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Coastal Cutthroat trout are similar in appearance to Rainbow trout, but are generally brassy in color and have more spots spread along their bodies, especially on their fins. They are more slender and bullet-like in shape than Rainbow trout, with pointed heads and forked tails. As juvenile Coastal Cutthroats become smolts to undertake ocean migrations, their spots disappear and the fish become silvery. Most, but not all, Coastal Cutthroats have characteristic red to orange slashes under their lower jaws, though the slashes are rarely visible until the fish are a year or more old. They are capable of reaching 70 cm (about 28 in.) in length, and 8 kg (nearly 18 lbs.), but rarely exceed 40 cm (16 in.) in California waters. Tagged Coastal Cutthroats in California have been known to live for up to 7 years.

Coastal Cutthroat trout once supported a substantial fishery and were even stocked in the Mad River (Humboldt County) as early as the 1920s to support harvest. Abundance data from California populations are typically incomplete and unpublished, but suggest that Coastal Cutthroat populations are probably significantly smaller than they were historically, and are either currently stable or in decline due to extensive estuary and stream alteration throughout their range in California.

Coastal Cutthroat trout are the least studied salmonid along the North Coast. They need cool, clean, oxygenated water with ample cover and deep pools for holding during the summer. They prefer small, low-gradient coastal streams with access to estuarine habitats, including lagoons, but may also live in small headwater streams. Coastal Cutthroats lurk in pools with fallen logs or undercut banks that provide shade and cover, where they can ambush small salmon, steelhead, and other fish. They may express one of four different life histories: (1) undertaking salt and fresh water migrations; (2) spending their lives in lakes; (3) dwelling in rivers but seasonally migrating to estuaries; or (4) remaining in small tributaries. Juveniles adopt a history based on habitat and food availability, water quality, temperature, and other environmental factors. Adults between two and four years of age migrate to natal streams after the first substantial rains in the fall, and spawn between December and April.

California’s Coastal Cutthroat populations are at the southern end of their range, and are considered part of the Southern Oregon-California Coast DPS for management. While separate species, Coastal Cutthroat and Rainbow trout hybridize naturally, but differences in spawning timing, habitat preferences, and behavior keep them distinct in watersheds where they overlap. In watersheds where hatchery-origin steelhead are present, higher rates of hybridization between the two species have been documented.