Thanks to high winds and heavy rains creating favorable conditions for salmon survival this year, Marin saw the second largest coho salmon migration in over a decade. An estimated 22,000 smolts left the Lagunitas Creek watershed for the ocean, and monitors saw high numbers of adult salmon coming from the ocean to spawn in freshwater. “The coho salmon run this past winter was really great,” said Eric Ettlinger, an aquatic ecologist with Marin Water. “Our estimate for how many survived in the ocean was well above average, so it seems like conditions in the ocean must have been quite good for these fish.” Coho, a critically endangered species, spend about a year and a half in freshwater and a year and a half in the ocean, so they are typically three years old when they return to spawn. Mr. Ettlinger said around 16,000 coho smolts left Lagunitas Creek this year. Michael Reichmuth, a fisheries biologist with the Point Reyes National Seashore, estimated that another 5,500 left Olema Creek, reflecting a survival rate of over 60 percent—a tenfold increase from recent years. “In 2010, in fact, we only counted 10 individuals leaving Olema in our small traps,” Mr. Reichmuth said. He and his team also counted 42 chinook smolts leaving Olema Creek. Ayano Hayes, a watershed biologist with the Salmon Protection and Watershed Network, reported that 281 coho smolts left San Geronimo Creek, along with 32 steelhead and 233 chinook. Around four percent of young salmon usually survive in the ocean, but this year around six percent survived. Ecologists base ocean survival rates on the number of nests in the creek, each of which represents two fish. Survival rates at sea are low due to predators like birds, seals and sharks, but this year, winds off the California coast caused strong upwelling—an annual process that brings nutrients to the surface and produces plankton blooms that salmon depend on for survival. Salmonids have evolved to head to sea as upwelling begins, and the phenomenon has a significant impact on how quickly young salmon grow. The strong, lasting winds felt on land this spring led to particularly powerful upwelling, resulting in more food for salmon and their predators alike. Ecologists say the concentrated, heavy winter rains caused higher-than-expected flows, creating ideal upstream migration conditions for adult spawners. For smolts in Lagunitas Creek, surviving the winter is a challenge. To support salmon populations, Marin Water is required to release water from Kent Lake, its largest reservoir, to boost habitat. Because the winter rains washed sediment into the lake, the releases filled streams with more turbid water, which likely made it harder for fish-eating birds such as mergansers to find prey. Mr. Ettlinger said the district plans to monitor for turbidity next winter to see if it’s a driving force in coho survival. (Thanks to the stream releases, almost all this year’s spawning occurred in Lagunitas Creek rather than Olema and San Geronimo Creeks, which do not receive any extra water.) Salmon face many existential threats, but at the June meeting of the Lagunitas Creek Technical Advisory Committee, Inverness Park resident Gordon Bennett described another: a toxic chemical found in tires called 6PPD that is known to kill coho. Tire manufacturers started using 6PPD, which reduces tire cracking and extends a tire’s life, in 1950 in response to higher ozone levels that were found to break down rubber. Last month, the California Department of Toxic Substances Control moved to protect coho from the chemical through a proposal that would require tire manufacturers to look for alternatives to 6PPD. But Mr. Bennett said the proposal has a huge loophole, exempting cars imported into California with tires already on them. Those imports account for roughly two-thirds of the state’s cars. Mr. Bennett has drafted a letter to the state urging it to require manufacturers that import cars to comply with California’s regulations. He cited a recent study of microplastics that identified rubber particles as one of the predominant types of plastic found in aquatic environments. Despite the threats that endangered coho and other salmonids face, Mr. Ettlinger said the public saw more salmon this year than it has in a long time. “Having these fish return every year and having people get excited about something you’d usually only see in Alaska or on a nature show is a great way to get people to think about the environment and how to protect it,” he said.