Northwest Fisheries Science Center

Juvenile Salmon Catch

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.

Average catches of juvenile coho (black bars) and yearling Chinook (red bars) during trawl surveys off the coast of Washington and Oregon. Figure JSC-01. Average catches of juvenile coho (black bars) and yearling Chinook (red bars) during trawl surveys off the coast of Washington and Oregon. Surveys were conducted in June (upper panel) and September (lower panel) from 1998 to present. Note the difference in the scale of the y-axis between plots.

Catch rates in June were very low for both species during 2005, but rebounded gradually from 2006-2008 and 2013, only to decline again. Catches in June 2017 were ranked 20th out of 20 for both yearling Chinook and coho salmon. Due to funding constraints, there were no surveys in September after 2012.

Abundance of yearling Chinook salmon during June surveys has a significant and positive relationship to spring Chinook jack counts at Bonneville the following spring and to adult spring Chinook counts at Bonneville two years later (Figure JSC-02). Abundance of yearling coho salmon during June surveys also has a significant and positive relationship to coho smolt to adult survival (Figure JSC-02). Thus, catches of yearling salmon in June may be a good indicator of first year ocean survival of yearling Chinook and coho salmon. There was no relationship between June catches of subyearling Chinook and Bonneville fall Chinook salmon jack counts or adults (not shown). Based on June 2017 catches of yearling Chinook and coho salmon, jack counts at Bonneville in spring 2018 and coho salmon survival in the fall of 2018, as well as adult returns of spring Chinook at Bonneville in 2019 should be well below average of the survey years of 1998 – 2017.

Figure JSC-02. 
Upper panel shows the regression of spring Chinook salmon jack counts (lag 1 year) 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 2017 (0.06) and predicted jacks from the regression (5,992) and was predicted from a linear regression model of log-transformed counts of jack Chinook salmon. Number symbols indicate the year of juvenile salmon outmigration.

Middle panel shows the regression of spring Chinook salmon adult counts (lag 2 years) 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 2017 (0.06) and predicted adult from the regression (96,362) and was predicted from a linear regression model of log-transformed counts of adult Chinook salmon. Number symbols indicate the year of juvenile salmon outmigration.

Lower panel shows the regression of the OPIH smolt-to- adult survival (SAR, lag 1 year) 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 2016 (0.19) and predicted coho salmon survival from the regression (1.5 %) and was predicted from a linear regression model of log-transformed coho survival. Number symbols indicate the year of juvenile salmon outmigration.