Test of Two Photogrammetric Measuring Instruments Used to Determine DolphinLengths from Vertical Aerial Photographs

摘要

Two photogrammetric measuring instruments having different, yet complementaryfeatures are used to derive body length frequency data from the vertical aerial photographs of eastern tropical Pacific (ETP) dolphins. Length frequency distribution data derived with these instruments are used to help describe and manage dolphin populations subjected to mortality in the ETP purse-seine fishery for tunas. Because these measuring instruments differed in design and image presentation, an experiment was conducted to test the hypothesis that there was no difference between instruments in dolphin image measurements. Results indicated no significant difference in length measurement values due to measuring instruments, readers, replicate measurements or interactions of these factors. Length measurements were precise (average < 1.0% coefficient of variation) and