Mapping the decline of California's Chinook salmon
Chinook salmon native to California's Central Valley are one of the most divisive and highly reported on animal species in the country. Like most California residents, a Chinook salmon's livelihood depends on the supply of fresh water that runs from the rivers in the Sierra Nevada out through the expansive California Delta system. This puts the species in direct conflict with municipalities and agricultural hubs, which rely on diverting water through the state's network of canals.
This water conflict has grabbed headlines in recent months, as California’s state water board is on the verge of passing of a plan aimed at preventing the extinction of native fish species. This proposal would drastically change the way water is managed in the state, requiring that 40 percent of the water in the San Joaquin river and its tributaries flow unimpaired, or untouched by humans, into the delta and eventually the ocean.
This project offers a visual look at the fluctuating populations of the Central Valley's three distinct Chinook Salmon species over the last 65 years.
The interactive map below shows the yearly salmon population densities of 17 waterways in the Sacramento-San Joaquin River system. Use the slider to view the population changes, which are represented by the changing widths of each waterway, and click on a specific river to see it's exact population for the given year.
There are three distinct "runs" of Chinook salmon that migrate into the Sacramento-San Joaquin River system. These runs — Fall, Winter, and Spring — are defined by the time of year that a majority of the species' adults return to their native, freshwater waterways to spawn.
Fall-run salmon are currently the most abundant in the Central Valley. They make up the bulk of California's commercial fishery in the ocean and support a large freshwater recreational fishery.
Winter-run salmon spawn in the upper reaches of the Sacramento River and have seen a dramatic population decrease since the early 20th century. The species gained endangered species protection under the California Endangered Species Act in 1989 and the federal Endangered Species Act in 1994. Most proposed water policy changes citing at-risk salmon populations are referring to this subspecies.
Spring-run salmon were historically the most abundant in the Central Valley, but have been in a state of collapse for most of the 20th and 21st centuries. The species was designated as threatened under both the state and federal endangered species acts in 1999.
The mainstem of the Sacramento River is both currently and historically the primary spawning ground for all three runs of Chinook salmon. Since the fall-run population peaked at a high of more than 400,000 individuals in 1953, the species' abundance in this important waterway has steadily declined. The Department of Fish and Wildlife's annual count recorded a historical low of just 2,260 salmon in 2017.
The following waterways have all had at least one year where the fall-run Chinook salmon population topped 1,000 individuals. While most of these waterways have seen declining populations, a few tributaries of the Sacramento River, like the Feather River, Butte Creek, and Clear Creek, had large spikes in population in the early 2000s. The spikes coincide with major flooding within the Sacramento River basin in 1998 and 1999 that connected waterways to their historic floodplains. Floodplains are an important habit for juvenile salmon, but almost 90 percent of California's waterways have been disconnect from their floodplains by the state's extensive system of levees and dams.
For years that have no data, either no adult salmon were present in the Department of Fish and Wildlife's annual count or the count didn't take place.
Data sources:
Central Valley Chinook salmon population data - GrandTab, California Department of Fish and Wildlife.
Population distribution shapefiles - https://www.westcoast.fisheries.noaa.gov/maps_data/species_maps_data.html.
River geojson generated with overpass-turbo.eu.
.