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ScienceShot: Hawaiian Paradise for Dolphins and Whales

Eighteen species of odontocetes—the toothed whales and dolphins, which include sperm whales and bottlenose dolphins—call the Hawaiian Islands home. But until now, little was known about where most of these 18 species dwell in these waters, what depths they prefer, and their population numbers. A team of scientists has helped fill in the blanks via a unique, 13-year survey made in small boats, ranging in size from 5.5 to 18 meters. Over the years, they covered 84,758 kilometers of survey lines, spotted 2018 odotocetes, and photographed as many of them as possible to ensure that each species was correctly identified. The slideshow above shows some of the rarer species. The team reports its findings online today in Aquatic Mammals. Knowing which cetaceans live where in the ocean and at what depths is important, the scientists say, in order to mitigate any problems that may occur from human activities, such as aquaculture, energy development, and Naval training exercises. Most troubling, the survey revealed that many of the cetaceans have strong preferences for living at specific depths. For instance, bottlenose dolphins and spinner dolphins were most often found in very shallow water (less than 500 meters), while striped and Risso’s dolphins and sperm whales preferred deeper waters (over 4000 meters). It’s unlikely, the scientists note, that aquaculture ventures will find a place free of fish-stealing dolphins, because they occupy such a range of depths. Similarly, the U.S. Navy will have trouble finding areas in Hawaii that don’t overlap with cetaceans, such as beaked and melon-headed whales, and pygmy killer whales, that are adversely affected by the type of active sonar used in training exercises. They live at the full range of depths that the Navy’s sonar uses, too.

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