Contrast of Degraded and Restored Stream Habitat Using an Individual-Based Salmon Model

Abstract

Stream habitat restoration projects are popular, but can be expensive and difficult to evaluate. We describe inSALMO, an individual-based model designed to predict habitat effects on freshwater life stages (spawning through juvenile out-migration) of salmon. We applied inSALMO to Clear Creek, California, simulating the production of total and large (>5 cm FL) Chinook Salmon Oncorhynchus tshawytscha out-migrants at a degraded and a restored site. The calibrated model reproduced observed redd locations and out-migrant timing and size. In simulations, the restored site had a much higher production of fry that established and grew before out-migration; it provided higher survival and positive growth due to moderate velocities, shallow depths, and cover for feeding and hiding. The restored site did not produce more total out-migrants because at both sites spawning gravel was sufficient and the vast majority of fry moved downstream soon after emergence. Simulations indicated that at both sites increasing food and cover availability could further increase production of large, but not total, out-migrants; spawning gravel, temperature, and flow appear nearly optimal already. Further gravel addition was predicted to increase total fry production but have little or even a negative effect on production of large out-migrants, illustrating that actions benefitting one life stage can negatively affect others. The model predicted that further enhancements (e.g., in cover availability) would be more beneficial at the restored site than at the degraded site. Restoration efforts may be most effective when concentrated in “hot spots” with good habitat for growth and predator avoidance as well as for spawning. Contradicting the traditional notion of “limiting factors,” the model indicated that several factors each have strong effects. The model provided more understanding of restoration effects than would field studies alone and could be useful for designing projects to meet specific restoration objectives.

Received June 23, 2012; accepted January 2, 2013

ACKNOWLEDGMENTS

This work was funded by the U.S. Bureau of Reclamation under the Central Valley Project Improvement Act, and by the USFWS. Claire Hsu was the initial project manager. Dan Cox, USFWS, provided the initial motivation and direction. Software and GIS support were provided by Steve Jackson, Charles Sharpsteen, Colin Sheppard, and Diane Sutherland Montoya, and by Jeff Anderson, Corin Pilkington, and Bonnie Pryor of Northern Hydrology and Engineering (McKinleyville, California). We especially thank Matt Brown, James Earley, and Sarah Giovannetti of the USFWS Red Bluff Office for the great deal of time, data, and knowledge they contributed to this work.