Coastal Cutthroat Trout

Coastal cutthroat trout are the nominate subspecies — the fish Richardson described in 1836 and the one that gives the whole group its scientific name — and they are the only cutthroat with an anadromous life history. They are also, in ecological terms, the least like the rest of the group: a small, short-river, estuary-using trout of the wet Pacific slope, rather than a fish of cold interior headwaters.

Range

The USGS Nonindigenous Aquatic Species database gives the coastal distribution as Pacific coast drainages from Prince William Sound, Alaska, to the Eel River in northern California. It is a long but narrow band: coastal cutthroat are a fish of the coastal rain belt and rarely penetrate far inland.

WDFW describes them as widely distributed throughout western Washington, west of the Cascades, in lakes and in tributaries to the Strait of Juan de Fuca, Hood Canal and Puget Sound, in coastal streams and in tributaries of the lower Columbia. The department adds a detail that shapes management everywhere in the range: the majority occupy small headwater streams above impassable barriers. Populations above barriers cannot be anadromous, cannot be recolonized after a local extinction, and are effectively independent units.

In Oregon, ODFW identifies the coastal resident form as the most common cutthroat in the state, alongside the sea-run form of the same subspecies, and describes them occupying coastal-drainage streams, beaver ponds and high-elevation lakes.

The Sea-Run Life History

Anadromy in coastal cutthroat looks nothing like anadromy in salmon or steelhead. ODFW describes sea-run fish moving to saline estuaries and growing to around 18 inches before returning to fresh water in July and August, and states plainly that they “don’t migrate far from their home river.” While at sea they feed on crustaceans and small fish and can grow up to one inch a month.

Three features distinguish this from salmon migration. Coastal cutthroat stay in estuaries and the nearshore zone rather than making open-ocean journeys. They are iteroparous, returning to spawn in multiple years rather than dying after one spawning. And they move between fresh and salt water repeatedly, on a seasonal rather than a once-in-a-lifetime schedule. The growth payoff is large — an inch a month against the slow accretion of a small forest stream — which is why sea-run fish are so much bigger than the resident fish they were spawned alongside.

The subspecies expresses the full range of alternatives too: fully resident stream fish, fluvial fish, and adfluvial lake fish. The same population can contain more than one strategy, and progeny of resident parents can go to sea. That flexibility is a genuine advantage under changing conditions, and it is the main reason coastal cutthroat have persisted through a century of heavy land-use change on the Pacific slope.

Identification

WDFW gives the working characters: red slash marks on the lower jaw and small teeth on the back of the tongue, which distinguish coastal cutthroat from rainbow trout. Spotting is heavy, irregular and distributed across the whole body including below the lateral line, on a body that is dark and heavily marked in fresh water. Sea-run fish returning from salt water go silvery-blue, which is the origin of the name “blueback”, and on those fish the slash can be faint enough to miss entirely. In lower coastal rivers where sea-run cutthroat share water with steelhead and coho smolts, the tongue teeth are often the only reliable check.

Size

WDFW gives an average of 7 to 9 inches, with 10 to 18 inches in quality populations. ODFW is more specific about the split: year-round residents of small streams typically reach only 8 to 9 inches, while sea-run individuals grow to around 18 inches. Small size in resident populations is normal, not a sign of a degraded fishery — a headwater stream above a barrier simply does not have the productivity to grow larger fish.

The exceptions are lakes. Washington’s freshwater state record of 12 pounds came from Lake Crescent on the Olympic Peninsula in 1961, a deep, cold, low-productivity lake whose cutthroat historically grew to remarkable sizes. The saltwater record of 6 pounds from Carr Inlet in 1943 reflects what an estuary-feeding fish can reach.

Spawning and Seasonal Movement

Coastal cutthroat spawn earlier than most of the group. WDFW places spawning in late winter, with adults moving into tributary streams — small ones, often the uppermost accessible reaches, and frequently streams too small for salmon or steelhead. This late-winter timing separates them temporally from the other salmonids sharing the same basins.

The rest of the year follows a recognizable pattern in coastal systems. Fish are most available in spring and again in fall, with a summer lull in July and August when they move into deeper, cooler water. Sea-run fish are returning to fresh water during exactly that lull, which is why late summer and early fall are when the two life-history forms overlap most in the lower rivers.

Conservation and Threats

WDFW designates coastal cutthroat a priority species and a Species of Greatest Conservation Need. No current ESA listing for any coastal cutthroat population was verified for this article; the U.S. Fish and Wildlife Service maintains a species profile whose regulatory timeline could not be retrieved, and readers needing current status should consult that profile directly.

The threats are those of the Pacific coastal lowlands rather than the interior West. Small headwater streams — the habitat this subspecies depends on most — are the streams most affected by road crossings, culverts, timber harvest and sedimentation, and they receive the least regulatory attention because they hold no salmon. Estuary loss removes the rearing habitat the sea-run form depends on. Barriers cut anadromous access and, as WDFW notes, most Washington populations already sit above impassable barriers.

Hybridization with rainbow trout and steelhead — the dominant issue for interior cutthroat — occurs here too, and the two species overlap far more completely in coastal rivers than they do inland, since both are native to the same water. The genetic dynamics of that native sympatry are different from the introgression documented in the interior by Muhlfeld and colleagues (2014), and the coastal case should not be read as the same problem.

Water Temperature

No thermal tolerance study specific to coastal cutthroat was verified for this article. The available benchmark, Bear, McMahon and Zale (2007), measured an ultimate upper incipient lethal temperature of 19.6 C (67.3 F) for westslope cutthroat against 24.3 C (73.7 F) for rainbow trout, with growth optima near 13-14 C and a recommendation to hold maximum daily temperatures near 13-15 C (55-59 F).

Two cautions apply on the coast. Coastal rain-belt streams under intact canopy run cold and stable through summer, so the practical thermal risk is concentrated in low-gradient, wide, logged or agricultural reaches rather than in the system as a whole. And the sea-run fish spends part of its year in estuarine and nearshore marine water, where a freshwater gauge reading says nothing about the conditions it is actually experiencing. A river temperature reading describes the resident and spawning environment for this subspecies, not the whole of its life.

Taxonomy

ITIS lists Oncorhynchus clarkii clarkii (TSN 201900) as the nominate subspecies of a valid Oncorhynchus clarkii, and USFWS, WDFW and ODFW all use that trinomial. Because this is the nominate form, it is the one lineage whose name survives any reorganization: under the American Fisheries Society’s 8th edition names list (2023), which raised cutthroat lineages to species rank, the coastal fish retains Oncorhynchus clarkii as a full species while the interior lineages take other binomials. The details of that arrangement could not be verified against a publicly accessible copy of the list for this article. The practical effect for readers is the reverse of the situation elsewhere in the group: for the coastal cutthroat, the two competing conventions converge on nearly the same name.