One of the most remarkable events of nature happens every year at this time, right here in our valley. Impossibly large fish make a heroic journey from the sea into our streams. They swim right under our bridges, through culverts, past our homes and fields, leaping and moving through murky storm-fed waters to find the right place upstream to begin their next generation. Some will return again to the ocean and come back. Most will not. The energy and intelligence required to perform this feat, and to use it as a way to continue the genes of this animal into the future, are enough to give any rational human animal pause to wonder. The fact that its effort links life in our valley directly to life around the oceans and the rest of the world is certainly worthy of real respect, if not wonder.

There are many people who are well versed in the life of the steelhead. Among the more notable in our area is Bill Cox, California Department of Fish and Game Aquatic Biologist for the region. Several people in the valley have worked in the field with him over the years, as we try to enhance our streams. In a conversation recently, we talked more about them.

Steelhead, Oncorhynchus mykiss, begin their lives here in winter, typically between December and early March. The parent fish must find just the right spot in the stream to spawn--to deposit and fertilize their eggs. A typical female will lay between 2500 and 4000 eggs. Of these, statistically, perhaps two will return to spawn. For the eggs to survive, all kinds of circumstances must be favorable. The gravel in which adult steelhead make their nest or "redd" must be just the right size--between "marbles and ping-pong balls". The redd must also have just the right flow of fresh water. If there is too much sediment, the eggs will not have enough water flow to bring oxygen and to take away metabolic wastes. After seven weeks, if the eggs survive and hatch, the larval fish then make their way up through the gravel. For several more days these fish continue to have an attached yolk sac, and at this stage they are often called "alevins". Eventually, the yolk sac disappears as its nutrients are used up, and the young or juvenile fish move to habitat nearby they will occupy until they migrate out to sea.

As juveniles, steelhead require cool, dark water, and places to hide from predators. Most of this habitat exists in the upper miles of Sonoma Creek, above Madrone Road, and on tributaries around the valley that have year-round flow and good cover. Good habitat for juveniles is felt to be the single most important factor in steelhead survival here. Streamside or "riparian" vegetation must be intact in order to provide shade, stable banks, and filtering of water as it runs off from nearby land. This vegetation should have several layers, including ground plants, shrubs and tall trees. The less of this cover there is, the more there will be an impact on steelhead survival. After one to three years, a juvenile steelhead will reach a size of about six and one half inches that will allow it to have a better chance at sea. Most then will migrate to the ocean in the spring. Young fish are called smolts as they make this migration. Some will remain and live out their lives in the stream as smaller fish, a trait thought to assure that some will survive if those that go to sea do not.

Perhaps the most improbable thing the steelhead does, it does as it makes this move--it rapidly transforms itself from a fresh-water to a salt-water animal. If a normal fish were moved from one water type to the other it would rapidly die from a salt imbalance. Unlike other salmon, once at sea no one understands steelhead movements or why some are found close or farther from shore. What is known is that the supply of food is much greater in the ocean, and a steelhead that survives will grow up to two and one half feet over the next one to three years. When it is mature, a biological signal tells the fish to move back toward its birthplace, and an acute chemical sense or "imprint" that the fish gained as it became a smolt is awakened, and is used to guide the fish back. It is speculated that every stream has a special chemical composition, from its geology and biology, which acts as a signal to the powerful senses of the steelhead. The steelhead then once again transforms to a fresh water animal, and returns--a huge and unlikely fish for the streams it will now spawn in as an adult.

What can you do to help these amazing fish? Mr. Cox has some suggestions, including: Protect streams and native stream vegetation whenever possible. Reduce runoff from driveways, streets, agriculture, and other human activity. DonÕt rescue fish--there is very little habitat available and it is almost always occupied by others. DonÕt feed them. Steelhead do fine on natural aquatic invertebrates (mostly insects). I'd also suggest getting involved in any one of a number of projects and groups here that help take care of creeks. Technical advisors at the Ecology Center would also be interested in learning when you see steelhead and where. With the good will of so many involved, it is quite possible in the future that large numbers of steelhead could return to our creeks, a distant and powerful memory for the long-time residents of our valley.