by Rosa Albanese, Watershed Stewards Project Member
This is the last in a year-long series celebrating the 40th anniversary of the Endangered Species Act.
What better way to end this series than with the enigmatic Oncorhynchus mykiss of the salmonidae family. This species exhibits more survival strategies than any other Pacific salmonid species, including flexible habitat preferences, differences in reproductive biology and adaptability in their life cycle types between generations. Step into any body of fresh water and the fish you would mostly likely encounter is O. mykiss. However, they are still faced with many of the same threats as other salmon and must be carefully managed to ensure their future success.
When referring to O. mykiss one may be talking about rainbow or steelhead trout. What’s the difference? If they never migrate, they are considered rainbow trout. But if they make the great migration to the ocean and back, they are known as steelhead. However, although rare, it has been reported that the offspring of a steelhead may grow up to be a resident rainbow trout and vice versa. But, basically, steelhead are anadromous (migratory) rainbow trout.
Steelhead also vary in when they migrate. Steelhead have two principal life history patterns: summer and winter runs. Summer steelhead enter streams as immature fish during the receding spring flows and spend the summer holding up in deep pools, typically near a stream’s headwaters, where they then mature to spawn in winter or spring. Lagunitas Creek, which originates on Mt. Tamalpais and flows west to Tomales Bay, is home to winter-run steelhead. These fish are similar to coho salmon in that they enter the streams from the ocean during winter rains as mature fish. However, steelhead generally spawn later than coho, between January and April. Also, unlike all other salmonid species, they may spawn more than once throughout their lives, which is referred to as iteoparity.
Regardless of life history path, for the first year or two of life steelhead/rainbow trout can be found in cool, clear and fast-moving streams with ample cover and diverse and abundant invertebrate life. Although highly variable in color and size, adults can generally be identified as a silvery trout with black spots covering their back, dorsal fins and tail and a reddish band along their sides. They can grow to be 45 inches long and weigh close to 50 pounds, but in Lagunitas Creek adult steelhead are typically closer to 30 inches long. These fish have adapted a streamlined body shape that helps them hold their position and swim in fast-moving water, which may be why they are considered by many anglers to put up a good fight and are so highly sought for sport.
Within California, native populations of coastal steelhead have experienced declines similar to those of other local salmonid species. The reasons are complicated but are largely due to competition with humans for habitat, dams and other alterations of landscapes, overfishing and introduction of foreign species as predators and competitors. Due to their diverse life history, management of steelhead is somewhat complicated. Steelhead stocks are placed into groups based on broad geographic distributions, plus run-timing, and many local populations are granted different taxonomic classification. For example, here in Marin County steelhead are classified as part of a Central California population and are federally listed as threatened, while populations further south are listed as endangered. Regardless of the terminology, steelhead are at risk.
There are many important reasons to protect such a unique fish species. Not only are they indicators of stream health, but preserving their wonderfully complicated diversity will allow them to adapt to changing environmental conditions. Steps to the recovery of steelhead and other salmonids start with support for projects that restore watersheds, ensure sustainable stream flows, reduce migratory barriers and minimize competition from non-native species. Protecting California steelhead and other andromous fish ensures that our fresh water and ocean habitats remain intact for future generations and a remarkably diverse species continues to adapt and thrive.