Relationship Between Spawner Density and Egg to Fry Survival of Chum Salmon

A water diversion at the Daisy Lake reservoir reduces downstream flows in the Cheakamus River, a glacial-fed, south coast river system in British Columbia. The quantity of water diverted from the Cheakamus River affects downstream productivity of salmonids. Outmigration of salmonids has been monitored on the Cheakamus since 2000 with more detailed monitoring starting in 2007 looking at both side channel and mainstem production. Additionally, escapement and distribution of adult chum salmon (Oncorhynchus keta) has been monitored since 2007. We can now determine egg to fry survival of chum salmon for 3 consecutive years and look at the relationship between spawner density and egg to fry survival for the mainstem and two sidechannel habitats.  Egg to fry survival has been consistently higher in side-channels than in the mainstem regardless of spawner density. Data from side-channel habitat areas indicate spawner abundance appears to have approached or exceeded habitat carrying capacity. An observed reduction in egg to fry survival is probably due to a limited quantity of ideal spawning habitat. Over the duration of the run, earlier formed redds may be dug up by later spawners and during peak run times, competition may result in spawners utilizing less ideal habitats. In the mainstem, egg to fry survival initially increased as spawner density increased but may have reached near capacity in one year because of high number of spawners utilizing a restricted geographic area of the river despite open access to areas of apparently suitable habitat upstream.