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age determina-
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<br />age determina-
<br />f marked Lake
<br />~X'ildlife Serr-
<br />1-59.
<br />of the use of
<br />'7[f f03l I171A11I ~,
<br />;v. 2, pp. 141-
<br />HOLMES. 19''9.
<br />on the Colum-
<br />~. S. Bur. Fish.
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<br /># a
<br />Ecology and Control of the Columbia Squawfish
<br />in Northern Idaho Lakes
<br />:'
<br />PAUL W. JEPPSON AND WILLIAl<I S. PLATYS
<br />Idaho Fith and Game Deparrnzent, Sa~Ce, Idaho
<br />ABSTRACT
<br />Columbia squawfish, Pt}chocheilul oregoncnci~, and trout were found to occup}' similar
<br />niches, resulting in competition for food and space, and predation on each other. Dlature
<br />squa~~fish are piscivorous with food habits similar to Doll}~• Varden, S.zlveliulls malnza, rainbow
<br />trout, Saln;o gait~dnari, and brown bullhead, Irr.tlurur nebu?r~rur. Age and growth data are
<br />presented and in northern ldahu lakes a l3-year-old female squawhsh attains a maxunum
<br />weight of approximately 9 pounds. Dlales g'ow slower, averaging less than one half the size
<br />of the females. Spawning by lake populations occurs in lakes and streams. Lake spawning is in
<br />schools during late A-fay and early June over wave-washed rubble on clear, calm days. The
<br />number of eggs in mature females varies from 12,000 to 100,000, averaging 40,000. Eggs
<br />batch in 7 to 8 days. In six years of squawfish control in 3,800-aae Hayden Lake by dyna-
<br />miting and gilt netting spawning schools, mature squawhsh were reduced to about one-tenth
<br />of their original abundance and an increase in trout noted.
<br />INTRODUCTION
<br />The Columbia squawfish, Ptyrhochrilru or~e-
<br />gonen.riJ, is an undesirable fish in many north-
<br />ern Idaho waters because it competes for food
<br />and preys upon more desirable game fishes,
<br />especially rainbow trout, Snlmo gr~rrdrzeri, cut-
<br />throat trout, S~rlrno clAn~ki, Dolly Varden trout,
<br />Slrlr~eliul~i ntnfnrn, and kokanee, Olscorhwrrlirr.r
<br />nerkn ken:~erl}i. Since complete eradication of
<br />squawfish is not practical in large lakes, con-
<br />trol methods are desirable which a>ill reduce
<br />the numbers and check the increase of this
<br />large cyprinid, In the lowland lakes of north-
<br />ern Idaho the squawfish has been increasing
<br />in abundance and extending its range because:
<br />it is adapted to most aquatic em°ironments,
<br />including streams and oligotrophic lakes; it is
<br />Ea.•orcd by selective fishing for other fish; it
<br />thrires in ^ew impoundments; and it is some-
<br />times inadvertently transported and stocked by
<br />man.
<br />
<br />To gather information on -this fish to rise
<br />in control of it, studies of its life histor}' and
<br />relationships to other fishes were made in three
<br />northern Idaho lakes: Cocolalla, 800 acres;
<br />Pend Oreille, 80,I100 acres; and Hayden 3..8t}tl
<br />acres. ~'ariaus control measures were instituted
<br />at Hayden Lake. These lakes are predominantl}'
<br />oligotruphic, relati~~ely infertile, and are fished
<br />mostly for tcout ut ko'.:anee (Figure 1) .
<br />-Fish were collected from the lakes in 1953,
<br />1457, and 1958 with kill ^ets, by use of dyna-
<br />R;itc and rotenone, and from the sport fishery.
<br />The experimental gill nets of nylon thread
<br />were 6 feet deep, of 25-foot sections and of
<br />I1~~_ 2_ 21~,_ 3_ and 4-inch mesh (stretch
<br />measure). Gangs of linen or cotton nets of
<br />3_ 3i~2_ 4-, and 5-inch mesh were also used.
<br />FISH ASSOCIATIONS AND SPORT F[SHERY
<br />From Hayden Lake the following species
<br />of fish were taken by netting: yellow perch,
<br />CA':ADA
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<br />Fiet:ar 1--1.'pprr Idaho showing location of lakes
<br />loon ~~1,ich squ.nvhsh :Ind as~Alilatrd hshts were
<br />arllrarJ.
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