Northwest Fisheries Science Center

Adult Returns of Chinook and coho salmon

For specific stocks of Chinook and coho salmon, the proportion of adult returns from a particular year class is not often known. This proportion, or escapement, is the number of juvenile salmon that survive to the smolt stage, migrate to the ocean, and return to spawn as adults after several months or years (Healey 1991). .

Ordinarily, the proportions of fish that die in freshwater vs. those that die in the ocean can only be estimated.  Thus adult return data, such as counts at dams or traps, can be used only as an index or surrogate measure of ocean survival.  With these caveats in mind, we present adult data from various sources with which we compare forecasts based on ocean indicators. 

Adult data are lagged behind ocean entry by 1 year for coho salmon and 2 years for spring and fall Chinook salmon; therefore, as of 2016, we have up to 19 years of indicator data but only 16 - 18 years of adult return data. We have two less years of data for the Klamath adult returns because those numbers are not available from the Pacific Fishery Management Council until the following February (PFMC 2016a).


Table ARD-01.  Ranks among years for adult returns by year of ocean entry, 1998 – present. Colors represent high (green), intermediate (yellow), and low (red) returns.
 
Adult returns by Year of Ocean Entry¹
Year
OPIH Coho
(adults:smolts)

Bonneville spring
Chinook (n)

Bonneville fall
Chinook (n)
Klamath River
fall Chinook
(n est.)
1998 17 7 15 8
1999 12 1 11 3
2000 3 2 6 5
2001 6 5 4 2
2002 4 8 5 12
2003 5 16 9 15
2004 14 14 14 16
2005 10 17 17 7
2006 9 12 13 14
2007 7 13 15 10
2008 2 3 7 11
2009 8 9 10 9
2010 11 10 12 1
2011 18 15 2 4
2012 15 6 3 6
2013 1 4 1 132
2014 16 11 8 --
2015 132 -- -- --

¹ Counts of spring and fall Chinook salmon are lagged by 2 years and returns for coho salmon are lagged by 1 year.
² Estimate based on jack returns.


Data used in the rank scores above are shown in the chart below. Again, counts of spring and fall Chinook salmon at Bonneville Dam are shown lagged by 2 years. For example, for fish that entered the ocean in 1998, the number listed for spring and fall Chinook salmon indicates adults that returned in 2000. Although we use a 2 year return lag for Chinook salmon, we acknowledge that there are different age classes of returning adults with lags of 2 - 5 years. For example, spring Chinook salmon that entered the ocean in 2000 may return to spawn in 2002 - 2005.


Table ARD-02.  Adult return data used for ranking among years, as shown in Table ARD-01. Again, the full data set for the year of ocean entry requires a lag time of up to 2 years: thus though we have 17 years of ocean ecosystem indicator data, we have only 13 - 16 years of adult return data.
 
Adult returns by Year of Ocean Entry¹
Year
OPIH Coho
(adults:smolts)

Bonneville spring
Chinook (n)

Bonneville fall
Chinook (n)
Klamath River
fall Chinook
(n est.)
1998 0.0128 178,302 192,793 123,856
1999 0.0227 391,367 400,205 187,333
2000 0.0459 268,813 473,786 160,788
2001 0.0258 192,010 610,075 191,948
2002 0.0399 170,152 583,754 78,943
2003 0.0282 74,038 417,057 65,227
2004 0.0193 96,456 299,161 61,374
2005 0.0238 66,624 161,415 132,131
2006 0.0250 125,543 314,995 70,554
2007 0.0255 114,525 283,691 100,644
2008 0.0461 244,384 467,524 90,860
2009 0.0251 167,097 401,576 101,977
2010 0.0234 158,075 350,083 295,322
2011 0.0092 83,299 952,944 165,025
2012 0.0163 188,078 854,503 160,396
2013 0.0648 220,250 954,140 77,7492
2014 0.0130 137,167 440,945 ––
2015 0.02102 ––
 

¹ Counts of spring and fall Chinook salmon are lagged by 2 years. Return ratios for coho salmon are lagged by 1 year.
² Estimate based on jack returns.

Note also that these estimates were not adjusted for catch in fisheries, which can have a major impact on adult numbers. For example, ocean fisheries for Chinook salmon off California and most of the Oregon coast were closed in 2008 and 2009; these fisheries typically catch hundreds of thousands of Chinook salmon annually (PFMC 2016b). Consequently, adult returns to basins most impacted by this closure (e.g., Klamath River) in those years reflect both substantially reduced harvest rates and the influence of ocean conditions on marine survival. Accordingly, direct comparisons of adult abundances across years should be made with considerable caution due to this high variation in harvest rates.