Chum salmon 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

In Puget Sound, chum salmon spawn in both large rivers, such as those in central and northern Puget Sound including the Skagit and Stillaguamish, and also many much smaller streams of Hood Canal and southern Puget Sound that are not used by pink salmon. In some of these streams, the vast majority of salmonids are chum salmon.

Adults

These small streams such as Kennedy Creek have very low flows in late summer and early fall (Figure 1) and the chum salmon enter in November and early December. In larger rivers such as the Skagit (Figure 2) they enter a bit earlier, but November is probably the modal spawning month in general, timed with the fall rains. They often spawn very close to tidal range in small streams and lower tributaries of larger rivers and so are commonly in a very advanced stage of sexual maturity when caught in the estuaries of rivers. In some of these streams they must struggle upstream through rocky intertidal areas with oysters and barnacles to reach their spawning sites.

How these fish behave in the final stages of maturation is not well known, but they can be taken in commercial fishing gear in nearshore and offshore areas. The extent of movement and duration of holding in marine waters, and the connection between tides and rainfall triggering upstream migration are intriguing for scientists, but also very important from conservation standpoints because they affect exposure to mortality agents of many kinds. 

In addition to the typical fall runs of chum salmon in Puget Sound, the summer run to Hood Canal streams (listed as Threatened under the US Endangered Species Act) and the winter run, chiefly in the Nisqually River, greatly expand the species’ range of return timing in the region. These patterns of timing and abundance are important, not only for exposure of salmon runs to fisheries but also to predators. Studies in Hood Canal revealed that harbor seals killed 8% (range: 1–28%) of the returning adult summer chum salmon, averaged over four rivers and five years (London 2006). London (2006) observed that most of the seal predation on chum salmon (chiefly in the Dosewallips and Duckabush rivers) took place on incoming tides and within a few hours of high tide because the salmon tended to enter on rising tides and the rising tide also facilitated entry by the seals.

Juveniles

Juvenile chum salmon, like pinks, migrate to sea in their first year of life. However, they are produced from larger eggs and so the fry are larger, about 38 – 40 mm. They have a somewhat greater tendency to feed in rivers than pink salmon, and also tend to stay longer in estuaries, but in many ways their ecology is similar (Munsch et al. 2016). Their parents spawn later in the fall than pink salmon, and the juveniles enter estuaries a bit later too but there is considerable overlap. 

There is also some overlap in the diets of chum salmon compared with those of pink salmon (Kaczynski et al. 1973), but small chum salmon feed on emerging insects such as chironomids and epibenthic crustaceans (Feller and Kaczynski 1975, Healey 1979). Then, as the fry move down the estuary and farther offshore (Healey 1982), they shift to more planktonic prey and drifting insects (Simenstad et al. 1982). Estuaries are highly productive but not infinitely so, and it has been noted that salmon foraging may be the cause of decreases during the season in density of their prey (Feller and Kaczynski 1975). The balance between consumption and production of prey is important as it determines the carrying capacity of the estuary (Wissmar and Simenstad 1988). Consequently, while estuaries are important for chum salmon, they soon move offshore and then migrate from Puget Sound. As with pink and sockeye salmon, only a very small fraction of the chum salmon originating in Puget Sound streams remain there to feed rather than traveling to the open North Pacific Ocean, though such "residents" do occur (Quinn and Losee 2022). 

Most of the Puget Sound chum salmon return as adults to spawn in the late fall and are not of special conservation concern. However, early returning “summer chum salmon” in Hood Canal experienced large declines in abundance and are listed as Threatened under the ESA. Their use of estuarine habitats differs only slightly from that of the more abundant fall chum salmon but they enter marine waters earlier in the year than do fall chum with peaks in February and early March compared to late March through April for fall chum fry (Tuohy et al. 2018).

It is important to note that pink and chum salmon are often by far the most abundant juvenile salmon in Puget Sound estuary and nearshore areas. Catches vary greatly, of course, depending on the time of year, area and proximity to spawning populations, and habitat features. However, several examples will illustrate some patterns. 

