Using GPS and GIS for navigation and mark-recapture for sightability correction in moose inventories

To increase survey efficiency and accuracy we used Global Positioning System (GPS) and Geographic Information System (GIS) technologies during a stratified random block survey of moose (Alces alces) in northeastern British Columbia. We used on-board computer mapping for navigation and data recording, and assessed the use of a mark-recapture procedure to correct for moose sightability bias. Aircraft position was visible on a GIS base map on a laptop computer. We used function keys to place numbered labels on the map indicating the sex and age class of the animals observed. The mapping program helped ensure that survey unit (SU) coverage was complete and aided in location decisions close to SU boundaries. We immediately resurveyed 1/4 of each SU at approximately twice the intensity, noting whether animals seen were previously observed or new moose. We calculated a sightability correction factor (SCF) for each stratum (1.31, 1.06, and 1.33 for low, medium, and high density strata, respectively) using standard double sampling methods, and obtained a population estimate about 15% lower than calculated using the mark-recapture based SCF of 1.44. The GPS and GIS technologies we used appeared to enhance survey efficiency, and we recommend these technologies in most survey situations. We also suggest further examination of mark-recapture correction factors and increased efforts to test aerial sightability models.