Southern Oregon and Northern California Coho salmon were once prevalent in coastal streams from Monterey Bay to Alaska. In the 1940s, California had an estimated 500,000 Coho salmon, a number which has plummeted to one percent or about 5,000 fish today. The coho salmon is one of seven species of Pacific salmon belonging to the genus Oncorhynchus and one of five species found in California. In California, it is found in many of the short, coastal drainages from the Oregon border south to Monterey Bay. In the larger coastal drainages, it is found primarily in the lower sections. Coho salmon populations found in the drainages south of the San Francisco Bay are termed ‘southern coho salmon'. However, studies thus far have not demonstrated that these populations are genetically distinct from other, more northerly coho salmon populations. For the most part, coho salmon's life cycle takes three years. They normally spend their first year in fresh water and their next two years in salt water prior to returning to spawn in their natal streams. Some males, called "jacks", return to spawn after only one season in the ocean. Spawning migrations begin after heavy, late autumn or winter rains encourage the returning adult to leave the ocean and move upstream. In many of the coastal streams south of San Francisco Bay, heavy river flows are needed to breach sand bars that have formed at the mouths of coastal streams before fish can migrate up. Description: Coho are fairly large salmon, with spawning adults typically attaining 55-70 cm FL and weighing 3-6 kg. They have 9-12 dorsal fin rays, 12-17 anal fin rays, 13-16 pectoral fin rays, and 9-11 pelvic fin rays. Lateral line scales number 121-148 and the scales are pored. There are 11-15 branchiostegal rays on either side of the jaw. Gill rakers are rough and widely spaced, with 12-16 on the lower half of the first arch. Spawning adults are dark and drab. The head and back are dark green, the sides are a dull maroon to brown, and the belly is gray to black. Females are paler than males. Spawning males are characterized by a bright red lateral stripe, hooked jaw, and slightly humped back. Both sexes have small black spots on the back, dorsal fin, and upper lobe of the caudal fin. The adipose fin is finely speckled, imparting to it a gray color; except for the caudal, the other fins lack spots and are tinted orange. The gums of the lower jaw are gray, except the upper area at the base of the teeth, which is generally whitish (Fry 1973). Parr have 8-12 narrow parr marks centered along the lateral line. The marks are narrow and widely spaced. Taxonomic Relationships: Coho salmon are one of five species of Pacific salmon (Oncorhynchus) found in California. They do not appear to have the genetically distinct, temporally segregated runs that characterize the more abundant chinook salmon and steelhead trout. However, given the homing capabilities of coho salmon, it is reasonable to expect that at least some coastal areas have their coho populations adapted for local environmental conditions (e.g., with regard to run timing and other life history characteristics). A recent study of allozyme variation in California coho salmon showed that most variant alleles occurred at three or fewer localities, although the distribution of those alleles did not follow any particular pattern (Bartley et al. 1992). It was concluded that gene flow among California populations was high from an evolutionary perspective, but low in terms of the actual number of individuals (1.4 per generation) being exchanged between populations. Further population genetic studies (e.g., using mtDNA) are needed. Overall, coho populations in California are the southernmost for the species and presumably have adapted to the extreme conditions (for coho salmon) of many coastal streams. There is some indication from allozyme data that California stocks may be somewhat genetically differentiated from stocks in more northern areas (Bartley et al. 1992). Life History: The life history of the coho salmon in California has been well documented by Shapavalov and Taft (1954) and Hassler (1987). A comprehensive account of coho salmon biology throughout their range is given by Sandercock (1991), and ocean-related aspects are covered by Pearcy (1992). Coho salmon return to their parent streams to spawn after spending one or two years in the ocean (up to three years in Alaska). Jack males may, however, return after one growing season in the ocean (at age two years), but most fish return after two growing seasons in the ocean (age three). The spawning migrations begin after heavy late-fall or winter rains breach the sand bars at the mouths of coastal streams, allowing the fish to move into them. However, migration typically occurs when stream flows are either rising or falling, not necessarily when streams are in full flood. The timing of their return varies considerably, but in general they return earlier in the season in more northern areas and in the larger river systems (Baker and Reynolds 1986). In the Klamath River, the coho run is between September and late-December, peaking in October-November. Spawning itself occurs mainly in November and December (USFWS 1979). The early part of the run is dominated by males, with females returning in greater numbers during the latter