The first film ever captured from the perspective of dolphins freely
hunting off the coast of North America is accompanied by a flurry of clicks
and triumphant squeals.
The US Navy fitted cameras to its dolphins, who are taught to spot
underwater mines and guard some of the country's nuclear arsenal, for a
scientific research that was published last year. The dolphins were then
given free freedom to hunt in San Diego Bay.
To the amazement of the researchers, the cunning marine animals delivered
thrilling chases and even targeted poisonous sea snakes.
We still don't fully understand many fundamental aspects of these very
gregarious and frequently disgusting cetaceans, including their regular
feeding habits, despite the fact that they are well-known and widely popular
creatures.
The general consensus among researchers is that there are at least two
methods: sucking up prey like noodles from a dish and chowing them down like
a state fair hot dog in between rides.
Yet a lot more was revealed by the video.
Six bottlenose dolphins (Tursiops truncatus) were equipped with cameras
from the US National Marine Mammal Foundation (NMMF), which captured footage
and audio over the course of six months. This new level of insight into
these mammals' hunting tactics and communication has never been possible
before.
Their lips and eyes were seen in startlingly off-angle positions when the
recording equipment was positioned on their sides or backs.
While these dolphins are not in the wild, they are regularly given the
chance to hunt in the open ocean as a supplement to their typical diet of
frozen fish. As NMMF marine mammal veterinarian Sam Ridgway and colleagues
said in 2022, it is thus conceivable that these creatures apply comparable
techniques to their wild counterparts.
They noted in their research that dolphins "clicked practically
continuously while they searched at intervals of 20 to 50 milliseconds."
"Click intervals become shorter as the prey gets closer, eventually morphing
into a terminal buzz and a shriek. Fish contact resulted in buzzing and
shrieking that continued virtually nonstop until the fish was eaten."
More than 200 fish, including bass, croakers, halibut, smelt, and pipefish,
were captured by the dolphins with cameras fastened to them. The smelt
frequently threw themselves into the air in an effort to flee the cunning
hunters.
Yet, the dolphins kept track of their every move and used a method they had
previously seen in wild dolphins, swimming upside down to provide their
swiveling eyes a clear view.
According
to Ridgway and colleagues, "These dolphins appeared to employ both sight and
hearing to detect food." "The dolphins always utilized echolocation to
locate fish from a distance. Close up, it looked that echolocation and
eyesight were employed in tandem."
The cameras also captured the sound of the animals' racing hearts as they
struggled to keep up with the demanding activities. This footage showed that
instead of ramming their prey to the ground, the dolphins used suction to
gulp down their still-fighting prey with their remarkably powerful throat
muscles.
The dolphins' neck muscles sprang into action, and their tongues retracted
out of the way as they largely swallowed fish into the sides of their open
mouths. Their muscles for sucking add to the negative pressure that is
produced by the increased inner mouth space.
Although dolphins have been observed playing with snakes in the past,
including river dolphins amusing a ridiculously huge anaconda, the video
provided definitive evidence that dolphins may also consume these
animals.
Eight very deadly yellow-bellied sea snakes were eaten by one dolphin (Hydrophis platurus).
The researchers
reported
that "our dolphin demonstrated no indications of disease after swallowing
the little snakes," however they recognized that this may possibly be
atypical behavior given that the dolphins are captivity animals.
"Maybe the ingestion of this unusual meal was caused by the dolphin's lack
of experience feeding with dolphin groups in the wild."
Just before the study was released, Sam Ridgway, the study's principal
author, passed suddenly at the age of 86, leaving behind a significant body
of research.
According
to NMMF ethologist Brittany Jones, "His innovative approach to teaming with
Navy dolphins to better understand the species' behavior, anatomy, health,
sonar, and communication will continue to teach and inspire future
scientists for centuries."
According to NMMF's website, the dolphins trained by the Navy "work in open water virtually every
day."
"They have the option to swim away, and several have throughout the years.
But the majority do."
This research was published in
PLOS ONE.
