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<br />ECOLOGY ANI) CONTROL OF THL• COLUMBIA SQUA~I'FISH 201
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<br />of annulus formation, assuming astraight-lire
<br />relationship between scale and body growth.
<br />These data, which are presented in Figure 2,
<br />show most rapid growth during the second
<br />and third years of life (annulus I to III) : 2 to
<br />3 inches a year. The oldest squawfish taken
<br />showed 13 annuli and a weight of 9 pounds,
<br />Spawning males in Hayden Lake had average
<br />total lengths of 15.4 and 14.0 inches in 1957
<br />and 1958, respectivel}', and weighed from 0.6
<br />to 3.0 pounds. Spawning females were larger,
<br />averaging 20.2 and 20.3 inches in these same
<br />years and weighing from 1.4 to 7.6 pounds.
<br />Total length and fork length of squawfish
<br />were compared, using 35 fish. Conversion fac-
<br />tors are: within a range in length of 50 to
<br />120 millimeters, total leagth equals 1.114
<br />times fork length which equals 1.150 times
<br />standard length; and within a range of 120
<br />to 530 millimeters, total length equals 1.087
<br />times fork length which equals 1.094 times
<br />standard length.
<br />are broadcast in shallow water, usually less
<br />than one foot in depth. Spawning is character-
<br />ized by t igorous splashing and vibrations. Both
<br />sexes strip easily when ripe and sex of males
<br />can be determined externally by the presence
<br />of spawning tubercles, darker coloration, and
<br />slender genital papilla. Eggs adhere loosely
<br />to the surface of rocks or form mats in the
<br />interstices. There is no parental care given
<br />eggs or young. Normally eggs hatch in 7 to 8
<br />days. Spawning generally occurs during aone-
<br />month period of late spring or early summer
<br />umess prolonged by periods of rough weather.
<br />After hatching, young squawfish school in shal-
<br />Iow water for several weeks, at, which time
<br />they are vulnerable to treatment with rotenone.
<br />At Hayden Lake the principal spawning
<br />grounds are located along one mile of the
<br />28-mile shoreline, where eroding bluffs deposit
<br />angular rubble along the edge of the water.
<br />Interstices in the rubble, together with wave
<br />action, make the site ideal for survival of eggs.
<br />squawfish at Cocolalla Lake spawned success-
<br />fully on wave-washed cobbles embedded in
<br />clay and sand.
<br />The fecundity of northern Idaho squawfish
<br />was estimated by measuring the total volume
<br />of eggs in each gravid female. The total num-
<br />ber of eggs was then determined by pro-rating
<br />from actual counts of eggs in known unit
<br />volumes. A ripe 16-inch, 11/2-pound female
<br />carries about 12,000 eggs. In larger female
<br />squawfish, eggs may total 100,000 or more,
<br />averaging ijg of the body weight. Egg pro-
<br />duction per pound of fish was found to be
<br />lowest at first spawning, 8,000 to 10,000 per
<br />pound of fish, but was from 12,000 to 16,000
<br />per pound of fish thereafter.
<br />Dynamiting, which --was presumably not se-
<br />lective to sex or size, showed a sex ratio of
<br />55 percent females to 45 percent males. Gill
<br />nets of 3- to 5-inch mesh were selective to fe-
<br />males because of their larger size. Because of
<br />selectivity of gilt nets, 81 and 85 percent of
<br />the squawfish collected from Hayden and Coco-
<br />laila Lakes, respectively, were females.
<br />SPAWNING AND FECUNDITY OF SQUAW FISH
<br />squawfish spawn in both lakes and streams.
<br />Migration from takes into streams for the pur-
<br />pose of spawning apparently occurs where
<br />lakeshores are unsuitable for spawning.
<br />squawfish congregate when the water tem-
<br />perature on the spawning grounds nears 60° F.
<br />Spawning occurs on clear, calm days. The eggs
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<br />SELECTIVITI' OF G[LL NETS IN
<br />SAhIPL1NG OF SQUAVi'FISH
<br />Freust , -Age, weights, and mean total lengths
<br />of squawfish in Idaho lakes, Length age data from Co-
<br />colalla and Pend Oreille Lakes. Length-weight data
<br />fmm Cocalalla, Pend Oreille, and Hayden Lakes.
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<br />Since gill nets are a_practical means of_ re-
<br />ducing squawfish populations, the selectivity ,
<br />of such gear for squawfish of different size is
<br />of interest. The nets fished, including experi-
<br />mental nets, allowed evaluation of catch effi- ~~ `-
<br />cicncy of seven mesh sizes; lI/Z-, 2-, 21/2-, 3-, ~
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