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<br />130
<br />
<br />CALIFORNIA FISH AND GAME
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<br />afwater temperatures in the lawer Calorado.ll Theircamparison shaws
<br />_ that all points in the study sectian have a similar and fairly regular
<br />pattern. That is, we can usually expect a law paint (af about 500 F.)
<br />in January, after which there is a rise to' a peak between 800 and 900
<br />which halds during most of the June-September periad, fallawed by a
<br />renewed decline. The available recards shaw that temperatures van'
<br />fram a maximum of 900 to a minimum af 400 F., but the normal ran;fo'
<br />appears to' be about 100 less extensive than this. ..
<br />Favorable temperatures far mast af the fishes found in the river 'Ufo'
<br />indicated. They are certainly satisfactor)' for the intraduced game fishfo's
<br />such as sunfishes, bass, and catfishes. They are not suitable for trout or
<br />other cold water species. There have -been times, -of-rourse,- when the
<br />summer flow in the ColoradO' has been very low, and even the main cur-
<br />rent must have reached temperatures far exceeding the ones recarded
<br />here. Some residents have reported many dead fish during such periods,
<br />Now that a gaod constant flow is assured we should not expect a repetition
<br />of these conditions.
<br />The influence of temperature upon many af the river's fishes is
<br />insufficiently understood to warrant much discussion here, but its effect
<br />on largemouth bass, the major game fish, can be treated with some assur-
<br />ance. It has been reported that at water temperatures belaw 500 F,.
<br />largemauth bass usually cease to take food. (Markus, 1933.) Their
<br />rate af metabolism is low and they can not be caught easily even at
<br />temperatures samewhat abave this point. Even sa, there wauld be
<br />anly a shart peri ad when the bass af the Calarada would nat be active,
<br />Cold water in the river daes not appear to have as decided an effect on
<br />channel catfish and these can usually be taken even when the bass
<br />are unresponsive. It may be nated here that the scientific callecting for
<br />fishes in 1942, with baited hoop-nets and gill"nets, was poarest durin!!
<br />the early manths of cald water.
<br />It seems to have been quite generally assumed that the spawning
<br />season of most fishes is regulated largely by water temperatures, Some
<br />recent work (Hoover and Hubbard, 1937; Swingle and Smith, 1943)
<br />has shown that botb tbe onset and duration of the spawning season may
<br />be influenced by other factors, such as light, physical condition of tbe
<br />fish, ar abundance of food. Nevertheless, it is still true that spa'\\Ding
<br />seasons generally show a correlation '\\ith temperature, and that the
<br />spawning of some fishes can be brought about almost at will b;y merely
<br />raising the '\\ater temperature. (See, for example, Creaser, 1934,)
<br />,Judging from the observations which have been made in other localities.
<br />we might expect the bass in the Colorado to spawn when the water
<br />attains a temperature of about 650 F. (See: Jones, 1941; Wiebe, 1 Y35,)
<br />Such a temperature is usually reached here about March or April, and
<br />
<br />n Fig, 59. Water temperatures taken by .he United States Geological Surny at
<br />its gaging station at Yuma, Arizona, Readings made 15 times a month on the average.
<br />usua.lly a.t about 8 a,m. (M,S,T,). Air temperatures from the United States 'WeatMr
<br />Bureau. Yuma, Arizona, '
<br />Fig, 60, Based on graphs furnished by the United States Bureau of Reclamation.
<br />Yuma Project, yuma, Arizona. '
<br />Fig, 61, Temperatures of the river at Yuma from Fig, 59. Temperatures of the
<br />river near BlYthe taken by the Palo Verde Irrigation District about 14 miles ab~~
<br />Blythe. Readings made daUy at 4 p,m. (P,S,T,) from February 14, 1932, to Septern
<br />30, 1943, except during the following periods: July 1-1711942 (no records) ; octobe\~
<br />1942-.1anuary 22. 1943 (no records), Temperatures OI the river at Parker taken.
<br />the United States Geological Surve)' at its gaging station at Parker, Arizona. 4,1 rnl~
<br />dO"'"I1stream from Parker Dam, Readings made 4 to 5 times a month on the awra....
<br />Two-thirds of the readings made in the morning; one-third made in the aften,,)On,
<br />
<br />THE FISHERY OF THE LOWER COLORADO RIVER
<br />
<br />
<br />- 4.It 'TI....IR4T....I "IAN
<br />.: -'- lOATlIt TI..lDE"..T..ioi....EAN ..,.. 'P -- ,- .,
<br />-:--.-.- WAnR T E.U"RATUR~, NICNE.ST "rem- UONTK'
<br />--- _TEA TE..PfAATURE. LOWEn 'OR MONTH
<br />
<br />...' 'monthly, ancim8.ximum and ml ' d d ,"nO'__
<br />rado River, and mean monthly air ntlmum recoturr e ....ater temperat..es of
<br />. c ,empera. €s. at Yuma, Arizona.-
<br />
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<br />FIG, 60, Approximate average of mean monthl
<br />water tempe.ratures of the Colorado Rlve~
<br />at Yuma, Arizona, for the years 1917-1924,.
<br />
<br />- BLYTHE
<br />'....... YuMA
<br />---- PARKER
<br />
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<br />1842
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<br />.143
<br />
<br />on Of mean monthly water temperatures ot the Colorado River at .
<br />uma, near Blythe, and at Parker,-
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