Coho salmon and estuary use in Puget Sound

For more information, view the original reports: The role of estuaries in the ecology of adult Pacific salmon and trout in Puget Sound and The role of estuaries in the ecology of juvenile Pacific salmon and trout in Puget Sound.

Overview

Unlike sockeye salmon, that are largely restricted to systems with lakes, and Chinook and pink salmon that primarily use large rivers in Puget Sound, coho salmon are found in many small streams flowing into Puget Sound as well as tributaries of larger rivers. Coho salmon occur in much lower densities in streams compared to pink and chum salmon because the coho fry typically feed in streams for a year (or two farther north) before migrating to sea, and streams have limited capacity to support them. 

Adults

They enter later in the year than the Chinook salmon, as seen in the Skagit and Stillaguamish rivers (Figure 1). However, these are entries into the river and not necessarily the tributaries where they will spawn. Coho salmon spawn not only later than Chinook salmon, but also over a much more protracted period in any given river. For example, spawning from November into February would not be unusual among wild coho in Puget Sound.

The patterns of arrival timing seen in larger rivers, which have more than enough water for the fish to ascend, and the Lake Washington Ship Canal (Figure 2) are not necessarily the same as those in smaller streams, which may have very little water in late summer. For example, counts of wild coho salmon ascending Big Beef Creek at a weir just above tidal influence in Hood Canal revealed a later pattern: none in August, 10% in September (in the latter half of the month), 46% in October, 39% in November, 4% in December, and 1% in January, based on five years of data collected by the Washington Department of Fish and Wildlife and provided by Dr. Joseph Anderson. In the late summer and early fall these fish congregate near the mouths of such streams, but to what extend individual fish move in and out of estuaries is not known. If water levels are very low, such entry seems unlikely, but not impossible.

Some of the adult coho salmon would have migrated in from the coast whereas others would have been feeding in Puget Sound as residents, like the Chinook salmon. As with Chinook salmon, the phenomenon of resident coho salmon is not unique to certain populations, nor does it systematically differ between wild and hatchery fish (Rohde et al. 2014). Throughout the year, some coho salmon are within 20 meters from shore and are caught by anglers standing knee-deep in the water, though others are farther offshore in deeper water (Smith et al. 2015). The Puget Sound resident coho salmon are smaller than those that feed off the coast (Allen 1959), as is also the case with coho salmon from the Strait of Georgia (Milne 1950). They tend to feed primarily on invertebrates, shifting to a diet more dominated by fishes as they grow (Kirkness 1948, Prakash 1962). After Chinook salmon they have the greatest tendency to feed on fishes of the Pacific salmon species (Beacham 1986), and Pacific herring are especially important in their diets (Healey 1976).

As the adult coho salmon reach the vicinity of their natal streams it is common for them to hold in nearshore waters, sometimes jumping conspicuously. Unlike Chinook salmon, which are primarily caught from boats in open water, coho salmon approaching their natal rivers are also caught from shore. How long each fish might spend near the mouth of the stream is not known, but if the flows are very low in the fall and the salmon arrive before the fall rains, they might hold for some time there. Indeed, their broad distribution of spawning timing is likely to be an adaptation to the variable flow regime of these rivers. Farther south, along the coast of California, some streams are blocked by impassable sand bars until the first fall rains wash the sand away, and coho salmon return late in the year (Shapovalov and Taft 1954).

Juveniles

The classic life history of coho salmon in the Puget Sound region is to migrate in the spring as age-1 smolts, and there are many that do so, commonly about 90 – 120 mm long (e.g., 93 mm in the Stillaguamish River). They feed in estuaries for a week or more, consuming larger prey than the pink and chum fry, such as larval crabs, larval fishes, and juvenile fishes. Indeed, coho salmon smolts commonly eat pink and chum fry (Hunter 1959). The movement of coho salmon smolts down the Chehalis River and into Grays Harbor on the Washington coast was salutatory – periods of movement were interspersed with periods spent holding (Moser et al. 1991).

In addition to the seaward migration of smolts, for many years it has been known that some coho salmon less than one year old (young-of-the-year) move downstream in the spring or fall. In some cases, this movements bring them to suitable riverine habitats, and in the Puget Sound region they find refuge during winter floods in side channels, ponds, and swamps that might not seem like salmon habitat in the dry days of summer. However, in other cases the juveniles enter estuaries or marine waters.

For some time, these fish had been more or less written off and assumed to not survive to adulthood, and they tended to be under-studied because fall migrants were not sampled in traps deployed in rivers to catch smolts in the spring. Recently, there have been increasing studies of these fish in the Salish Sea (Bennett et al. 2011, Quinn et al. 2013, Bennett et al. 2015), lower Columbia River (Craig et al. 2014), coastal Oregon (Jones et al. 2014) and northern California (Rebenack et al. 2015), and they seem to be more common than was perhaps thought in the past. Enough of these fish survive to return as adults to merit more attention from scientific and conservation perspectives (Jones et al. 2014).

