Chinook Salmon (Oncorhynchus tshawytscha)
Also known as King Salmon or Spring Salmon
The Cosumnes River was once abundant with migratory Chinook Salmon in the late fall through early spring. In other river systems, such as the Sacramento, American, and Feather rivers, the salmon runs have been restored through various conservation efforts. However in smaller streams, like the Cosumnes River, these native fish are still threatened due to habitat degradation.
Chinook are anadromous — what does it mean?
Like the Steelhead trout, Chinook salmon are anadromous. Anadromous means that the fish migrate up the river stream, from the ocean, to spawn.
When do the Cosumnes River Chinook migrate?
The Chinook salmon leave the Pacific Ocean and migrate into the Cosumnes and Mokelumne rivers in the late fall when rain runoff causes the flows to surge into the Delta. The adult fish migrate into the reaches of both streams to deposit their eggs in the river gravels. In dry years, very few salmon ascend the Cosumnes River.
The salmon spawn in October and November, depending on the occurrence of adequate stream flow and cooler temperatures. The adult salmon die soon after spawning. The eggs hatch and the young fish then begin to migrate down the Cosumnes and Mokelumne rivers, passing through the Preserve in March and April. Instinct and changes within their body make the young seek more saline water and, under natural conditions, they reach the ocean before temperatures become too warm in the Delta.
So, Chinook don’t like warm water?
Correct. Chinook salmon are a cold water species. They typically don’t like to be in water higher than 20 degrees Celsius as adults, and need even cooler water as young fish. The salmon are impacted by temperature and water levels — if it is a warm and dry winter, you may not see as many of them making the trip upstream. They also time their migration to be back in the ocean before the summer heat arrives.
Chinook are semelparous — what’s that?
Chinook salmon only spawn once in their lifecycle (semelparous). After making the trip upstream the salmon lay their eggs. The adults then die and their bodies become nutrients back into the river. The young fish then make the trip back down to the ocean to repeat the cycle.
How big are they?
Average weight of a Chinook salmon is 40 lbs and grows to be about 27 inches long. The longest, however, grew to be over 50 inches!
What do they eat?
As juveniles, they usually eat insects and crustaceans. As adults, they’ll eat squid and other smaller fish.
What are some threats to Chinook salmon habitat?
There are many factors that go into the degradation of salmon habitat.
- Toxic chemicals that enter the water systems, such as pesticides and perchlorate.
- Siltation/pollution of spawning beds from streamside erosion.
- The decline in riparian forest cover, which results in the water having warmer temperatures.
- Drawdown of the water table to meet the water needs of urban sprawl.
State of Salmon, The Nature Conservancy, https://casalmon.org/statewide-status/#fall-and-late-fall-run-chinook