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<br />350 <br /> <br />CHAPTER 14 <br /> <br /> <br />Figure 14.6 Seining operation for rough fish removal from a lake. <br /> <br />Netting must occur regularly to be effective. Vulnerability of the target species is <br />an important consideration in netting and trapping efforts. Common carp, buffalo <br />fish, freshwater drum, and bullhead catfishes can be effectively harvested with <br />nets and traps during periods of spawning aggregations. Certain species of fish <br />(such as common carp) assemble into huge schools just before freeze-up and can <br />be effectively removed at that time. Nevertheless, netting and trapping programs <br />have produced varying results. Rose and Moen (1953) reported a sixfold increase <br />in game-fish stocks when competing species were reduced to about 35% of former <br />abundance in Lake Okoboji, Iowa. However, removal of over 27,000 longnose <br />suckers over a 7-year period did not improve the rainbow trout fishery in Pyramid <br />Lake, Alberta (Rawson and Elsey 1950). Such controls are temporary because fish <br />exhibit compensatory survival, growth, and reproduction. <br />Mechanical devices such as fishways and screens may have potential for <br />controlling fish. Fishways are usually used to pass desirable fish species over <br />obstacles such as dams, falls, or rapids. By careful design of fishways, passage of <br />undesirable species of fish can be prevented (Broach 1968). Fish screens are used <br />