Diadromous Fish in Humboldt County

By Natascha Pearson

January 8, 2021

As the rivers fill with rainfall and fish fill the once empty streams, fishers cast their lines and enjoy catching Humboldt County’s gorgeous aquatic creatures. The California Department of Fish and Wildlife clearly states their fishing regulations (https://wildlife.ca.gov/) but why are these rules important to follow? For various reasons that span from extinction/ overfishing and protection during spawning, fish also help transport energy and marine-derived nutrients to the forest and ecosystem. These fish are called diadromous fish and they help keep our forest healthy similar to how the omega and other nutrients in fish keep you healthy. Diadromous fish spend an equal amount of time in the ocean as they do in freshwater, their bodies transition to survive the different environments.

Fish in Humboldt County that are diadromous fish include Pacific lamprey, Pacific salmon, steelhead (trout,) Pacific herring, and American shad. The nutrients come from a lifetime of fish-eating nitrogen-rich food which is dispersed by their waste and decomposing bodies. Diadromous fish load up on nitrogen 15 while living in the ocean and they bring these nutrient backs to freshwater which is later distributed into the surrounding ecosystem.  The salmon need the forest to canopy their breeding ground. After they spawn their life cycles end and their bodies will find solid ground and their nutrients will go back into the earth. When fish die and sink to the bottom, mass fungus and bacteria grow over the carcasses and dead flesh attracting bugs and other aquatic life that eat the fungus and bacteria. When the fry hatch after their parent’s spawning, they eat the bugs and algae that accumulated from the bacteria from their parents then return to the sea bringing with them these rich nutrients. When the river is flooded it spreads these nutrients throughout the forest. When the beds are dried up the richest soil comes from these streams. Like the seagull will catch fish and its waste or the fish carcass will find land, other animals such as wolves and bears who eat up to 600 fish (per year), catch them out of the river and distribute nutrients into the forest. The bears distribute the fish into the woods only eating certain parts of the fish like the brain, guts, and eggs. Therefore, they leave room for other animals to feed and disperse the leftover carcass until finally the maggot’s consumer what is leftover and eventually become food for the birds returning in the spring and further disperse the nutrients to the north and south continents.

         While many fish are abundantly available through hatcheries some of these same fish are hardly surviving in the wild. For example, the “Lingcod has an estimated 92.5% decline in the population [in North America},” according to researchgate.net. American shad, Pacific herring, and Pacific salmon all face a natural and human-induced decline in population. These fish are essential to our ecosystem. You can find all fishing regulations for Humboldt county here: https://wildlife.ca.gov/Fishing/Ocean#310671027-finfish-and-invertebrates. Thank you for reading and enjoy your local wilderness.


  1. Senator George J. Mitchell Center for Sustainability Solutions. Diadromous Fish Species. The University of Maine. 
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  2. California Department of Fish and Waterlife. (2021). Finfish and Invertebrates. Wildlife.CA. https://wildlife.ca.gov/Fishing/Ocean#310671027-finfish-and-invertebrates
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  4. Bland, A. (Dec. 10, 2019). What’s Behind the Decline of the West Coast’s Herring? 

East Bay Express. https://www.eastbayexpress.com/oakland/whats-behind-the-decline-of-the-west-coasts-herring/Content?oid=28151512

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