Abundance, size structure, and growth rates of Sacramento pikeminnow (Ptychocheilus grandis) following a large-scale stream channel restoration in California

Anthropogenic disturbances have degraded habitat quality of watersheds worldwide, ultimately leading to river and stream restoration projects. Historically, these restoration attempts have focused on augmenting the populations of species with economic and ecologic value, such as salmonids in California. Yet, few studies have looked into how other native species are affected by efforts to restore salmon populations. Here, we present the results of a study that assessed how an abundant and widespread native fish species fared in a river segment that was 'restored' relative to an upstream, "unrestored" reach. Designed to create spawning habitat for salmon, the restoration project consisted of a large-scale channel re-configuration and gravel augmentation effort in a reach of California's Merced River. We examined the abundance, population size structure and growth rates of juvenile Sacramento pikeminnow (Ptychocheilus grandis) collected in the restored channel and compared with those of the juvenile Sacramento pikeminnow collected from the upstream, unrestored reach that was not manipulated. We show that fish were significantly less abundant in the restored reach; yet, they grew to significantly larger sizes. Growth rates were also significantly faster for all size classes of juvenile pikeminnow in the restored region. In each day of their first 90 days of life, pikeminnow from the restored reach averaged faster growth. Our data suggest that while the restoration effort may have created habitat conducive to enhanced per-capita growth rates, it also may have contributed to a decline in the population sizes of the Sacramento pikeminnow.