 Photo courtesy of Freddy Otte.
This 22-inch pikeminnow is the largest fish removed from the Chorro Creek to date.
|
The Threatened Steelhead Trout
by the Morro Bay National Estuary Program
The Morro Bay watershed and estuary supported a thriving population of threatened steelhead trout in years past. Restoring the local population of this magnificent ocean-going fish is one of the goals of the Estuary Program as well as a measure of a healthy watershed. It requires work on many fronts including designing bridges and culverts to allow fish to move freely; ensuring healthy riparian, or streamside, vegetation that keeps the creeks cool and supports the aquatic food chain; preventing excess sediment in our streams, which harms juveniles and buries clean spawning gravels; and maintaining the flow of freshwater itself.
Steelhead trout belong to the family Salmonidae which includes all salmon, trout, and chars. Steelhead are the anadromous form of rainbow trout. The term anadromous refers to fish species born in the stream that migrate to the ocean for their adult phase. Steelhead spend their first 1 - 3 years of life in fresh water streams. They then emigrate to the ocean where most of their growth occurs. After spending up to four growing seasons in the ocean, steelhead return to their native fresh water stream to spawn.
In California, most steelhead spawn from December through April in small streams and tributaries where cool, well-oxygenated water is available year-round. Southern steelhead are survivors, adapted to our seasonally dry streams. Tens of thousands of these prized fish used to return to southern California streams every year. Today, dams and other barriers, as well as low flow conditions stop migration. Even for the lucky few that succeed, poor water quality or a silted creek bottom (due to excessive erosion on adjacent lands) can prevent steelhead eggs from surviving. These impacts have decimated southern steelhead runs, and our regional population has been listed as threatened under the Endangered Species Act.
Unfortunately, steelhead in Chorro Creek must also deal with a hungry and abundant population of the Sacramento pikeminnow, a non-native fish that eats steelhead and competes with them for space and food.
The Sacramento pikeminnow was introduced into the Chorro Creek system decades ago, likely by someone discarding unused live bait fish in the Chorro Reservoir. These 'minnows' grow to over three feet and are now abundant in Chorro Creek. In 2006, a partnership was formed to address these invaders among the Estuary Program, California Dept of Fish and Game, the California Conservation Corps, Cal Poly graduate students and volunteers. The team also depends on consultations and assistance from Padre Associates and HydroTerra Consulting. The group is undertaking a multi-year effort to address the pikeminnow threat to local steelhead trout populations, funded in part by Fish and Game, the Estuary Program, and the CCC.
The first step of the process was to target pikeminnow in the Chorro Reservoir that sits in the upper Chorro Creek system and likely supplies abundant juveniles to downstream areas. This phase is largely complete, with over 31 adult pikeminnow removed from the reservoir with gillnets. Additional follow up work will ensure this population does not recover.
The second phase began in summer of 2008 with the active removal of pikeminnow from Chorro Creek itself. Covering just five miles of creek, the team captured and removed over 500 pikeminnow. Encouraging numbers of steelhead have been found in the lower main stem of Chorro Creek, but numbers are still well below those of creeks that are not impacted by non-native organisms. Immediate next steps include surveying and possible pikeminnow removal work in some of the tributaries to Chorro Creek. In addition to working to reduce the number of pikeminnow in the system, the team will also monitor how the removal of the minnow positively affects native steelhead trout populations.
More information on this and other estuary related topics can be found at the Morro Bay National Estuary Program website.
|
