Video cameras hooked up to mine-hunting US Navy dolphins have filmed them searching and consuming fish and, to the scientists’ shock, swallowing venomous yellow-bellied sea snakes.
It’s the first time video and sound has captured bottlenose dolphins feeding on dwell fish, from the bursts of sonar clicks used to pinpoint the prey to the victory squeals after grabbing a meal.
The footage confirmed that dolphins use suction to gulp down their prey, produced by increasing their throats and flaring their lips. Beforehand, researchers thought the primary technique was to hurry on the fish, an strategy referred to as ram raiding.
All six of the dolphins studied are based mostly in California and are educated by the navy to find and mark mines. The animals exit swimming within the open ocean every single day.
Dianna Samuelson Dibble, on the Nationwide Marine Mammal Basis (NMMF) in San Diego and a part of the examine staff mentioned: “They clicked virtually continuously at intervals of 20 to 50 milliseconds. On approaching prey, click on intervals shortened right into a terminal buzz after which a squeal. On contact with fish, buzzing and squealing was virtually fixed till after the fish was swallowed.”
The fish chases have been strenuous and the dolphin’s heartbeat may very well be heard on the movies, she mentioned. The scientists have been additionally capable of see how the dolphins used their eyes to house in on the fish once they received shut.
Probably the most sudden discovering was the consuming of yellow-bellied sea snakes. Dolphins had been seen enjoying “cat and mouse” video games with snakes earlier than, however by no means consuming them. One dolphin was seen to eat eight.
“The dolphin clicked because it approached the snake after which sucked it in with a bit extra head jerking because the flopping snake tail disappeared and the dolphin made a protracted squeal,” the scientists reported.
“This snake does have the potential to trigger neurotoxicity after ingestion and its venom is taken into account pretty harmful,” mentioned Barb Linnehan, director of drugs on the NMMF. “Maybe as a result of the snakes ingested have been considered juveniles they’d a decrease quantity of venom current.”
The dolphin, which had been born in captivity, appeared unaffected by its serpent meal. “Maybe the dolphin’s lack of expertise in feeding with dolphin teams within the wild led to the consumption of this outlier prey,” the scientists mentioned. Linnehan mentioned leopard seals had been reported consuming the snakes, however then regurgitating them.
The examine, printed within the journal PLOS One, noticed the dolphins within the open Pacific Ocean throughout mine detection coaching, and in San Diego Bay and a sea water pool. Their prey included sand bass, high smelt, yellowfin croaker, California halibut and pipefish. The smelt would typically soar out of the water when being pursued, resulting in the dolphins swimming the wrong way up to trace the prey and snap it up because it landed again within the water.
Dr Brittany Jones, a scientist on the NMMF mentioned: “These findings are an unbelievable addition to the literature offering detailed analyses throughout prey seize within the open ocean, which might be very troublesome to attain with wild dolphins.”
The lead writer of the examine, Dr Sam Ridgway, died lately on the age of 86. “His inventive strategy to partnering with Navy dolphins to raised perceive the specie’s behaviour, anatomy, well being, sonar, and communication will proceed to coach and encourage future scientists for generations,” mentioned Jones.