Spawning by Female Chinook Salmon Can Be Detected by Electromyogram Telemetry

New methods to detect spawning of anadromous salmonids in their natural environment are needed to improve understanding of breeding behavior patterns, natural selection on reproductive traits (e.g., spawn timing), and interactions between artificially propagated and wild fish. We implanted maturing female Chinook salmon Oncorhynchus tshawytscha with coded electromyogram (CEMG) transmitters and continuously recorded spawning activity to develop an algorithm capable of accurately detecting spawning events from CEMG data. Marked increases in female digging frequencies immediately after spawning (cover digging) strongly correlated with CEMG values. The algorithm detected averages of 65% and 86% of the actual spawning events in 2003 and 2004, respectively. The algorithm accurately detected zero spawning events for the two female salmon that did not spawn. The presence of CEMG transmitters did not affect the digging frequency, number of nests constructed, or the reproductive life span of implanted fish. However, the CEMG tagging procedure or the presence of tags significantly increased egg retention. Pedigree analyses of DNA confirmed that females implanted with CEMG transmitters exhibited significantly lower individual reproductive success relative to that of nontagged females (73% and 66% reduction in two separate experiments). Subsequent research in adult steelhead O. mykiss has indicated that alternative implantation techniques hold promise for reducing the effects of the tags on reproductive success. We suggest that remote monitoring of salmonid spawning behavior is now possible with CEMG technology and should be tested in natural habitats.