Donning their best wading attire, FOSC staff Ella Matsuda and Kate Berlin and volunteer Camille Potts joined ecologist Dr. Robert Leidy in a stretch of Sausal Creek in the Fruitvale District in late May. This was one of several research excursions to understand the distribution and abundance of the native rainbow trout population–a huge environmental asset for the City of Oakland, and key conservation priority for Friends of Sausal Creek.
This stream is home to a genetically wild population of resident rainbow trout (Oncorhynchus mykiss)–the same species as steelhead but with a different lifestyle. Steelhead are anadromous—meaning they spend part of their lives in the sea before going back to freshwater streams to breed—while rainbow trout reside their entire lives in freshwater. Historically, Sausal Creek supported both anadromous and resident rainbow trout life history forms.
Typically, juvenile ocean-going steelhead rear in San Francisco Bay creeks for two to three years before swimming out to the Bay and the Pacific Ocean. There, they mature for several more years before returning home as adults, ready to reproduce.
However, urbanization has created barriers like culverts, drop structures, and road crossings that effectively block steelhead-spawning migrations returning to Sausal Creek and degrade habitat suitable for the resident rainbow trout. Therefore, the trout population is relatively small, fragmented, and extremely vulnerable to multiple threats and stressors resulting from human activities, past and present.
Below Interstate 580, in what is referred to as the lower watershed, the stream bed is heavily altered by urbanization. The stream channel is mostly concrete lined on the bottom with some sand and gravel on top. Banks have been replaced by vertical concrete walls; several dark, shallow culverts are interspersed between open reaches approaching the final large concrete culvert near Josie de la Cruz Park that connects Sausal Creek underground all the way to the bay. There are fewer deep pools for good trout habitat, and many barriers to their movement in the stream. Native riparian plants are more sparse amongst hoards of non-native plants escaped from gardens bordering the creek, but flowing water and a few spots of good habitat hint at the creek of the past.
Inlet of the last large concrete culvert that connects Sausal Creek to the bay.
Wading judiciously upstream, the FOSC Trout Crew sampled for fish while documenting and assessing fish migration barriers–data which will be combined into an interactive map. The first hour yielded only a handful of small three-spined stickleback (Gasterosteus aculeatus)–a common native fish species that lives in the lower watershed.
Where were the rainbow trout?
Dr. Leidy indicated that during the winter’s heavy storms, many trout likely washed downstream or even out to the estuary.
"The impacts are more severe in channelized reaches; the water moves much more rapidly and there are fewer places for the trout to hunker down."
Rainbow trout also spawn from November to March, so it’s possible that many redds–nests that female trout dig out in the gravelly bottom of stream riffle to deposit their eggs–were washed out in these reaches that don’t provide adequate protection such as deep pools, undercut streambanks, and instream logs and boulders.
"Restoring reaches of the creek will provide more suitable habitat for fish to spawn, eggs to successfully develop and hatch, and juvenile fish to grow into healthy adults. It’s likely that enough trout survived the storms, especially in more natural reaches, that fish populations can recolonize," Dr. Leidy added.
As the Trout Crew waded up to the last deep pool of the day one final dip of the net restored their hope. There it was–a shimmering, multi-hued beauty with the signature pink streak along its sides, silvery-white underbelly, and black spots along its back and fins–a healthy young adult rainbow trout, nearly 21 centimeters long. After measuring, photographing, and documenting our location, the fish was safely released back into the creek.
Sausal Creek’s wild rainbow trout population is a vital natural and cultural resource of Oakland. Protecting and preserving their habitat conserves biodiversity in our urban environment and ensures the long-term health of the creek ecosystem. You can help protect the fish by eliminating the use of chemicals in your yard, cleaning up litter, keeping pets and their waste out of the creek, and keeping storm drains free of anything but rain water.
Join us next month for a Rainbow Trout Tour in Dimond Park, led by Dr. Leidy on Saturday, August 19, 10 a.m.-12 p.m.
Attendance will be limited to 30 people, so register soon!