Visual-Acoustic Survey of Cetaceans during a Seismic Study in the South- east Caribbean Sea, April–June 2004

Abstract
Lamont-Doherty Earth Observatory’s monitoring and mitigation program during an academic seismic study in April–June 2004 was the largest cetacean survey undertaken to date in the southeast Caribbean Sea. A total of 10,007 km (904 h) of visual observations occurred from the seismic vessel R/V Maurice Ewing and from the support vessel R/V Seward Johnson II. In addition, 7375 km (846 h) of passive acoustic monitoring for vocalizing cetaceans occurred from the Ewing via a towed 250-m hydrophone array. Approximately 1293 cetaceans in 46 groups were seen from the two vessels, and 78 acoustic detections were made. Nine cetacean species were identified of which the long-beaked common dolphin (Delphinus capensis), Atlantic spotted dolphin (Stenella frontalis), and bottlenose dolphin (Tursiops truncatus) were sighted most frequently. The striped dolphin (S. coeruleoalba), spinner dolphin (S. longirostris), pantropical spotted dolphin (S. attenuata), short-finned pilot whale (Globicephala macrorhynchus), sperm whale (Physeter macrocephalus), and Bryde’s whale (Balaenoptera edeni) were also identified during visual surveys. Only the sperm whale was positively identified by acoustic monitoring alone. At least 17 sperm whale detec- tions (visual and/or acoustic) were made around the islands and atolls of the Venezuelan Archipelago near and beyond the 1000-m depth contour. Overall cetacean density in intermediate-depth water (100 to 1000 m deep) was five times greater than in deep (>1000 m) water. This study addresses previous data gaps on the occurrence of cetaceans in shelf and offshore waters across a wide area of the southeast Caribbean Sea in spring.