>>DAVID CADE: The whale behavior is only half the story if you want to study feeding, right.
You also want to look at the context of how much prey there is and where is it located.
The way we do that is we've rigged up a system on the back of our boats
that actually has these echosounders on them that allow us to determine the density
and distribution of prey in the water column.
>>JEREMY GOLDBOGEN: So, there's a saying on the California coast called “wind to whales.”
And so, every spring we get really, really high winds and that creates upwelling. So, those winds
basically take the surface waters away from the coast and that's replaced with really nutrient-
rich deep water. And so, that in turn causes a trophic cascade—all of those rich nutrients
will allow the phytoplankton to bloom. It also, in turn,
allows the zooplankton and the krill to bloom. So, that's why it's a very seasonal pattern of
krill going boom and bust throughout the foraging season for blue whales.
>>CADE: So, what the echosounder allows us to do is actually determine the density and
distribution of prey in the water column. So, if you look at this graph, on the vertical
axis you have the depth, on the horizontal axis you have essentially time or distance.
The ship moves across the surface of the water. It's actually mapping—each
one of these vertical lines is one individual ping where it's listening for the return echo.
How strongly that signal bounces off of an object in the water
tells you how much of it there is and how far away it is.
If that click [CLICKS] takes longer for it to come back that means that the object it's
bouncing off of is further away. The louder it comes back, the more stuff there is in the water.
So, what this is, is then a map of the loudness of the return signal
and the red areas are areas of high intensity. That's an area where you have a lot of stuff
in the water column. In this case, it's krill. The white areas mean that that
sound just traveled through there without bouncing off of anything. The blue areas are areas where
there's a little bit of stuff in the water, but not so much in there.
So, then because we've done this- these finely calibrated experiments,
we can actually tell you how much krill that actually corresponds to.
>>GOLDBOGEN: So, we think that krill will migrate
deep into the ocean during the day to avoid predation from other predators,
but also because they're deep and aggregated, trying to avoid predators, blue whales appeared
to have evolved foraging strategies that take advantage of that dense patchiness at depth.
Understanding the vital rates of an animal, such as how an animal feeds and its feeding rate,
is really fundamental to the conservation and management
of these animals. Because blue whales are specialists on a very specific resource,
we have very good studies and models that can tell us exactly what the energetic efficiencies are
of blue whales, especially how it relates to changes in their food supply.
>>CADE: One of the things that we have to monitor and think about and predict into the future
is as the oceans warm and if they continue to warm at the current rate
how that might affect those oceanographic processes, how that might affect
upwelling which leads to these big blooms, which lead to these krill hot spots.
As the ocean warms, those processes might change and how those are going to be changed is a matter
of a big scientific debate. Like, is there going to be increased upwelling or is there
going to be- or will warmer surface waters lead to increased stratification that inhibits that cold,
cold bottom water, that nutrient-rich bottom water from coming up to the surface and
providing nutrients to the phytoplankton that everything in the ocean thrives on.
So, how climate change is going to affect these blue whale populations
is unknown, but it will probably have a big effect one way or the other.
>>GOLDBOGEN: Blue whales face a number of different threats due to our increasingly
urbanized oceans. One specific threat relates to ship strikes. Our tags give us a really
detailed view of where these foraging hot spots intersect with the shipping lanes.
And if those foraging hotspots change, hopefully in the future we can have a dynamic management
solution where we can say, “Hey, we're predicting that the foraging hotspot is actually going to
move west and perhaps if we just move the shipping lanes a little bit to this side
or a little bit to this side we can significantly decrease the amount of ship strikes that occur.”
Because blue whales are such tremendous filter feeders—they process
vast amounts of the ocean—we think that they might be susceptible to ingesting
microplastics and they might be sentinels for ocean pollution, specifically microplastics.
>>MATT SAVOCA: One of the ways to determine what you're eating is to look at what you're pooping
out. And so, what we have here is a fecal sample from a blue whale that we collected in Monterey
Bay last summer. The reason why it's deep red like that is because they eat krill. Blue whales,
especially, eat only krill and krill are this dark, you know, deep orange and red color. And
what we intend to do is analyze these samples to look for plastics within the fecal sample.
>>CADE: Martin, Musculus.
Blue whales are coming back from centuries of exploitation. These new devices have really,
like, opened up a whole new world for studying these animals that we really know so little about.
>>GOLDBOGEN: Every time we’ve learned something, there's actually 10 more questions that pop
up. How blue whales migrate across the ocean from their breeding grounds to their feeding grounds
and how they impact the resources that the entire ocean ecosystems rely on is really interesting
and important. And that's why we should try to better understand these ocean giants.
[EXCITED YELL]