Salmon—A Keystone Species in Trouble

Chinook salmon, also called “king salmon”, grow to the largest size of all salmon species. They come from the Pacific Ocean and are found from California all the way to Alaska, and across the ocean in Russia and Japan. People have also introduced them to other parts of the world, such as New Zealand and Chile.

These amazing fish begin their lives in rivers. As juveniles, or young salmon, they grow in freshwater for a while before starting their long-distance journey. First, they swim downstream to the ocean, where there is plenty of food to help them grow for several years. Then, as adults, they leave the ocean and swim back to the exact river where they were born to lay eggs and start the cycle again (Figure 1).

Salmon are known as a keystone species, which means they play a key role in keeping ecosystems healthy [1]. During their migrations, they connect the ocean and rivers by carrying nutrients. They transport a lot of nutrients from the ocean to rivers, supporting the growth of plants and insects and providing a food source for animals. When salmon die, their bodies are either eaten by scavengers or decompose, which introduces even more nutrients to the river and ecosystem. So, when salmon thrive, rivers and forests thrive too. However, when their numbers drop, other species, including people, suffer.

Salmon have been a crucial food source for a long time, especially for Indigenous communities. Today, salmon are still honored as part of the Pacific Coast of North America’s cultural and spiritual heritage, but they are disappearing. In California, the number of salmon has dropped sharply, putting ecosystems in danger. There are many reasons for this decline, such as the construction of large dams, which have blocked salmon migration, the loss of habitats, and pollution of the rivers they live in. Overfishing has also reduced their numbers, and climate change makes conditions worse by warming the ocean and rivers.

How Can We Help Salmon?

To help salmon recover, scientists need to understand how salmon interact with their surroundings and how their behavior has changed over time. We want to rediscover what salmon used to do during different stages of their lifecycle, such as where they lived in freshwater, what they ate, and how old they were when they returned to their home river to lay eggs. With that knowledge, we can make better choices to protect them and the ecosystems they depend on.

Today, salmon live very different lives than they did hundreds or even thousands of years ago. Dams, pollution, and climate change have changed the rivers and oceans they use. If we only study salmon from the last few decades, we see just a small piece of their full story. That is why it is so important to include Indigenous knowledge and historical records to help us see the bigger picture.

This problem is called shifting baseline syndrome (SBS). It happens when each generation accepts the environment they grew up with as “normal”, even if it has already changed a lot. For example, our grandparents might remember rivers packed with salmon, but younger people have only seen a few. When those younger people grow up and describe what is “normal”, the baseline shifts again and, over time, we forget what a healthy salmon population originally looked like [2].

By studying salmon from the past and listening to the stories passed down by Indigenous peoples, we can better guide modern salmon through the challenges of today’s changing world. In other words, to help salmon in the future, we need to listen carefully to their ancient stories.

Listening to the Past

There are many ways to learn from the past. Archaeologists study the objects that people left behind, such as tools, houses, and even waste. Geologists look at ancient layers of rock, soil, and ice to learn what Earth’s climate was like long ago. Paleontologists study fossils to discover what extinct animals looked like and how they lived.

Indigenous communities also have deep connections to the past. Their knowledge is passed down through stories, songs, dances, and ceremonies. These traditions share important lessons about the land and how to care for it [3]. Today, we call this traditional ecological knowledge (TEK). In California, tribes such as the Maidu have lived alongside salmon for thousands of years (Figure 2). The Maidu caught salmon for food, but they also took care of the rivers and landscapes that salmon depend on. Their knowledge, built over many generations, helps scientists and conservationists today understand how to protect and restore salmon populations.

There is one more way scientists can “listen” to the past: by asking the salmon themselves. Ancient fish bones, still preserved in the ground, can tell stories about how salmon once lived and traveled.

Asking the Fish

Imagine, after catching a fish and preparing it for dinner, you sit down and look at the remaining bones. What most of us would consider waste holds important information about the life of the fish you consumed. Of the many bones in front of you, two are very important for scientists: otoliths and vertebrae (Figure 3).

