3. The expense per unit of area covered is low. 
4. The distribution and relative magnitude of sea otter popula- 
tions over a large area are easily and quickly obtained. 
Disadvantages: 
1. Weather conditions must be ideal; in most Alaska areas, delays 
caused by bad weather may be considerable. 
2. Considerable danger is involved in low flight over water and 
rugged isolated areas. 
3. Only adult and subadult otters can be enumerated; pups with 
mothers are difficult to see. 
4. Otters beneath the surface on food dives are missed because 
of the rapidity of flight. 
5. Sea birds, other sea mammals, and certain species of kelp 
(Nereocystis) may cause confusion. 
Dory surveys 
Advantages: 
1. Areas may be covered thoroughly, both inshore and offshore, 
more rapidly than by a shore survey. 
2. Food-diving otters usually appear on the surface while in the 
range of vision from the boat, giving a fairly complete 
coverage. 
3. Pups with mothers are easily seen and counted. 
Disadvantages: 
1. Much time is necessary to properly cover an extensive area. 
2. Changing weather conditions may interrupt surveys, causing 
inaccuracies in censusing because of movements of otters from 
one area to another. 
3. If large areas are to be covered, the considerable time in- 
volved with attendant crew maintenance costs is considerable. 
4. The distance of visibility from a boat is limited, necessitat- 
ing time-consuming inshore and offshore trips along the same 
coastal area. 
Shore surveys 
Advantages: 
1. Through the use of telescope and binoculars, the most nearly 
complete coverage of a unit of area is possible at a given 
time. 
2. Counts of adults, subadults, and pups is probably most ac- 
curately obtained. 
3. Observations additional to population counts may be carried on. 
4. Sample counts may be obtained repeatedly from established 
observation points. 
