Whales are more important ecosystems engineers than previously thought


Date:
November 3, 2021
Source:
Stanford University
Summary:
Research on whale feeding highlights how the precipitous decline
of large marine mammals has negatively impacted the health and
productivity of ocean ecosystems.



FULL STORY ==========================================================================
From 1910 to 1970, humans killed an estimated 1.5 million baleen whales
in the frigid water encircling Antarctica. They were hunted for their
blubber, baleen -- the filtering fringe they have in place of teeth --
and meat. One might assume that from the perspective of krill -- the tiny shrimp-like creatures the whales feast on -- this would be a boon. But new research published Nov. 4 in Naturefrom a collaboration led by Stanford University's Goldbogen Lab suggests the opposite: that the decline of
baleen whales in the Southern Ocean has led to a decline of krill.


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This paradoxical result is a sign of just how much the precipitous
decline of the large marine mammals has negatively impacted the health
and productivity of ocean ecosystems, the researchers say.

"Fifty years after we stopped hunting whales, we're still learning what
impact that had. The system is not the same," said Matthew Savoca,
a postdoctoral scholar in the Goldbogen lab at Stanford's Hopkins
Marine Station and lead author of the paper. "We're looking into
ways of using this information to restore ocean ecosystems and bring
whales back. And hopefully, that will have benefits for everything
from biodiversity conservation to fisheries yield to carbon storage."
The researchers came to their troubling conclusion after asking a very fundamental question: How much do whales eat? Modernizing whale research
Large whales are inherently difficult to study because they can't be
studied in captivity. So, previous estimates of how much whales consume
were generally limited to either studies of dead whales or metabolic extrapolations based on much smaller animals.



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For this study, the researchers looked at blue, fin, humpback and minke
whales -- all whales that feed by gulping a large amount of water and
filtering it through their mouths' fringed baleen plates until only their
prey remains. They employed several high-tech tagging devices that attach
to whales typically for about five to 20 hours, recording their movements, acceleration, sound and, if light allows, video. Drones, operated
by the Duke Marine Robotics and Remote Sensing Laboratory, measured
the length of individual, tagged whales, which helps the researchers
estimate the size of their gulp. In collaboration with the Environmental Research Division at NOAA and the University of California, Santa Cruz,
the researchers also ran an underwater device called an echo sounder --
which Savoca likens to "a fancy fish finder" -- which uses sound waves
at several different frequencies to measure how much prey is around.

"All of that put together really gives us this amazing view," said Shirel Kahane-Rapport, a graduate student in the Goldbogen lab and co-author
of the paper. "From each one, you can learn a lot about whales, but
the combination takes the research to another level." Analysis of the
data they captured revealed that whales in the Southern Ocean eat about
twice as much krill as previous estimates suggested, and that krill-
feeding blue and humpback whales off the coast of California eat two to
three times as much as previously thought. Fish feeding humpback whales, however, might eat the previously estimated amount or even less. This
range seems to reflect the energy density of the food -- whales need
to eat more krill to get the same energy as they would from a smaller
amount of fish.

"As large baleen whales get bigger, the anatomical machinery that
allows them to eat also gets relatively bigger," said Jeremy Goldbogen, co-director of Hopkins Marine Station and associate professor of biology
in the School of Humanities and Sciences, who is senior author of the
paper. "They have evolved these systems that allow them to be eating
machines. That disproportionately bigger gulp size allows them to take advantage of abundant food, like krill." The researchers made their
estimates of consumption based on their data about prey density, gulp
size and lunge frequency, as recorded by the tags. Going from hours of
data to general estimations -- and applying those to whales around the
world -- required careful calculations.



