Monitoring Thiamine Deficiency in California Salmon

A project of the Southwest Fisheries Science Center’s Salmon Life History Team.

Scientists Ask for Anglers’ Help in Solving Salmon Mystery

Anglers have unique opportunity to help scientists unravel a marine mystery that appears to be affecting native Chinook salmon through a deficiency of thiamine, or Vitamin B1, which is essential to all life. This deficiency was recently found to be increasing mortality of juvenile Chinook salmon in California’s Central Valley.

The magnitude of its effect is not clear. However, it could affect endangered winter-run Chinook salmon and fall-run Chinook salmon, which comprise major California sport and commercial fisheries.

>> Anglers, look up your fish!

Scientists are now teaming up with charter fishing boat operators in the summer of 2021 to collect certain parts of the salmon caught by the anglers aboard. The heads, stomachs, and eggs of Chinook salmon that have been feeding in the ocean off the California Coast can help researchers understand what is causing the deficiency, and what might help remedy or mitigate its effects.

In the laboratory, for example, the eyes of fish can reveal what they have been eating over the course of their lifetimes, while samples of muscle and the stomach contents can reveal what they have been eating in recent weeks, as well as in the last day. That, in turn, can help determine how their diets have changed depending on when and where they are caught. Each angler will get a card with a code number for their fish, which they can enter online to see the findings from their fish.

“We need all hands on deck to catch the fish so we have the samples to study,” said Rachel Johnson, a fisheries scientist with NOAA Fisheries’ Southwest Fisheries Science Center and UC Davis. “They are as much a part of this research as we are.”

Piecing Together the Puzzle

The mystery emerged in 2020, when experts at the California Department of Fish and Wildlife’s Fish Health Laboratory and UC Davis Aquatic Animal Health Laboratory wondered whether an emerging virus was causing young salmon in fish hatcheries to swim in corkscrew patterns and die at unusually high rates. When they could not pinpoint a cause for the high losses at hatcheries and in rivers, they shared their results with the U.S. Fish and Wildlife Service’s California-Nevada Fish Health Center.

^{In the video above, two winter-run Chinook at a UC Davis laboratory show symptoms of thiamine deficiency: one on its side at the bottom and another revolving in a corkscrew pattern. The affected fish would be easy targets for predators. Two other fish behave normally.}

Investigators there noticed that a bath of thiamine immediately revived the ailing juveniles.

They now suspect the problem is linked to a deficiency of thiamine in returning adult salmon that fed off the coast of central California in 2018 and 2019. Anchovy populations were booming, and other salmon prey were scarce. Anchovies have a hidden liability for salmon: They produce an enzyme called thiaminase that breaks down thiamine, which typically supports nerve, muscle, and heart function.

Scientists hypothesize that female Chinook salmon preying on anchovy in the ocean returned to rivers and streams with depressed thiamine concentrations in their eggs. The concentrations were so low it caused Thiamine Deficiency Complex, or TDC, in their offspring.

How Anglers Can Help Scientists and Salmon

Biologists have now observed TDC in multiple Central Valley Chinook salmon hatcheries, where they have proven methods for treating the condition. However, they know little about effects on naturally spawned juvenile salmon in rivers, where similar treatment is not possible.

An interdisciplinary team is researching the cause and impacts of TDC on California salmon. The team includes NOAA Fisheries, California Department of Fish and Wildlife, U.S. Fish and Wildlife Service, California Department of Water Resources, SUNY Brockport, Idaho State University, Moss Landing Marine Lab, and Monterey Bay Aquarium Research Institute.

The research includes a major marine focus. Scientists from the NOAA Fisheries Southwest Fisheries Science Center need help from fishermen to catch salmon and document what they are eating offshore. Scientists at University of California Davis and the U.S. Fish and Wildlife’s Livingston Stone National Fish Hatchery are also collaborating. They are investigating the effectiveness of thiamine injections in pre-spawning adult female winter-run Chinook salmon to mitigate TDC impacts on juvenile salmon behavior, performance, and survival.

