Southern steelhead in urbanized Mission Creek, Santa Barbara; photo courtesy Dr. Craig Fusaro
Southern Steelhead are an important part of California's natural heritage. Life history and genetic studies lead biologists to believe that the evolutionarily significant unit (ESU) from Santa Barbara County south is genetically distinct from and ancestral to the remaining steelhead stocks of the Pacific Northwest.
The coastal steelhead/rainbow trout, Oncorhyncus mykiss iridius, was listed under the Endangered Species Act in August 1997; various populations were listed as threatened or endangered. In February 2000 most South Coast streams below impassable manmade barriers were listed as critical habitat for steelhead. This left much of the habitat the fish historically used as unprotected. Steelhead can be considered an umbrella species for the recovery of coastal streams and the restoration of beaches and creeks from water pollution. Part of the improved habitat for steelhead is re-establishment of canopy trees to shade the creeks; this also provides habitat for terrestrial animals, and open space available to the public.
South Coast Watershed Alliance, of which Santa Barbara Audubon is a member, has promoted steelhead recovery and especially barrier removal projects as an adjunct to "Project Clean Water" efforts to clean up creeks and beaches. Healthy riparian corridors with native canopy trees, understory and groundcover provide for bird and other wildlife habitat, provide biofiltration of run-off from surrounding land to improve water quality, shade the creek from the hot summer sun detrimental to aquatic life, and reduce streambank erosion, which can choke fish spawning grounds and cause siltation of downstream estuaries such as Goleta Slough. More information on recovery efforts can be found on the website for Southern California Steelhead Coalition.
Several characteristics of the southern ESU steelhead have evolved since the end of the last glacial period some 12,000 years ago that make these ocean-going fish uniquely fit for survival in the semi-arid "Mediterranean" climate and rainfall patterns found in Southern California.
Having behavioral and physiological adaptations to warmer water is an obvious characteristic in view of the warm climate in Southern California over the last several thousand years. The higher incidence of "straying" into other than the stream in which they were born means that the likelihood of spawning, of leaving offspring, in the Southern California region is higher than if they were "programmed" to spawn only in their natal streambed. This is so because in any given year, a particular stream may not be open to the sea in winter due to low flows and sandbar formation, while a neighboring stream might be open.
In general, the life history of Southern Steelhead begins with eggs deposited and fertilized by spawning adults into stream gravels during the winter months. Depending on water temperature, these eggs hatch into small fish called alevins in five to eight weeks. The alevins still have some egg yolk attached, from which they take nourishment until it is all absorbed. When that happens, the "swim-up" fry emerge from the gravels and begin to feed actively on streamborne foods in the shallows, avoiding as best they can the other creatures in the stream that eat young fish. A large proportion of these young fish do become food for other fish or birds. But as they grow and become more competent swimmers and more wary, they begin to use the riffles, runs, and deeper waters of the stream for feeding and refuge from predators. These steelhead young usually stay in fresh water for a year, sometimes two, before getting the urge to return to the ocean. Some young Southern Steelhead may remain as local resident fish and spend their entire life in freshwater, and may spawn in subsequent years with other resident fish or with ocean-run fish, creating offspring that likewise could become anadromous or remain in fresh water. This diverse life history strategy is believed to be a beneficial adaptation to the feast-or-famine rainfall pattern of Southern California that has helped Southern Steelhead survive, and, along with their tendency to stray more frequently from stream to stream, increases their genetic diversity and long-term chances for survival.
The alternation between stream and ocean habitats for all anadromous fish is related to growth rate, food availability and relative predation rates in freshwater and marine environments. The ocean is a food-rich habitat compared to a stream, and once in the ocean, steelhead grow much more rapidly than their resident-type cousins that don't run to the ocean; freshwater streams provide a relatively protected habitat for young steelhead. A large body size is directly related to how many eggs can be produced by an individual fish. Since juvenile mortality is over 80 or 90 percent, a lot of eggs are necessary to contribute as many genes as possible to the next generation of steelhead.
Once the yearling fish gets the urge to return to the sea, it undergoes a process called "smoltification" during which physiological changes happen that allow the freshwater fish to deal with the saltiness of ocean waters. When the smolt is ready, it begins the long swim downstream to a coastal lagoon, where fresh and salt water mix. Some biologists think that coastal lagoons are more important to Southern Steelhead than they are to northern steelhead populations due the relative scarcity of water in southern creeks. As a result, Southern Steelhead may spend more time in lagoons than their cousins to the north. Since lagoon environments are rich in food, this helps the smolt to grow quickly, increasing its chances of survival in the ocean. After some time accommodating to salt and growing in the lagoon, the young steelhead enters the sea, where it will spend a year or two growing large quickly, maturing into an adult steelhead.
