Freshwater and marine migration and survival of endangered Cultus Lake sockeye salmon (Oncorhynchus nerka) smolts using POST, a large-scale acoustic telemetry array

Abstract

Freshwater and early marine migration and survival of endangered Cultus Lake sockeye ( Oncorhynchus nerka ) salmon were studied using the Pacific Ocean Shelf Tracking (POST) array. Smolts were acoustically tagged in 2004–2007, and their migration was recorded within the lower Fraser River and coastal southern British Columbia waters. Most smolts showed rapid directional movement (swimming speeds of ~15–30 km·day–1). Average exit time from the Fraser River was 4.0–5.6 days after release, and average residence time within the Strait of Georgia was 25.6–34.1 days. Most individuals migrated northward, generally close to the mainland coast. Survival rates, assessed using standard mark–recapture methods, were generally high during the downstream migration (50%–70%), except in 2005 when survival was <20%, possibly because of a late release. Marine survival rates were stable among years, between 10%–30% at a subarray sited 500 km away from the release site. Movement rates were similar to those of previously published work, but the POST array provided direct measurements of movement and estimates of survival and demonstrated the feasibility of establishing continental-scale acoustic arrays for management and conservation of marine species.

In situ measurement of coastal ocean movements and survival of juvenile Pacific salmon

“…The smolts were implanted with specially programmed tags that transmitted during both the outbound smolt and subsequent 2009 inbound adult migration phases, with an intervening 25-mo quiet period to conserve battery power (49). Although the 2007 smolts experienced 28% survival after migrating downriver and out of the Salish Sea (which was equal to or higher than the survival in the previous 3 y) (44), only 1% of the released smolts (two of 200) returned as adults, consistent with the smolt-toadult survival of both the untagged Cultus Lake hatchery smolts (0.5%) and wild-origin smolts (1.4%) (49). Both adults were detected returning to BC within 1 d of each other via the JDF Strait in 2009, even though they had emigrated via QCS as smolts in 2007 1 wk apart (Movies S2 and S3).…”

“…The median survival of the steelhead and sockeye populations estimated in this study was 16.5% (i.e., one in six juveniles surviving to exit from the Salish Sea), with population-specific marine travel times as long as 28 d depending on the distance traveled. In contrast, survival over the entire juvenile-to-adult lifespan of many Salish Sea salmon populations has decreased to only 1% to 4% in the past two decades (28,(41)(42)(43)(44)(45), with concerns raised about the relative role of salmon aquaculture, hatcheries, climate change, and ecosystem changes in causing the decline (46)(47)(48). Our measurements of survival within the first weeks of the migration (i.e., one of six smolts surviving) can thus be compared with total survival over the period of approximately 2.5 y until adult return generated by other methods (approximately one in 25-100 of outmigrating juveniles); the implication is that the cumulative total mortality beyond the Salish Sea is approximately four to 17 times larger than what is experienced within the geographic limits of the Salish Sea array in roughly the first month of life in the sea, making it unlikely that year-class strength is primarily determined very early in the marine life history.…”

Tracking wild sockeye salmon smolts to the ocean reveals distinct regions of nocturnal movement and high mortality

“…Using acoustic telemetry tags and infrastructure to track small fish (e.g., Welch et al 2002, 2009, Cooke et al 2011a), the present research program was conducted to provide the first insight into the movements and survival of wild sockeye salmon smolts during their migration from natal rearing grounds to the open ocean. The Chilko Lake population was selected for the study (Fig.…”

Estimating behavior in a black box: how coastal oceanographic dynamics influence yearling Chinook salmon marine growth and migration behaviors

“…To understand behaviors employed or stimuli used by migrating fish, movement dynamics must be estimated with fairly high precision (e.g., hourly or daily). However, many estimates of fish movement rely solely on net distance and speed between capture/release and recapture locations, assuming a straight-line trajectory (Thorstad et al 2007, Welch et al 2009, Welch et al 2011, Tomaro et al 2012. While such information is useful for characterizing spatial distributions, it cannot resolve the ecological and behavioral processes involved in a fish moving between two locations.…”