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146 CALIFOR~ FISH A..~ GAME It may be argued that physical changes in the river (whether bene. ficial or adverse) would affect both the native and alien species alike, and that, therefore, the population of the natives should have increased again. This argument is probably a valid one. The native fishes probably had a high biotic potential which allowed them to survive tlfe great environ. mental resistance of the "pre-Boulder" Colorado River. .And-had it not been for the presence of competing exotics-with lowered environm~ntill resistance the realization of this potential might have resulted in iln increase in their numbers even exceeding the high points of pre\"i"lls populations. But it is equally true that the biotic potential of the intro. duced fishes bad been suppressed, and with the erection of Boulder Dam it had its first cbance for full expression-an expression culminating ill their ascendancy. We are assuming here that the "new" river pre- sents a more favorable habitat for both native and exotic fauna, \Vhilf' this is probably true, one must not overlook the possibility that changes in the stream may not have been entirely advantageous to tbe silt-adapted resident forms, Doan (1941), for example, suggests that higber turbidi- ties in western Lake Erie actually increase the survival of young sangers (Stizostedion canadense). HiS work is cited, not because similar cOIlrli- tions are believed to obtain in tbe Colorado, but merely to point out That a factor which is generally considered to be unfavorable may actually be beneficial. The foregoing discussion is purely theoretical, of course. Whether it was the complete set of peculiar circumstances related above, or whether it was some other factor or combination of factors can not be determinedYi But we have apparently witnessed a rather complete biological revolution in which a native fauna bas been largely replaced by a new one within only a few short years. No att.empt is made in this report to present an up-to-date checklist of the fishes of the lower river.16 Only those fishes are discussed \l'l1i(~h are known to be of importance to the present fishery, or which mil." he expected to come to the angler's attention, In general, literature on Colorado River fisbes prior to Gilbert and Scofield (1898) has not been consulted. In the following account each species is treated under some or all d these headings, Local Names. Those names known to be applied by residents of the Yuma-to-~eedles section, (The lists could undoubtedly be extended,) Recognition Characters. There is as yet no single key or descri ptin list which v.-ill enable one to identify all of the fishes of the lower riwr, Nor will the brief treatment of recognition characters given here fUlfill this purpose, It has been thought advisable, however, to list enough characters for each fish or group of fishes so that the most common ones 1ll TarzweIl (1939) has described changes In the Clinch River caused by the con- struction of Norris Dam which released water of about 4S' F. Into a stream whose nonna! summer temperature was SO' or over. "Most of the bottom organisms and fish formerly present in this section moved out or were destroyed." While the change to a low temperature below Boulder Dam might have caused some change In the fauna. similar tQ, that In the Clinch River, this ef!ect would be confined to but a short section of the lower Colorado, A most Ingenious explanation of the decline of the native fishes has been propnsed by several rlvermen, They believe that during one of the droughts In the pre.Boulder period, most of the fishes swam far up the river seeking cooler water. Here. 50 theY say. one can still find them-trapped by the dam, 1ll The references cited by Hubbs and Miller (1941) otl'er a good start f(,r the compilation of su<;:h a list. 147 THE FISHERY OF THE LOWER COLORADO RIVER !jecognized. It should be understood that they they do not COID- ,describe each fish anq that this list does not include all of the ~cies which have been recorded. In some cases a fairly large ;~ of negative characters (such as "absence of spines") has been , 91'der to avoid the use of technical terms. -:f-idicn}. Abundance; H<ibitat. With but a few exceptions no t bas been made to indicate the distribution or abundance of any ide the limits of the surveyed section.~ Similarly," habitat" ,to the type of environment frequented by each species in the >';area. In indicating collections, the use of the term' 'survey" refers :ftions JD.adeby Mr. Ohe~erYY q()c!h]l!Lanj.Jp.e~~!hoz:~ i~ 1~42.:_._ , - -""-- Jkowth; Condition. All records of lengths and weights are given es and pounds. (While it is often convenient for the scientific ":[1.0 use the metric system for such measurements, the use of the . '8yBtem is more intelligible to fishermen.) Unless otherwise 19n9ths denote measurements from tip of snout to fork of caudal ion. 'Under this heading such subjects as spawning season, ~tnritt, etc. are discussed. ~though a considerable number of stomachs was examined, the N large samples of several species of fish taken from the same .{)r type of habitat at the same time makes it impossible to indicate tlIe food preferences of individual species. In most cases only " eof the stomach analyses is presented. .A general picture of food ,~~ 'ps has already been given (Table 2). -"c:Jhe Fishery. .An attempt is made to summarize briefly the role , species in the lower Colorado: its value either as a sport, food, bait, ;'01" forage fish; its interrelationships with the other fishes; its 'in tbe stream's economy. ",'.. rather elaborate system of subheadings by no means implies we have even a fairly complete kno\vledge of any of the fishes of the . ;On the other hand it should enable one to see clear]v just how 'large blanks remain to be filled by further study. . Elopidae. Ten-pounders '~II,!,~~~I E.laps "fiais Regan ames. It seems likely that the" gars," "pikes," and" anchovies" _,by local fishermen are Elops. A few people insist on calling /tarpon.' '11 "'ition Characters. Tbe slender, graceful body, bright silver color, tked tail, and large eyes make it easily recognizable, No other ~.the river has the following combination of characters: absence . .~, in the fins; dorsal and anal fins depressible into a high sheath "~i ~othed mouth; bony plate between the branches of the lower , ny names have been applled to EloPB (awa, awaawa, big-eyed herring, big- . bonefish bonyfish. chiro, horse mackerel, jaclunariddle, John ~!ariggle, th herring, Usa francesca. matajuelo real). The term ten-poun<;l.er (inappro- ~t may be for this fish) seems to be most generally accepted In literature.