Geology topics

David L. Ward

Publications and source records attributed to David L. Ward.

21 records · Page 2Linked to original sources

USGS2012

Effects of capture by trammel net on Colorado River native fishes

Trammel nets are commonly used to sample rare fishes; however, little research has assessed delayed mortality associated with this capture technique. We conducted laboratory experiments to evaluate the effects of capture by trammel net on bonytail Gila elegans, razorback sucker Xyrauchen texanus, and roundtail chub Gila robusta, at 15, 20, and 25uC. Fish (139–288 mm total length) were entangled in a trammel net for 2 h or captured by seine net and then monitored for mortality for at least 14 d. Blood samples were collected immediately after capture, and plasma cortisol levels were quantified as an index of capture-related stress. The cortisol response varied by species, but mean cortisol levels were higher for fish captured by trammel netting (295.9 ng/mL) relative to fish captured by seine netting (215.8 ng/mL). Only one fish (of 550) died during capture and handling, but 42% of the trammel-netted fish and 11% of the seine-netted fish died within 14 d after capture. In general, mortality after capture by trammel net increased with increased water temperature and at 25uC was 88% for bonytail, 94% for razorback sucker, and 25% for roundtail chub. Delayed mortality of wild-caught fish captured by trammel net has the potential to be high, at least under some circumstances. We suggest that sampling frequency, timing of sampling (relative to reproductive cycles), and water temperature all be considered carefully when using trammel nets to sample diminished populations of imperiled native fishes.

Colorado River↗

USGS2011

Spatial and temporal variation in proportional stock density and relative weight of smallmouth bass in a reservoir

Population data for smallmouth bass Micropterus dolomieui in 20,235 ha John Day Reservoir on the Columbia River were used to (1) determine whether Proportional Stock Density (PSD) and Relative Weight (Wr) varied spatially and temporally in two areas of the reservoir with established smallmouth bass fisheries; (2) explore possible causes of any observed variation; and (3) discuss some management implications and recommendations. Both PSD and Wr varied spatially and monthly in all years examined. On an annual basis, PSD varied at one area but not at the other, whereas Wr showed little variation. Possible explanations for the variation in PSD and Wr are differences in growth, mortality, recruitment, and exploitation. Our data suggested that regulations established or changed on a reservoir-wide basis may have different effects on the fishery, depending on location in the reservoir. Also, pooling data from various areas within a reservoir to yield point estimates of structural indices may not represent the variation present in the population as a whole. The significant temporal variability reflects the importance of determining the proper time to sample fish to yield representative estimates of the variable of interest. In areas with valuable fisheries or markedly different population structures, we suggest that an area-specific approach be made to reservoir fishery management, and that efforts be made toward effecting consistent harvest regulations in interstate waters.

Journal of Freshwater Ecology↗

USGS1995

Index of predation on juvenile salmonids by northern squawfish in the lower and middle Columbia River and in the lower Snake River

We developed a predation index to describe the relative magnitude of predation on juvenile salmonids by northern squawfish Ptychocheilus oregonensis throughout the lower and middle Columbia River and lower Snake River. The predation index was the product of an abundance index and a consumption index. We evaluated various catch indices and found that catch per unit effort best reflected differences among northern squawfish abundances. Northern squawfish abundance was higher in the lower Columbia River than in the middle Columbia or lower Snake rivers and was highest in Bonneville Reservoir and the Columbia River downstream from Bonneville Dam. The consumption index was based on the concept of meal turnover time for a sample of northern squawfish. Variables needed to calculate the consumption index (CI) were water temperature ( T ), mean weight of the northern squawfish ( W ), mean number of salmonids in each gut ( S ), and mean weight of the gut contents (GW): CI = 0.0209· T 1.60 · W 0.27 ·( S ·GW −0.61 ). Generally, northern squawfish consumption of juvenile salmonids was highest in tailraces downstream from dams and higher in the Columbia River than in the Snake River. Predation on juvenile salmonids was much higher in the lower Columbia River than in the middle Columbia or lower Snake rivers and was usually higher in summer than in spring. Predation was highest in the Columbia River downstream from Bonneville Dam and in John Day Reservoir. The predation index identified areas where predator control efforts can be most effective. Angling for northern squawfish at dams should be concentrated in tailraces. Removal efforts concentrated in the lower Columbia River would have the greatest effect on predation.

Oregon, Washington↗