Poster presented at the Sixteenth Biennial Conference, Society for Marine Mammalogy,
San Diego, CA, December 2005
Using compass and reticle binoculars to measure animal position: An evaluation and comparison to theodolite data
Suzanne Yin¹, Adam S. Frankel¹,², Christine M. Gabriele¹, and Susan H. Rickards¹
¹Hawai‘i Marine Mammal Consortium
P.O. Box 6107
Kamuela, HI 96743
²Marine Acoustics, Inc.
706 Giddings Ave
Annapolis, MD 21401
Shore-based theodolite tracking of coastal cetaceans is a useful and widespread technique that is not always feasible due to expense, geography, the experience-level of observers or other issues. We tested the feasibility of using reticle binoculars to replace or supplement theodolite tracking for determining whale and vessel locations from a shore based observation site with known elevation above sea level. We compared the accuracy and precision of (n= 278) binocular versus theodolite fixes of 2003 and 2004 humpback whales off the island of Hawai‘i, collected during scan samples. Theodolite positions are recorded in azimuth and declination and then converted into x/y coordinates. Reticle binoculars allow users to report azimuth and declination from the horizon. Both methodologies allow calculation of distance, dependent on a known elevation above sea level. We found close agreement between distances to whales obtained from binocular and theodolite fixes when measured reticles >1. A linear regression of binocular reticle distance on theodolite distance was significant (F(1,276) = 5120, p<0.00001, r² = 0.948). A similar regression of binocular bearing on theodolite bearing was even more predictive (F(1,275) = 26619, p < 0.0001, r² =0.989). Binocular measurement distance error increased greatly when measurements with reticles <1 were used (i.e. closer to the horizon). Marine binoculars with compass bearings and reticles cost less than a theodolite, are very portable and have a wider field of view than theodolites. Tracking animals with binoculars also requires less training and can be used by several observers at the same shore station. Locations derived from marine binoculars may be less precise, and may not be suitable for distant or detailed tracking, but this technique opens the possibility of measuring animal locations to a greater range of observers (e.g. schools and citizen science groups).