part of the run. The coho run in the Eel River occurs 4-6 weeks later than that in the Klamath River; arrival in the upper reaches of the Eel River peaks in November-December (Baker and Reynolds 1986). In the short coastal streams of California, most coho return during mid-November through mid-January (Baker and Reynolds 1986). In the southernmost populations in Scott and Waddell creeks (Santa Cruz County), spawning migrations often do not occur until November or December (Shapovalov and Taft 1954) and spawning may extend into February (J. Smith, pers. comm.). In Oregon streams, spawning can occur as late as March if drought conditions delay rains or runoff (Sandercock 1991). Coho salmon migrate up and spawn mainly in streams that flow directly into the ocean or in tributaries of large rivers. Generally, coho spawn in smaller streams than those used by chinooks. Females choose the spawning sites (redds) usually near the head of a riffle, just below a pool, where the water changes from a smooth to a turbulent flow and there is medium to small gravel substrate. Flow characteristics of the redd location usually ensure good aeration, and the circulation facilitates fry emergence from the gravel. Each female, moving upstream, builds a series of redds and deposits a few hundred eggs in each. Thus, spawning may take about a week to complete and a female can lay between 1,400-7,000 eggs. There is a positive correlation between fecundity and size of females. A dominant male accompanies a female during spawning, but one or more subordinate males also may engage in spawning (Hassler 1987). Both males and females die after spawning, although the female may guard a nest for up to two weeks (Hassler 1987). Embryos hatch after 8-12 weeks of incubation, the time being inversely related to water temperature. Hatchlings remain in the gravel until their yolk sacs have been absorbed, 4-10 weeks after hatching. Under optimum conditions, mortality during this period can be as low as 10%; under adverse conditions of high scouring flows or heavy siltation, mortality may be close to 100% (Baker and Reynolds 1986). Upon emerging, they seek out shallow water, usually along the stream margins. Initially they form schools, but as they grow bigger the schools break up and juveniles (parr) set up individual territories. Larger parr tend to occupy the heads of pools; smaller parr are found farther down the pools (Chapman and Bjornn 1969). As the fish continue to grow, they move into deeper water and expand their territories until, by July and August, they are in deep pools. Optimal habitat seems to be deep pools containing rootwads and boulders in heavily shaded sections of stream. Growth rates slow down at this stage, possibly due to lack of food or because the fish reduce feeding as a result of warmer temperatures. During December-February, winter rains result in increased stream flows and by March, following peak flows, fish are feeding heavily on insects and crustaceans and grow rapidly. Toward the end of March and the beginning of April they begin to migrate downstream and into the ocean. Outmigration in California streams typically peaks in mid-May, if conditions are favorable. Migratory behavior is related to rising or falling water levels, size of fish, day length, water temperature, food densities, and dissolved oxygen levels. At this point, the outmigrants are about one year old and 10-13 cm in length. The fish migrate in small schools of about 10-50 individuals. Parr marks are still prominent in the early migrants, but the later migrants are silvery, having transformed into smolts. After entering the ocean, the immature salmon initially remain in inshore waters close to the parent stream. They gradually move northward, staying over the continental shelf. Coho salmon can range widely in the north Pacific, but the movements of California fish are poorly known. Most coho caught off California in ocean fisheries were reared in coastal Oregon streams (natural and hatcheries). In 1990, for instance, 112,600 coho were caught in commercial and recreational ocean fisheries, which greatly exceeds the present production capability of California populations alone (A. Baracco, pers. comm.). Oceanic coho tend to school together. Although it is not known if the schools are mixed, consisting of fish from a number of different streams, fish from different regions are found in the same general areas. Adult coho salmon are primarily piscivores, but shrimp, crabs, and other pelagic invertebrates can be important food in some areas. Habitat Requirements: Coho salmon move upstream in response to an increase in stream flows caused by fall storms, especially in small streams when water temperatures are 4-14 C. Spawning sites are typically at the heads of riffles or tails of pools where there are beds of loose, silt-free, coarse gravel and cover nearby for the adults. Unlike other salmon species, coho salmon redds can be situated in substrates composed of up to 10% fines (Emmett et al. 1991), but spawning success and fry survival generally are favored by very clean gravel (<5% fines) (CDFG 1991). Spawning depths are 10-54 cm, with water velocities of 0.2-0.8 m sec-1 (Hassler 1987). Optimal temperatures for development of the embryos in the gravel is 4.4-13.3 C, although eggs and alevins