Ted McKinney

Rainbow Trout in a Regulated River below Glen Canyon Dam, Arizona, following Increased Minimum Flows and Reduced Discharge Variability

Abstract We examined the effects of dam operation on the relative abundance and relative condition of rainbow trout Oncorhynchus mykiss captured by electrofishing between 1991 and 1997 in the Lees Ferry tailwater below Glen Canyon Dam, Arizona. Higher minimum, higher mean, and more stable flow releases from the dam after 1991 provided conditions that supported greater relative abundance of rainbow trout. Though the relative abundance of most length-classes increased following the onset of a stabilized flow regime, relative condition declined, particularly in large rainbow trout (≥305 mm). Correlation analyses suggested that the small rainbow trout (<305 mm) were more strongly influenced by physical factors (flow variation, mean discharge, and water temperature) than the large trout (≥305 mm). However, the relative condition of small trout was negatively correlated with that of all trout, and the condition of trout 305–405 mm in length was negatively correlated with the relative abundance of trout within ...

EFFECTS OF A TEST FLOOD ON FISHES OF THE COLORADO RIVER IN GRAND CANYON, ARIZONA

A beach/habitat-building flow (i.e., test flood) of 1274 m3/s, released from Glen Canyon Dam down the Colorado River through Grand Canyon, had little effect on distribution, abundance, or movement of native fishes, and only short-term effects on densities of some nonnative species. Shoreline and backwater catch rates of native fishes, including juvenile humpback chub (Gila cypha), flannelmouth suckers (Catostomus latipinnis), and bluehead suckers (C. discobolus), and all ages of speckled dace (Rhinichthys osculus), were not significantly different before and after the flood. Annual spring spawning migrations of flannelmouth suckers into the Paria River and endangered humpback chub into the Little Colorado River (LCR) took place during and after the flood, indicating no impediment to fish migrations. Pre-spawning adults staged in large slack water pools formed at the mouths of these tributaries during the flood. Net movement and habitat used by nine radio-tagged adult humpback chub during the flood were no...

AQUATIC FOOD BASE RESPONSE TO THE 1996 TEST FLOOD BELOW GLEN CANYON DAM, COLORADO RIVER, ARIZONA

We examined the impact of the 1996 test flood released from Glen Canyon Dam (GCD) on the aquatic food base in the Colorado River through Grand Canyon National Park, Arizona, USA. Benthic scour and entrainment of both primary and secondary producers occurred at all study sites along the 385-km river corridor. The majority of the organic drift occurred within the first 48 h of the test flood with the arrival of the hydrostatic wave. Recent macrophyte colonizers (Chara, Potamogeton, and Elodea) of fine sediment in the tailwaters were scoured from the channel bottom, with recovery to pre-flood estimates within 1–7 months depending on taxa. Macroinvertebrates and filamentous algae recovered within three months depending on taxa. The test flood removed suspended particles from the water column and increased water clarity, which enhanced benthic recovery. The test-flood hydrograph was designed primarily as an experiment in sand transport and occurred during a period of sustained high releases from GCD starting i...

Effects of Flow Reductions on Aquatic Biota of the Colorado River below Glen Canyon Dam, Arizona

Abstract We examined influences of 3 d of reduced flows on biotic assemblages in the Colorado River below Glen Canyon Dam, Arizona. Exposure in the varial zone reduced standing crops of periphyton, pondweed Potamogeton pectinatus, and benthic macroinvertebrates, and losses following the drawdown were not explained by expected seasonal trends. Losses in macroinvertebrate densities and mass and in periphyton mass and chlorophyll a suggest that effects of a sudden reduction in dam discharge of moderate duration and magnitude are comparable with losses associated with the varial zone of fluctuating daily flows. Compared with expected seasonal changes, abundance of rainbow trout Oncorhynchus mykiss increased during and following reduced flows. Proportional composition of fish less than 152 mm total length (TL) was greater after the drawdown, whereas the percentage of trout 406–558 mm declined. Relative condition factor before, during, and after the drawdown did not differ significantly for all fish combined, f...

