Cetacean Community Ecology in the Waters of Sri Lanka and the Bay of Bengal.

摘要

The Indian Ocean contains arguably the highest diversity of cetaceans in the world s oceans, yet research in this region is extremely limited. The strong environmental variability imposed on the northern Indian Ocean by the seasonal monsoons likely causes a wide variety of niches in both space and time that support the observed diversity of cetaceans. In addition to shelf, slope, and oceanic habitats, there are regions dominated by the input of fresh water (e.g., Bay of Bengal), by evaporation and low river runoff (e.g., Arabian Sea), as well as coastal currents, eddy activity, and large-scale oceanic currents. Moreover, the Arabian Sea and Bay of Bengal have well-developed oxygen minimum zones (mesopelagic regions with O2 concentrations <0.5 ml l-1) that likely have a significant influence on the behavior and distribution of cetacean prey. Our long-term goal is to understand the physical and biological oceanographic processes that influence the distribution and occurrence of tropical and subtropical cetaceans. We believe the northern Indian Ocean is particularly well suited for investigating these processes because of the large spatial and temporal variability in environmental conditions imposed by the monsoons. However, very little is known of the distribution, abundance, or behavior of cetaceans in the oceanic waters of the Bay of Bengal. What little research has been done in the region has focused on the river dolphins and nearshore porpoises (e.g., Smith et al. 2008). Indo-Pacific humpback dolphins and spinner dolphins are endemic to the coastal waters of the Bay of Bengal (de Boer et al. 2002), while a wide variety of oceanic dolphins, blackfish (pilot, melon-headed, and false killer whales), sperm whales, beaked whales, pygmy and dwarf sperm whales, and several baleen whale species occur over the continental slope and abyssal plain of the oceanic Bay (Leatherwood et al. 1984, Ballance and Pittman 1998, de Boer et al. 2002).