The Amazing Life Cycles of Anadromous Fish
Let's talk about anadromous fish and their amazing life cycles and how they relate to the health of a Watershed. In particular, I would like to focus on Coho Salmon (Oncorhynchus kisutch) and Steelhead Trout (O. mykiss). They are both anadromous fish, which means they begin their lives in freshwater and migrate to saltwater, then return to freshwater to spawn. One of the most amazing aspects to the life cycles of these fish is that they return to their original stream system after being at sea for 1-2 years. These fish have always been a high priority in terms of habitat management and are important species to the Navarro Watershed. Coho are listed as endangered under the Endangered Species Act and Steelhead are listed as threatened. They need clean, cool water to survive and thrive. Because of that they are often thought of as an 'indicator' species, reflecting the overall health of a river ecosystem. If the streams are too choked up with sediment or the temperatures are too warm Salmon and Steelhead will not survive. The Navarro Watershed historically supported important runs of Salmon and Steelhead. In the past 50 years we have witnessed a decline in numbers, most dramatically of Coho, but also of Steelhead. Understanding the life cycles of these fish and their habitat needs helps us to know how best to steward the land for the optimum health of the watershed as a whole.
Coho salmon have a life span of about 3 years. They spend their adult life in the ocean, returning to their natal streams to migrate upstream to spawn and then die. They spend about half of their life(18months) in freshwater and the other half in saltwater. Spawning usually occurs in late Fall or early Winter and coincides with high water flows from winter storms. Coho usually spawn at the heads of riffles with gravel substrate. Females will dig a pit in the gravel with her tail where she will deposit her eggs and often more than one male will fertilize the eggs before the female will cover them up with gravel. (Navarro Watershed Restoration Plan p. 4-11) These Salmon egg nests are called redds. It is important to keep an eye out for redds in the late winter or springtime at the heads of riffle areas if you are walking in the creek. After spawning, adult Coho die. With good stream conditions which means good oxygen flow throughout the pea size gravel without any fine sediments choking the gravel and cool temperatures, the juveniles will emerge from the gravel in the spring. They will continue to live and to grow in the stream environment for one year before they migrate out to Sea.
In the stream environment, the juvenile salmon like to hang out at the heads of pools where there is an abundance of food and oxygen, and good cover for protection. This area also offers the easiest swimming effort. Since they depend on cool temperatures for survival, deep pools are essential as well as good cover over the streams from trees and plants to keep the temperature down. Downed logs and big rocks and overhanging vegetations are also essential for fish to hide and take cover from predators and the warmth of the sun. Ideal water temperatures are around 55 degrees for these fish will begin to lose their equilibrium to sustain life around 75 degrees. With higher temperatures oxygen levels in the water decrease and the fishes metabolic rate increases and they need more food intake to maintain their balance. If there is low survival rate one year then the number of spawners to return to the system will be less in 3 years time.
The Navarro, and other North Coast rivers, have experienced a dramatic decline in Coho populations in the past 50 years. Primarily the decline has been attributed to habitat loss. Large pools have drastically decreased. Large Woody debris is not nearly as present as it used to be and loss of basic tree cover over streams has caused temperatures to rise. Climate change may also be a contributing factor and may increasingly become so. The one sub-basin in the Navarro where Coho have still been found on a regular basis is the North Fork Navarro. The Coho have also been spotted, albeit in small numbers, on Mill Creek, Indian Creek, and lower Rancheria Creek. The Coho populations are fragmented in this ecosystem making the North Fork Navarro ever more important as a haven for the species. It may prove to be important someday for repopulating the rest of the Navarro.
Steelhead trout are also an important species to the Navarro Watershed and Northern California Coastal Watersheds in general. They are an anadromous form of rainbow trout. They live longer (4-5 years) than Coho. They usually spend 1-2 years in the ocean before they return to the stream where they were born to spawn. Unlike other anadromous pacific salmon species they may survive after spawning and return to the ocean and spawn again. Steelhead typically start their spawning runs between January and March. Steelhead spawn in the similar conditions to that of Coho. Here in California, juveniles usually spend 1-3 years living in the fresh water streams before heading out to Sea sometime between March and June. Steelhead are more habitat generalists than the Coho and depending on their age will make use of both riffles and pools for habitat. They can also tolerate slightly warmer temperatures than Coho, with 55-60 degrees being ideal for rearing habitat. 85 degrees is their upper limit for survivability.
Steelhead have fared better in the Navarro than the Coho. They are still found in all of the Navarro sub-basins (see last weeks article in AVA) even though their numbers have declined dramatically since earlier days. You may have been lucky enough to see one of them thrashing through the waters to accomplish it's task of finding a suitable place to fulfill the all important business of reproducing it's species. Keep an eye out in the coming months, after these dramatic winter storms have settled down and the waters turn a lovely blue green, it's the perfect time to spend some time streamside to see if you can catch a glimpse of these beautiful fish. These amazing, ancient creatures provide us with an opportunity to form a deep connection to place, as they return to the Navarro Watershed generation after generation after generation.
Much of this information has been gleaned from the Navarro Watershed Restoration Plan and the forthcoming Navarro River Guide to Watershed Care and Restoration.
Written by Linda MacElwee. Email at lsmacelwee@hotmail.com