November 15, 1999

Mattole salmon and steelhead are anadromous fish, which means they begin life in fresh water, rear in streams and then migrate to the ocean where they spend anywhere from 1 to 5 years depending on the species, and finally return to their “home stream” to spawn and complete the cycle.

Eggs
Each female salmon and steelhead produces between 1,500 to nearly 7,000 eggs, the number depending upon the species and size of the fish. The eggs are pink to reddish to orange in color, and are about the size of peas.

Alevins
About 6 to 8 weeks after fertilization, the embryos hatch and become alevins, or sac fry. Over the next 3 to 4 weeks the alevins remain within the gravel, living on the rich nutrAlevins
About 6 to 8 weeks after fertilization, the embryos hatch and become alevins, or sac fry. Over the next 3 to 4 weeks the alevins remain within the gravel, living on the rich nutrients contained in their large yolk sac.ients contained in their large yolk sac.

Resident Rainbow Trout – Sustaining a Sense of Place

Resident rainbow trout are the non-migratory form of steelhead, opting to remain in freshwater for their entire life. Relatively little is known about their specific habits and environmental requirements. Because of the limited food supply in freshwater streams, resident rainbows grow slowly and a 12-inch long fish may be 5 years old. Populations of resident rainbow trout tend to occur above impassable barriers such as debris jams and waterfalls, although in some areas the distribution of the resident and anadromous forms overlap. During summer in the Mattole and many of its tributaries, what many people call "trout" are actually juvenile steelhead that have not yet gone to the ocean.

The life histories of steelhead and resident rainbows differ primarily in the extremes of wanderlust, growth rate and fish size. In fact, the two forms are genetically indistinguishable. Interestingly, a small fraction of the surviving progeny produced by a pair of steelhead spawners might not develop the urge to migrate seaward, but rather may residualize as resident fish. Apparently the reverse scenario can also occur, with a few offspring of resident rainbow parents developing into smolts and becoming anadromous steelhead.

Life in the Ocean
Very little is known about the oceanic distribution of salmon and steelhead originating from the Mattole and other small rivers and streams in northern California. Smolts are thought to stay close to the continental shelf in shallower water. Their first year of life in the ocean is the most critical, as the smolts are highly susceptible to predation by larger fish, seals and sea lions, and a variety of birds. Gradually, the fish venture further out to sea, growing rapidly as they feed voraciously on small fish (e.g., herring, anchovies, needlefish, etc.), squid, and crustaceans such as shrimp and krill. Apparently, most California salmon stocks migrate northward after ocean entry, and may travel vast distances in search of food and suitable environmental conditions. In the mid-1980s a Mattole chinook, tagged as a smolt in the river before release, was caught one year later off southeast Alaska by a commercial salmon fisher. Unlike salmon, which often travel in large schools within 200-300 miles of shore, steelhead are solitary and may roam far out into the open ocean.

The Urge To Return
In the spring and summer of their return year, maturing fish begin migrating back toward their “home streams.” Scientists speculate that the uncanny precision of homing is achieved through a combination of celestial navigation, orientation to the earth’s magnetic fields, and a very highly developed sense of smell.

Spawning
When the female finds a good place to lay her eggs, she flips on her side and flaps her tail against the gravel bottom of the stream, creating a pit, 8 to 16 inches deep. The male has been hovering close by defending the nest (or “redd”) from competing males. When there is a pit dug the mating pair position themselves side by side and she lays a few hundred eggs into the pit, then he releases his "milt" to fertilize the eggs. the female moves slightly upstream and digs another hole, thereby covering the previous “egg pocket” with gravel – and the dance begins again. This process can last for several days, as the fish extends the redd upstream.

To Complete The Cycle...
Salmon spawn one season and then they die. Steelhead may return to the ocean after spawning and live to spawn again. Some steelhead spawn as many as 4 or 5 times, though twice is most common. The carcasses serve as an important source of nutrients and organic matter which contributes to the health of the watershed. Animals and birds that feast on the carcasses fertilize the forests upslope and the carcasses that remain in the stream are part of the nutrient cycle as well.


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Table of Contents for Mattole Restoration Newsletter, Issue 14 - Winter/Spring 2000