A significant proportion of common seals will be at sea even during this period and it is therefore much more difficult to be precise about the total population based on these minimum figures.Year1974-1980(Boat survey)1988-1994(Helicopter)1996-1997(Helicopter) Adults PupsAdultsAdults 9,328 1,49526,66729,600The increases between boat and helicopter survey results are partly due to the extension of the area surveyed by helicopter (successive surveys have covered larger areas), partly due to the change in methodology (up to twice as many...