The spawning season for endangered coho salmon of Marin is the worst recorded in 12 years, causing high levels of concern by biologists who have been working to monitor and restore the endangered populations following a decade of stable or slightly increasing spawning numbers. Marin’s Lagunitas Watershed, located just 25 miles from downtown San Francisco, and one of the Bay Area’s most beloved salmon runs, boasts the largest remaining population of coho salmon left in Central California and upwards of 20% of the State’s total. Coho have already gone extinct in 90 percent of California streams that once supported this species.
To understand coho salmon population dynamics, it is useful to compare population levels of year-classes, i.e. comparing numbers of fish returning this year to the numbers of parent fish returning 3-years ago when this year’s fish were spawned.
“This year’s decline is extremely serious for Lagunitas coho salmon. When an endangered population is already jeopardized from decades of habitat destruction, its ability to bounce back from such a large decline is greatly diminished,” said Todd Steiner, biologist and Executive Director of SPAWN. “This year’s count has turned the best year-class into the worst.”
Coho salmon have a three-year life-cycle. In the winter, spawning fish return to the streams in which they were born to spawn and then die. Young fish hatch from eggs in the gravel in the spring and then spend another year in the streams feeding and growing while seeking refuge in deep, cold pools along lushly forested riparian areas. After enduring one hot, dry summer and one, oftentimes stormy, winter they then head out to sea in their second spring (1.5 years after they were spawned) to feed along the productive California coast. Fish return to their natal streams to spawn, die, and continue on they cycle of life at the end of their three-years of life.”
This year’s results include:
* The small tributaries of the San Geronimo Valley (undammed headwaters of the Lagunitas Watershed) spawning numbers were down 93% with 121 redds recorded three years ago compared to only 9 this year.
- In the Redwood Creek Watershed in Muir Woods National Monument, no coho returned this year, versus 93 redds recorded three years ago. Concerns have been raised about possible oil spill impacts on this run.
- In Olema Creek, which runs through Pt Reyes National Seashore lands, numbers were down 82% with 25 redds this year compared to 139 three years ago.
- In the Lagunitas/Devil’s Gulch/San Geronimo Creek Watersheds as a whole, populations have dropped 70% (from 493 just three years ago to 148 this year), compared to when this year’s fish’s parents returned to spawn and die.
While many conditions impact salmon populations including dams and water diversions that reduce available freshwater habitat by over 50% in Marin, loss of habitat from development, pollution, and now changes in ocean patterns due to global climate change are all taking their toll. Development, especially adjacent to stream banks and in floodplains, continues to be a growing problem. And a recent limiting factors analysis for the Laguntas Watershed indicated that heavy spring storms greatly reduce the survival of both newly hatched salmon fry and one-year old fry likely because of the lack of available refuge habitat these fish require to avoid being washed out by high flows during storms. Shelter from high flows provided by instream woody debris and off-channel habitats have been greatly reduced due to development in the floodplains, channelization of creeks, and culverts under roads that prevent migration into smaller creeks with lower flow rates.
“Many of us feared that the statistically over-due drought was what we really going to threaten our salmon with potential extirpation, so it is ironic that heavy doses of stormwater may be the current culprit. Our “footprint” on streams is huge in Marin and is only increasing as habitat and the natural hydrology of the land is lost to development” commented Paola Bouley, SPAWN’s watershed biologist. She continued, “We need to take urgent actions now to protect functioning riparian ecosystems and natural floodplains, including smaller tributaries, and to reduce our impact on water resources if we are ever going to have any serious hope of recovering Marin’s coho population. Ultimately, these actions can benefit not only our salmon streams, but also our human communities by reducing flooding and property damage.”
“This severe decline demonstrates how fragile this population is and how important it is to re-double our efforts to protect and restore this population. Global climate change is likely to cause larger storm events and more severe droughts in the future, making it even more important to safeguard remaining habitat, to increase ecological resiliency, and to also restore the habitat that has already been degraded,” said Todd Steiner.
This coho population setback comes on the heels of a September 2007 open letter to Marin County Supervisors from California’s leading scientists stating that current and proposed policies regarding Marin’s coho salmon do not adequately protect this critically endangered species and are likely to lead to their extirpation. The letter was signed by 100 of the State’s salmon and aquatic biologists, including one of the world’s most prominent salmon experts, Dr. Peter Moyle of UC Davis, and California Academy of Sciences Senior Scientist and Chair of Aquatic Biology, Dr. John McCosker. A separate letter from the Executive Committee of the American Fisheries Society California-Nevada chapter representing 550 fisheries and aquatic biologists was also sent to Supervisor’s in September.