Their use of estuaries is apparently more extensive and variable compared to yearling smolts, but they are difficult to study because of their small size.  Unlike the yearlings, that are large enough for acoustic transmitters and have been tracked in river-estuary systems, including the Chehalis River in coastal Washington (Moser et al. 1991), the Campbell River in the Strait of Georgia (Chittenden et al. 2008), and Humboldt Bay in Northern California (Pinnix et al. 2013), the movements of individual young-of-the-year coho salmon are poorly known.

References

Allen, G. H. 1959. Growth of marked silver salmon (Oncorhynchus kisutch) of the 1950 brood in Puget Sound. Transactions of the American Fisheries Society 88:310-318.

Beacham, T. D. 1986. Type, quantity, and size of food in Pacific salmon (Oncorhynchus) in the Strait of Juan de Fuca, British Columbia. Fishery Bulletin 84:77-89.

Bennett, T. R., P. Roni, P. Denton, M. McHenry, and R. Moses. 2015. Nomads no more: early juvenile coho salmon migrants contribute to the adult return. Ecology of Freshwater Fish 24:264--275.

Bennett, T. R., R. C. Wissmar, and P. Roni. 2011. Fall and spring emigration timing of juvenile coho salmon from East Twin River, Washington. Northwest Science 85:562-570.

Chittenden, C. M., S. Sura, K. G. Butterworth, K. F. Cubitt, N. Plantalech Manel-La, S. Balfry, F. Økland, and R. S. McKinley. 2008. Riverine, estuarine and marine migratory behaviour and physiology of wild and hatchery-reared coho salmon Oncorhynchus kisutch (Walbaum) smolts descending the Campbell River, BC, Canada. Journal of Fish Biology 72:614-628.

Craig, B. E., C. A. Simenstad, and D. L. Bottom. 2014. Rearing in natural and recovering tidal wetlands enhances growth and life-history diversity of Columbia Estuary tributary coho salmon Oncorhynchus kisutch population. Journal of Fish Biology 85:31-51.

Healey, M. C. 1976. Herring in the diets of Pacific salmon in Georgia Strait. Fisheries Research Board of Canada Manuscript Report 1382:1-38.

Hunter, J. G. 1959. Survival and production of pink and chum salmon in a coastal stream. Journal of the Fisheries Research Board of Canada 16:835-885.

Jones, K. K., T. J. Cornwell, D. L. Bottom, L. A. Campbell, and S. Stein. 2014. The contribution of estuary-resident life histories to the return of adult Oncorhynchus kisutch. Journal of Fish Biology 85:52-80.

Kirkness, W. 1948. Food of the chinook and silver salmon of Puget Sound. Annual Report, Washington Department of Fisheries 1948:28-31.

Milne, D. J. 1950. The difference in the growth rate of coho salmon on the east and west coasts of Vancouver Island in 1950. Fisheries Research Board of Canada, Progress Report of the Pacific Coast Stations 85:80-82.

Moser, M. L., A. F. Olson, and T. P. Quinn. 1991. Riverine and estuarine migratory behavior of coho salmon (Oncorhynchus kisutch) smolts. Canadian Journal of Fisheries and Aquatic Sciences 48:1670-1678.

Pinnix, W. D., P. A. Nelson, G. Stutzer, and K. A. Wright. 2013. Residence time and habitat use of coho salmon in Humboldt Bay, California: an acoustic telemetry study. Environmental Biology of Fishes 96:315-323.

Prakash, A. 1962. Seasonal changes in feeding of coho and chinook (spring) salmon in southern British Columbia waters. Journal of the Fisheries Research Board of Canada 19:851-866.

Quinn, T. P., N. Harris, J. A. Shaffer, C. Byrnes, and P. Crain. 2013. Juvenile coho salmon, Oncorhynchus kisutch, in the Elwha River estuary prior to dam removal: Seasonal occupancy, size distribution, and comparison to nearby Salt Creek. Transactions of the American Fisheries Society 142:1058-1066.

Rebenack, J. J., S. Ricker, C. Anderson, M. Wallace, and D. M. Ward. 2015. Early emigration of juvenile Coho Salmon: implications for population monitoring. Transactions of the American Fisheries Society 144:163-172.

Rohde, J., K. L. Fresh, and T. P. Quinn. 2014. Factors affecting partial migration in Puget Sound Coho Salmon (Oncorhynchus kisutch). North American Journal of Fisheries Management 34:559-570.

Shapovalov, L. and A. C. Taft. 1954. The life histories of the steelhead rainbow trout (Salmo gairdneri gairdneri) and silver salmon (Oncorhynchus kisutch) with special reference to Waddell Creek, California, and recommendations regarding their management. California Department of Fish and Game Fish Bulletin 98:1-375.

Smith, J. M., K. L. Fresh, A. N. Kagley, and T. P. Quinn. 2015. Ultrasonic telemetry reveals seasonal variation in depth distribution and diel vertical migrations of sub-adult Chinook and coho salmon in Puget Sound. Marine Ecology Progress Series 532:227--242.