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.', i\ .... ,.;!::; -R713~rd~G~:- ~ir<1 7~q JQ8'5 \ i t 1 I I I I j, ,,/" /i I I ( -',oJ', ! j r.0707G REPRODUCTIVE ECOLOGY OF THE HUMPBACK CHUB AND TIlR ROUND1'AIL COOD IN THE UPPER COJ,ORADO RIVER Bob D. Burdick and Lynn R. Kaeding United Stat.es .'ish and Wildlife Service Colm'ado River Fishery Project 551 25 1/2 Road -- Suite B113 Grand Junctiont Colorado 81505 ABSTRACT The endangered humpback chub (gila fXPha) is sympatric with the more abundant roundtai I chub (qUg, r~~H~tl:!) in some deep--water hubi t.ats of the upper Colorado River. Some gene exchange might occur between these two species, and there is concern thut further alteration of t.he river ecosystem might jeopal-dize the humpback chub genome. Research was conducted at Black Rocks on the Co] or'ado River in western Colorado in 1983 and 1984 to obtain information about the spatial and temporal spawning relationship of these two species. Discriminant analysis was used to objectively classify mature-size Gi.!~ to the humpback chub or roundtail chub taxon on the basis of nine taxonomic characters measured from fish afield. Spawning of humpback chubs and roundtail chubs temporally overlapped in both 19B:~ and 1984. Gonadosomatic indices and mean ovum diameter were the most definitive data available to estimate spawning time. The occurrence of expressable ova was correlated with the changes in gonodosODlatic indices and was the best non-lethal method to estimate spuwning time. Roundtail chubs spawned between the first of June and mid--July 1983 whereas hwapback chubs spawned near the end of June. Spawning time for both fishes occurred later in 1984. Roundtail chubs spawned between mid-June and mid-July; humpback chubs spawned near t.he end of JuLy. OccuITence of nuptial tubercles, expressable milt and relative body condition generally had limited application as a dcfinH:ive indication of spawning time. The location of radio-equipped humpback chubs during the spawning period in both years suggested that they spawned in deep--water areas adjacent to met.amorphic rock formotions, near locations where they were initially captured. Information obtained from humpback chubs that were equipped with radiotransmitters over {I thret~hmonth period both years and from the recapture of tagged fish indicated li tt Ie longi tudinal movement froll the 2-km rest.ricted habit.at of Black Rocks. Radio'-cquipped roundtail chubs exhibited long-distance movementt both upstream and downstream from the Black Rocks areat and were located outside the Black Rocks river reach during the estimated spawning period in 1984. 163