Otoliths

Fish otoliths, also called “ear stones” are made of calcium carbonate and proteins. They are part of a sensory organ that gives fish information about their body’s position and movement. Otoliths grow by the biological deposition of material every day of the fish’s life (Figure 3). The growth of the otolith is like how trees grow, with new rings that can be identified at both daily and yearly time scales. The chemical signature of the rings can give scientists lots of information about the fish’s life story, such as where the fish was born, how old a juvenile was when it migrated to the ocean, and the temperature of the water it lived in.

Vertebrae

Vertebrae are the bones that make up the spinal column (or backbone) of a salmon. Like otoliths, vertebrae grow continuously throughout a salmon’s lifetime. The growth occurs on the outside of the vertebrae, where new bone is formed and, like otoliths, produces growth rings. Measurements taken from each vertebra can help scientists estimate the size of the salmon. If the vertebra is well-preserved, scientists can count rings on the vertebra to estimate the age of the salmon. Additionally, chemical analysis from the vertebra can inform researchers about the environment in which the salmon lived, and the food sources it consumed.

What are our Fish Saying?

For thousands of years, Maidu ancestors relied on Chinook salmon for food. They lived in California’s Central Valley, which connects to the Pacific Ocean through the San Francisco Bay estuary [3]. They fished in local rivers before returning to the village to clean and cook the salmon that they would eat and store for the winter months. Working with the Maidu people of today, archaeologists excavated several ancient Maidu villages and collected otoliths and vertebrae from salmon carcasses that were thrown away [4].

Once collected, the otoliths and vertebrae were brought to a research lab and studied with microscopes and other specialized equipment. Using these fish remains, the life history of the ancient Chinook salmon was compared to modern Chinook salmon. We found that life for salmon in California hundreds and thousands of years ago was very different from what it is today. For example, before the Europeans came to California, salmon grew to older ages (4–5 years old) before returning to the rivers to reproduce [5]. Today, Chinook salmon in California are usually 2–3 years old when they return. Fish in the past also preferred staying for a longer time in freshwater and estuarine habitats of the San Francisco Estuary. Whereas today, juveniles usually migrate to the ocean early during their first year of life. In the past, adults migrated to high mountain streams to reproduce. Juveniles lived and grew in large food-rich freshwater and estuarine wetlands. But today, dams have blocked access for adults to many of their high mountain habitats and so they reproduce in the low, warm valley. Juveniles also lost access to many of the wetlands that have been drained for agriculture. They now grow and feed in rivers and quickly move to the ocean to find more food.

Ancient otoliths and vertebrae tell us that Chinook salmon had a large diversity of behaviors, and that, in modern times, a lot of these behaviors have been lost. We cannot turn back time, but we can restore and re-connect the freshwater habitats that are important for salmon, and we can better manage our fisheries to avoid overfishing. By listening to the stories preserved in ancient salmon bones, and to the Indigenous groups tied to them, we can help restore salmon populations, which will also support the ecosystems and people who depend on them.

Glossary

Juvenile: ↑ A young organism that has not yet reached full size or reproductive maturity.

Keystone Species: ↑ A plant or animal that has a strong influence on an ecosystem; its loss can cause major changes or ecosystem collapse.

Ecosystem: ↑ A group of living organisms interacting with each other and with their physical environment.

Indigenous: ↑ People or cultures that originate from a region and have long-standing cultural, social, and ecological connections to that land.

Overfishing: ↑ Harvesting fish faster than populations can reproduce, causing population declines and long-term damage to ecosystems and fisheries.

Shifting Baseline Syndrome (SBS): ↑ A process where gradual environmental change alters our perceptions of what is considered a normal or healthy condition.

Traditional Ecological Knowledge (TEK): ↑ Knowledge and practices developed by Indigenous and local peoples through long-term interaction with their environment.

Estuarine: ↑ Relating to estuaries, where freshwater from rivers mixes with seawater, creating dynamic and often productive environments.

Conflict of Interest

JR and JE were employed by Far Western Anthropological Research Group.

The remaining author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We thank the Delta Stewardship Council for funding our research and outreach activities. Delta Science Fellowship (Award No. 2013-R/SF-61). Financial support was provided by the Delta Stewardship Council (DSC-21022).

AI Tool Statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.