Data on behavior may help address relative differences in sightability and identifiability among species. As part of the 1992–1994 GulfCet program of shipboard and aerial cetacean surveys in the north-central and western Gulf of Mexico, we assessed cetacean responses to survey ships and aircraft. Pygmy and dwarf sperm whales and beaked whales showed the most avoidance reactions towards the ships (73%, 11 of 15 sightings), with large delphinids (e.g., blackfish) at 15% (7/48), small delphinids (e.g., Stenella spp.) at 6% (15/247), and Atlantic spotted and bottlenose dolphins at 0% each (26 and 88 sightings, respectively). Striped dolphins moved to avoid the ships in 33% (9/27) of sightings. Species which responded to the ships (either approaching or avoiding) also changed behavior in response to the survey airplane. Pygmy/dwarf sperm whales changed their behavior in response to the airplane during 40% (12/30) of sightings, and beaked whales during 89% (8/9). Several of the smaller delphinids also showed sensitivity to disturbance by the airplane. “Diving” and “other” were the most common responses to the airplane. Over all cetacean species, the behavioral states “milling” and “resting” appeared to be sensitive to disturbance; over 39% of initial observations of these behaviors were followed by a new behavior. Cryptic species, such as pygmy and dwarf sperm whales and beaked whales, which were seen resting on most occasions, responded to the airplane a high proportion of the time. Less cryptic species, such as the small delphinids, may have responded as often, but their response did not necessarily make them harder to identify. These data indicate that the sightability and identification of cetaceans may change with the variable behavior of species, and should be taken into account when extrapolating from sightings to population status. These behavioral differences may have effects on resulting density estimates. Density estimates for long-diving cetaceans, such as sperm whales, and species which often react negatively to the survey vessel, such as striped dolphins, may tend to be biased downwards, while the reverse may be true for species which tend to approach the ship, unless data can be collected to estimate the value of the detection function.
Würsig, B., S. K. Lynn, T. A. Jefferson, and K. D. Mullin. 1998. Behavior of cetaceans in the northern Gulf of Mexico relative to survey ships and aircraft. Aquatic Mammals 24(1):41-50.