Estimation Of Age-0 Chinook And Coho Salmon Rearing Habitat Area Within The Restoration Reach Of The Trinity River At An Index Streamflow - Annual Report 2010.

The Trinity River is the focus of a restoration effort designed to improve riverine function and increase anadromous fish populations. Chinook and coho salmon populations are limited by age-0 rearing habitat and are a primary focus of the restoration effort. We evaluated the effects of the restoration effort on Chinook and coho salmon rearing habitat over a 64-km (40 mi) restoration reach in 2009 and 2010. Each year habitat area was measured at 32 randomly selected 400m study sites and then extrapolated to estimate habitat area for the restoration reach. The objectives of this assessment include: (1) estimation of rearing habitat area in 2010 and comparison to the 2009 estimate, (2) an evaluation of site-specific predictors of habitat area and (3) an assessment of correlation between fry and presmolt habitat area. No significant difference was detected for restoration reach habitat area estimates between 2009 and 2010. However, a significant decrease was detected in all cases when evaluating paired-sites surveyed in 2009 and again in 2010. The mean decrease in habitat area at paired sites ranged from 7% to 19%. The cause of the decrease is not clear and will be evaluated in future assessments. Site-specific predictors were related to habitat area estimates using multiple regression modeling and Akaike’s information criterion. The best fit model for optimal habitat area included bank length and proportion of low slope channel. The best fit model for total habitat area included bank length, bar length, channel rehabilitation construction phase, and proportion of low slope channel. These models may be used by restoration site designers to develop predictions of changes (and prediction of error intervals) in rearing habitat area from channel rehabilitation actions or compare among preferred design alternatives. Finally, despite a high correlation between fry and presmolt habitat area, a significant difference was detected in the slope of linear regression analyses among years. These results indicate the importance of measuring both types of habitat during surveys and information may be lost if the study effort was reduced to a single life stage.