Uncertainty in the interpretation of telemetry data: A matter of significance

Distance measurements in telemetry studies are generally made in the coordinate system in which data were recorded.  Projected coordinate systems (e.g. UTM) are generally recommended for distance calculation over geographic coordinate systems (e.g. Latitude and Longitude), but few fisheries researchers distiguish between coordinate systems when working with GIS or GPS.  Impacts of coordinate system selection on interpretation of movement data from radio-tagged animals are poorly documented.  To illustrate potential impacts, movements of grass carp were determined with both latitude and longitude (decimal degrees) and UTM (NAD83).  Effects of season and stocking location on movement calculated by each coordinate system were evaluated.  Significant effects of season, but not stocking location, were observed on movement using latitude and longitude; conversely, significant effects of stocking location, but not season, were observed on movement using UTM.  These results indicate that the same study could yield contradictory results depending on the coordinate system used.  Most published telemetry studies do not report coordinate systems, making it difficult to draw meaningful comparisons between studies even for the same species.  We recommend that coordinate systems used in telemetry studies should be reported in research methodologies and subjected to peer review.