Whales sing when they’ve had a good meal - new research
The six-year study took place in whale foraging habitat in the eastern North Pacific, off the coast of California in the United States.
PTI
-
PHOTO: Wikipedia
LISMORE, 27 FEB
Spanning more octaves than a piano, humpback whales sing
powerfully into the vast ocean. These songs are beautifully complex, weaving
phrases and themes into masterful compositions. Blue and fin whales richly fill
out a bass section with their own unique versions of song.
Together,
these three species can create a marvellous symphony in the sea.
Published
today in PLOS One, our new research reveals these baleen whale species’
response to major changes in their ecosystem can be heard in their songs.
Food
for long-distance travel
The
six-year study took place in whale foraging habitat in the eastern North
Pacific, off the coast of California in the United States. From this
biologically rich foraging habitat, the whales migrate long distances each year
to breeding habitats at lower latitudes.
They
eat little to nothing during their migration and winter breeding season. So
they need to build up their energy stores during their annual residence in
foraging habitat.
This
energy, stored in their gigantic bodies, powers the animals through months of
long-distance travel, mating, calving, and nursing before they return to waters
off California in the spring and summer to resume foraging.
The
whales eat krill and fish that can aggregate in massive schools. However, their
diets are distinct.
While
blue whales only eat krill, humpback whales eat krill and small schooling fish
such as anchovy. If the prey species are more abundant and more densely
concentrated, whales can forage more efficiently. Foraging conditions and prey
availability change dramatically from year to year.
We
wanted to know if these changes in the ecosystem were reflected in the whales’
acoustic behaviour.
Piecing
together a complex puzzle
To
track the occurrence of singing, we examined audio recordings acquired through
the Monterey Accelerated Research System. This is a deep-sea observatory
operated by the Monterey Bay Aquarium Research Institute and funded by the US
National Science Foundation.
Analysis
of sound recordings is a highly effective way to study whales because we can
hear them from quite far away. If a whale sings anywhere within thousands of
square kilometres around the hydrophone, we will hear it.
Yet,
piecing together the complex puzzle of whale behavioural ecology requires
diverse research methods.
Our
study used observations of the whales, including sound recordings, photo
identification and diet analysis. It also used measurements of forage species
abundance, characterisation of ecosystem conditions and theoretical modelling
of sound propagation.
Our
ability to probe the complex lives of these giants was enhanced for humpback
whales because we had a unique data resource available for this species:
extensive photo identification.
The
Happywhale community science project combines photos supplied by researchers
and ecotourists, and identification enabled by artificial intelligence, to
recognise individual whales by the shape and coloration of their flukes.
This
unique resource enabled us to examine the local abundance of humpback whales.
We could also study the timing of their annual migration and how persistently
individual whales occupied the study region.
An
increase in food – and in song
The
study began in 2015, during a prolonged marine heatwave that caused major
disruption in the foraging habitat of whales and other animals throughout the
eastern North Pacific.
All
three whale species sang the least during the heatwave, and sang more as
foraging conditions improved over the next two years.
These
patterns provided the first indications that the singing behaviour by whales
may be closely related to the food available. Remarkably, whale song is an
indicator of forage availability.
Further
evidence was found in the striking differences between humpback and blue whales
during the later years of the study.
Continued
increases in detection of humpback whale song could not be explained by changes
in the local abundance of whales, the timing of their annual migration, or the
persistence of individuals in the study region.
However,
humpback song occurrence closely tracked tremendous increases in the abundances
of northern anchovy — the largest increase in 50 years. And when we analysed
the skin of the humpback whales, we saw a clear shift to a fish-dominated diet.
In
contrast, blue whales only eat krill, and detection of their songs plummeted
with large decreases in krill abundance. Our analysis of blue whale skin
revealed they were foraging over a larger geographic area to find the food they
needed during these hard times in the food web.
Predicting
long-term changes
This
research shows listening to whales is much more than a rich sensory experience.
It’s a window into their lives, their vulnerability, and their resilience.
Humpback
whales emerge from this study as a particularly resilient species. They are
more able to readily adapt to changes in the ecology of the foraging habitats
that sustain them. These findings can help scientists and resource managers
predict how marine ecosystems and species will respond to long-term changes
driven by both natural cycles and human impacts.
At a
time of unprecedented change for marine life and ecosystems, collaboration
across disciplines and institutions will be crucial for understanding our
changing ocean.
This
work was enabled by private research centres, universities and federal agencies
working together. This consortium’s past work has revealed a rich new
understanding of the ocean soundscape, answering fundamental questions about
the ecology of ocean giants.
Who
knows what more we will learn as we listen to the ocean’s underwater symphony?
(The Conversation)
Leave a Reply
Your email address will not be published. Required fields are marked *