Something's Fishy in the Alameda Creek Watershed!
Did you know? Oncorhynchus mykiss (rainbow trout, steelhead trout) is a unique species in that individual fish develop differently depending on the enviornment. All trout hatch in gravel-bottomed, fast-flowing, well-oxygenated rivers and streams. Those that stay in fresh water their entire lives are called rainbow trout. Those that migrate to the ocean and back are called steelhead, and they develop a much more pointed head, become more silvery in color, and typically grow much larger than the rainbow trout that remain in fresh water. Steelhead are quite agile, and can jump as much as 10 vertical feet in favorable conditions!
Historically, fish stockings on Arroyo del Valle and Arroyo Mocho created rainbow trout fisheries in the upper reaches of these streams, and small populations still exist today. It's unknown if the trout that reside in the upper watershed (including a significant population in Calaveras Reservoir) have retained any anadromous (ocean-migrating) characteristics.
Steelhead trout were listed under the federal Endangered Species Act as a threatened species in in 1997, and this threatened status was reaffirmed in 2006. The Central California Coast steelhead population includes, among other areas, all naturally spawned anadromous steelhead populations below natural and manmade impassible barriers in the drainages of San Francisco Bay.
For the Fish
In the early 2000s, Zone 7 installed fish ladders along Arroyo las Positas, which could help create suitable steelhead habitat should steelhad migrate to the Valley arroyos after downstream improvements (including removal of barriers) are made to Alameda Creek downstream.
Zone 7 has been working closely with an Alameda Creek Fisheries workgroup, a collaboration of roughly a dozen agencies that formed to address the local implications of the Endangered Species Act listing. The primary benefit of a collaborative fisheries effort for Zone 7 and other participating agencies is regulatory assurance and protection from potentially violating provisions of the Endangered Species Act in the course of operations and maintenance of the watershed. In addition to Zone 7, members include the Alameda County Water District, San Francisco Public Utilities Commission, the Alameda Creek Alliance, the East Bay Regional Park District, the National Marine Fisheries Service, the California Coastal Conservation and the California Department of Fish and Game. For more information, click here.
Meanwhile, the National Marine Fisheries Service is preparing a plan to address the threatened steelhead species, both in our watershed and beyond. Zone 7 and other Bay Area agencies are participating in a joint effort to provide NMFS with relevant information about steelhead habitat enhancement potential in order to establish realistic, site-specific actions. To support these efforts, Zone 7 has been identifying potential barriers to steelhead migration in Arroyo Mocho and Arroyo del Valle.
To view Zone 7's main Watershed & Environment page, click here.