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>> My name is Nate Dominy.
I'm a Professor of Anthropology at Dartmouth.
And my specialty is human evolution.
In particular I'm interested in how humans
and non human primates discern edible objects
in their environment.
Ultimately finding food is the most important thing
that any organism does during its day and so it stands
to reason that natural selection might favor attributes
that allow organisms to find food resources.
And one of the most interesting ways
that humans finds resources, such as sharks, for example,
is to use rattles to capitalize on the cork
of the sharks sensory system to attract sharks to their boat.
So what happens is men go on these lone oceanic voyages
where they use rattles and you can see there's rattles
of different types and there's variation in the types
of rattles that people use.
So one of the questions is why does the material
that people use vary when things
like coconuts are widely available
and anyone could use coconuts if they wanted to
but instead they choose to use different kinds of materials.
So that could suggest that in particular type
of reef environments some materials work better
than others for attracting sharks.
Or it could suggest that the acoustic properties
of these different kinds of rattles don't matter at all
and instead what men are trying to do is simulate the sounds
of frightened, fomenting fish at the ocean surface
because that sound may be particularly conspicuous
to reef sharks.
And then what men do is when the shark approaches the boat they
can lasso it and the lasso is tied
to a floating buoyant propeller and the propeller spins
and creates drag in the water
and the shark quickly becomes tired.
And so then at that point a man can hoist the shark
onto his outrigger canoe and then he can sort
of cudgel it to death.
So we're interested generally in this interface
between human hunting behavior
and the sensory biology of the sharks.
We're interested in understanding how
and why sharks are attracted to these rattles.
And the nice thing about this project is it integrates objects
with practical, functional value
but they also have artistic value so many
of these objects are on display in museums.
For example, this helmet shell rattle is on loan
from the Bishop museum.
And this bean pod rattle is
in the collections here at the Hood Museum.
So this is a really neat project in the sense
that we can take objects of art that have functional value
and practical value and we can understand how
and why these objects look and function the way they do.
I'm going to Australia, Western Australia, to capitalize
on the maternal behaviors of these sharks
because these sharks congregate off the reef
of Western Australia and there are particular hot spots
or locations where mother sharks like to lay their eggs
and then they patrol the region to protect their eggs.
And so we are capitalizing on this behavior
to capture the reef sharks, bring them on board of a boat,
put them in a large tank of anesthesia and what
that does is the shark quiets down and then that allows us
to put electrodes on the external surface of the shark
and we can record brainwaves from the shark.
So the idea is to understand how the sharks perceive stimulus
in their environment like these rattles by rattling the rattle
in the tank of anesthesia
and then recording how the brain responds to the rattles
as we adjust the intensity and frequency of the rattling.
It's possible that the acoustic properties
of the rattles don't matter at all
because what really matters is the way water is perturbed.
So one hypothesis is that sharks don't hear
in the conventional sense but actually
that they use mechanical sensation,
that they can use a sense of touch to hear.
And the idea is that they can actually detect perturbations
of water particle in motion.
So normally as an animal is moving
through a water column there's sort of this background level
of water hitting the surface of its body
but when there's a disturbance somewhere
in the environment the shark can detect that disturbance
when it hits, when the disturbance reaches its body.
So we can do that with electromagnetic shakers.
We can put that into the tank of anesthesia
and we can actually just simulate vibrations
that resemble the vibrations from the rattles to see
if the shark responds more strongly
or I should say the brain of the shark responds more strongly
to the vibrations rather than the acoustic properties.
So one of the main goals of this project is to distinguish
between these two hypotheses.
Are sharks primarily hearing the acoustic properties
or are they primarily responding to the detection
of water particle motion?
One of our big goals is
to understand how the sharks perceive the sound because in
so doing we better understand why humans developed these
different kinds of rattles for attracting sharks.