"Whistles are omni-directional, like turning on a light bulb in a room," Benoit-Bird said. "Clicks, on the other hand, are directional like a laser. We think it may be a strategy to communicate only within the group and not to other potential lanternfish predators. Tuna and billfish are looking for the same prey and they can hear the whistles but not the clicks because the frequencies are too high and so focused.
"If you're lined up to eat this great smorgasbord, would you want to tell the tuna next door about it?"
Benoit-Bird's co-principal investigator on both papers was Whitlow W.L. Au, from the University of Hawaii.
Spinner dolphins are found primarily in tropical and subtropical waters, offshore and near island chains. They grow to a length of about six to seven feet, and feed on small, deep-ocean prey including lanternfish, shrimp and juvenile squid.
During their hunting forays, these athletic, acrobatic dolphins catch and consume a single fish at a time and each lanternfish may only be 3-5 inches long. To match their 3,200-calorie-per-day diet, they need to eat at least 650 fish each night plus enough extra to fuel the energy they burn during the hunt, perhaps another 200 to 300 fish.
"To make that work, they need to eat about a fish a minute," Benoit-Bird said, "and we think that's why they've developed this elaborately complex system of group predation. Dolphins can't open their mouths like baleen whales and swallow large amounts of food at once. They have to target individual fish and it's too difficult and energy-consuming to hunt solo."
"It's tough to make a living in the subtropical ocean, which is something of a biological desert," she
|Contact: Kelly Benoit-Bird|
Oregon State University