James M. Grassley

Abundance and Consumption of Fish by California Gulls and Ring-billed Gulls at Water and Fish Management Structures within the Yakima River, Washington

Abstract During 1999-2002, we studied the abundance of fish-eating birds, primarily Ring-billed Gulls (Larus delawarensis) and California Gulls (L. californicus), and estimated their consumption of fish at Horn Rapids Dam and the Chandler Irrigation Canal return pipe on the Yakima River in eastern Washington. Earlier observations of gulls at these structures suggested a high level of predation of juvenile salmonids. The relationship between river flow, gull use at the sites and fish taken was also examined. Numbers of gulls (instantaneous counts of foraging and non-foraging individuals) at the structures varied daily between their arrival in late March-early April and departure in late June. Daily averages across the four years were 9.8 (SE ± 1.5) and 19.1 (SE ± 2.5) gulls at Horn Rapids and Chandler, respectively. Gull numbers at Horn Rapids peaked dramatically during the last two weeks in May, reaching maxima of 37 (SE ± 2.2) to 133 (SE ± 4.2) gulls/day. This increase appeared to be associated with the hatchery release of one to two million juvenile autumn Chinook (Oncorhynchus tshawytscha) above the dam. A comparable peak in gull abundance was not observed at Chandler. Diurnal patterns of gull abundance differed between sites and among years. Relationships between fish take and water flow also varied within and among years at the two sites. Low seasonal flows were associated with increased predation at Chandler, whereas high seasonal flows were associated with increased predation at Horn Rapids. Assuming all fish taken were salmonids, consumption at both sites combined was estimated to be ≤10.3% of the juvenile salmonids passing the two sites.

A Vacuum Water Pump/Filtration Sampler for the Collection of Aquatic Invertebrates

ABSTRACT We describe construction of a vacuum water filtration device for the collection of aquatic invertebrates. The unit is assembled from materials found in most laboratories and hardware stores. Its simple design allows for the extraction and filtration of aquatic invertebrates from the water column within open water as well as among submersed or emergent vegetation.

Efficacy, fate, and potential effects on salmonids of mosquito larvicides in catch basins in Seattle, Washington

Abstract We investigated the efficacy, fate, and potential for direct effects on salmonids of 4 common mosquito larvicides (Mosquito Dunks® and Bits® (AI: Bacillis thuringiensis var. israelensis, [Bti]), VectoLex® WSP (AI: Bacillus sphaericus [Bs], VectoLex CG [AI: Bs], and Altosid® Briquets [AI: s-methoprene]) in Seattle, WA, during 3 summers. During efficacy trials in 2006, all treatments resulted in a rapid reduction in number of mosquito pupae (Mosquito Dunks and Bits and VectoLex WSP) or emergence success (Altosid Briquets). VectoLex CG was chosen for city-wide application in 2007 and 2008. The average counts of pupae within round-top basins remained significantly below the control average for 11 wk in 2007, whereas efficacy in grated-top basins was short-lived. In 2008 the average counts of pupae within grated-top basins remained significantly below the control average for 10 wk. Altosid XR was also effective in reducing adult emergence within grated basins in 2008. In 2007 and 2008, frequent precipitation events made the evaluation of efficacy difficult due to reductions in pupae across control and treated basins. Four separate analyses of VectoLex products revealed that the product was a combination of Bs and Bti. Both Bs and Bti were detected in 3 urban creeks connected to treated basins in 2007 and 2008. Laboratory toxicity test results suggest that concentrations of Bs and Bti detected in each of the watersheds pose little direct hazard to juvenile salmonids.

Development of an Index to Bird Predation of Juvenile Salmonids within the Yakima River, 1999 Annual Report.

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