A comparison of temporal patterns in the ocean spatial distribution of California's Central Valley Chinook salmon runs

Abstract

We developed a broadly applicable method for estimating stock-specific spatial distributions based on patterns in contacts per unit effort determined from data collected in ocean fisheries. The method fully accounts for fishing effort and quantifies uncertainty in total contacts due to sampling error and the effects of annual variability in size-at-age on estimated contacts with sublegal-sized fish. As a case study, we used coded-wire tag recoveries to compare ocean spatial distributions among fish from four return run timings (fall, late-fall, winter, and spring) of Chinook salmon from the Central Valley, California, USA, and explored how distributions varied annually, seasonally, and with fish age in the data-rich fall run. All runs were rarely contacted in ocean fisheries north of Cape Falcon, Oregon (45°46′N). Late-fall and winter run fish appeared relatively restricted to the south compared with fall run fish, corresponding to life history differences and highlighting the ability of spatial management to control impacts on the endangered winter run. For the fall run, the location of highest relative contacts per unit effort of age-3 fish varied across years. This variation correlated with sea surface temperature the previous summer, suggesting ocean distributions may be more responsive to the environment than previously appreciated.