Numbers of juvenile salmon caught during our June and September trawl surveys can serve as an index or surrogate measure of ocean survival for spring Chinook and coho salmon. Figure JSC-01 shows catch per unit effort (CPUE) during our trawl surveys from 1998 to present.
Catch rates in June were lowest for both species during 2005, but rebounded gradually from 2006-2008 and 2013, only to decline again. Catches in June 2016 were ranked 11th out of 19 for yearling Chinook salmon, and 13th out of the 19 years for yearling coho salmon. Due to funding constraints, there were no surveys in September after 2012.
Figure JSC-02 Upper panel shows the regression of spring Chinook salmon jack counts at Bonneville Dam vs. average CPUE of yearling Chinook salmon caught during each June cruise. Years indicated are for catches of juvenile fish. Open blue circle indicates observed CPUE in June 2015 (0.57) and predicted jacks from the regression (9,220). Numbers indicate the years. 2010 (red) was an outlier and was excluded from the regression.
Lower panel shows the regression of the OPIH smolt-to-adult survival (SAR) of coho salmon on the average CPUE of juvenile coho salmon catches in trawl surveys the previous June. Years indicated are for catches of juvenile fish. Open blue circle indicates observed CPUE in June 2015 (1.95) and predicted coho salmon survival from the regression (2.8%). Numbers indicate the years.