can be found in 4.4-21.0 C water (Emmett et al. 1991). Dissolved oxygen levels should be above 8 mg l-1 for eggs and above 4 mg l-1 for juveniles (Emmett et al. 1991). Juveniles prefer deep ( 1 m), well-shaded pools with plenty of overhead cover; highest densities are typically associated with instream cover such as undercut banks or logs and other woody debris in the pools or runs. Juveniles require water temperatures not exceeding 22-25 C for extended periods of time and oxygen and food (invertebrates) levels that remain high. Preferred temperatures are 10-15 C (Hassler 1987); preferred water velocities for juveniles are .09-.46 m sec-1, depending on habitat. High turbidity is detrimental to emergence, feeding and growth of young coho (Hassler 1987, Emmett et al. 1991). Young and adult coho salmon are found over a wide range of substrates, from silt to bedrock. Distribution: Coho salmon are widely distributed in the northern temperate latitudes. In North America, they spawn in coastal streams from California to Alaska. In Asia, they range from northern Japan to the Anadyr River in the Soviet Union. In California, principal populations are located in the Klamath, Trinity, Mad, Noyo, and Eel rivers, with other populations in smaller coastal streams south to Scott and Waddell creeks, Santa Cruz County. In the Eel River system, they formerly ascended 390 km (246 mi) of stream in 69 tributaries (Mills 1983) of the South Fork Eel, the lower mainstem Eel River, and the Van Duzen River (Brown 1987). Annual runs in the Eel River system in earlier years have been estimated at over 40,000 fish (U.S. Heritage Conservation and Recreation Service 1980); current runs are less than 1,000 fish (Brown and Moyle 1991). Brown and Moyle (1991) found historical records of occurrence of coho in 582 California streams, ranging from the Smith River near the Oregon border to the Big Sur River on the central coast. More recent records of surveys were available for only 244 of the streams; of those streams, 46 % had lost their populations. Generally, the farther south a stream was located, the more likely it was to have lost its coho population (Brown and Moyle 1991). Coho salmon are rare in the Sacramento River even though several attempts have been made to establish runs (Hallock and Fry 1967). It is likely that runs occurred at one time at least in tributaries to San Francisco Bay, if not in more interior streams. Coho salmon of hatchery origin also have been stocked in reservoirs such as Lake Berryessa with considerable success. The coho do not reproduce in reservoir tributaries, however, and therefore must be restocked annually to support angling. Abundance: Historical figures of statewide coho salmon abundance were essentially guesses made by fisheries managers, based on limited catch statistics, hatchery records, and personal observations of runs in various streams. Maximum estimates for the number of coho spawning in the state in the 1940s range from 200,000-500,000 (E.R. Gerstung, pers. comm.) to close to 1 million (Calif. Advisory Committee on Salmon and Steelhead Trout 1988). Coho numbers held at about 100,000 statewide in the 1960s (California Advisory Committee on Salmon and Steelhead Trout 1988), with 40,000 in the Eel River alone (U.S. Heritage Conservation and Recreation Service 1980), and then dropped to a statewide average of around 33,500 for the 1980s (Brown et al. 1994). The reliability of these estimates is uncertain, and so must be viewed only as "order-of magnitude" approximations. Coho salmon in California, including hatchery stocks, presently are less than 6% of their abundance during the 1940s, with probably at least a 70% decline in numbers since the 1960s. Brown et al. (1994) estimated that the total number of adult coho salmon entering California streams in 1988-90 averaged about 31,000 fish per year. However, hatchery fish made up 57% of this total, and many big-river populations contain at least some fish of recent hatchery ancestry. The hatchery stocks, without exception, have in their ancestry fish from other river systems and often from outside California (Brown and Moyle 1991, Brown et al., unpubl.). This may explain the overall lack of genetic differentiation of coho salmon from different California streams (Bartley et al. 1992). Coho salmon are widely distributed in coastal streams of California. Their populations show large fluctuations, but the general trend has been downward in the wild populations of small coastal streams. Of 582 coastal streams that historically held coho salmon, at least 19% and perhaps up to 40-50% have lost their coho runs (Brown et al. 1994). In Del Norte County, 45% of the streams for which there are reliable records have lost their coho populations, mainly in the Klamath-Trinity system. Corresponding percentages for other counties are: Humboldt County, 31; Mendocino County, 41; Sonoma County, 86. Farther south, the value is 56%, but this excludes streams in the Sacramento drainage and includes streams with extremely low populations that are enhanced by hatchery production. The big-river populations presently are largely maintained by hatchery production. Early accounts indicate that the Sacramento drainage supported coho salmon in the 19th century (U.S. Comm. Fish and Fisheries 1892, Evermann and Clark 1931), but