叠辞迟迟濒别苍辞蝉别听dolphins are clever hunters. Some work alongside human fishers, coaxing fish ashore. Others use shells to catch their food. In the Florida Keys, some use 鈥渕ud rings鈥� 鈥� and now the behaviour has been documented in the Caribbean too.
The mud ring hunting strategy is a case of blindsiding prey. A 鈥渞ing maker鈥� dolphin circles near the ocean floor and traps fish behind a ring of mud as others lie in wait with mouths open, and lunge to catch any fish attempting to escape the mud by jumping out of the water.
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This behaviour had been seen only in the Keys. Now, at the City University of New York and his colleagues have found that dolphins living in the Chetumal-Corozal Bay in Mexico and Belize, in the Caribbean Sea, also use this technique.
Their research used footage obtained from drones operating from boats. The researchers hope using drones in this way will advance the study of foraging behaviour.
鈥淎 couple years ago, my friend sent me a drone video from the Bay. I said, 鈥極h, crap.鈥� That鈥檚 exactly what my colleague Zoe had shown me 鈥� pictures of circles in the mud from planes years ago. But at the time we did not see dolphins and I thought, 鈥榖ut they only do that in Florida鈥�,鈥� says Ramos.
鈥淚n the new videos, we clearly see dolphins making the rings,鈥� he says. 鈥淭hey鈥檙e also feeding in a bunch of rings. I thought maybe we can see them in satellite images, went to Google Earth and sifted through historical imagery in Mexico. We saw a picture of a mother and her calf [generating a mud ring] and we compared that to satellite imagery in the Florida Bay.鈥�
The comparison revealed that, while the dolphins in the Caribbean tend to lie in wait outside the plume to catch the fish, dolphins in the Florida Keys will often dive into the plume.
The researchers say dolphins are specialised in the way they feed and developing tactics like mud ring hunting is complex. It is a learned behaviour tailored to specific circumstances. Even so, it appears that the dolphins near Mexico and Belize have developed the technique independently of those near Florida.
鈥淒olphins in the Caribbean aren鈥檛 near those in Florida. It鈥檚 too far to travel. We don鈥檛 believe they cross paths,鈥� says Ramos. 鈥淭he same species in a different area appears to be independently developing that mud ring strategy.鈥�
The researchers say the findings are instructive for conservation. A dolphin that has spent its life developing the special skill of making mud rings in the shallows won鈥檛 do as well when it has to try to catch fish in deeper water, says Ramos 鈥� a point he thinks conservationists need to keep in mind when planning conservation strategies.
Marine Mammal Science
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