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"We came up with a very involved process and we try to do our best
to retain as much uncertainty as possible along the way," said Max
Czapanskiy, a graduate student in the Goldbogen lab and co-author of
the paper. "No one else has data like this. It's a huge step forward,
but at the same time, it's a hard system to study and there's still a lot
of uncertainty." With these new consumption estimates, the researchers calculated that the early 20th-century abundance of krill in the Southern
Ocean had to be about five times what it is now in order to feed the pre-whaling whale population. This implies a complex role for whales in
their ecosystems where the decline or recovery of their populations is
strongly tied to overall ecosystem productivity and functioning.

"Hopefully work like this can really get people to consider the
ecosystem-wide repercussions of human activities because we are still continually affecting their environment," said Kahane-Rapport.

Mobile processing plants The Southern Ocean is among the most productive ecosystems on Earth, largely due to the abundance of microscopic algae,
called phytoplankton. Phytoplankton are a vital food source for krill,
small fish and crustaceans -- which are, in turn, consumed by larger
animals, including whales, birds and other fish. But whales also help
sustain phytoplankton. Through eating krill and then defecating, whales
release iron locked within krill back into the water, making that iron available to phytoplankton, which need it to survive.

"Without phytoplankton, you're never going to get all the animals and everything that we care so much about," Czapanskiy said. "When whales
were very numerous, they had this incredible role in bolstering the
ecosystem." "Think of these large whales as mobile krill processing
plants," Savoca added.

"Each fin whale or blue whale is the size of a commercial airliner. So,
in the first half of the 20th century, before whaling, there were an
additional one million of these 737-sized krill processing plants moving
around the Southern Ocean eating, pooping and fertilizing." The many
twists and turns of these findings demonstrate the potential impact of
asking simple questions. By trying to pin down how much whales eat, this
work has cast doubt upon what people thought whales needed to survive,
and how the activities of whales and humans affect ocean ecosystems.

"Just this idea that if you remove large whales, there's actually
less productivity and potentially less krill and fish is amazing,"
said Goldbogen.

"It's a reminder that these ecosystems are complex, highly intricate,
and we need to do more to fully understand them." Additional Stanford co-authors of this research include graduate students William Gough and
James Fahlbusch; postdoctoral scholar Paolo Segre and Elliott Hazen,
adjunct professor at Hopkins Marine Station. Other co-authors are from
Cascadia Research Collective, Duke University Marine Lab, Oregon State University, University of Copenhagen in Denmark, University of Southern Denmark, Aarhus University in Denmark, Nelson Mandela University in South Africa, National Oceanic and Atmospheric Administration (NOAA)/Stellwagen
Bank National Marine Sanctuary, Smithsonian National Museum of Natural
History, the Burke Museum of Natural History and Culture, University
of California, Santa Cruz and NOAA Southwest Fisheries Science
Center. Goldbogen is also a member of Stanford Bio-X and an affiliate
of the Stanford Woods Institute for the Environment.

This research was funded by the National Science Foundation, the Office
of Naval Research Young Investigator Program, the Defense University
Research Instrumentation Program, the National Geographic Society, the
Percy Sladen Memorial Trust, the PADI Foundation, the Society for Marine Mammalogy, Torben og Alice Frimodts Fond, the Volgenau Foundation, the International Fund for Animal Welfare, and MAC3 Impact Philanthropies
which is part of the Stanford One Ocean Initiative.

========================================================================== Story Source: Materials provided by Stanford_University. Original written
by Taylor Kubota.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Matthew S. Savoca, Max F. Czapanskiy, Shirel R. Kahane-Rapport,
William
T. Gough, James A. Fahlbusch, K. C. Bierlich, Paolo S. Segre, Jacopo
Di Clemente, Gwenith S. Penry, David N. Wiley, John Calambokidis,
Douglas P.

Nowacek, David W. Johnston, Nicholas D. Pyenson, Ari
S. Friedlaender, Elliott L. Hazen, Jeremy A. Goldbogen. Baleen
whale prey consumption based on high-resolution
foraging measurements. Nature, 2021; 599 (7883): 85 DOI:
10.1038/s41586-021-03991-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211103140108.htm

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