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<br />
<br />132
<br />
<br />CALIFORNIA FISH AND' GAME
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<br />in 1942 it is known that spawning was in progress then. Not enough
<br />information is at hand to determine the exact spawning periods of the
<br />different species of the Colorado. Those of some (bluegills, for example)
<br />may be fairly extended, However, with the exception of the mullet
<br />known to spawn in the autumn, it seems probable that most of the fishe~
<br />spawn here during the period when the water temperature is risin"'.
<br />That is, they are spring spawners, rather than fall spawners. ' .,
<br />The gromng season for fish is also lar-gely dependent upon tem-
<br />perature. During the warm periods more food is produced and the
<br />metabolism of fish is increased, In Norris Reservoir, Tennessee.
<br />__=__ Jones.(1941), determined the growing season of the largemouth bass
<br />to be. about four months in duration,' ccirrespondingclosely.to that
<br />period during which the water is 750 F. or above. If his findings are
<br />applicable here we might expect a gromng season of about the same
<br />duration-roughly from mid-May to mid-September.
<br />It should be noted that while the graphs for the river show tbe
<br />general trend of water temperature, they do not necessarily present a
<br />complete picture of the conditions prevailing in all parts of the Colo-
<br />rado district. These temperatures were taken in the main river channels,
<br />Much higher temperatures undoubtedly occur in the bays "and coves,
<br />in shallow expanses of the lakes, in quietly flowing sloughs, and in cut-off
<br />waters. Since it is in such areas that the game fishes are most abundant
<br />we might expect a somewhat longer growing season and an earlier
<br />spawning season than has been indicated above.
<br />So far we have dealt only with surface water temperatures, How-
<br />ever, there is usually but little difference in the temperature of surface
<br />and subsurface waters in streams. This is especially true in a river such
<br />as the Colorado where the flow is fairly rapid and which lacks, in the
<br />ordinary sense of the word, deep pools. Temperatures at depths were
<br />taken only in Lake Havasu, On February 15, ,1942, temperatures ,"ere
<br />taken in the expansion of the lake opposite Needles Boat Landing
<br />Here there was a difference of only 30 F. between the surface water
<br />(550 F,) and the bottom at 27 feet (520 F.). On :May 20, 1942, another
<br />series was taken at the lower end of the reservoir a few hundred feet
<br />above the dam, A difference of 100 obtained between the surface (SaC F,\
<br />and the bottom at 40 feet (700 F.), The lake was being lowered on
<br />this occasion, Any discussion of the thermal characteristics of Lake
<br />Havasu awaits the collection of temperature records at different depth,:,
<br />stations, and seasons, and under varying conditions of draw-off, It
<br />seems doubtful, however, that there would ordinarily be any degree of
<br />thermal stratification which could markedly affect the fishery.
<br />The thought has been expressed by a few people that the sectioll of
<br />the Colorado River immediately below Parker Dam has been so altered
<br />bv the dam that it is now suitabie for trout, It is true that below Boulder
<br />Dam a portion of the stream has been changed to trout water through
<br />removal of the silt and reduction of the water temperature. Aside froIll
<br />the similarity in clarity of the river for some miles below Parker DaIll,
<br />there can'1>e no comparison of the two areas, \Vater at Lake Mead is
<br />usually released at depths of from 120 to 320 feet below the surface.
<br />depending on the water level and on the discharge gates used. The water
<br />from such depths is c.Jld, ranging between 54 and 610 F. during l~l-!O
<br />'!nd 1941. (Moffett, 1942.) At Parker Dam, the normal discharge
<br />
<br />
<br />.. THE FlSH~Y - OF-iiiE- ~WER (JOwWo ..vER - --i'3:r.'cc: ----;-'F'
<br />
<br />,throUt~ ~pillway gates whose lower level is only 50 feet below
<br />".~me Ig -water mark of the reservoir. Fig. 61 shows that the
<br />,temperature here continues to f-ollow the same fluctuatin ,e de:
<br />further .d~WDstream. It is but little cooler during th .g Y d
<br />than It IS at Blythe and Yuma. e spnng an
<br />
<br />"COlorado River downstream view {rom Parker Dam.
<br />,';'7" but warm, .\Iay 1942, The water here is clear
<br />
<br />7 ~; ,- -
<br />
<br />'.~ m.v~B~~~::Sb to this .Mo~eft (1942). describes th~ water 10 miles
<br />_ :~,,~"'" d 1 am (\VIllo" Beach, ArIzona) as haYlDcr a remarkablv
<br />_ ~_""" 1m. coo temperature "Th t ,'" .1
<br />_ _ ~;;:-:o~r one or tw ',ese. emperatures dId not fluctuate
<br />-':.;{~-a9 and 1940 ~,de~[e~s F~hrenheIt v.:mte.r or .summer during the years
<br />. _ thi '. . 0 ett s graph (his FIg. 23) shows the temperatur@
<br />'tobe s f~~~od to average about 550 F. During the five-veal' period
<br />B:ach w t~~~ctober ~941 the highest temperature ~ecorded at
<br />_ f as {{ F. ThI:'l was an unusual occurrence due to the dis-
<br />~ ~ater over the ~rIz?na spillway of Boulder Dam. During
<br />o 0 Bmb~, 1941 thIS dIscharge raised the averacre temperature
<br />w ,,~~c ul~ 61-h69.50~. In speaking of this, ~Ioffett (1942)
<br />J O. suc. a spIllway dIscharge reach the river durin
<br />er, r.e~ultmg hIgh temperatur~s might be disastrous to trouf
<br />~kelY. that any further spIllway discharge will be made."
<br />}~d easily seen that temperatures considered extreme just
<br />'.c. ra:J ~am are the usual ~hing below Parker. Here, the mini-
<br />_' 0 .emperatures 4..1 mIles below the dam were above 700 F
<br />~ths ill 1942, a~d f~r over four months in 1943. Temperature~
<br />~'-ess19~12 and 84 F. ill 1943 have been recorded here, and these
<br />-:,,.:arl y represent extremes.
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