Once again this fish gets an urge; this time it's a call to return to freshwater, often, but not always, to the same stream in which it emerged from the gravel. It will meet up with a member of the opposite sex and spawn. A female Southern Steelhead, accompanied by a male, will begin to beat her tail against the gravel streambed, digging out a shallow pit called a "redd," in which she will deposit her eggs. When the redd is deep enough, she deposits eggs while the male fertilizes them. She then moves quickly upstream a bit and vigorously digs again, causing gravel to cover the eggs downstream. This process is repeated for days to weeks, and several different males may be involved in fertilizing the same redd over that time period. Having spawned, the adults then typically return to the ocean, unlike other salmonids, that usually die after spawning. A small percentage of adult steelhead may become trapped in low flow conditions in streams or elect to over-summer in the streams, and can survive given proper conditions until the next winter rains provide an opportunity for movement. Although the percentage of return spawners is typically low for any given stream, steelhead can return to freshwater more than once to spawn, and can live up to 8 years.
For Southern Steelhead, the spawning migration into coastal streams happens during the big winter rains we have periodically in Southern California. The frequency and intensity of storms determines whether or not there is enough flow in a particular stream for the rushing water to break open the sandbar that may have formed where the stream enters the sea. In El Niño years it's nearly certain that these conditions exist, and in many other heavy winters as well. Although the time period is highly variable, a "typical" year would find spawning fish in the stream from January through March. Adult steelhead that have gathered near the mouths of these streams detect this high flow and enter a stream swimming strongly against heavy current upstream to suitable spawning habitat. They sometimes need to jump over waterfalls and other possible barriers to upstream travel, dodging rocks and trees being transported by the high flow. The strength and agility of steelhead have become the stuff of legend among streamwatchers.
The specific freshwater habitat these spawning fish seek consists of medium size gravels covered by moderate speed currents in a foot or two of water depth. This combination of gravel and water flow allows good water circulation in the spaces between rocks, carrying fresh oxygen to the developing eggs and flushing out carbon dioxide and other metabolic waste products of growth and development. Healthy streamside vegetation nearby can also be helpful during the summer, shading the water from the hot sun for the young fish, and providing a source of invertebrates as fish food.
For the Southern Steelhead, two aspects of human land and water use have reduced the number of these fish returning to Southern California streams by about 99 percent.
So, in general, most of the spawning fish don't reach the spawning areas because access to these areas is blocked by structural passage barriers. When the fish are able to migrate to historic spawning areas, stream flows there may be impaired by surface water diversions and riparian well pumping. Over the last century, all of this has taken its toll on the Southern Steelhead.
Scientists who have studied this problem point to a few things about the life history and habitat needs of the fish that they believe are important. As pointed out above, the Southern Steelhead are probably ancestral to all Pacific Coast steelhead. They have been around for over 10,000 years. In that amount of time, they have built up considerable genetic diversity; the highest diversity, in fact, of any steelhead along the west coast. Geneticists believe that one of the ways that high genetic diversity was achieved and maintained is by interbreeding of the resident rainbow trout form with the ocean-going (anadromous) steelhead form of the fish. In reality, the resident and anadromous forms constitute both ends of a continuous spectrum of life history patterns. And having a high level of genetic diversity can be an advantage to a given population of a species, especially if the environment they find themselves in is rapidly changing. And California's and the world's environment in general is changing with growing human appropriation of natural resources and the potential for global climate change. One of the genetic types might be uniquely pre-adapted to some new change in the environment, but the likelihood of that is reduced if the genetic diversity is reduced. One question that has been raised about human impacts to this life history has to do with the future maintenance of this high genetic diversity. If genetic diversity is maintained in part by the oceangoing steelhead interbreeding with the resident rainbow form, what will happen to that diversity as we increasingly prevent the anadromous form from getting to the spawning grounds? The likely answer is that the relatively high genetic diversity of Southern Steelhead will decrease, reducing adaptability, and therefore survivorship, ever closer to extinction.
Another facet of this has to do with the potential for global climate change. Conventional wisdom holds that the coastal steelhead/rainbow trout, Oncorhyncus mykiss iridius, does not tolerate warmer water very well. What will happen to this warm water intolerant fish should the southern West Coast of North America become warmer and drier, as is predicted by most climate change models? It may just be that we need to keep the Southern Steelhead ESU alive and healthy as a species subunit because they are the most tolerant of warmer water. And finally, the tendency to "stray" a little bit more than other steelhead populations may be beneficial in a warming environment when, in any given winter, any particular stream may not flow to the ocean as frequently as it used to do.
Many steps can be taken to improve conditions for Southern Steelhead in California.
The California Department of Fish and Game and the National Marine Fisheries Service need to take a lead role in providing the funding and expertise to do the work, including trained experts and an organized plan or approach to implementing recovery of this endangered species. If state and federal agencies cannot develop timely and cost-effective programs to recover southern steelhead, they should concentrate on securing funding for restoration projects and contract the recovery work to professional experts in watershed and fisheries restoration.
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Updated: July 2, 2002