Observations on the abundance and behavior of marine mammals exposed to the Heard Island source transmissions

Marine mammal density and behavior were measured in a 70-×70-km square centered on the site of the Heard Island feasibility test 4 days before and throughout the transmissions. Observers were stationed on two large vessels; they conducted line-transect surveys, and monitored marine mammal behavior during transmissions. Observers surveyed 590 nm of tracklines before and 598 nm during transmissions; they made 123 h of observations before and 149 h during. Transmission source characteristics are described elsewhere. Forty schools of cetaceans and 18 pinnipeds were sighted before the transmissions; 40 schools and 25 pinnipeds were sighted after. Sightings of endangered cetaceans were equally common before and during transmissions (3 schools each), but the number of hourglass dolphin (Lagenorhynchuscruciger) schools increased and schools of midsized whales, chiefly southern bottlenose whales (Hyperoodonplanifrons) and minke whales (Balaenaacutorostrata), decreased. These changes could be explained by the transmissions, the survey vessel, or unknown natural factors. Cetacean school size may have changed during transmissions, but there were no consistent changes in direction of travel or calling behavior. Endangered whales showed changes in respiration rate and rate of reorientation. However, these whales were able to aggregate and probably feed during transmissions.