By Dave Beatty

Sockeye Salmon and the River (Riverine Sockeye) Ecotype By David Beatty, Emeritus Board Member of the Nooksack Salmon Enhancement Association Sockeye salmon (Oncorhynchus nerka) throughout their Pacific Rim range, from the Columbia River watershed to Alaska’s Kuskokwim/Yukon River watersheds and westward to Asia’s Kamchatka Peninsula, exhibit a greater diversity of life history patterns than either Chinook, coho, chum or pink salmon.

Most stocks of sockeye have a life history dependent on lake (lacustrine) ecosystems, in which the anadromous “lake ecotype” (lacustrine sockeye) spawns in a lake’s inlet or outlet streams or along the lakeshore having suitable gravel with upwelling water. A wild salmon stock (those not of hatchery origin) is usually defined by its run (time of return) and its race (river or lake of origin); for example, the Nooksack River South Fork Spring Chinook and the Nooksack River Fall Chinook are each a stock.

The “lake ecotype” juveniles rear for one to three years (longer in northern populations) in the nursery lake before migrating to the ocean as smolts. This life history pattern requires precise homing to the natal river associated with the nursery lake of the adult sockeyes’ origin.

However, there are sockeye that spawn in a river, its floodplain backwaters and tributaries. Subsequently, the juveniles rear without dependence on a nursery lake even when an accessible lake exists within the watershed. This is the “river ecotype” (riverine sockeye) also found throughout the Pacific Rim range of lacustrine sockeye. Riverine sockeye progeny rear in a river for one or two years as yearling “river-type” sockeye before seaward migration or they migrate downstream to the estuary and ocean after a few months in freshwater as the underyearling “sea-type “ sockeye. Riverine sockeye are more commonly found in glacially fed rivers in North America, suggesting they were the early colonists of these rivers as glaciers retreated. Unlike the lake ecotype, which is dependent on having its spawning run into a river (home stream) associated with a “home nursery” lake, the river ecotype has the flexibility of straying and very likely does so, thus contributing to the genetic composition of the river ecotype populations. Riverine sockeye are genetically more similar for a given geographical separation than are lacustrine sockeye.

Riverine Sockeye

In North America, riverine sockeye are more common in northern areas (transboundary rivers of northern British Columbia and southeast Alaska and north to the Yukon River). Riverine sockeye abundance may be greater when compared to lacustrine sockeye in some northern river systems. Riverine sockeye are very common in rivers of eastern and western Kamchatka (Asia) and may predominate in some watersheds. In western Washington, riverine sockeye spawn in at least 11 rivers, including the Nooksack, Samish and Skagit/Sauk, and most of these rivers don’t have a suitable lake in its watershed (the Skagit does at Baker Lake for lacustrine sockeye that are transported past two hydroelectric dams). The Nooksack River and the Skagit/Sauk River have the most persistent riverine sockeye runs among Puget Sound rivers.

None of the Washington riverine sockeye populations is considered as an Evolutionary Significant Unit, unlike the ESU determination for at least seven lacustrine sockeye ESUs, with the Snake River ESU (Idaho’s Salmon River and Redfish Lake) listed as endangered and the Lake Ozette ESU (Olympic Peninsula) listed as threatened under the ESA. Riverine sockeye is not considered in the decisions for harvest management unlike that done for runs of lacustrine sockeye.

River vs. Lake

There are differences in the morphology and ecology of river ecotype juveniles and lake ecotype juveniles. Each type faces different conditions for feeding and of its habitat, including the deeper water of a lake for diurnal movement, differences in lake and stream temperatures, the presence of flow in a stream, and predation. Morphologically, river ecotype juveniles are more robust compared to the more streamlined lake ecotype. The river ecotype has a deeper, shorter caudal peduncle associated with swimming against a current and a deeper body. Behaviorally, lake ecotype juveniles school to a greater extent than river ecotype juveniles that may be more territorial while in freshwater.

Studies have demonstrated that sea-type and river-type juveniles have superior adaptability to seawater compared to underyearling lake-type juveniles when each type is seawater challenged. This indicates a heritable physiological adaptation advantage in riverine juveniles when compared to lacustrine juveniles of the same age.

Nooksack Spawners

Since the early 1900s, small to relatively large numbers of riverine sockeye have been reported to spawn in the forks of the Nooksack River from late August to late October. For the North Fork, spawning is reported to occur along side channels upstream from Glacier and in the Kendall Creek, Maple Creek and Cornell Creek reaches, including in the floodplain side channels. Spawners are also seen in reaches of the South Fork.

Riverine sockeye are reported as being caught as by catch in the lower mainstem during the tribal fishery – a sockeye run timing that coincides with the run timing of lower Fraser River riverine sockeye. There are anecdotal reports of the release of in-basin and out-of-basin hatchery juveniles for riverine sockeye supplementation in the Nooksack River much earlier in the 1900s. Studies of the Nooksack River and Skagit River riverine sockeye populations indicate very little genetic differentiation between the two, and this is likely true for the Samish River riverine sockeye.

Riverine sockeye occur in the Harrison River and Pitt River, two tributaries of the lower Fraser River. These sockeye appear to be genetically similar to those in the Nooksack and Skagit rivers.

Kokanee

Another sockeye ecotype is the non-anadromous kokanee (little redfish) found in many lakes throughout the anadromous sockeye’s natural range. Kokanee is often considered an evolutionary descendant of that lake’s lacustrine sockeye. A key feature of these two ecotypes is the juveniles of both and the adult kokanee feed (filter feeders) on the lake’s zooplankton and insect larvae. Some lakes have what are called “residual sockeye” whose parentage is the anadromous lacustrine sockeye, but as juveniles never go to the ocean and therefore become adults in the lake.

The history of the Samish River and Skagit/Sauk River riverine sockeye is equally interesting and has the further consideration of the presence of a lake in each watershed: one, the Skagit’s Baker Lake, having lacustrine sockeye and kokanee, and the other, Lake Samish, having kokanee and, historically, likely lacustrine sockeye. Likewise, the history of the origin and distribution of kokanee, whether ever anadromous, and the genetics of this ecotype is worthy of a further discussion.

Among the other four species of eastern Pacific ocean salmon (Chinook, coho, chum, and pink), there is none having native populations of the anadromous lake ecotype (lacustrine sockeye), the non-anadromous lake ecotype (kokanee) or the non-anadromous “residual” sockeye. All four are a river ecotype with its own type of juvenile pattern(s) for freshwater residence timing.

However, Chinook, coho and pink, but not chum, juveniles released into lakes (e.g., U.S. Great Lakes) do successfully complete the life cycle entirely in freshwater. Likewise, brood stocking programs (Captive Rearing throughout the life cycle), for example for Spring Chinook in the Nooksack’s South Fork, have successfully produced adults without any anadromous component, i.e., entirely in fresh water.