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<br />202 YAtiL \X', )EPPSON AND WILL]ADI 5. PLATYS
<br />31/2-, 4-, and 5-inch mesh. It should be re-
<br />peated that the three smaller mesh sizes were
<br />of nylon thread and the larger were of linen
<br />and cotton, since this may have affected the
<br />efftciency of the nets, nylon being subject to
<br />slight stretching when wet (Lawler, 1950).
<br />Mean size of squawfish (in inches) taken from
<br />the different size meshes with associated stand-
<br />ard deviations are: 11/~-inch mesh-8.3±0.7
<br />inches; 2-inch mesh-10.1±0.9; 21/~-inch-
<br />13-3+1.7; 3-inch-14.3±2.0; 31/2-inch-I5:8
<br />± 1.3; 4-inch-18.1 ± 1.7; and 5-inch mesh-
<br />20.4±0.8 inches. These means represent meas-
<br />urements of 356 squawfish taken from Ha}~-
<br />den, Pend Oreille, and Cocolalla Lakes in
<br />1953, 1957, and 1958.
<br />squawfish taken by dynamiting on spawning
<br />beds of Hayden Lake in 1957 and 1958 (35
<br />males and 85 females) showed a mean length
<br />of 14.4 inches for males and 20.3 inches for
<br />females with associated mean weights of 1.2
<br />and 3.2 pounds. It is apparent that the best
<br />mesh sizes for taking spawners are 3, 312, and
<br />4 inches.
<br />CONTROL bIEASURF.S
<br />Reduction of squawfish numbers in Hayden
<br />Lake began in 1953 with gill netting and dyna-
<br />miting of spawning schools (Jeppson, 1957).
<br />Control work by dynamiting and partial spot
<br />treatment of the lake with rotenone was done in
<br />following years. In order to appraise the ef-
<br />fectiveness of the six-year program, gill nets
<br />were again used in 1957 and 1958 along the
<br />one mile of shoreline where squawfish concen-
<br />trate for spawning, duplicating the work done
<br />in 1953 when the project started. Four- and
<br />5-inch mesh gill nets were set on the bottom
<br />in 6 to 30 feet of water in gangs or at angles
<br />to the shoreline as bottom contour and ob-
<br />structions permitted.
<br />Effect on Squaw f i.th
<br />An estimated 24,000 pounds of squawfish
<br />were killed during the six seasons of work at
<br />Hayden Lake. This represents a kill of about
<br />6~ pounds of squawfish per surface acre;
<br />considerably more than the estimated standing
<br />population of squawfish in Cocolalla Lake-
<br />which amounted to less than one pound per
<br />surface acre, as determined by sampling dead
<br />fish following total eradication with rotenone
<br />in 1957.
<br />At Hayden Lake the catch indices (catch
<br />per 100 feet of net per 24-hour period) of
<br />squawfish declined 90 percent (3.46 in 1953;
<br />0.77 in 1957; and 0.34 in 1958) in 4-inch
<br />mesh and 52 percent (0.44 to 0,21) in 5-inch
<br />mesh during the period of study. Four-inch-
<br />mesh nets were operated for 215, 137, and
<br />235 net days and five-inch mesh nets for 57,
<br />51, and 130 net days in 1953, 1957, and 1958,
<br />respectively.
<br />More frequent tending of gill nets has been
<br />demonstrated to haee the effect of increasing
<br />catches, especially when levels of fish abun-
<br />dance are high (Kennedy, 1951). Nets were
<br />lifted at arerage intervals of 2.8, 2.0, and 2.6
<br />days in 1953, 1957, ~ and 1958, respectively.
<br />Since levels of squawfish abundance and total
<br />catches mere higher during 1953 and tending
<br />nets was less frequent, bias from this source
<br />tends to make the estimate of squawfish re-
<br />duction consen~ative.
<br />Effect ott other fish
<br />A slight increase in the catch indices for
<br />tench was likely due to the suspension of an
<br />effective trap-netting program in shallow bays
<br />after 1953- The catch index for trout during
<br />the six years was doubled. Sport fishing was
<br />much improved as shown by creel ch°cks; the
<br />ratio of marked hatchery ratnbows indicated
<br />that improved trout fishing was due in part to
<br />stocking but, apparently, survival of trout as a
<br />result. of squawfish control was a contributing
<br />factor.
<br />LITERATURE CITED
<br />FOERSTER, R. E. AND W. E. RICICER. 1941. The ef-
<br />fect of reduction of predaceous fish on survival
<br />of young sockeye salmon at Cultus Lake. Jour.
<br />Fish- Res. Bd. Canada, 5(4), pp, 315-336.
<br />JEPPSON, PnUr.. 1957. The control of squawfish by
<br />use of dynamite, spot treatment, and reduction
<br />of lake levels. Prog Fish-Cult. 19(4), pp. 168-
<br />171.
<br />KENIIEDY, \X~. A. 1951. The relationship of fishing
<br />effort by gill nets to-the interval between lifts.
<br />)our. Fish. Res. Bd. Canada, B(4), pp. 264-274.
<br />LAWL6R. G. H. 1950. The use of n}-Ion netting in
<br />the gill-net fishery of the Lake Erie whitefish.
<br />Canadian Fish. Cult., No. 7, pp. 22-24.
<br />T~1('
<br />The his'.
<br />Present dis;
<br />is examinr~.:
<br />gested.
<br />The recent api
<br /><arpio, in Saskat.
<br />vestigation of its
<br />water systems ~
<br />(1955) has re~i~
<br />into Ontario be
<br />points out the in
<br />Fisheries persona,.
<br />In Manitoba s
<br />food supply for
<br />report of Mr. .
<br />Fisheries, Manit~~'r
<br />sional Papers of
<br />1886. This office
<br />bet, 1885, he rerc
<br />age, from the ha i
<br />These fish were l~'
<br />Portage la Prairie
<br />lowing year a fur
<br />rained from the
<br />individual, but n
<br />success of either
<br />the species.
<br />Failure to establ
<br />(Sessional Papers
<br />upon those charge.
<br />for is -late autumn
<br />was obtained fron-
<br />sioner, Washingt~
<br />these fish in a mil
<br />in Lake Minnea a~
<br />Manitoba. It thin
<br />introduced into ~~
<br />boine River s~~st~.~.
<br />early as 1889. In
<br />was a strong re<< ~;
<br />Christ, Fishery (?~.
<br />District of AssiniF
<br />'Contribution from
<br />pan Department of is
<br />Saskatchewan.
<br />
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