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Coastal Cutthroat Trout, Oncorhynchus clarki clarki
Detail on Coastal Cutthroat
Conservation Status in California: Class 3, Near threatened (Moyle et al. 2011).
Coastal cutthroat trout are apparently in no immediate risk of extinction but there is also high degree of uncertainty about their status in California. Coastal cutthroat trout apparently persist in many streams on the northern California coast but in fact populations are rarely monitored and best evidence indicates that most are very small. Coastal cutthroat should be assumed to be in decline until evidence shows otherwise.
Life History: Coastal cutthroat trout possess a variable life history strategy ranging from fully anadromous to resident (DeWitt 1954; Pauley et al. 1989, Moyle 2002). This plasticity is among the most extreme in Pacific salmonids and variations in anadromy and potadromy are found both between and within populations. Offspring of resident fish can be anadromous and vice versa. The Smith River in California has both anadromous populations and resident populations isolated in small streams upstream of anadromous barriers (e.g., Little Jones Creek). Anadromous cutthroat trout generally make their first migrations when two to three years old, although they can enter sea water as late as their fifth year. When multiple forms coexist, temporal and spatial segregation presumably influence genetic structure of the population and may lead to genetic differentiation between sympatric ecotypes within a watershed. Environmental conditions that affect growth rate, such as food availability, water quality, and temperature markedly influence the migratory behavior and residency time (Hindar et al. 1991, Northcote 1992, Johnson et al. 1999). Johnson et al. (1999) noted that the large variability in migratory behavior may be due to habitat being most available for cutthroat trout at times when it is not being used by more rigidly anadromous (but competitively dominant) salmonids; this flexibility may release cutthroat trout from competition and predation pressures at certain times of year.
Coastal cutthroat trout have ecological requirements analogous to those of resident rainbow trout and steelhead and when the two species co-occur, cutthroat trout occupy smaller tributary streams while the competitively dominant steelhead occupy larger tributaries and rivers. As a consequence, cutthroat trout tend to spawn and rear higher in watersheds than steelhead. Age at first spawning ranges from 2 to 4 years depending on migratory strategy and environmental conditions (Trotter 1991). Their life spans are 4-7 years with non-migratory fish often reaching sexual maturity earlier and at a smaller size than anadromous fish (Trotter 1991, Johnson et al. 1999). Resident fish generally reach sexual maturity between the ages of 2 and 3 years whereas anadromous fish rarely spawn before age 4 (Johnson et al. 1999). Sexually mature trout can demonstrate precise homing capabilities in their migrations to their natal streams. In northern California, coastal cutthroat trout migrate upstream to spawn after the first significant rain, beginning in August. Peak spawning occurs in December in the larger streams and January to February in smaller streams (Johnson et al. 1999). Ripe or nearly ripe females have been caught from September to April in California streams, however, indicating a prolonged spawning period.
Females dig redds predominantly in the tails of pools in low gradient reaches, often with low flows (less than 0.3 m3/second summer flows) (Johnston 1982, Johnson et al.1999). Females excavate redds in clean gravel with their tails. The completed redds average around 35 cm in diameter by 10-12 cm deep. After spawning is completed, the female covers her redd with about 15-20 cm of gravel by pushing upstream gravel over it with her tail. Each female digs a series of redds and may mate with numerous males. Fecundity ranges from 1,100 to 1,700 eggs for females between 20 and 40 cm TL. Coastal cutthroat trout are iteroparous with a higher incidence of repeat spawning than steelhead. They can spawn every year, but post-spawning mortality can be quite high.
Eggs hatch after 6-7 weeks of incubation depending on temperature. Alevin emerge as fry between March and June, with peak emergence during mid-April then spend the summer in backwaters and the stream margins (Johnson et al. 1999). Juveniles remain in the upper watershed until approximately 1 year in age at which point they may move about extensively through the watershed. Once this age is reached, it is difficult to determine the difference between sea-bound smolts and silvery parr moving back up into the watershed (Johnson 1999). Smolts or adults entering the salt water environment generally remain close to the shore and do not venture more than about 7 km from the edge of the coast (Johnson et al. 1999).