Surveys off the West Coast in 2019 found the highest abundances of northern anchovy off central and southern California since systematic surveys began in 1983. The 2019 annual report of the California Cooperative Oceanic Fisheries Investigations called the conditions a “novel anchovy regime.” Fishermen reported catching salmon with stomachs full of anchovy, but not other typical prey items such as krill, squid, juvenile rockfish, or sardines.

“We are trying to understand how the unusual ocean conditions off the West Coast in recent years affect the salmon that spend much of their lives in these waters,” said research scientist Nathan Mantua of the Southwest Fisheries Science Center.

A Home-Grown California Mystery

Large populations of anchovy and some other marine forage fish have been found to cause deficiencies of thiamine among predators that consume them in other parts of the world, including the Great Lakes and Baltic Sea. Research in Alaska indicated thiamine deficiency may have reduced productivity of western Alaska’s Chinook salmon in the mid-2010s.

This is the first time TDC has been documented in California salmon.

“We had never seen TDC issues at the Coleman National Fish Hatchery prior to this year, but the Service has some experience dealing with it at some of our other hatcheries back east,” said Bob Clarke, deputy assistant regional director for Fish and Aquatic Conservation with the U.S. Fish and Wildlife Service. “Once our staff began to suspect TDC, we were able to move very quickly to a diagnosis and treatment for these hatchery fish.”

Researchers and fisheries managers are concerned about potential impacts on endangered winter-run Chinook salmon, which spawn in the Sacramento River below Shasta Dam. Recent drought years took a toll on the species. Winter-run Chinook rely on cool water released from Lake Shasta to keep their incubating eggs and embryos alive.

At Livingston Stone National Fish Hatchery, U.S. Fish and Wildlife Service biologists have injected some returning female winter-run Chinook salmon with thiamine. That will help determine whether such supplementation reduces the likelihood of TDC in their offspring.

“This is similar to women taking prenatal vitamins when they are pregnant to make sure their babies get the important vitamins they need,” said Rachel Johnson, a research fishery biologist at the Southwest Fisheries Science Center and a leader of the research. “We are giving female salmon a nutritional boost to help produce healthy young fish.”

The Hidden Toll

Researchers are also concerned, however, about lingering, “sub-lethal” effects of TDC. Treating young fish in hatcheries may correct visible effects such as swimming in circles. While low levels of thiamine may not directly kill the juvenile fish, they may have a harder time fighting off diseases or escaping predators as they migrate into the ocean and back.

“That is a very real risk, but it is also very difficult to measure,” Johnson said. “The outcome is the same whether there is initial reproductive failure or whether juveniles die later due to their poor physical condition—fewer fish in the ocean for marine mammals to eat or for us to catch.”

Scientists will track the eventual fate of juvenile fish that had shown signs of TDC, including whether they were treated. That will help understand the magnitude of any sub-lethal risk to juvenile fish, and what might be done to reduce it.

“Thiamine Deficiency Complex is one example of how events in one ecosystem can have repercussions in others. We need to observe and better understand ongoing changes in ocean and freshwater ecosystems, and be ready for surprises,” said Steve Lindley, director of the Southwest Fisheries Science Center’s Santa Cruz Laboratory.

Our Funding Partners

Funding partners supporting this multidisciplinary effort include:

• NOAA Cooperative Fisheries Research Program
• Delta Stewardship Council, Delta Science Program
• California Department of Fish and Wildlife, Proposition 1

More Information

• Researchers probe deaths of Central Valley Chinook, with possible ties to ocean changes
  (NOAA Fisheries feature story, October 28, 2020)
• The ocean’s mysterious vitamin deficiency
  (Hakai Magazine, January 28, 2021)
• California salmon deaths linked to thiamine deficiency
  (Los Angeles Times, January 26, 2021)