Robyn Bilski

 

Thesis: The Effects of Structure Enhancement on Chinook Salmon (Oncorhynchus tshawytscha) spawning habitat

Construction of dams, gravel mining and water diversion have severely degraded river channels in Northern California. To mitigate this damage, habitat restoration often involves adding gravel and structural features such as woody debris to improve egg deposition sites. Merz et al. (2004) provided strong evidence that addition of spawning gravels significantly increased Chinnok salmon embryo survival, while House and Boehne (1986) established that large woody debris and rock gabion structures have significant impacts on river channel morphology and trap sediments suitable for spawning. However, a more detailed understanding of exactly how these additions affect salmonid reproduction will lead to more effective and efficient deployment. For example, structural elements within the river channel may alter hyporheic flow patterns -- the movement of water through the gravel (Biron et al. 2005) -- and these patterns may potentially have a large impact on the survival of salmonid embryos (Malcolm et al. 2005).

I propose to test these ideas, namely (1) that large woody debris and boulders can increase hyporheic flow, and (2) that increased hyporheic flow around structure results in increased growth and/or survival of Chinook salmon embryos.

This project will be conducted within a 16-kilometer spawning reach in the lower Mokelumne River, California. Paired sites will consist of one location containing a structural element and another nearby location not associated with structure. Surface an hyporheic flows will be characterized using a velocimeter and nested mini-piezometers. Dissolved oxygen, pH, and electrical conductivity measurements will be taken using a peristaltic pump, a flow-through chamber, and serveral meters (Horner and Bush 2000). Intergravel water temperatures will be recorded using waterproof temperature loggers. Ionic tracers will be used to measure gravel permeability. Egg tubes, used by Merz et al. 2004, will be used for egg incubation. Four tubes, containing 200 Chinook salmon eggs each, will be placed in artificially constructed redds, at a depth of 22 cm. Salmon embryo survival and development will be recorded at each site after a 26-day incubation period. A one-tailed paired sample t-test will be used to analyze the results.

This research will lead to a better understanding of how structure influences the incubation environment of salmonid embryos and result in more effective placement of large woody debris to help maximize salmon restoration efforts.

 

Robyn joined the lab in January of 2006.

CSUS BIO SCI