Geology topics

Timothy L. Hoffnagle

Publications and source records attributed to Timothy L. Hoffnagle.

3 recordsLinked to original sources

USGS2012

Parasites of fishes in the Colorado River and selected tributaries in Grand Canyon, Arizona.

As part of the endangered humpback chub (HBC; Gila cypha) Adaptive Management Program, a parasite survey was conducted from 28 June to 17 July 2006 in 8 tributaries and 7 adjacent sections of the main stem of the Colorado River, U.S.A. In total, 717 fish were caught, including 24 HBC. Field necropsies yielded 19 parasite species, 5 of which (Achtheres sp., Kathlaniidae gen. sp., Caryophyllaidae gen. sp., Myxidium sp., and Octomacrum sp.) are new records for Grand Canyon, Arizona, U.S.A. Spearman's correlation coefficient analyses showed no correlations between parasite burden and fork length for various combinations of fish and parasite species. Regression analyses suggest that no parasite species had a strong effect on fish length. The most diverse parasite community (n=14) was at river kilometer (Rkm) 230, near the confluence of Kanab Creek. The most diverse parasite infracommunity (n=12) was found in the non-native channel catfish (CCF; Ictaluris punctatus). Overall parasite prevalence was highest in CCF (85%) followed by that in HBC (58%). The parasite fauna of humpback chub was mainly composed of Bothriocephalus acheilognathi and Ornithodiplostomum sp. metacercariae.

Arizona↗

USGS2006

Parasitism and body condition in humpback chub from the Colorado and Little Colorado Rivers, Grand Canyon, Arizona

Glen Canyon Dam has greatly altered the Colorado River in Grand Canyon. The Little Colorado River (LCR) provides a small refuge of seasonally warm and turbid water that is thought to be more suitable than the Colorado River for endangered humpback chub Gila cypha. However, the LCR has low productivity and contains nonnative fishes and parasites, which pose a threat to humpback chub. The Colorado River hosts a different suite of nonnative fishes and is cold and clear but more productive. We compared condition factor (K), abdominal fat index (AFI), and presence and number of two introduced pathogenic parasites (Lernaea cyprinacea and Bothriocephalus acheilognathi) between juvenile (<150 mm total length) humpback chub from the LCR and those from the Colorado River during 1996a??1999. Both K and AFI were lower and L. cyprinacea prevalence and B. acheilognathi prevalence were higher in LCR fish than in Colorado River fish for all years. Mean K and AFI were 0.622 and 0.48, respectively, in the LCR and 0.735 and 2.02, respectively, in the Colorado River, indicating that fish in the Colorado River were more robust. Mean prevalence of L. cyprinacea was 23.9% and mean intensity was 1.73 L. cyprinacea/infected fish in the LCR, whereas prevalence was 3.2% and intensity was 1.0 L. cyprinacea/infected fish in the Colorado River. Mean prevalence of B. acheilognathi was 51.0% and mean intensity was 25.0 B. acheilognathi/infected fish in the LCR, whereas prevalence was 15.8% and intensity was 12.0 B. acheilognathi/infected fish in the Colorado River. Increased parasitism and poorer body condition in humpback chub from the LCR challenge the paradigm that warmer LCR waters are more suitable for humpback chub than the colder Colorado River and indicate the need to consider the importance and benefits of all available habitats, as well as biotic and abiotic factors, when managing endangered species and their environment.

Arizona↗

USGS2001

Effects of pool formation and flash flooding on relative abundance of young-of-year flannelmouth suckers in the Paria River, Arizona

Flannelmouth sucker, Catostomus latipinnis , a fish endemic to the Colorado River basin in the western United States, appears to experience poor recruitment to adult size in the Colorado River, downstream of Glen Canyon Dam. Lack or impermanence of rearing areas for young-of-year (YOY) fish is hypothesized to be the problem. Knowing the importance of tributary mouths as rearing areas in other river systems, we studied use of the mouth of the Paria River, a tributary of the Colorado River, by YOY flannelmouth suckers, and the availability of rearing area in the mouth at different flow levels in the Colorado River in 1996 and 1997. We also examined the relationship between flash floods in the Paria River and catch-per-unit-effort (CPUE) of YOY in the Paria River between 1991 and 1996. Maximum mean daily discharge in the Paria River was inversely correlated with CPUE of YOY flannelmouth suckers (Spearman Rho=−0.9856, p =0.0003) during their critical rearing period (15 March–30 June). Thus, it appears that YOY flannelmouth suckers rear longer in the Paria River in years when flash flooding is minimal. Recruitment of YOY flannelmouth suckers at the Paria River may also be improved by enhancing pool formation during spring and summer rearing seasons. YOY flannelmouth sucker was captured in a pool created by high Colorado River flows (≥336 m 3 /s) that inundated the mouth of the Paria River during spring and summer, 1996. In 1997, high flows (about 550–750 m 3 /s) in the Colorado River during winter and spring initially inundated the Paria River and formed a pool in the mouth. However, these high flows eventually caused 0.5–1.0 m of suspended sediment from the incoming Paria River to deposit in the mouth. Thus, despite higher flows than 1996, the slackwater area formed only occasionally in 1997. Differences in pool formation between 1996 and 1997 demonstrate that pool formation cannot be inferred solely from Colorado River flows.

Arizon↗