Research detects water temperatures that may affect salmon survival.
By NOAA Fisheries
Many thousands of fall-run Chinook salmon migrated beneath the Golden Gate Bridge into the upper Sacramento River to spawn this fall. About 100 of the adult fish carried small tags that signaled their location as they went.
A monitoring network tracked the fish, showing their progress online in real time as part of a joint project by scientists at NOAA Fisheries and UC Santa Cruz. They followed adult salmon through the Sacramento-San Joaquin River Delta into Central Valley Rivers and their tributaries. The scientists want to know what affects salmon survival and how many fish reach their spawning grounds.
“Are the salmon burning too much energy, and what factors affect this?” asked Miles Daniels, who leads the project for NOAA Fisheries’ Southwest Fisheries Science Center. The center operates a research laboratory adjacent to UC Santa Cruz, focusing on salmon. Adult salmon need cold water; they may stop if they hit water that is too warm. Since they do not eat on the way back upriver, delays could deplete the energy they need to complete their migration and spawn.
The research is funded by California’s State Water Board to learn more about how water temperatures influence the salmon that support valuable commercial and recreational fisheries. Officials are interested in whether water can be managed to benefit fish while still supplying Central Valley farms with irrigation water. Irrigation is vital to the production of billions of dollars worth of produce and other agricultural products every year.
Fall Chinook salmon are among today’s most abundant California salmon and have long formed the backbone of West Coast salmon fisheries. However, low numbers of returning salmon have closed California ocean waters to most recreational and all commercial salmon fishing for the last 3 years.
Fishing for Science
The scientists began working with local fisherman Johnny Atkinson to tag about 100 salmon each year starting in 2022. Atkinson is a longtime charter boat captain who runs New Rayann Sportfishing in Sausalito. The boat attracts anglers eager to fish for salmon off the Northern California Coast. With California waters closed to most salmon fishing for the last 3 years, the tagging project gave anglers a rare chance to catch salmon—for a good cause.
Although scientists return tagged fish to the water to continue their migration, participating anglers got the tracking numbers of fish they caught so they could follow the fish online. Fishermen support science that helps managers understand and address the risks to the fish they love to catch, Atkinson said.
“These are people who don’t go golfing, they fish for salmon,” Atkinson said. “They’re so excited to be able to participate. They get to fish, and that helps us all better understand what these fish are facing and how we can give them a better chance to survive.”
The scientists and fishing crew also improved their procedure for tagging salmon reeled aboard to reduce stress and other impacts on the fish. For example, they switched from internal tags that had to be surgically implanted in the fish to external tags the biologists can attach quickly. That means less stress on the fish, since they no longer have to be anesthetized.
“It’s also much faster,” Daniels said. “On average the fish are only on board now for about 5 minutes before they’re safely released back into the ocean.” He said the improvements “are part of our ongoing effort to handle fish responsibly and ensure that our research has as little impact on them as possible.”
Tracking Migration Online
Atkinson checked the progress of the tagged fish online each morning, eager to see how far they migrated upriver. So far the monitoring stations detected more than 50 fish moving through the Sacramento-San Joaquin Delta. The Delta is a maze of canals and river channels where enormous pumps move water to important agricultural lands to the south. It may be one of the most perilous parts of the migration of California salmon, both towards the ocean as juveniles and back to their spawning grounds as adults.
While most fall Chinook salmon in the Central Valley come from hatcheries, many spawn naturally in the upper Sacramento and San Joaquin rivers and their tributaries. A few tagged salmon have been detected near their spawning grounds more than 200 miles upriver from the Golden Gate Bridge.
While many studies have tracked outbound juvenile salmon, few have examined adult salmon survival on their migration upriver. Tracking their movement can reveal trouble spots, such as warmer water that can slow or stop their migration until temperatures cool.
Research has looked at how higher temperatures affect some species of salmon in the Pacific Northwest. California salmon may respond differently amid the warmer conditions at the southern edge of their range.
Initially it appears that salmon with a higher fat content (as measured by a “fat-meter” that does not harm fish) may be more likely to make it through the Delta into the upper Sacramento River, Daniels said. Their greater fat content may give them more energy to draw on. Once this year’s data are available, scientists will analyze it in more detail to tell if such findings hold up over the longer term.
New studies show that California salmon are returning to their rivers deficient in thiamine, also known as Vitamin B1. Understanding how water temperature affects their physiology and migration may be particularly important. “Thiamine plays an important role in metabolic and bioenergetic capabilities in salmon, so if migrating fish are deficient, they may have an even harder time in warmer waters,” suggests Rachel Johnson, research scientist with NOAA Fisheries Southwest Fisheries Science Center.
Johnson has worked with Atkinson and anglers to understand how salmon diets can cause thiamine deficiency. “Learning from what Johnny sees in our changing ocean in the Gulf of the Farollones and how salmon respond is something you can’t get from reading a book,” she said. “His willingness to share his deep knowledge of salmon helps our research and the salmon fishing industry that relies on healthy stocks.”
“We want to leave the fishery better than we found it,” Atkinson added. While he also takes anglers fishing for rockfish, salmon is the driver. “Nothing brings people out more than salmon, so ensuring the best life for these fish is a win for us.”
