Low rainfall during November contributes to smaller salmon runs
Salmon managers are reporting dismal returns of chum and coho salmon to Puget Sound streams this fall, and a sparsity of rainfall during November could result in low salmon survival during the next generation.
Low streamflows in November made it difficult for chum salmon to make it past obstacles, such as this log weir at the mouth of Chico Creek.
Photo: Meegan M. Reid, Kitsap Sun
"The run (of chum) was pretty darn small," said Jon Oleyar, salmon biologist for the Suquamish Tribe who walks many streams on the Kitsap Peninsula. His surveys of living and dead salmon are used to estimate escapement — the number of migrating salmon that return to their home streams.
"Some of the streams had no fish at all in them," Jon told me, "and many of the fish did not get very far up into the system."
Low rainfall in November led to low streamflows in the upper portions of many streams, where the water levels were often too low to allow passage of chum and coho. The fish were forced to lay their eggs in the larger channels, where heavy rains this winter could wash the eggs out of the gravel before they hatch.
Low flows disrupted the normal run timing of the chum salmon, according to Aaron Default of the Washington Department of Fish and Wildlife. The final in-season estimate of run size for Central and South Puget Sound was 240,000 chum — barely half of the preseason forecast of 444,000. The 10-year average is about 527,000, as I reported in Water Ways in October. Final estimates for the year will come later.
Chum returns to Hood Canal also were low this year, Aaron reported in an email.
For the Kitsap Peninsula, average rainfall in November is second only to December in the longterm records, but this year more rainfall was seen in October and even September. The graphs on this page include nearly flat lines (blue), representing very low rainfall through most of October and November this year. Click on the images to enlarge them.
In Hansville, at the extreme north end of the peninsula, total rainfall for November was 1.14 inches. That was the lowest precipitation recorded in 30 years of records maintained by Kitsap Public Utilities District. The median average rainfall for November is 4.37 inches in Hansville.
In Silverdale, only 1.03 inches of precipitation was recorded during November. That's just a fraction of the median average of 9.96 inches seen over the past 29 years. It was also the lowest rainfall ever seen for November except for 1994, when 0.90 inches established the current low record.
Holly, one of the wettest parts of the Kitsap Peninsula, received 2.47 inches of rain in November, compared to a median average of 12.41 inches. This November's rainfall in Holly, as in Hansville, is the lowest amount going back 29 years. The previous record low was 3.29 inches set in 1994.
The shifts in rainfall from one year to the next are hard to explain. Just two years ago, Holly received 22.89 inches of rain in November, followed by 12.41 last year — which just happens to match the median average.
Overall, the low rainfall was detrimental to the salmon, which ended up spawning in the lower portion of streams where flows are higher. But Jon Oleyar observed a few positive features this year, such as beaver dams on Chico Creek — the largest producer of chum salmon on the Kitsap Peninsula.
Although beaver dams can impede the movement of chum during low flows, they also can hold back water during high flows, reducing the risk of extreme currents that can scour salmon eggs out of the gravel.
"In the Chico system, we had about 10,000 fish total, and 95 percent of them spawned below river mile 1.5," Jon said.
That means most chum and even coho spawned this year in the mainstem of Chico Creek, with very few fish getting to Lost or Wildcat creeks. Those tributaries of Chico Creek normally support large numbers of juvenile chum and coho.
"The only saving grace that I can point to is the beaver dams," Jon said. "In bad weather, the dams can hold back the water instead of having it shoot downstream like a fire hose."
Jon spotted only handfuls of chum in some important salmon streams, including Scandia Creek in North Kitsap, Steele Creek in Central Kitsap and Blackjack Creek in South Kitsap.
"This might be the smallest run I've ever seen," said Jon, who has been surveying salmon streams for years, "and some streams didn't get any fish at all."
The three-month precipitation forecast calls for above-average rainfall from now into February.
Map: NOAA Climate Prediction Center
Hatcheries in the region may not have enough returning salmon for full production next year, and the coho that did make it back were much smaller than normal. Jon said. Conditions leading to fewer and smaller salmon probably relate to temperatures in the open ocean and upwelling currents off the Washington coast. I'll have more to say about those conditions along with some observations about chinook salmon in a future blog post.
For now, we can hope for adequate rains — but not enough to cause serious flooding — over the next few months, as the baby salmon emerge from the gravel and begin their fight for survival.
December 6, 2019 Fishing interests, Salmon, Streams, weatherChico Creek, coho salmon, Fish, Kitsap Peninsula, Precipitation, Puget Sound streams, Rainfall, Salmon, weather
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3 thoughts on "Low rainfall during November contributes to smaller salmon runs"
John Williams says:
I understand the idea of having water years, sort of, in order to have a standard way to compare long-term trends. However, when illustrating a comparison of current (short term) rain levels with historic levels, why have graphs in which less than 25% of the chart has current data relevant to the discussion, and over 70% of the chart not only has no current data, but causes the scale of the current data to be so small that it is difficult to make out what the message is. It's not like it's difficult to get a spreadsheet to generate a custom plot!
Christopher Dunagan says:
I like these graphs, produced by Kitsap Public Utilities District, because they show not only the current water year but also last year, the average and the highest and lowest water years. If you zoom in by clicking on the graph, you can see where we stand with respect to the lowest water year on record, even though we are early in the year. I've added links in the text for those who wish to delve further into the data.
Ole Birkland says:
No Coho in Naylors Creek, a tributary of Chimacum Creek in Jefferson County, this year either. A decade ago runs were so heavy it was possible to walk up the stream on my property and step on a dead Coho with every step. Low fall rainfall and downstream beaver dams apparently are the reason there are no fish making it up this far.
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