Methods for Successful Recovery of Pop-up Satellite Tags: Finding a Needle in a Haystack

Although pop-off satellite archival tags (PSAT) have been used extensively in marine environments, they have only recently been used in the Great Lakes region. In 2014 and 2015, lake trout were tagged with PSATs to test hypotheses related to bathymetric distribution in Lake Superior. Initial tagging operations indicated that the data transmission rate after pop off was often low, likely due to short periods of suitable sunlight in northern latitudes. Satellite data transmission was largely limited to raw data summaries and not detailed enough for this study. The potential time and effort necessary for tag recovery was justified, however Lake Superior is the largest freshwater lake in the world and has great expanses of shoreline with limited access. Over two years, 58 of 66 (88%) PSATs were recovered using handheld radio scanners with doppler direction finders deployed off small vessels. Tag recovery efficiency varied due to factors such as pop-off location, weather conditions, and Argos location quality. Communication with staff on shore to obtain updated Argos positions was critical. Recovery of tags prior to reaching nearshore areas also increased recovery success. Lessons learned during physical recovery of tags on Lake Superior could benefit other studies which attempt to recover PSATs.