Data for the calculation of these correction factors are generally derived from tags deployed on individual animals.
Tag-derived data offers the opportunity to collect high resolution information on individual whales' diving behaviour continuously, over long periods of time and distances, accounts for diurnal variation and in many cases reduces the bias due to the presence of a research vessel in the vicinity.
Despite the disadvantage of having to recover archival tags to retrieve data, they provide fine-scale information about critical sub-surface behaviours such as foraging that cannot be collected through visual surveys (Johnson and Tyack, 2003).
The limitations associated with visually collecting dive data such as the necessity for calmweather, good visibility, the fact that data collection is limited to daylight hours and the short-term nature of the data sets likely biases correction factors as has been shown in studies that compared tag data vs visual data.