A adults feed on benthic macroinvertebrates, terrestrial insects in drift, and small fish, while juveniles feed primarily on zooplankton, macroinvertebrates, and microcrustaceans. (Romero et al. 2005, Wilzbach 1985). White and Harvey (2007) found that cutthroat trout of all sizes in small creeks fed mainly on aquatic insects in low numbers, but that earthworms washed in by winter storms may be bioenergetically most important for overwintering survival. In the marine environment, cutthroat trout feed on various crustaceans and fishes, including Pacific sand lance (Ammodytes hexapterus), salmonids, herring and sculpins. Marine predators include Pacific hake (Merluccius productus), spiny dogfish (Squalus acanthias), harbor seals (Phoca vitulina) and adult salmon (Pauley et al. 1989). Freshwater predators include the typical array of herons, mergansers, kingfishers, otters, snakes, and piscivorous fishes.
Habitat Requirements: Variability in life history including resident, adfluvial (lagoon) and anadromous forms means that coastal cutthroat populations depend on many different costal environments. Generally, coastal cutthroat trout require cool, clean water with plenty of cover and deep pools for holding in summer. They prefer small, low gradient coastal streams and estuarine habitats. Preferred water velocities for fry are less than 0.30 m/sec, with an optimal velocity of 0.08 m/sec (Pauley et al. 1989). Summer flows in natal streams are typically low, averaging 0.12 m3/sec in Oregon (Pauley et al. 1989). Adults overwintering in streams, rather than estuaries, prefer pools with fallen logs or undercut banks but will also utilize boulders, depth, and turbulence as alternative forms of cover if woody debris is not available (Gerstung 1998, Rosenfeld et al. 2000, Rosenfeld and Boss 2001). Juveniles generally rear in smaller streams with dense overhead cover and cool summer temperatures (Rosenfeld et al. 2000, 2002) Fish using large woody debris as cover are less affected by winter high flow events than those without such cover (Harvey et al. 1999). Spawning takes place in small streams with small to moderate sized gravel ranging from 0.16-10.2 cm in diameter. Cutthroat preferentially use riffles and the tails of pools for spawning with velocities of 0.3-0.9 m/sec, though they have been observed spawning in velocities as low as 0.01-0.03 in small streams in Oregon (Pauley et al. 1989).
Optimal stream temperatures are less than 18° C, with preferred temperatures being around 9-12°C. This may explain why they occur mainly in more northern streams in California, in the coastal fog belt. In Washington streams, most rapid growth occurred at 8-10°C, in early summer, with rates declining as temperatures rose to 12-14°C (Quinn 2005). Spawning has been recorded at temperatures of 6-17° C, with preferred temperatures of 9-12° C (Pauley et al. 1989, Moyle 2002). Coastal cutthroat require high dissolved oxygen levels and will avoid areas with less than 5 mg/L DO in summer months (Pauley et al. 1989). Feeding and movement of adults are impaired at turbidities of greater than 35 ppm. Embryo survival is greatly reduced at turbidities greater than 103 ppm and dissolved oxygen levels.
Distribution: Coastal cutthroat trout are distributed from the Seward River in Southern Alaska to Salt Creek, a tributary to the Eel River estuary in Humboldt County, California. There are additional reports of small populations of cutthroat in Fortuna area tributaries and possibly in the lower Van Duzen River tributaries (Tom Weseloh, pers. comm. 2008). The interior range of the subspecies in Washington, Oregon, and California is bounded by the rain forests on the western slope of the Cascade Range; their range rarely extends inland more than 160 km and is usually less than 100 km (Johnson et al. 1999). In California, this band is only about 8 km wide at the mouth of the Eel River and 48 km wide at the Oregon border (Moyle 2002). However, a small resident population exists in Elliot Creek in Siskiyou County, about 120 km from the ocean. Elliot Creek is a tributary to Applegate River in Oregon, which drains into the Rogue River. Fish from Elliot Creek have been transplanted successfully to Twin Valley Creek in the Klamath River watershed (Moyle 2002).
In California, coastal cutthroat trout are at the southern edge of their range and have been observed in 182 named streams (approximately 71% of the 252 named streams within their range in California) and an additional 45 streams may support populations (Gerstung 1997). Self-sustaining populations apparently occur in many coastal basins including Humboldt Bay tributaries, Little River, and Redwood Creek (Gerstung 1997). The principal large interior basins where coastal cutthroat trout are the Smith, Mad and lower Klamath Rivers. Cutthroat trout also rear in approximately 1875 ha of habitat in five coastal lagoons and pondsBig, Stone, and Espa Lagoons, and the Lake Earl-Talawa complex (Gerstung 1997). However, the largest populations are currently in the Smith River, and to a lesser extent, the lower Klamath River and tributaries (Gale and Randolph 2000). Gerstung (1997) indicates the lower Mad River as another area of high cutthroat occupancy, but more recent assessments indicate that it contains only a small population (T. Weseloh, pers. comm. 2008). Thus, as Gerstung (1997) noted, almost 46% of California coastal cutthroat trout populations occupy habitats in the Smith and Klamath River drainages.
