of stocking that has received little consideration. Potential problems should be identified and prevented.
All stages from fry to adults can be stocked depending on the species and condition of the ecosystem. Table 2 suggests some guidelines for selected species. The stocking schedule for a good, new 200-acre lake filling in the spring following these suggestions would be:
Late spring - adult golden shiner, fathead minnow.
Early fall - fingerling bluegill, black crappie, redear sunfish, channel catfish.
Early summer - young-of-the-year largemouth bass, smallmouth bass and walleye.
Spring - adult gizzard shad, adult bass if the initial stock will not mature and reproduce.
Early fall - large young-of-the-year northern pike. If natural recruitment of pike is inadequate in the future, there should be a maintenance stocking at two or three year intervals.
Progess in stocking programs depends on accurate evaluation. The determinants of success or failure must be identified in order to achieve the most efficient use of the hatchery product. Management observations and evaluations must be published in order to benefit the profession.
In fishery management I can think of no one activity that can generate more pride and satisfaction, critical approval and recognition in a state or federal fishery program than a sound and progressive stocking program. Elements of success require input from and coordination of administration, hatcheries, research, management, education and enforement. An important part of the strategy is the team effort.
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