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Minnesota lake, Johnson (1977) was able to remove 85% of the <br />estimated standing crop of adult white sucker by trap-netting - <br />during the spring of 1966; recovery of the population through <br />recruitment was not evident until 1972. However, in 14 Minnesota <br />lakes, Moyle et al. (1950) found that 25 years of seining did not <br />reduce populations of undesirable fishes. They estimated that <br />e <br />only one-third of targeted fish was removed each year. <br />Biological Control.-Biological control methods can be <br />grouped into three categories: (1) grazing and predation by <br />protozoa, zooplankton, fish, birds, insects, snails, crayfish, <br />turtles, and mammals; (2) use of pathogens (viruses, bacteria, <br />and fungi); and (3) biomanipulation, which adjusts <br />interrelationships among plants, animals, and their environment <br />to achieve the desired control or ecological balance (Wiley and <br />Wydoski 1993). For purposes of this report, we included the <br />prevention of additional introductions and stocking under <br />biological control. <br />Biological control of fish and aquatic plants is becoming <br />increasingly popular with fisheries-management agencies. <br />Biomanipulation is the most promising biological-control <br />technique because it has the potential to minimize competition <br />and establish balanced predator-prey populations (Wiley and <br />Wydoski 1993). However, because biomanipulation often requires <br />the introduction of predator or prey species, it is only <br />addressed in this paper when native fishes can be manipulated. <br />28