(Table 2) Survey effort and number of sightings of narwhals (Monodon monocero...

Note that the number of unique sightings is the number of sightings seen by observer 1 plus the number seen by observer 2, minus duplicates.需注意，唯一目击记录的数量等于观察者1观测到的目击次数与观察者2观测到的目击次数之和，再减去其中的重复记录数量。