Are salmon native to San Jose? South Bay volunteers are hopeful for an answer

A South Bay organization is cleaning up creeks and rivers and recording the return of the king – salmon, that is.

The East Bay Municipal Utility District recorded over 30,000 salmon returning to the Mokelumne River since September due to conservation efforts, but sights of jumping salmon in San Jose and Campbell are also capturing attention.

The South Bay Clean Creeks Coalition, a volunteer group that aims to clean up waterways so native wildlife can survive and grow, has been recording increasing salmon populations in the South Bay over the last eight or nine years. They primarily focus on the Guadalupe River, Los Gatos Creek and Coyote Creek.

They are working with the California Fish and Game Commission and UC Davis scientists to record salmon populations spawning in South Bay waterways. After a few years of recording the salmon that have spawned and died in San Jose and Campbell creeks and rivers, they discovered that some of these fish may be wild and not just hatchery strays.

“I think that the fish are symbolic of a healthier ecosystem, so having them gives people something to care about, gives them some connection to the watershed, and so I think there’s some cycle there,” said Mike Tamaro, a team leader with the coalition. “When people learn it’s a viable watershed and salmon can live in it and spawn in it, it increases awareness and increases their interest in cleaning it up and keeping it clean.”

The group mainly monitors Chinook salmon, also known as king salmon. The South Bay is home to another species of salmonid: steelhead trout, which is known as rainbow trout when landlocked. According to Tamaro, they see one salmon run every year in the late fall or early winter. The fish come into the San Francisco Bay around August. When increased rainfall makes water levels rise, the fish swim upstream from the Alviso Slough to spawn in the freshwater Guadalupe River and its tributary creeks in San Jose and Campbell.

The fish swim until they reach a barrier they can’t pass. Throughout December and January, the female salmon make nests while male salmon find a female fish to spawn with. After spawning, the exhausted fish die and their carcasses fertilize the soil near the river and are eaten by other animals.

According to records kept by South Bay Clean Creeks Coalition executive director and founder Steve Holmes, the number of Chinook salmon spawning in the South Bay has been increasing each year. The group collected samples from just eight fish in 2021, but that number shot up to 51 the next year. In 2023, they recorded a little over 100 salmon in the Guadalupe River, Los Gatos Creek, Lake Almaden and Alamitos Creek. As of Dec. 17, the group harvested 51 fish carcasses in South Bay waterways. Holmes added that the fish carcasses they see probably account for only 25% of the total fish in the river.

“Salmon are back in the South Bay, and we’re bucking the decline across California thanks to the work of the South Bay Clean Creeks Coalition,” said San Jose Mayor Matt Mahan in a statement to the Bay Area News Group. “We can create cleaner and healthier communities by working together, and for the past 11 years Steve and his team have provided a platform for neighbors to clean up and restore our rivers and creeks.”

For the last four or five years, the group has been sending fish eyeballs to UC Davis scientists to determine if their sulfur isotope levels matched those in hatchery fish. Of the 26 samples they sent from the last few years, four were found without the eye lens signature of hatchery salmon, indicating that they were wild fish that were either born in the Guadalupe River watershed or strayed to it. Tamaro said 10% of the fish they sampled in 2022 might be native. Holmes said the next step is to test the strontium isotopes in the fishes’ earbones to see if they can trace the fish’s birth back to the Guadalupe River or its Los Gatos Creek tributary.

Richard Lanman, president of the Institute for Historical Ecology, said that he and the group are aiming to answer the question of whether or not these salmon were born in the South Bay and were returning to spawn. He expected the results to return in the next six months.

“We’ve got a stream that’s producing, we need to protect these fish. So it’s economic for the salmon fishery so people can eat salmon,” Lanman said. “It’s also an important part of our ecosystem. They spawn and die and then they become nourishment for everything, from fertilizer for redwood trees to food for eagles and ospreys.”

Lanman and scientists from Santa Clara University and the University of Oklahoma worked on a research paper in 2021 that asserted that Chinook salmon were historically native to the South Bay through DNA analysis. According to the paper, ancient DNA from an archaeological excavation of fishbones found at Mission Santa Clara de Asís identified three different Chinook salmon, which means that salmon spawned in the Guadalupe River in the 1800s.

In an email statement to this news organization, the Santa Clara Valley Water District contended that their highest priority was maintaining the Central California Coast steelhead population, which were “more imperiled” than Chinook salmon.

“Fall-run Chinook salmon in Santa Clara County do not have any protections under state or federal Endangered Species Acts as they are not endangered, threatened or a candidate for listing,” the water district said in a statement.

However, Lanman said that although many of the fish might be hatchery strays, the possibility that some of these wild stray fish are native may connect them to the California Coastal Chinook salmon population, which are federally endangered. Holmes said that trash, poaching and low water flows have been the biggest killers for South Bay salmon.

Valley Water’s Fish and Aquatic Habitat Collaborative Effort plans water releases from the Guadalupe and Stevens Creek watersheds in the winter and summer to support fish life cycles. Streams that aren’t fed by these reservoirs rely on precipitation for increased water flow. Valley Water said in a statement that their projects have also remediated over 20 fish barriers and improved streams to provide habitats for steelhead and Chinook salmon.

“[Valley Water] takes its environmental stewardship mission seriously and is doing what we can to support both steelhead and Chinook salmon while balancing the county’s water supply and flood protection needs,” the water district said in a statement.

Although the South Bay salmon population is far from recovered, their increasing numbers are providing hope for sustainability.

When asked why people should care about these fish, Holmes said, “What are we leaving to future generations?”