Life Cycle
 Steelhead trout (Oncorhynchus mykiss) belong to the family Salmonidae which includes all salmon, trout, and chars. Steelhead are the anadromous form of rainbow trout, a salmonid species native to western North America and the Pacific Coast of Asia. The term anadromous refers to fish species born in the stream that migrate to the ocean for their adult phase. Steelhead are similar to some Pacific salmon in their life cycle and ecological requirements.
They are born in fresh water streams, where they spend their first 1-3 years of life. They then emigrate to the ocean where most of their growth occurs. After spending between one to four growing seasons in the ocean, steelhead return to their native fresh water stream to spawn. Unlike Pacific salmon, steelhead do not necessarily die after spawning and are able to spawn more than once.
In California, most steelhead spawn from December through April in small streams and tributaries where cool, well oxygenated water is available year round. The female selects a site with gravel substrate where there is good flow through the gravel. She then digs a nest, called a redd, and deposits eggs, which the male then fertilizes. The eggs are covered by gravels and cobbles when the female excavates another redd just upstream.
 The length of time it takes for eggs to hatch is heavily dependent on water temperature. In hatcheries with carefully controlled conditions, steelhead eggs hatch after 30 days at a temperature of 51° F. The optimal temperature for egg incubation is between 44 and 50° F (7-10° C). Eggs hatch sooner in warmer water, but the young fish are smaller and generally have lower survival rates. If the temperature goes too high, eggs will not hatch at all. After hatching, the developing steelhead will remain in the gravel for another four to six weeks. During this time, they are called alevins and obtain nutrients from a yolk sack attached to their body. When they emerge from the gravel, they are called fry, and are able to catch their own food.
Newly emerged fry move to shallow, protected areas of the stream (usually in the stream margins). They establish feeding areas which they defend. Most juveniles can be found in riffles, although larger ones will move to pools or deep runs.
Source:
Steelhead Restoration and Management Plan for California, by Dennis McEwan and Terry Jackson, CA Department of Fish and Game |