Historical coastal cutthroat trout distribution may have once extended farther south to the Russian River in Sonoma County. There are anecdotal reports of cutthroat trout in several streams from the Mattole River down to the Garcia River (Gerstung 1997); however, there are currently no known populations south of the Eel River.
Trends in Abundance: There are a limited number of long-term data sets readily available to evaluate population trends in coastal cutthroat trout and those data sets that do exist are primarily related to adult fish in Oregon and Washington. Data is spotty, scattered, and typically unpublished. There is no agency systematically keeping track of ongoing surveys. Records suggest that coastal cutthroat trout were more abundant historically and, in some locations, supported substantial fisheries (Gerstung 1997). Current coastal cutthroat trout abundance is thought to generally be low in most waters, particularly where juvenile steelhead are present (Johnson 1999, Griswold 2006).
Effective population size in California streams is difficult to determine, but Gerstung (1997) estimated that there are likely less than 5,000 spawners each year in all of California. The largest population apparently exists in the Smith River, where a local watershed monitoring group, the Smith River Alliance (SRA) conducts snorkel surveys for salmon and trout. For example, SRA surveyed various reaches of the South and Middle Forks of the Smith River in 2005 (totaling 34 miles) and the South, Middle and North Forks, totaling 47 miles surveyed in 2006 (Reedy 2005, 2006). The SRA 2006 surveys observed a total of 922 CCT in 2005 and 1361 adult CC T in 2006 (Reedy 2005, 2006). Previous population and trend data collections from the Smith River have been intermittent and represent only a small portion of the CCT range with inconsistent locations and methods over the years (Table 1). The Yurok Tribe has conducted anadromous salmonid surveys on the lower Klamath River and many of its tributaries and found cutthroat widely distributed in medium to high densities in nearly all of the lower Klamath tributaries downstream of Mettah Creek (Gale and Randolph 2000). Data covering a wider geographic area (Johnson et al. 1999) suggest that populations are generally low, if persistent, but with insufficient data for long-term trend analysis (Figure 1).
However, because quantitative measures of historical abundance are lacking it is difficult to say with any certainty whether populations are in decline, increasing, or stable (Johnson et al. 1999, Griswold 2006). Decline is the most likely scenario because there have been changes to estuaries and watersheds and loss of structure and flows in cutthroat streams throughout its range in California. Fortunately, there is increasing protection for some of their streams (e.g. Smith River, streams in Redwood National Park) in part to protect listed coho salmon.
Description: Coastal cutthroat trout are similar to coastal rainbow trout (O. mykiss) but have heavier spotting, particularly below the lateral line and heavy spots on paired and anal fins. The spots become nearly invisible when the fish become silvery when migrating to sea. The body color of mature fish in fresh water has dark coppery or brassy appearance (Behnke 1992, Moyle 2002).
Cutthroat trout tend to be more slender-bodied than rainbow trout and possess characteristic red to orange to yellow slashes under the mandibles although the slashes are seldom visible until the fish reach over 80 mm total length (TL) (Scott and Crossman 1973, Behnke 1992). Larger fish have long maxillary bones extending past the eye giving them a predatory appearance. Well-developed teeth are found on the jaws, vomer, palatines, tongue, and on the basibranchial bones. The dorsal fin has 9-11 rays, the anal fin 8-12 rays, the pelvic fins 9-10 rays, and the pectoral fins 12-15 rays. There are 15-28 gill rakers on each arch and 9-12 branchiostegal rays. The caudal fin is moderately forked and scales are smaller than those of the rainbow trout, with 140-200 along the lateral line (Behnke 1992).
Parr possess 9-10 widely spaced parr marks (vertical bars) along the lateral line and are difficult to distinguish from rainbow trout parr. Anadromous forms rarely exceed 40 cm fork length (FL) and 2 kg, but individuals reaching 70 cm and 8 kg have been recorded. It is uncommon individuals from landlocked populations to exceed 30 cm FL.
(Source of detail: http://pisces.ucdavis.edu/content/oncorhynchus-clarki-clarki)