Table 3. Simple comparison of strengths of vessel and aircraft survey platforms for the Mediterranean Sea.

VESSEL	AIRCRAFT
Area covered
Small vessels: coastal watersLarge vessels: high seas	Generally limited to coastal waters but depends on fuel capacity/endurance and availability of airports
Travel speed around 10 knots limits area coverage with time	Travel speed around 100 knots means around 10 times greater search distance with time
Poor for areas with complex coastlines and small islands	Deals with complex coastlines and small islands well
Species
Relates to area that can be covered and behaviour, but in principle all species either visually or acoustically	Better suited to the non long-divers given speed of platform; not good for high seas species given endurance limitations
Need to account for potential responsive movement	Responsive movement not a problem
School size estimation for some species can be difficult	Generally easier to estimate school size
Generally poor for estimating other megafauna	Good for other megafauna (e.g. sea turtle, giant devil ray, sharks, tuna) at least in the Mediterranean Sea
Environmental conditions
Cannot operate in ‘unacceptable’ conditions (these will depend on species) – swell can be a major problem	Cannot operate in ‘unacceptable’ conditions (these will depend on species) – swell less of a problem
Given speed limitations, relatively poor use of good weather windows	Efficient use of good weather windows (higher survey speed, ability to move to good weather areas quickly)
Data collection
Measurement of key parameters, especially distance, and to a lesser extent angle, is problematic	Measurement of perpendicular distance easier and better
Estimation of g(0) using double platform methods well established and space on board usually not a problem	Difficult to use double platform methods in smaller planes (for some species ‘circle back’ works [60]) but possible in larger planes
Allows collection of additional data: acoustic, environmental, photo-identification data	Collection of additional data difficult or impossible
Usually can incorporate more scientists	Limited number of scientists
Cost
More expensive than aerial surveys but:can operate on high seas;can collect additional data.	More cost-effective where they can operate and better able to take advantage of good conditions when they are scarce (both geographically and seasonally)