Evaluation of Factors Potentially Influencing a Desert Bighorn Sheep Population

Abstract We studied a desert bighorn sheep (Ovis canadensis) population in the Mazatzal Mountains (primary study area) in central Arizona and population indices on reference areas between 1989 and 2003. We evaluated disease exposure and nutritional status of desert bighorn sheep, vegetation parameters, predator diets, and mountain lion (Puma concolor) harvest and abundance (1999–2003) and mountain lion predation (1995–2003) as factors potentially affecting desert bighorn sheep and population parameters. We measured rainfall monthly, monitored demography and relative abundance of desert bighorn sheep using aerial surveys, captured and placed radio collars on desert bighorn sheep, and collected samples of blood, parasites, and other pathogenic agents from captured animals. We measured mineral content, relative use, and structural composition of vegetation and determined diets of desert bighorn sheep adults and lambs, dietary intakes of nitrogen (FN), 2,6-diaminopimelic acid (FDAPA), neutral detergent fiber, and minerals using fecal analyses. We incorporated mountain lion reductions as an experimental element, monitored harvest, and used track surveys as an index of relative abundance of the predator and monitored radio-collared desert bighorn sheep to determine mortalities and causes of death. We determined diets of bobcats (Lynx rufus), coyotes (Canis latrans), and mountain lions using fecal analyses. Drought conditions occurred during summer (July–September) and winter (November–April) during 4 and 3 years, respectively, between 1999 and 2003. Annual surveys indicated that the Mazatzal Mountains population declined during drought between 1994 and 1997, experienced low growth and lamb production coincident with above-normal rainfall in 1998 and drought in 1999, and exhibited higher growth, production, and productivity during 2000–2003 despite persistent drought conditions during this period. We observed no clinical symptoms of disease in radio-collared desert bighorn sheep, and hematological and other evidence of exposure to disease agents was unremarkable. Population indices on the primary study and reference areas were positively correlated with winter (November–April) rainfall. We found no evidence of forage overutilization on the primary study area. Rainfall on Mazatzal Mountains was associated with differences in primary production, particularly of forbs, forage mineral concentrations, and diets, nutritional status, and demographic attributes of desert bighorn sheep between 1999 and 2003. Higher winter rainfall was associated with higher forb growth, and higher rainfall was associated with higher concentrations of P and Se but lower levels of Fe in browse; higher concentrations of Ca, P, and Zn in forbs; and higher levels of P, Se, and Zn in grasses. Narrower mean Ca:P ratios of browse and forbs were associated with higher rainfall. Diets of desert bighorn sheep adults and lambs generally were similar, particularly near summer, and forbs tended to predominate in diets during wetter and drier years. Higher winter rainfall was associated in adult feces with more prolonged winter-to-spring increases in FN and FDAPA concentrations, higher fecal phosphorus, lower fecal Ca levels, and narrower fecal Ca:P and Na:K ratios, but levels of fecal Na increased during the driest year. Higher winter rainfall corresponded in lamb feces with higher levels of FN, FDAPA, and fecal P; lower concentrations of fecal Ca; and narrower fecal Ca:P ratios. Thus, we hypothesized that diets and nutritional status of desert bighorn sheep adults and lambs tended to correspond with rainfall patterns and associated differences in relative abundance and mineral content of forages. We found no evidence that bobcats or coyotes preyed on or scavenged desert bighorn sheep. Decline of desert bighorn sheep abundance during 1994–1997 was greater than declines on reference areas lacking mountain lions despite continually higher, and a lesser decline in, winter rainfall on the primary study area. In comparison, population indices on a reference area and on Mazatzal Mountains increased between 1999 and 2003 in association with predator reductions and lower abundance of mountain lions and predation of radio-collared animals despite continued occurrences of drought during this period. We thus identified 2 proximate factors that likely acted to influence demographic trends of the Mazatzal Mountains desert bighorn sheep population: nutritional status (higher rainfall [ultimate factor] was associated with higher availability and differences in mineral content of forages and improved indices of desert bighorn sheep nutritional status) and predation by mountain lions. We hypothesize that nutritional status and mountain lion predation during a period of drought influenced desert bighorn sheep population parameters in Mazatzal Mountains and that short-term removal of mountain lions by lethal harvest contributed to higher growth and productivity of the small, isolated population, even during periods of drought.

EFFECTS OF MIDSUMMER DROUGHT ON MORTALITY OF DOE PRONGHORN (ANTILOCAPRA AMERICANA)

Abstract We found that the number of doe pronghorn (Antilocapra americana) seen on summer surveys in 3 areas in the Southwest was related to midsummer drought indices, and that annual variations in doe mortality might be more important in determining population levels in dry years than fawn recruitment. If carrying capacity is indeed limited by a lack of nutritious forage during dry years, pronghorn managers might want to consider reducing interspecific and intraspecific competition during such periods and forgoing predator control and translocation efforts.

