Freshwater Survival and Developmental Timing of Summer Chum in Salmon Creek, Washington

Hood Canal summer chum, listed as threatened in 1999 under the Endangered Species Act, have benefited from supplementation programs, harvest reductions, and freshwater habitat restoration. Although these conservation efforts have been notable, studies that assess the freshwater (juvenile) life history and survival of Hood Canal summer chum have been limited. In Salmon Creek, concurrent monitoring of juvenile and adult abundance began with the 2007 brood year. In this presentation, we describe inter-annual variation in out-migrant timing and egg-to-migrant survival observed for this summer chum population. In addition, we investigate whether out-migrant timing is correlated with stream temperatures and whether survival is correlated with stream flows. Egg-to-migrant survival ranged between 7% and 21%, and median migration dates ranged between March 16 and April 1. A daily migration model was developed to predict the combination of cumulative temperature units and egg-to-migrant survival that best explained the pattern of outmigration. Cumulative temperature units (TU) between egg deposition and emergence were estimated to range between 700 and 1,130 TUs (ºC) with median emergence timing for each redd ranging between 890 and 1,000 TUs. Among brood years, median emergence timing was earlier in years with higher incubation temperatures. Egg-to-migrant survival was lower in years when peak flows between egg deposition and emergence were greater in magnitude. Summer chum are among the earliest juvenile salmonids to enter the marine environment. Our results suggest that the relative abundance and timing of marine entry should vary based on a potential 3-fold difference in freshwater survival and a two week difference in migration timing. Additional years of life cycle monitoring will be used to further understand the roles of stream temperatures and flows on juvenile life histories.