Southern California Steelhead |
TAXONOMIC RELATIONSHIPS: Southern steelhead are winter-run steelhead that persist in streams that have warm, dry lower reaches on the coastal plain, which present substantial migration passage problems to and from distant headwater spawning and rearing habitats. Their occurrence in such a demanding environment suggests the development of distinctive ecological and physiological adaptations. According to J. J. Smith (CSU, San Jose), river basins with southern steelhead are also drier, resulting in exaggerated effects of year-to-year rainfall variation. Most streams from San Luis Obispo County southward are definitely "southern steelhead streams", and the Pajaro, Salinas, and Carmel rivers in Monterey County are ecologically similar. The wetter coastal streams between the Carmel River and SLO County are ecologically more like steelhead streams in northern California (J. Smith, pers. comm.). This broad ecological definition of southern steelhead is the one used by Titus et al. (in press) in their monograph on the status of steelhead in California south of San Francisco Bay. A narrower definition of southern steelhead is emerging from ongoing genetic studies which are helping to define "metapopulations" within the general ecological type described above. Genetic groupings may conform to the concept of an evolutionary significant unit of the biological species (sensu Waples 1991). Both allozyme studies (Berg and Gall 1988) and mitochondrial DNA studies (J. Nielsen, pers. comm.) indicate that a north to south gradient of genetic characteristics occurs along the California coast. However, the mtDNA studies also indicate that steelhead populations found south of Point Conception may form a distinct genetic unit (J. Nielsen, Abstract, Amer. Fish. Soc. meeting, July 26-29, 1993, Sacramento). Because Point Conception is also a major zoogeographic boundary for marine organisms, the mtDNA studies may mean that steelhead entering streams south of this point probably do not intermingle much in the ocean with fish from more northern localities. Until the mtDNA and other genetic studies are completed, we prefer to use the broader ecological definition for southern steelhead, recognizing that southern steelhead are probably several distinct stocks. However, all these stocks are in decline and need special protection to preclude extinction. LIFE HISTORY: Southern steelhead have received little study, although the life-history characteristics of steelhead in general are well known (Emmett et al. 1991). Winter steelhead in California typically spawn from December to May, but mostly in January-March (E. Gerstung, pers. comm.), and spent fish may return to the ocean and spawn again in a later year. The frequency of repeat spawning varies according to the stock and with habitat quality (Emmett et al. 1991), and it is not known if repeat spawning is common among southern steelhead. Juvenile steelhead remain in fresh water 1-4 years (usually 1-3 in California) and then spend 1-5 years (usually 2-3 in California) in the ocean (Emmett et al. 1991, E. Gerstung, pers. comm.). Southern steelhead, however, probably spend less time in fresh water because of the often inhospitable conditions in the lower reaches of southern California streams; they may, therefore, migrate to the ocean or have greater dependence on coastal lagoons during their first year (E. Gerstung, memorandum to R. Rawstron, CDFG, November 22, 1989). Early emigration may also occur because of rapid growth in the warm, productive streams, allowing the juveniles to reach smolt size at a younger age. Because of frequent drought in southern California, the streams may be inaccessible during some years so that adult steelhead are forced to spend additional years in the ocean before having a chance to spawn. The increased growing time in the ocean, plus richer food sources in southern coastal waters due to the reduction of marine mammals there, might account for the large size (9+ kg) evidently attained by steelhead in some southern California streams (e.g., the Santa Ynez River); these fish may have been 5-6 years old, compared to the typical 4-year old spawners (E. Gerstung, memorandum to R. Rawstron, CDFG, November 22, 1989). However, during wet years a high percentage of the southern steelhead returning to spawn have spent only one year in the ocean, indicating that a bet-hedging strategy of attempting to spawn every year is adaptive in this unpredictable environment (J. Smith, pers. comm.). Despite the intermittent nature of southern California streams, steelhead production during wet years was probably higher in these streams than in northern California streams because of greater biological productivity and more favorable growing temperatures (E. Gerstung, pers. comm.). The ability of some southern steelhead to survive in warm (>21 C) isolated pools (Higgins 1991) possibly is due to greater physiological tolerances to higher temperatures and lower oxygen levels than are shown by other steelhead stocks. However, the relative physiological capabilities, and their possible genetic basis, of southern steelhead have not been studied. Although juvenile steelhead in the Columbia River (Oregon-Washington) spend little time in that estuary (Dawley et al. 1986, Emmett et al. 1991), juvenile steelhead in central California streams evidently do spend considerable time rearing in