Fig. 2

Error distributions from visual accuracy tests. Distributions of (left) angular errors in the bearing from the observer to the whale, and (middle) errors in range expressed as a percentage of true range. Grey bins represent scaled histograms of the observation errors and black lines represent the pdfs of the fitted distributions (wrapped Cauchy for bearing; Normal for range). The scatterplots in the right panels illustrate: (top) the range estimated by the observers during tests as function of the true range derived from GPS positions, and (bottom) the range percent errors vs. true range, with the fitted linear regression line indicating little tendency for under- or overestimation