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ABS77?ACTS OF PRESENTATIONS
<br />LUPHER, M.L.; CLARKSON, R. W. h41-L and RWC - Arizcma Game and Fish Department, Research Branch, Phec nis, AZ. MLL eur e l addro,, I IC 60, Box 870,
<br />Ruby Valley, NV 89833. Paper preserved at rneetirng by Dennis Kubly of Arizona Game and Fish Department, Phoenix.
<br />Temperature tolerance of humpback chub (Gila cypha) and
<br />Colorado squawfish (Prychocheilus lucius)
<br />Tolerancia de temperatura en humpback chub (Gila cypha) y
<br />Colorado squawfish (Prychocheilus lucius)
<br />KEYWORDS: temperature tolerance; temperature shock; Gila cypha; Ptychocheilus hrcius; larvae; juveniles; Little Colorado River; Colorado
<br />River
<br />CLAVES: tolerancia a la temperature; shock termico; Gila cypha; Prychocheilus lucius; Larvas; juveniles; Pequefio Rio Colorado; Rio Colorado
<br />ABSTRACT
<br />The closure of Glen Canyon Dam near the head of Grand Canyon, Arizona, in 1963 resulted in a depression
<br />of spring-summer downstream water temperatures. Post-dam temperatures likely have precluded successful mainstem
<br />reproduction of most native species due to mortality during incubation. In addition, movements of early life stage
<br />fishes from the Little Colorado River, a major undammed tributary used for spawning and rearing, to the Colorado
<br />River mainstem across a large thermal gradient have been surmised to negatively affect survival and growth. We
<br />exposed early life stages of endangered humpback chub (Gila cypha) and Colorado squawfish (Prychocheilus lucius)
<br />to several temperatures to examine effects on survival and growth in the laboratory. All eggs were incubated at
<br />18.6°C and moved to 20°C at swimup for a minimum of 24 h. When transferred from 20°C to 10°C for 4 h, 5-7
<br />d old humpback chub larvae lost equilibrium and mobility for 90 min, but recovered. Same age humpback chub
<br />larvae became lethargic but did not lose equilibrium when transferred from 20°C to 12°C, and no behavioral effects
<br />were observed when moved to 14°C. Similar cold shock experiments with 11-13 d chub larvae affected only the
<br />10°C group, which lost equilibrium for 15 min before recovering. No mortality was observed under any treatment
<br />during the 4 h observation period. Growth patterns of 6-8 d humpback chub larvae reared at 10°C, 14°C, and 20°C
<br />averaged 10%, 37%, and 83% length gain, respectively, and 28%, 195%, and 951% weight gain, over 30 d.
<br />Overall patterns of growth of 13-15 d humpback chub and Colorado squawfish larvae and 39-41 d chub post-larvae
<br />reared at these temperatures were similar. Results suggest that detrimental effects of reduced growth on individuals
<br />and populations of native fishes in Grand Canyon can be ameliorated through modification of Colorado River
<br />seasonal and daily hydrological patterns. We also recormnend consideration of thermal modification of discharges
<br />from Glen Canyon Dam.
<br />RES UMEN
<br />El cierre de la presa Glen Canyon, cerca de la cabeza del Gran Canon, Arizona, en 1963 resulto en una
<br />depresion en primavera-verano de ]as temperaturas del agua corriente abajo. Las temperaturas posteriores a la presa
<br />probablemente ban impedido el exito de la reproduccion en 1a corriente principal de la mayorfa de los peces nativos
<br />debido a ]a mortalidad durante la incubation. Adicionalmente, los movirnientos de los peces de primeros estadios
<br />de vida de el Pequeno Rfo Colorado, un tributario principal no represado usado para desove y crianza, a la corriente
<br />principal del Rfo Colorado cruza un gradiente t6rmico grande, ban sido supuesto que provoca efectos negativos en
<br />la supervivencia y crecimiento. Expusimos los estadios de Vida iniciales del humpback chub (Gila cypha) y el
<br />Colorado squawfish (Prychocheilus lucius) a varias temperaturas para examinar los efectos sobre sohrevivencia y
<br />crecimiento en el laboratorio. Todos los huevos fueron incubados a 18°C y movidos a 20°C a nadar por un mfnimo
<br />de 24 h. Cuando las larvas de 5-7 d de humpback chub fueron transferidos de 20°C a 10°C por 4 horas, perdieron
<br />equilibrio y movilidad por 90min, pero se recuperaron. Las larvas de humpback chub de esta mjsina edad, se
<br />aletargaron pero no perdieron el equilibrio, cuando transferidos de 20°C a 12°C, y no se observaron efectos sobre
<br />el comportamiento cuando se cambiaron a 14°C. Un experimento similar con larvas de G. cypha de 11-13 d afecto
<br />unieamente al grouo de 10°C, el cual perdio el equilibrio por 15 min antes de ]a recuperacion. No se observo
<br />mortalidad bajo ningdn tratamiento durante el perfodo de 4 h de observacion. Los patrones de crecimiento del las
<br />larvas de 6-8 d del humpback chub mantenidos a 10°C, 14°C y 20°C, promediaron 10%, 37 %, y 83 % de ganancja
<br />en longitud, respectivamente, y 28 %, 195 %, y 951 % de gananeia en peso, en 30 d. En conjunto, los patrones de
<br />crecimiento de larvas de 13-15 d y post-larvas de humpback chub y de Colorado squawfish, mantenidos a estas
<br />temperaturas fueron similares. Los resultados sugieren que los efectos detrimentales del crecimiento reducido sobre
<br />individuos y poblaciones de peces nativos en el Gran Canyon pueden ser aminorados mediante la modificacion de
<br />los patrones hidrologicos estacionales y diarios del Rio Colorado. Tambien recomendamos considerar la
<br />modificacion tennica de las descargas de ]a presa Glen Canyon.
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