Geology topics

L.G. Coggins

Publications and source records attributed to L.G. Coggins.

3 recordsLinked to original sources

USGS2011

Distribution and movement of humpback chub in the Colorado River, Grand Canyon, based on recaptures

Mark-recapture data from the federally endangered humpback chub Gila cypha in the Colorado River, Grand Canyon, were analyzed from 1989 to 2002 to determine large-scale movement patterns and distribution. A total of 14,674 recaptures from 7,127 unique fish were documented; 87% of the recaptures occurred in the same main-stem river reach or tributary as the original captures, suggesting restricted distribution by most fish. A total of 99% of all recaptures were from in and around the Little Colorado River (LCR), a tributary of the Colorado River and primary aggregation and spawning location of humpback chub in Grand Canyon. Time at liberty averaged 394 d, but some fish were recaptured near their main-stem capture location over 10 years later. Proportionally fewer large (>300-mm) humpback chub exhibited restricted distribution than small (<200-mm) fish. However, several fish did move more than 154 km throughout Grand Canyon between capture and recapture, suggesting that limited movement occurs throughout Grand Canyon. The majority of the recaptured fish remained in or returned to the LCR or the Colorado River near the LCR. Although many large-river fishes exhibit extensive migrations to fulfill their life history requirements, most of the humpback chub in Grand Canyon appear to remain in or come back to the LCR and LCR confluence across multiple sizes and time scales. Detecting trends in the overall abundance of this endangered fish in Grand Canyon can probably be accomplished by monitoring the area in and around the LCR.

Transactions of the American Fisheries Society↗

USGS2006

Abundance trends and status of the Little Colorado River population of humpback chub

The abundance of the Little Colorado River population of federally listed humpback chub Gila cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture-recapture-based abundance estimators. Analyses of data from all sources using various methods are consistent and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high proportion (>80%) of the adult population being marked by the mid-1990s. Analysis of these data using both closed and open abundance estimation models yields results that agree with catch rate indices about the extent of the decline. Survival rates for age-2 and older fish are age dependent but apparently not time dependent. Back-calculation of recruitment using the apparent 1990s population age structure implies periods of higher recruitment in the late 1970s to early 1980s than is now the case. Our analyses indicate that the U.S. Fish and Wildlife Service recovery criterion of stable abundance is not being met for this population. Also, there is a critical need to develop new abundance indexing and tagging methods so that early, reliable, and rapid estimates of humpback chub recruitment can be obtained to evaluate population responses to management actions designed to facilitate the restoration of Colorado River native fish communities. ?? Copyright by the American Fisheries Society 2006.

North American Journal of Fisheries Management↗

USGS2005

Influence of topographic complexity on solar insolation estimates for the Colorado River, Grand Canyon, AZ

Rugged topography along the Colorado River in Glen and Grand Canyons, exemplifies features common to canyon-bound streams and rivers of the arid southwest. Physical relief influences regulated river systems, especially those that are altered, and have become partially reliant on aquatic primary production. We measured and modeled instantaneous solar flux in a topographically complex environment to determine where differences in daily, seasonal and annual solar insolation occurred in this river system. At a system-wide scale, topographic complexity generates a spatial and temporal mosaic of varying solar insolation. This solar variation is a predictable consequence of channel orientation, geomorphology, elevation angles and viewshed. Modeled estimates for clear conditions corresponded closely with observed measurements for both instantaneous photosynthetic photon flux density (PPFD: ??mol m-2 s-1) and daily insolation levels (relative error 2.3%, CI ??0.45, S.D. 0.3, n = 29,813). Mean annual daily insolation levels system-wide were estimated to be 36 mol m-2 d -1 (17.5 S.D.), and seasonally varied on average from 13.4-57.4 mol m-2 d-1, for winter and summer, respectively. In comparison to identical areas lacking topographic effect (idealized plane), mean daily insolation levels were reduced by 22% during summer, and as much as 53% during winter. Depending on outlying topography, canyon bound regions having east-west (EW) orientations had higher seasonal variation, averaging from 8.1 to 61.4 mol m-2 d-1, for winter and summer, respectively. For EW orientations, 70% of mid-channel sites were obscured from direct incidence during part of the year; and of these sites, average diffuse light conditions persisted for 19.3% of the year (70.5 days), and extended upwards to 194 days. This predictive model has provided an initial quantitative step to estimate and determine the importance of autotrophic production for this ecosystem, as well as a broader application for other canyon systems. ?? 2004 Published by Elsevier B.V.

Ecological Modelling↗