estuaries (Smith 1987, 1990). It has been surmised that steelhead in southern California also rely heavily on estuaries, because many of their streams seasonally had very low flows or dried completely in the alluvial fan areas (Higgins 1991). In addition, although many lowland stream areas were perennial, they also may have dried out during the driest years (C. Swift, pers. comm.). Evidently large numbers of juvenile southern steelhead often could be caught in coastal lagoons in the 1930s and earlier (Swift et al. 1993). Most of the estuaries today are much shallower and warmer than they were originally. A particularly severe problem is the lack of adequate inflowing fresh water, which keeps lagoons cool, deep, and thermally unstratified (J. Smith, pers. comm.). Steelhead in general are known to have well-developed homing abilities (Moyle 1976), although it has been suggested that southern steelhead commonly stray from their natal streams (Higgins 1991). Straying, if it actually occurs at significant levels in southern steelhead, may be selectively advantageous because it would allow spawners to opportunistically utilize more favorable streams when their natal streams dried up or were blocked by sand berms (Higgins 1991). An additional feature of southern steelhead is that they "miraculously" reappeared in large spawning runs when flows became suitable in streams that had been dry or otherwise inaccessible during the previous one or more years. The implication is that the fish, finding their natal stream unavailable during a given year, return the following year(s) until access can be gained. HABITAT REQUIREMENTS: The basic environmental requirements for southern steelhead probably are similar to those of more northern steelhead stocks, although it is likely that southern steelhead have greater physiological tolerances to the warmer and more variable conditions they commonly encounter in southern California streams (Higgins 1991). Major streams in southern California originate in the coastal mountains and often cross broad alluvial areas before flowing into the sea. These low-elevation alluvial flats present inhospitably warm and fluctuating temperatures and the streams themselves may be intermittent. The higher-elevation headwaters, therefore, are the primary spawning and rearing areas for steelhead today, although lowland reaches once may have been important, especially in wetyears. It is likely that the largest steelhead populations historically occurred in streams where the upstream spawning and rearing habitats were closest to the ocean, such as in the Ventura, Santa Clara and Santa Ynez rivers (M. Cappelli, in USFWS 1991). San Mateo Creek, a former steelhead stream, typifies the southern California streams (Higgins 1991, Woefel 1991). Its headwaters lie in the Santa Ana and Santa Margarita mountains, where winter temperatures can drop below freezing and annual rainfall averages about 63 cm near Elsinore Peak. The creek descends the mountains through a deeply cut canyon. The steep and rocky upper San Mateo Creek and its tributaries contain pools that harbored juvenile steelhead during the summer, while the depositional areas in the canyon probably served as the spawning areas. Flows in the upper reaches may be as low as 0.5 cfs during the summer and can average over 500 cfs during wet months. The lower reach of the creek flows along 17 km of alluvial valley to the coast, where average rainfall is 34 cm per year. Large quantities of natural sediment deposition evidently have rendered the lower stream course unstable and unsuitable for spawning. During the dry season, the creek went underground even in times prior to human-related water losses, thus presenting a temporally impassable barrier to steelhead. This stretch of the creek now is permanently dry, due to the lowered water table. The creek reemerges about 8.4 km from the ocean to mark the upper end of the estuary. The estuary has been substantially diminished in extent since the end of World War II (Higgins 1991). Originally the native riparian vegetation along the coastal reach of the creek probably was dominated by arroyo, red, and yellow willows, but introduced tamarisk recently has been replacing the native species. In the upper reaches, the dominant riparian plants are poison oak, wild grape, and wild rose. The terrain around the creek near the coast is covered with grasses and coastal scrub, southern oak and woodland higher up, and chaparral on the mountain slopes, all of which are subject to fire. Periodic fires and subsequent erosion may be an integral feature of this environment, posing particularly challenging conditions to the steelhead of these southern streams. DISTRIBUTION: Swift et al. (1993) state that at least a few southern steelhead have been found in virtually every coastal stream in Monterey, San Luis Obispo and Santa Barbara counties north of Point Conception within the last ten years. Southern steelhead evidently once utilized most of the major coastal streams in southern California as well. Today they still occur in Malibu Creek, Ventura River, Santa Clara River, and Santa Ynez River, although in greatly reduced numbers. Swift et al. (1993) also report recent records for Mission and Atascadero creeks (Santa Barbara County) and Mulholland, Big Sycamore, and Topanga canyons (Los Angeles County). Steelhead have been extirpated from at least 11 southern