Sampling with beach seines in Hood Canal and the Strait of Juan de Fuca in January – June of 2016 and 2017 yielded 106,131 juvenile Pacific salmon, of which 96.7% were chum, 3.1% were pink, 0.2% were coho, and 0.1% were Chinook (Tuohy et al. 2018). Beach seining in Cornet Bay, near Deception Pass at the north end of Whidbey Island over 10 years between 2009 and 2023 yielded 150,028 juvenile salmon, of which 63.5% were pink, 35.9% were chum, 0.6% were Chinook, and only 64 fish (0.04%) were coho (Foundation 2024). 

The dominance of the pink salmon, most impressively, was based on only 5 of the 10 years of sampling. In the odd numbered years not a single pink salmon fry was caught, whereas on even numbered years they averaged 19,054. This phenomenon results from the well-known pattern of numerical dominance of adult spawning during odd-numbered years in this region, though the reasons for this pattern are far from clear (Quinn 2018). 

For one more example to make the point, trapping in the Stillaguamish River by biologists working for the Stillaguamish Tribe caught 876,977 wild-origin juvenile salmonids from 2003 – 2017. Of these, fully 54.4% were pink salmon (even though they were only taken in even-numbered years!), followed by chum salmon (32.6%), coho salmon (9.1%), Chinook salmon (3.3%), steelhead (0.5%) and cutthroat trout (0.1%). As stated above, the proportions of all juveniles that are pink and chum salmon vary among streams and years, but from a numerical standpoint, their relative abundance is striking.

References

Feller, R. J. and V. W. Kaczynski. 1975. Size selective predation by juvenile chum salmon (Oncorhynchus keta) on epibenthic prey in Puget Sound. Journal of the Fisheries Research Board of Canada 32:14109-11429.

Foundation, N. S. 2024. Juvenile salmon and nearshore fish use response to beach restoration at Cornet Bay. Island County Marine Resources Committee.

Healey, M. C. 1979. Detritus and juvenile salmon production in the Nanaimo estuary: I. Production and feeding rates of juvenile chum salmon (Oncorhynchus keta). Journal of the Fisheries Research Board of Canada 36:488-496.

Healey, M. C. 1982. Juvenile Pacific salmon in estuaries: the life support system. Pages 315-341 in V. S. Kennedy, editor. Estuarine Comparisons. Academic Press, New York.

Kaczynski, V. W., R. J. Fellar, J. Clayton, and R. J. Gerke. 1973. Trophic analysis of juvenile pink and chum salmon (Oncorhynchus gorbuscha and O. keta) in Puget Sound. Journal of the Fisheries Research Board of Canada 30:1003-1008.

London, J. M. 2006. Harbor seals in Hood Canal: predators and prey. University of Washington, Seattle.

Munsch, S. H., J. R. Cordell, and J. D. Toft. 2016. Fine-scale habitat use and behavior of a nearshore fish community: nursery functions, predation avoidance, and spatiotemporal habitat partitioning. Marine Ecology Progress Series 557:1-15.

Quinn, T. P. 2018. The Behavior and Ecology of Pacific Salmon and Trout, second edition. University of Washington Press, Seattle.

Quinn, T. P. and J. P. Losee. 2022. Diverse and changing use of the Salish Sea by Pacific salmon, trout, and char. Canadian Journal of Fisheries and Aquatic Sciences 79:1003-1021.

Simenstad, C. A., K. L. Fresh, and E. O. Salo. 1982. The role of Puget Sound estuaries in the life history of Pacific salmon: an unappreciated function. Pages 343-364 in V. S. Kennedy, editor. Estuarine Comparisons. Academic Press, New York.

Tuohy, A. M., M. Wait, J. F. Healy, and A. Jorgenson. 2018. 2018 Hood Canal juvenile chum salmon nearshore habitat use assessment. Wild Fish Conservancy, Duvall, WA.

Wissmar, R. C. and C. A. Simenstad. 1988. Energetic constraints of juvenile chum salmon (Oncorhynchus keta) migrating in estuaries. Canadian Journal of Fisheries and Aquatic Sciences 45:1555-1560.