Mountain Lion Predation of Translocated Desert Bighorn Sheep in Arizona

Abstract We analyzed data for 422 unmarked and 369 radiocollared desert bighorn sheep (Ovis canadensis) translocated into vacant historical habitats in 12 Arizona locations between 1979 and 1995. We evaluated factors potentially influencing predation of radiocollared desert bighorn sheep by mountain lions (Puma concolor) by determining relationships between predation rates, number released, size of releases, escape terrain, available terrain (escape terrain as a percentage of area with slopes ≥40%), habitat quality associated with release locations, and mule deer (Odocoileus hemionus) and predator abundance. We hypothesized that numbers of radiocollared animals released, quality of habitat and available terrain associated with release locations, and relative abundance of mule deer influenced predation of translocated desert bighorn sheep by mountain lions.

Observations of Size-related Asymmetries in Diet and Energy Intake of Rainbow Trout in a Regulated River

We examined diet and diel energy intake of rainbow trout, Oncorhynchus mykiss, of different lengths captured by electrofishing between 1991 and 1997 in the Lees Ferry tailwater, Colorado River, below Glen Canyon Dam, Arizona. Trout diets reflected a depauperate food base and indicated limited potential of different fish size-groups to partition food resources. As evidenced by relative stomach volumes of ingested matter, mid-sized and large trout tended to consume more algae than did small fish, suggesting that they consumed diets of lower nutritional quality. An energy intake model indicated that median consumers among mid-sized and large fish generally failed annually to surpass estimated maintenance energy requirements and that median consumers among mid-sized trout failed to meet or exceed maintenance requirements during all seasons. In contrast, median consumers among small trout met or surpassed maintenance energy requirements during most years and in summer. Results support a hypothesis that larger rainbow trout in lotic systems are food-limited more often than smaller fish.

Diets of sympatric bobcats and coyotes during years of varying rainfall in central Arizona

Abstract We collected fecal samples (scats) of sympatric bobcats (Lynx rufus) and coyotes (Canis latrans) between 2000 and 2003 in a 53,600-ha area of the Upper Sonoran Desert in central Arizona. Our objective was to investigate composition, diversity, and overlap of diets of bobcats and coyotes in relation to varying rainfall in the Sonoran Desert of central Arizona. In general, bobcats ate more rodents than did coyotes, and coyotes ate more lagomorphs, large prey, and fruit/seeds than did bobcats. Composition of bobcat diets was independent of differences among years in annual rainfall and seasonal rainfall during summer–autumn (May–October) and winter–spring (November–April). Composition of coyote diets also was independent of drought conditions among years during summer–autumn, but coyotes ate more large prey and fewer rodents during years with winter–spring drought. Seasonally, bobcats ate more rodents than did coyotes in summer–autumn and winter–spring, whereas coyotes ate more lagomorphs than did bobcats during winter–spring, and more large prey and fruit/seeds in both seasons. Coyotes ate more large prey and lagomorphs during winter–spring, when seasonal rainfall was higher, and more fruit/seeds in summer–autumn, when seasonal rainfall was lower. Diversity of diets was consistently higher for coyotes than for bobcats, and increased for bobcats but not for coyotes during winter–spring drought and during higher seasonal rainfall in winter–spring. Overlap of diets between predators was independent of rainfall levels. We suggest that bobcats in the Sonoran Desert are more selective, specialized predators and that coyotes are more generalist, opportunistic predators. We hypothesize that, although diversity of bobcat food items and composition of coyote diets differ with varying rainfall in the Sonoran Desert, patterns of feeding strategy are independent of seasonal differences in precipitation and effects of drought, and bobcats and coyotes partition food resources independently of varying rainfall.

Winter Precipitation and Recruitment Of Pronghorns In Arizona

Abstract Recruitment of pronghorns (Antilocapra americana; fawns∶100 females) through late summer was positively correlated with precipitation during the previous winter (October–April) on 10 areas in Arizona during 1983–2002. There was no evidence of serial autocorrelation in recruitment of fawns and no strong within-year effects, even after accounting for differences in winter precipitation among sites. There was no evidence that the relationship between winter precipitation and recruitment differed among populations. Winter precipitation explained 38.5% of variability in recruitment among years within populations. We hypothesize that winter precipitation is a limiting factor affecting recruitment in populations of pronghorns in arid and semi-arid habitats in Arizona.