Pink 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

After sockeye and Chinook salmon, the next species to arrive in Puget Sound rivers is the pink salmon. Runs in Puget Sound are almost exclusively on odd-numbered years. The species is almost invariably two years of age at maturity, and for reasons not entirely understood, the two “lines” differ in abundance. Odd year runs predominate in the southern end of the distribution (e.g., Puget Sound and southern British Columbia); the runs are about equal and variable in the middle of the range, and in northern areas even-year runs commonly are more abundant (Krkošek et al. 2011). In Puget Sound, the Snohomish River seems to have the only even-year run (Hard et al. 1996). Thus, use of estuaries by adult pink salmon is limited to odd-numbered years, and their offspring use the estuaries on their seaward migration in the spring of even-numbered years. 

Adults

Like sockeye salmon, pink salmon are scarce in Puget Sound prior to the spawning season, with only a very small resident component, though in past decades there apparently were more residents than there are now (Jensen 1956, Quinn and Losee 2022). This scarcity of resident pink salmon is not because the species itself is scarce. Indeed, pink salmon (virtually all wild) have been enjoying a great increase in abundance over the last few decades. Adult pink salmon runs to southern Puget Sound tend to arrive at terminal areas in mid-July to mid-August, a bit later to Hood Canal, and later still to the Skagit River (Hard et al. 1996). These rivers do not present a challenge to migrating adults, either in terms of distance to the spawning areas or flow regimes, as the species spawn in large rivers where there is always sufficient water in late summer. In contrast, farther north in southeastern Alaska pink salmon spawn in very small streams. Such streams in Puget Sound might not have enough water to support adult salmon in late summer but are used by later migrating coho and chum salmon. 

Because adults are undergoing the initial stages of maturation in marine waters (e.g., changes in color and shape), there is likely to be some holding period in estuaries but, like other salmon, this does not seem to have been explicitly studied in any Puget Sound population. Examples of the changes in color patterns for male and female pink salmon are shown in the photo below.  

Pink salmon are commonly caught in the summer by anglers in boats trolling in Puget Sound, and those casting from shore at points of land where they come close enough to be reached. There does not seem to be any systematic study of their migratory behavior, depth of travel, and other features relevant to their use of estuaries in Puget Sound. One study, conducted decades ago, tracked individual pink salmon (assumed to be destined for the Fraser River) around the San Juan Islands (Stasko et al. 1973). The fish were categorized, based on their movements, as active and passive. Active fish swam northward, towards the Fraser River, on flooding and ebbing tides, and did not follow shorelines, whereas passive fish made little net progress. As noted above, these patterns exemplify the difficulties in determining why fish do what they do, especially in these complex environments.

Juveniles

Pink salmon juveniles are the smallest downstream migrants, about 30 – 32 mm long. They are small both because they come from small eggs, and also because they do not tend to feed for long in rivers. For example, those trapped in the Stillaguamish River averaged 32 – 34 mm long throughout the migration period, indicating that as the fry emerged, they migrated more or less immediately downstream. When they emerge from the gravel they are ready to enter seawater (Gallagher et al. 2013), with the counter-shading colors (white belly, silvery sides, and green-blue back) of other smolts. Observations indicated that they enter Puget Sound primarily in April (Figure1), were near the surface along Puget Sound shorelines in April and May and largely gone thereafter (Munsch et al. 2016). The main Puget Sound populations are in the large rivers such as the Nisqually, Puyallup, Green, Snohomish, Stillaguamish, and Skagit, though there are others as well, including Hood Canal rivers.

Both juveniles and adults  move quickly through estuaries, and in general, their use of estuaries is not extensive. In general, species migrating at a small size spend more time in the estuary than those arriving at a larger size such as steelhead and sockeye salmon, but pink salmon are an exception to this rule. The vast majority exit Puget Sound for the North Pacific Ocean (Healey 1982), which they share with sockeye and chum salmon, and few remain in the Salish Sea (Quinn and Losee 2022). When feeding in estuaries, juveniles eat crustacean zooplankton such as copepods and larval barnacles (Kaczynski et al. 1973, Godin 1981, Simenstad et al. 1982). Their habitat use patterns along the Puget Sound nearshore are most similar to chum and less so to other salmon species, and both species school in marine waters (Munsch et al. 2016).

References

Gallagher, Z. S., J. S. Bystriansky, A. P. Farrell, and C. J. Brauner. 2013. A novel pattern of smoltification in the most anadromous salmonid: pink salmon (Oncorhynchus gorbuscha). Canadian Journal of Fisheries and Aquatic Sciences 70:349-357.

Godin, J.-G. J. 1981. Daily patterns of feeding behavior, daily rations, and diets of juvenile pink salmon (Oncorhynchus gorbuscha) in two marine bays of British Columbia. Canadian Journal of Fisheries and Aquatic Sciences 38:10-15.

Hard, J. J., R. G. Kope, W. S. Grant, F. W. Waknitz, L. C. Parker, and R. S. Waples. 1996. Status review of pink salmon from Washington, Oregon, and California. U.S. Department of Commerce, Seattle.

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.

Jensen, H. M. 1956. Migratory habits of pink salmon found in the Tacoma Narrows area of Puget Sound. Fisheries Research Papers, Washington Department of Fisheries 1:21-24.

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.

Krkošek, M., R. Hilborn, R. M. Peterman, and T. P. Quinn. 2011. Cycles, stochasticity, and density dependence in pink salmon population dynamics. Proceedings of the Royal Society of London B 278:2060-2068.

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. 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.

Stasko, A. B., R. M. Horrall, A. D. Hasler, and D. Stasko. 1973. Coastal movements of mature Fraser River pink salmon (Oncorhynchus gorbuscha) as revealed by ultrasonic tracking. Journal of the Fisheries Research Board of Canada 30:1309-1316.