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<br />
<br />140
<br />
<br />CALIFORNIA FISH AND GAME
<br />
<br />Only a few quantitative bottom samples were taken in 1942. All
<br />were taken with an Ekman dredge anq represent the organisms takel1
<br />from one-quarter'square foof of bottom after screening through a No. 30
<br />soil sieve. In Lake Ha\'asll nine samples were taken in February near
<br />Needles Boat Landing at depths ranging from 1.5 to 27 feet. The aver.
<br />age number of organisms taken per, sample from here was as follows:
<br />0.11 ma;yfly nymphs; 0,33 caddisfly larv\l.e; 11.0 chironomid larvae. TW0
<br />samples taken at Palo Verde Slough near Palo Verde at 8 and 12 feet on
<br />February 9th had an average of: 2 oligochaetes; 0,5 snails; 21.5 ell irn.
<br />nomid larvae, Three from Haughtelin Lake taken on January 30th, at
<br />depths ranging from 3 to 5,5 feet, averaged: 7 oligochaetes; 1.66 snails;
<br />---::=---'l~33Inayfiynymphs; -2:33 caddis lar-vae-;--l~.o.~nomids,_~The n UliI bel'
<br />of organisms taken per unit area was not large. However tlie-Samples, few
<br />as they are, at least indicate the presence of more bottom food than was
<br />. found by :Moffett (1943) at Lake Mead. In twelve one-quarter square foot
<br />samples he found no organisms large enough to be retained in 'a 30-mesh
<br />per inch screen, with the exception of a single midge larva.
<br />The population of fishes is large in the three sampled areas, and it is
<br />considered that it is far better to depend upon their abundance and good
<br />condition as an indicator of food production than to rely heavily on a few
<br />bottom samples. For a general picture of the food relationships of the
<br />fishes of the lower Colorado see Table 2.
<br />
<br />Plant Foods
<br />
<br />Microscopic algae are utilized directly by some fishes, especially h!'
<br />mullet. They are, of course, the primary food of the invertebrate ani,
<br />mals which, directly or indirectly, form the basic food of most of thi'
<br />riyer's fishes, The larger filamentous forms were also found in some fish
<br />stomachs. Fragments of higher plants (N ajas, cattail, and lean"s of
<br />terrestrial plants) and their seeds are also eaten by some fishes, A ?!reater
<br />importance of the larger algae and aquatic spermatophytes in foed pr".
<br />duction probably lies in their affordance of a habitat for cr11~tact'a.
<br />rotifers, and insects,
<br />
<br />Animal Foods (Invertebrate)
<br />
<br />Among the invertebrate animals which are 11sually classed as imp,,]".
<br />tant fish foods, only a few types were not found during the sun-ey. :-itoIl.':
<br />flies (Plecoptera) and heUgramites and alderflies (Neuroptera) seelli'" ,
<br />to be unrepresented. among the aquatic insects,12 No" shrimp" (Rlllph
<br />pods) were seen, No clams or mussels were taken. Grinnell ')9H
<br />stated that" As far as known · · · [i.e., to him] · · " Jl1 tt:
<br />Needles-to-Yuma section of the river yalley there are no aquatic lD""
<br />luscs · · .." However, in 1942, snails were fairly commOll alo!'~
<br />the shores of Lake Havasu and were also found in the river itself llCJ:
<br />Blythe, in Palo Verde Slough, and in Haughtelin Lake. :
<br />Small crustacea (cladocerans, ostracods, and copepods) were fouD'-
<br />in many fish stomachs. These forms were most abundant in cut-off ",aW'"
<br />_ but were also numerous in waters connected d.irectly with the riw~
<br />Surface plankton hauls taken at Haughtelin Lake on January 31, 194-
<br />
<br />1lI Moffett (1942) reported stonefiy nymphs as occurring rarely In the ri'cer be"-
<br />Boulder Dam.
<br />
<br />
<br />
<br />
<br />THE FISHERY OFTHE' LOWER--COWRADO' RrvER---
<br />
<br />_TABLE 2 ,.
<br />
<br />o'1"elatio:s of some commonCoioradoRiver- -fishes .. determined from
<br />om~c analyses. ?<o pre.::lominant food jtem. x,food of Inser
<br />Importance; p, present
<br />
<br />Food item!,
<br />
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<br />Aquatic inoecl. I
<br />~ ~, I~ : ~ ~IQlrIQ ~1121:z: ~ ~ ~ =I~ ~ ~ ~ ~
<br />! ~~ ~~~~l~ i"i ~.fg:i~j r~ g,~
<br />t ~,~., ~ ~" J ~ ~ I! I ~ I ~ ~ ~ I I t I
<br />II I; - li ., ',' "-I" r il il -, =' E: 61 ~,', "'-
<br />~ i~~'";'" : :..:1: ~,,~~ii 'e;r-L~.
<br />5. , Iii ' . :. !: Ii tll 3y ~ ~ '5' .". go
<br />.,,:,:: '''Tr;c;''-~..r::''''-
<br />!"-.'.. :~-I:flie,~!>"',,::
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<br />:jj .ir~~1:-rI~iii~
<br />: : ~ : : t ~: : : : : : : : ~
<br />: : : : : . : : : : : 1: : : :
<br />
<br />"' , ~~=I r ~' , ',' 'f-I( I'~-
<br />"1'1==1=1'1-;' '~xrx i,1 ch
<br />'. I'~II'H'FI'II II~I=I'~~~I'
<br />
<br />!-'_I~I.:J.:J_I_I-.:.I.~J,~J I I x 1-1-1- -!~I-
<br />!_i_i_i~I_I_i_j_~..ij~i -i-I-;I-I-[-I-!-:-
<br />IXiX,X;., i ! Ix! 'xl-:~!X!~'Xi-i-l-i-
<br />I xi .i . ':=1=1] I i x ;xi~i~rxi-,i~i-!,!-Xl~l-
<br />Iii ' . I I .-'-'--1----'--
<br />i ! i lit. I IX!,: 11'1 i',Ix:xixi
<br />. ! ,! Iii.' I i ( ,
<br />
<br />Crust&ceans
<br />
<br />F'1Ih..
<br />
<br />':'_~dtbout 80 per cent cope pods and 20 per cent cladocerans. Great
<br />,,0_ D..~phma an.d copepods were found in Palo Verde Slough on
<br />ltfoc-caslOlls, QUlet waters such as the mouth of the intermittent
<br />irY~ may also support such forms in abundance. As yet crav-
<br />'!l'/1l. arus) seem to be established only near Yuma. ,.
<br />~~, ry, dragonfly, mayfly, caddis, and chironomid larvae appear
<br />ant and staple food items of the fishes here as in most waters.
<br />.ihet>ther common aquatic insects found in stomachs and seen
<br />,~:;ters were beetles and backswimmers (Notonectidae).
<br />f.j,Elli~
<br />
<br />b'1<lssupply of forage fis.h appears to be a requisite for the needs
<br />;~.. The larger crappIes and perhaps the larger channel catfish
<br />~lSC!VOrous. In the Colorado River are found at least three
<br />,;a~e acknowledged food for bass: bluegill sunfish; green
<br />V Ultofish. All of these species are abundant. Possibly the
<br />era! other of the abundant fishes such as the carp and mullet
<br />~o.
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