The Tilt-Tag: a Micro-Processor Controlled Tag for Determining Lifespan in Fish and Improving Survey Efficiency in Area-under-the-curve Estimates of Salmon Escapement
Tom F. Shardlow and Kim D. Hyatt
Abstract.—A micro-controlled fish tag which records post-tagging lifespan was developed, tested as a prototype, and then evaluated in field applications for measuring survey life. The method of constructing the Tilt-Tag and the results of tank test trials on Chinook salmon Oncorhynchus tshawytscha, preliminary field trials on chum salmon Oncorhynchus keta are reviewed, and full-scale field applications on sockeye salmon Oncorhynchus nerka are presented. Survey life (SL) is an essential component for area-under-the-curve (AUC) estimation of Pacific salmon Oncorhynchus spp. spawning escapements. However, direct estimates of SL are often unavailable because the estimates mostly require extensive and costly tag-recapture programs. In this study, the Tilt-Tag was used to estimate SL by measuring the elapsed time from tagging until the fish came to rest permanently on its lateral or dorsal surface. Tilt-Tag derived estimates of SL, combined with specification of survey rules that were based on historical run-timing and stream temperature, reduced survey costs by approximately 50% when compared to conventional tag-recapture methods. Abridged details on how to construct the Tilt-Tag are provided so that researchers will be able to make their own tags.