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UNDESIRABLE SPECIES 349 Table 14.4 Species lhal are controlled by mechanical methods. Values given for each rank are percenlages. Rank" Species 2 3 Common carp 23 6 17 Olher cyprinids 21 9 Suckers 12 6 4 Sunfish 17 16 17 Yellow perch 9 16 4 While perch 9 4 Gizzard shad 6 13 4 Crappie 6 4 Trout 6 3 4 Tilapia 6 Gar 3 4 Sacramento black fish 3 Goldfish 3 Northern pike Sea lamprey 9 Freshwater drum 4 Largemouth bass 4 "Ranked in order of importance by state and provincial agencies in response to a 1988 questionnaire. increased productivity. However, water leve[ manipulations may conflict with other reservoir uses such as domestic or irrigation water supply, power genera- tion, flood control, and recreation. Water manipulation has some limitations because this method can only be used on reservoirs with water control structures. Drawdowns will reduce the inverte- brate biomass in the fluctuating littoral zone and, if done in [ate summer or fall, may provide conditions for winterkill. The reduction in invertebrate biomass can be compensated by revegetating the fluctuating littoral zone to increase produc- tivity during the following spring. Game fish populations may benefit from commercial fishing of undesirable species (including competitors or predators) if the numbers are reduced signifi- cantly. For example, nearly 80 million kilograms of commercial fish (mostly freshwater drum) were removed by trap nets and trawls from Lake Winnebago, Wisconsin, between 1955 and 1966 (PriegeI1971). This removal coincided with an increase in populations of walleye, sauger, white bass, yellow perch, and black crappie (all desirable species). Commercial fishing is an acceptable way of removing less desirable fish species at no cost to the managing agency; however, most inland commercial fisheries do not remove enough of the undesirable species to benefit game fisheries (Grinstead 1975). Intensive harvest of preferred com- mercial species usually results in reduction of average size and catch rate that ultimately makes fishing unprofitable. Other undesirable species may remain unharvested because of [ow market value. Energy transfer (i.e., productivity) is complex in fish communities and some biologists believe that suppression of game fish by other less desirable species may be greatly exaggerated (Marrin and Erman 1982). Trapping or netting of fish is practiced to control fish in small waters (ponds or lakes) or for partial control in larger waters (Figures [4.6 and [4.7). Mechanica[ controls are effective only if there is a significant decrease in the target species.