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Scientists Explore how Sardine Populations and Fisheries Harvest Control Rules May Respond to Climate Change

November 27, 2023

A new study examines different ways climate change could affect West Coast sardines and evaluates how well fishing rules and dynamic management will work when ocean conditions change

Image of vessel sailing out of port with bridge in the background

Sardines have long been managed under a harvest control rule tied to average sea surface temperatures, which are thought to influence sardine numbers. The rule adjusts catch limits as temperatures change. However, there are now signs that climate-driven changes in the productivity of the West Coast offshore ecosystem may also impact sardine numbers. 

Scientists at NOAA Fisheries’ Southwest Fisheries Science Center assessed whether management measures for the sardine fishery will still be effective if climate change alters the productivity of the species.

“The goal as climate change continues is to develop information and tools that help fishery managers stay on top of the changes,” said Robert Wildermuth, lead author of the new management strategy evaluation for the West Coast sardine fishery. The evaluation tests different strategies by modeling how they would play out under varying conditions including the shifts in ocean conditions accompanying climate change.

Recruitment Drives Change

Recruitment refers to how many young sardines survive to join the population as reproducing adults, which affects the trajectory of the population. That in turn affects how much fishing the population can support. Most sardine fisheries off the West Coast have been closed since 2015. The number and size of the fish—collectively known as biomass—have fallen below the current harvest control rule cutoff, forcing closure of the fishery.

Wildermuth and NOAA Fisheries colleagues at the Southwest and Northwest Fisheries Science Centers worked in collaboration with University of California Santa Cruz scientists. They examined nine different ways of setting the harvest control rule for sardines off the West Coast under different future recruitment scenarios. The research is part of Future Seas, a collaboration between scientists at NOAA Fisheries and other organizations. It examines strategies for managing fisheries as climate change affects the California Current off the West Coast.

The evaluation was recently published in the Canadian Journal of Fisheries and Aquatic Sciences.

“We’re trying to look at the different ways climate change will affect fisheries and ask, ‘How do we maintain sustainable fisheries when the environment is changing around us,’” said Annie Yau, Director of the Fisheries Resources Division at the Southwest Fisheries Science Center.

Sardine fluctuations are intertwined with California history, fueling the boom and subsequent bust of Cannery Row in Monterey in the 1950s. Researchers have long probed the factors behind the rise and fall of sardine numbers. They have tied sardine fluctuations to oceanic conditions, such as the Pacific Decadal Oscillation. That climate pattern can drive warm and cool phases of Pacific Ocean waters that have been found to affect many species including salmon. Recent research has also found links to food availability.

Dynamic Drivers

Wildermuth’s team looked at sardine management options that included the current method, which is tied to sea surface temperatures. They also considered using dynamic reference points for the population to determine changes in harvest. Usually, the reference points assume a static amount of recruitment. However, they can also be “dynamically estimated,” which means that they fluctuate according to changes in recruitment or sardine biomass. They found that this approach that adjusts over time better reflected changing conditions and reduced the odds that the fishery would close.

The approach does not identify exactly what factors affect sardine biomass. However, the annual adjustments in reference points help capture patterns and relationships between ocean conditions and reproductive capacity over time, independent of fishing. That better reflects how biomass fluctuates with changing ocean conditions. Incorporating that relationship into the harvest control rule leads to a more stable fishery with fewer closures.

“We get a more realistic picture of both the biomass and how it may be changing over time,” Wildermuth said.

NOAA Fisheries’ annual California Current Ecosystem surveys regularly measure the biomass of coastal pelagic species such as sardines to support fishery management decisions. Catch records also supplement the survey data.

"These data are essential to the stock assessments, which are developed to track changes in the sardine population through time,” said Desiree Tommasi, a co-author in the study. “Thus, to be able to continue to effectively manage sardine under changing ocean conditions, it is also essential to maintain NOAA’s survey efforts into the future."

Key Findings 

  • The current survey and assessment process can track changes in the population status of sardine
  • Harvest control rules that are responsive to environmentally driven changes can improve outcomes compared to static management 
  • Management success may depend more on understanding and modeling drivers of climate-driven changes in recruitment dynamics than on refining harvest control rule functional form
  • As new information on climate-driven changes in recruitment dynamics become available, future studies can use this tool to evaluate their value for management decision-making and near-term stock forecasting

Climate-driven changes pose additional challenges to understanding and managing sardine, and other small pelagic fishes. Future Seas and other NOAA Fisheries initiatives to develop “Climate Ready Fisheries” are seeking new tools to support such management. That includes new methods of collecting and analyzing data to support real-time changes in fishery management.

Q and A 

What does the new research tell us about using stock assessments as compared to using biomass index numbers obtained directly from the coastal pelagic surveys to set catch limits? We found that given the current timeline for when survey data is available relative to when catch limits are set and the current stock assessment frequency, the stock assessment performed better at predicting biomass than solely using the survey index-based biomass estimates. Stock assessments incorporate more biological and fishery information than survey biomass estimates. 

What’s new for coastal pelagic surveys? Currently, we conduct two fishery-independent surveys to gather data on coastal pelagic fishes and Pacific Hake. We have developed a new vision for an Integrated West Coast Pelagics Survey, which would be a robust fisheries-independent survey that collects data that supports sustainable Pacific hake and coastal pelagic fisheries, increases ecosystem data collection, and maintains the survey schedule. It is an opportunity to ensure we maintain the scientific integrity of the hake and CPS fisheries’ biomass time series in the face of a changing ocean while giving us more flexibility, developing resource and process efficiencies, and incorporating the latest technologies into the survey and data analysis. Currently, NOAA Fisheries is working with partners to prepare and test new survey methods and gears. The Integrated West Coast Pelagics Survey is scheduled to begin in 2026. Read more: Integrated West Coast Pelagics Survey


Future Seas

Climate-Ready Fisheries

California Current Ecosystem Survey