Large–scale Ocean and Atmospheric Indicators

Local and Regional Physical Indicators

Local Biological Indicators

Indicators Under Development

Introduction to Pacific Northwest Oceanography

Ocean Sampling Methods

Adult Returns of Chinook and Coho Salmon

For specific stocks of Chinook and coho, the proportion of adult returns from a particular juvenile year class is not often available.  To obtain this information, one would first need to know the number of juveniles that survived to migrate to the ocean, and then wait 0.5–2 years for coho or 1–5 years for Chinook to obtain the number of returning adults (Healy 1991; Sandercock 1991). 

Even then, it would be difficult to distinguish the proportion of fish that died prior to entering the ocean vs. those that died at sea.  Therefore, adult return data that is available, such as counts at dams or traps, can be used only as an index or surrogate measure of abundance.  With these caveats in mind, we present adult return data from various sources with which to compare forecasts based on ocean indicators. 

The table below is color–coded according to ranks of adult return data from each year for which we have corresponding ocean indicator data.  Lower numbers indicate higher returns of fish, and returns among years were ranked against one another, with 1–4 coded green, 5–7 yellow, and 8–11 red. 

Data used in the rank scores above are shown in the chart below.  Note that counts of spring and fall Chinook salmon at Bonneville Dam are shown lagged by 2 and 3 years, respectively.  For example, the number listed for spring Chinook in 1998 indicates fish that returned in 2000.  Note also that return numbers of a single year may represent multiple age classes:  spring Chinook that returned as adults in 2000 may have entered the ocean in 1998, 1997, or 1996. 

Age at maturity of Chinook salmon may differ depending on genetics, stream of origin, migration timing, and a number of other factors (Myers et al. 1998).  Therefore, lag times for spring and fall Chinook may vary:  those used here were selected based on age–class of the largest proportion of runs for which we had corresponding information (Whiteaker and Fryer 2007).  For coho salmon, age at maturity is more constant within a given area and varies within a shorter time frame (Sandercock 1991; Weitkamp et al. 1995).  Lag times for coho will likely remain at 1 year.

Estimates of SARs for OPIH coho and adult counts for Klamath River fall Chinook were provided by the Pacific Fishery Management Council (PFMC 2008).  Counts of spring and fall Chinook at Bonneville were provided by the Columbia River DART project (1996–present).  These sources are publicly available via the internet.

Note also that these estimates were not adjusted for catch in the fisheries, which can have a major impact on adult numbers.  For example, in 2005, the subyearling Chinook fishery in the the Klamath River was closed, and adult numbers were far higher than in either the preceding or following year.  This was likely due to the fishery closure, which would have masked any change related to ocean conditions or other factors.