Concerns have been raised with respect to the use of GoPro cameras for length based
measurements as (1) they rely on image stabilisation algorithms that are unique to each individual
camera and (2) GoPros utilise rolling shutters instead of global shutters, which can distort high
speed objects, and thus lead to high RMS values (Liang et al., 2005). In the former case, we found no
systematic variation in RMS values by rig. In the latter, a preliminary analysis of RMS values associated
with objects of known lengths moving between 0.4 and 1.4 m/s showed no effect of speed (Meeuwig
unpubl.), the slowest of which are equivalent to the cruising speeds calculated for reef sharks from
stereo BRUVS (Ryan unpubl.). GoPro derived lengths are therefore unlikely to be problematic for most
individuals apart from those moving at speeds more than three times that of a cruising shark. As
analysts can also choose windows of relatively slow movement, this concern is likely largely irrelevant