The Life History Fundamentals of Sea-Run Cutthroat Trout Compiled by John Crocker September 13, 1995

NATIVE RANGE

The native range of sea-run cutthroat trout corresponds remarkably with the Pacific coast rainforest. The northernmost limit of their range is Prince William Sound of southern Alaska. The southern limit is the Eel River of California.

The limits of their inland migration in coastal streams is to the crest of the Cascade mountains. However, they do migrate up the Columbia River to about the mouth of the Klickitat River. On the Fraser River system in British Columbia, the inland limit of migration appears to be Hells Gate.

SPAWNING

Sea-run cutthroat trout spawn in the smallest tributaries of small and moderate-size streams. They migrate to the very headwaters of these streams to spawn in reaches often less than two feet wide. Cutthroat spawning tributaries are smaller and higher in the stream system than those used by coho salmon and steelhead.

The spawning period for sea-run cutthroat trout can extend from December through May. February appears to be the peak spawning period for sea-run cutthroat in most Oregon streams.

Sea-run cutthroat spawn in shallow riffles, often not more than a few inches in depth, which have a gentle gradient and clean, pea-sized gravel, often not far from pools or other cover. Redds are 4 to 6 inches deep and slightly shorter than the length of the fish. Two to three redds are used by each female in the same general area.

Spawning activity for sea-run cutthroat trout takes place both day and night and can extend over a period of 2 to 3 days.

Each female sea-run cutthroat trout produces 1,000 to 1,200 eggs on the average. Their eggs are much smaller than the eggs of salmon and steelhead. Larger females produce a greater number of larger eggs, and these become larger alevins, which have size-dependent advantages in growth and survival.

ALEVINS & FRY

Cutthroat eggs incubate in the spawning gravel for 6 to 7 weeks before hatching. Alevins hatch from the eggs and remain in the spawning gravel another 2 weeks while the yoke sac is reabsorbed. They are a little over 1/2 inch in length at this stage. The cutthroat fry "swimup" through the spawning gravel to emerge into the free flowing stream. Fry are about 1 inch in length when they emerge from the spawning gravel. Fry quickly move to "lateral habitats" such as slower currents near stream banks, behind rocks or logs and side channels in the stream. The cutthroat fry will stay in the lateral habitats throughout the summer unless they are driven out by larger and more aggressive fish such as coho salmon fry. Cutthroat fry grow rapidly during their first summer. By September of their first year the cutthroat have grown to 2 to 3 inches in length.

JUVENILE CUTTHROAT (PARR)

During their first winter, juvenile cutthroat trout (otherwise known as "parr" because of the vertically-striped parr marks along their sides) move into off-channel pools and side channels to find relief from the high water flows. At one year of age, during their second spring, the parr range throughout the river system, often migrating downstream to the mainstem portion of the stream. They feed opportunistically through the summer months on insects, earthworms, crayfish, salmon and sculpin eggs and small fish. With the approach of their second winter, the young cutthroat move back upstream to the protection of the slower current and cover found in the pools and side channels of the tributaries. During their second spring, the older juvenile cutthroat that do not make their first trip to the ocean (smolt) move downstream into the lower portion of the river. Many times they migrate all the way downstream into the estuary where the freshwater of the stream mixes with the saltwater of the ocean. These areas have abundant food for the young fish to feed on and grow larger prior to ocean migration in some future year. Some of the older juvenile cutthroat trout have been shown to migrate up to 50 miles downstream to the estuary. These parr then migrate back upstream again in the late summer and autumn to reside in the tributaries for the winter.

SMOLTS (FIRST OCEAN MIGRATION)

Most juvenile cutthroat trout that migrate to the ocean for the first time (smolts) do so after their third winter. However, this varies considerably. In some streams the majority of juveniles smolt after the second winter, in others it occurs after the fourth winter. Age one is the earliest and age six is the latest recorded age at which sea-run cutthroat trout have been documented to migrate to salt water for the first time. This movement downstream peaks about a month after the outward migrating spawned-out adults (kelts). The average size of a sea-run cutthroat trout smolt is 10 inches. While in the ocean, cutthroat trout travel in schools of five to fifteen fish. They follow the tides into shallow areas where they forage on scuds, sand fleas, shrimp, crab megalops and the occasional stickleback, sculpin, sand lance or small baitfish. They stay close inshore and avoid crossing bodies of deep, open water. While in salt water, juvenile cutthroat trout grow about 1 inch per month. Predation on juvenile sea-run cutthroat trout is believed to be their major cause of marine mortality. Pacific hakes, spiny dogfish, harbor seals, birds and adult salmon are the most likely marine predators of cutthroat trout. Mortality is greatest for young cutthroat trout entering salt water for the first time. Sixty to eighty percent of the smolts succumb to predators. As few as 2% of the fish going to salt water for the first time survive to return to the stream in the fall.

ADULT SEA-RUN CUTTHROAT TROUT

Adult sea-run cutthroat trout begin to congregate in the estuary and tidal waters of their spawning streams in July to prepare for their upstream migration to freshwater. Unlike salmon and steelhead which spend two or more winters in salt water, sea-run cutthroat trout return to fresh water only four to six months after they have migrated to the ocean. Adult sea-run cutthroat trout returning to fresh water from the ocean for the first time measure about 12 to 14 inches in length. Migration of adult cutthroat trout upstream into fresh water usually occurs in two or three groups. Those that have spawned before return to the streams first, usually in late July or early August. A later group of younger fish typically re-enters freshwater in late August or early September. Not all coastal cutthroat trout returning from the sea for the first time spawn that same year. Few female fish mature sexually before age 4. Sexually immature fish return to the sea the next spring and migrate to fresh water a second time before spawning. This trait is inherited in individual populations, and the percentage of fish exhibiting this behavior varies by geographical area. Details of overwintering periods for adult cutthroat that have returned to fresh water from the ocean are not documented. Their movements are probably like those of the older juveniles which move throughout the upper reaches to the pools and side channels which are sheltered from the high water flows of winter.

KELTS (SPAWNED-OUT ADULTS)

Significant weight loss occurs during spawning. One study of an Oregon sea-run cutthroat trout population documented approximately 30% to 40% weight loss during the spawning period. Sea-run cutthroat trout withstand the rigors of spawning well. Up to 40% of spawned-out adults (kelts) survive to return to salt water. In Sand Creek, Oregon, in the absence of a fishery, 39% of the cutthroat returned to spawn a second time, 17% spawned a third time and 12% returned a fourth time. After spawning, sea-run cutthroat trout kelts migrate downstream. They return to salt water within 6 weeks of spawning, slightly before their offspring (fry) emerge from the spawning gravel.

REFERENCES

Giger, R. D. 1972. Ecology and Management of Coastal Cutthroat Trout in Oregon. Oregon State Game Commission, Fishery Research Report Number 6, Corvallis.

Trotter, P. C. 1987. Cutthroat: Native Trout of the West. Colorado Associated University Press

Trotter, P. C. 1989. Coastal Cutthroat Trout: A Life History Compendium. Transactions of the American Fisheries Society 118: 463-473.


John Crocker Conservation Director Lower Umpqua Flycasters P.O. Box 521 Reedsport, OR 97467 Home phone: (541) 271-5640 Office phone: (541) 271-2163 fax: (541) 271-4058 email: 75213.1307@compuserve.com