the coho were extirpated before any good records were kept. Historical annual spawning escapements for the Klamath River system have been estimated at 15,400-20,000 fish, with 8,000 for the Trinity River (USFWS 1979). Only 1,700 cohos returned to Klamath Basin hatcheries in 1990 (A. Baracco, pers. comm.) and 3,100 returned in 1991 (CDFG 1992a). Probably the largest concentration of wild fish (with little or no hatchery influence) is in the South Fork of the Eel River, which has been estimated to have runs of about 1,300 fish. The latest (1990) survey, however, indicates a population one-half to one-third that size. This stock seems to be the only remaining wild, big-river coho run in California. Lagunitas Creek (Marin County) supports one of the better small-stream coho runs. This stream and its tributaries historically supported 500-2,000 adult spawners yearly (E. Gerstung, pers. comm.); the 1991-1992 run has been estimated at 500 fish (L. Cronin, pers. comm.). A similar self-sustaining run apparently exists in nearby Redwood Creek. Brown et al. (1994) considered 5,000-7,000 fish to be a realistic assessment of the total number of naturally spawned adults returning to California streams each year since 1987, although this number includes some stocks that contain fish of recent hatchery derivation. Presently, there are probably less than 5,000 wild coho salmon (no hatchery influence) spawning in California each year. Many of these fish are in populations of less than 100 individuals. These small populations are probably below the minimum population size required to preserve the genetic diversity of the stock and to buffer them from natural environmental disasters. There is every reason, therefore, to think that California's coho populations are continuing to decline. Higgins (1992) divides California's coho populations into 18 "stocks", ten of which are considered to be "at high risk of extinction." Abundance of wild coho salmon in both Washington and Oregon also is low and declining (Nehlsen et al. 1991), and the species is classified there as "sensitive-critical" (Weeks 1992). In 1993, the Audubon Society and other groups petitioned the Pacific Fisheries Management Council to ban all harvest of coho salmon south of Canada because of its alarming declines throughout the Pacific northwest. A petition to list all coho salmon populations in Washington, Oregon, and California as endangered was filed with NMFS by a coalition of environmental groups in October 1993. In addition, the populations of coho salmon in Scott and Waddell creeks (Santa Cruz County) were petitioned for endangered status to the state Fish and Game Commission (January 1993, by David Hope).
Fish Species of Special Concern in California, Coho Salmon. CA Dept of Fish and Game, 1995. |
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 Central California Nine coastal streams south of San Francisco Bay historically supported self-sustaining spawning runs of coho salmon. These streams are San Gregorio, Pescadero, Gazos, Waddell, Scott and San Vincente creeks, the San Lorenzo River, and Soquel and Aptos creeks in San Mateo and Santa Cruz counties. Presently, only Scott Creek is known to support all three brood-year lineages. A lineage is defined as the direct ancestor-descendent line. For the southern populations of coho salmon, there are three distinct and separate maternal brood-year lineages. The Scott Creek population has been supplemented in recent years by stocking of coho juveniles from a small hatchery on Big Creek, a tributary of Scott Creek. Waddell Creek, five miles north of Scott Creek, is known to support two of the three brood-year lineages, although one of the two appears to total less than 20 returning adults. The size of the coho salmon populations in these coastal streams is not known; however, some limited sampling for juvenile coho salmon has been conducted on all the streams. Juveniles have been found in Pescadero, Gazos, Waddell, Scott, and San Vicente creeks. However, due to the difficulties in sampling, it has not been possible to estimate juvenile population sizes. The few existing southern coho salmon populations are small and in danger of extirpation. The decline of southern coho is primarily due to unfavorable climate conditions in recent decades. Droughts during the 1970s and 1990, intense floods in the 1980s and late 1990s, and recent unfavorable ocean conditions have all contributed substantially to the continuing decline of southern coho salmon. Very poor (warm, nutrient-poor) ocean conditions in the fall of 1997 resulted in most adult coho returning to central coast streams having very poor fertility. In addition most of the limited production from this group of adults was probably destroyed by extraordinarily high rainfall amounts in February 1998, and associated high levels of streambed scour. More favorable ocean and precipitation conditions during the winter of 1998-99 produced a substantial 1999 year-class. Fall 1999 juvenile surveys have found evidence of successful reproduction in Pescadero, Gazos, Scott, Waddell, and San Vicente creeks. Approximately 4,000 juvenile coho are being reared at the Big Creek Hatchery for release in the spring of 2000.
See also TU Projects>North Coast Coho |
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