Comparisons of measured and estimated distances and angles from sightings surveys

Photogrammetric systems using video cameras were used to measure radial distances sightings during the SCANS-II, CODA and SOWER surveys. These surveys included of a variety species from harbour porpoise, at few hundred metres, large baleen whales greater than 10km. A total 910 initial with estimated reticles measured video, 7 × 50 (636) or 25× ‘Big Eye’ (274) binoculars, compared. Bearings also still images. The CVRMSE in varied between 0.19 0.33 for reticle binoculars. Comparisons simultaneous by other observers naked eye gave 0.39 estimates. There was consistent, non-linear pattern all data sets, over-estimating close surfacing cetaceans under-estimating those further away. However, this not evident distance experiments on fixed targets which had much lower variance (CVRMSE = 0.13). Bearing SCANS-II showed around 5% estimates gross errors 20º that attributed mistakes. For remaining values, RMS range 5.7º–7.2º 4.9º SOWER. Both angle will make substantial contribution abundance simulated observed nature may cause considerable bias even when linear regressions might suggest little bias. remain technological challenges operating complex electronic sea bearings, but investment these methods should be cost effective way reducing improving precision cetacean