California streams: San Luis Rey River, San Mateo Creek, Santa Margarita River, Rincon Creek, Maria Ygnacio River, Los Angeles River, San Gabriel River, Santa Ana River, San Onofre Creek, San Juan Creek, San Diego River, and Sweetwater River (Nehlson et al. 1991, Swift et al. 1993). Steelhead have been caught in the lower Tijuana River, bordering Mexico (Hubbs 1946), and runs are known to have occurred historically in Baja California streams (Barnhart 1986). Southern steelhead historically may have occupied as much as 15% of the winter steelhead range in California, but the present distribution in southern California has been reduced to perhaps 1% of the stream miles they formerly inhabited (E. Gerstung, memorandum to R. Rawstron, CDFG, November 22, 1989). ABUNDANCE: Southern steelhead have been either significantly depleted or extirpated in all rivers and streams in which they historically occurred. Estimates of historical run sizes are highly subjective and probably correct only within an order of magnitude (USFWS 1991). They nonetheless attest to the substantially higher numbers of southern steelhead that once existed. Past runs have been estimated at 7,000-9,000 fish in the Santa Clara River, 4,000-6,000 for Matilija Creek (a tributary to the Ventura River), and 20,000 for the Santa Ynez River (USFWS 1991). In 1940, CDFG personnel "rescued more than 525,000 young steelhead trout ... from the drying Santa Ynez River" (Shapovalov 1940). CDFG rescue operations also saved 9,800 juveniles from isolated pools in the lower San Mateo Creek in 1939, and the Department proposed at that time that a recreational fishery be promulgated in this highly productive stream (Higgins 1991). There have been no comprehensive surveys conducted in recent years to provide a reliable estimate of total population size for southern steelhead. The current number of steelhead using southern California streams south of Point Conception is unknown, but judging from recent accounts they probably number in the several hundreds, an indisputable severe decline from historical levels. There are at most only three or four streams and rivers that presently support significant remnants of southern steelhead runs. The largest extant stock probably occurs in the Santa Ynez River, where "a substantial number" were reportedly taken by anglers in 1993 (F. Reynolds, CDFG memorandum to B. Bolster, October 13, 1993). Another stock occurs in the Ventura River, aided by the preservation efforts of local citizens groups. In May 1991, 14-25 adult steelhead were observed in the upper estuary of the Ventura River (R. Leidy, EPA, memorandum to B. Harper, USFWS, May 8, 1991), but no steelhead were reported in 1992 and only one pair was reported in 1993 (F. Reynolds, ibid.). An annual run numbering up to 60 spawners in some years has persisted in Malibu Creek (USFWS 1991); this is the southernmost self-sustaining run of southern steelhead. Consistent stream flows in Malibu Creek have been maintained since the late 1960s, aided in the 1980s by influx from the Tapia Water Reclamation Facility. It has been suggested that the perennial flows may have attracted remnants of southern steelhead runs that have been extirpated from other streams, and therefore Malibu Creek could be a valuable "genetic repository of locally adapted steelhead" (Higgins 1991). A fourth remaining stock may exist in the Santa Clara River drainage, mainly in Sespe Creek (within the National Condor Sanctuary), which still contains considerable steelhead habitat, and perhaps Santa Paula Creek. Adult steelhead were observed in Santa Paula Creek in March 1987 and 1988 (B. Harper, unpubl. data), but none were found in March 1991 or in January 1992 (S. Parmenter, pers. comm.; D. McEwan, CDFG memorandum, March 26, 1992). Other streams that have had at least a few steelhead when flows were sufficiently high are Santa Rosa Creek (San Luis Obispo County), Arroyo de La Cruz (near San Simeon), San Simeon Creek, San Luis Obispo Creek and Gaviota Creek (USFWS 1991). It is not known if any of these runs are self-sustaining. In terms of the stream habitat presently utilized, southern steelhead occur in about 16 km of the Ventura River, 5 km of Malibu Creek, 16 km of the Santa Ynez River, and, if they still occur there, within 80 km of suitable habitat in Sespe Creek (E. Gerstung, pers. comm.). The once large steelhead runs in San Mateo Creek and Santa Margarita River have been completely eliminated (Higgins 1991). Other now extirpated runs occurred in the San Luis Rey, San Diego, and San Dieguito rivers, and San Onofre Creek (all in San Diego County), Santa Ana River and San Juan Creek (Orange County), San Gabriel River (Los Angeles County), Sisquoc River (Santa Barbara County) and the Cuyama River (USFWS 1991). A detailed stream-by-stream account of southern steelhead distribution and abundance is currently being completed by R. Titus, W. Snider (CDFG) and D. Erman (UCD). FEDERAL STATUS: Endangered, 1997 (Southern California coastal basins from the Santa Maria River, south to the southern extent of the range (presently considered to be Malibu Creek. Proposed rulemaking 12-19-2000 to extend southern portion of the range to San Mateo Now $800,000 has been allocated to restoring San Mateo Creek to increase the chances of significant population return. |
Southern California Steelhead Trout
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