Chicago Zoological Society, Sarasota Dolphin Research Program

ScienceShot: Getting the Straight Poop From Dolphins

It's not that easy to figure out what dolphins eat. They refuse to fill out food diaries and you can't watch them without bothering them—humans are pretty conspicuous out there with our scuba gear and boats. What scientists know about the dolphin diet comes mostly from the stomachs of animals that turn up dead on the beach or in fishing gear. But nobody knows if those animals are good representatives for their species. For a new study, researchers focused on the well-studied bottlenose dolphins that live in Florida's Sarasota Bay. While the animals were getting routine health assessments in the summers of 2005 and 2006, researchers collected 15 samples of poop—most straight from the anus, some out of the water. They also drained gastric juice from the stomachs of nine dolphins, which didn't hurt the animals. Then they did DNA analysis to figure out which species the cetaceans had been snacking on. The scientists compared their results to those obtained from the stomach contents of 32 stranded dolphins over 22 years. The bottom line: Actually, stomach contents are a pretty good indicator of dolphin diet. The live and dead dolphins were eating many of the same species, mostly ray-finned fish, in similar amounts, the team reports online today in Biology Letters. Among other things, the study confirms that the dolphins' most-eaten food is a fish that lives in seagrass, a sensitive ecosystem. It also means that the data biologists have been using are fine—at least for a population like this that hangs out close to shore. Things could be different for farther-ranging animals.

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