The Number of Redds Constructed per Female Spring Chinook Salmon in the Wenatchee River Basin

Abstract

AbstractThe number of redds in a watershed is routinely used to monitor the population status of Pacific salmon Oncorhynchus spp. One limitation of this approach is that spawning escapement estimates derived from redd counts often assume one redd per female. We tested this assumption on spring‐run Chinook salmon O. tshawytscha in the Wenatchee River watershed, Washington. Female spring Chinook salmon (N = 3,590) were injected with passive integrated transponder (PIT) tags at Tumwater Dam and were monitored annually on the spawning grounds over a 3‐year period. Female Chinook salmon were observed on 75% of the 1,784 redds that were counted, and PIT‐tagged females were detected on 42% of the redds. Of the female Chinook salmon detected on the spawning grounds, only 10 were detected on more than one redd. The number of redds constructed per PIT‐tagged female (1.01 redds/female) was identical during each year of the study despite differences in the abundance of spawners. These results support the common assumption of one redd per female spring Chinook salmon.