A summary of the use of electronic tagging to provide insights into salmon migration and survival

Abstract

IntroductionThe status of Pacific salmon populations has been ofincreasing concern for many decades, with many pop-ulations now under legal protection. The causes oftheir declining status are manifold and untanglingthem has been difficult due to the complex life histo-ries, which involve migrations among freshwater, es-tuarine, and marine habitats. Finding solutions tosalmon management problems requires understandinghow salmon respond to threats in these different envi-ronments. Telemetry provides an attractive approachto monitoring salmon as they move among these envi-ronments, and advances in miniaturization and massproduction have made it feasible to monitor salmonthroughout their life cycle.Recent advances in acoustic telemetry have provid-ed for the first time an opportunity to greatly expandknowledge and understanding of mortality and themigratory behavior of salmonids on the western coastof North America. Firstly, these electronic tags havebeenreducedinsizesufficientlytofitintotheperitonealcavity of smolts (ocean-ready juveniles). Secondly, thesignals emitted from these beacons are unique so thateach tagged fish can be recognized by its code, whichenables recording movement patterns and mortality ofindividual fish. This has been accomplished with twotypes of coding, pulse interval modulation or frequencyphase shifting (McMichael et al. 2010). Thirdly, auto-mated monitors have been developed that identify andrecord the passage of individual fish from the uniquesignals emitted from these beacons (Klimley et al.1998).Thecostofthese autonomousreceivershasbeenreduced sufficiently to permit the establishment of largescale arrays that can monitor salmon throughout theirmigratory cycle.These advances have led to a burst in telemetrystudies of Pacific salmon (genus Oncorhynchus).Until recently, the movements and mortality patternsof juvenile salmonids were determined by a series ofcross-shelf arrays of tag-detecting monitors that wereestablished along the continental shelf, from PointReyes in northern California to Prince William Soundin Alaska (Pacific Ocean Shelf Tracking Program -POST; Welch et al. 2002). Additionally, monitors havebeendeployedinmanyofthe estuaries and riversalongthiscoastline.CodedtagsandthePOSTarrayhavebeenused to determine the overall survival of salmon smolts