These fish work together by the hundreds of thousands to make waves


Date:
December 22, 2021
Source:
Cell Press
Summary:
In the sports arena, spectators sometimes create a spectacle known
as a wave, as successive groups stand up in unison to yell with
arms in the air. Now, researchers have shown that small freshwater
fish known as sulphur mollies do a similar thing, and for life
or death reasons. The collective wave action produced by hundreds
of thousands of fish working together helps to protect them from
predatory birds.



FULL STORY ==========================================================================
In the sports arena, spectators sometimes create a spectacle known as a
wave, as successive groups stand up in unison to yell with arms in the
air. Now, researchers reporting in Current Biology on December 22 have
shown that small freshwater fish known as sulphur mollies do a similar
thing, and for life or death reasons. The collective wave action produced
by hundreds of thousands of fish working together helps to protect them
from predatory birds.


==========================================================================
"The surprises came once we realized how many fish can act together
in such repeated waves," said Jens Krause of the Leibniz Institute
of Freshwater Ecology and Inland Fisheries in Berlin and Cluster of
Excellence Science of Intelligence. "There are up to 4,000 fish per
square meter and sometimes hundreds of thousands of fish participate in
a single fish wave. Fish can repeat these waves for up to two minutes,
with one wave approximately every three to four seconds." When you're
in the vicinity of these unusual fish, found in sulphuric springs that
are toxic to most fish, this behavior is hard to miss. That's because
the mollies do the same thing in response to a person nearby.

"At first we didn't quite understand what the fish were actually doing,"
said David Bierbach (@CollectiveBRL), co-first author along with Carolina
Doran and Juliane Lukas, also at the Leibniz Institute of Freshwater
Ecology and Inland Fisheries and Cluster of Excellence Science of
Intelligence. "Once we realized that these are waves, we were wondering
what their function might be." It reminded the researchers of La-Ola
or Mexican waves known from football (soccer) stadiums. The presence of
many fish-eating birds around the river made them think it likely that
the fish waving behavior might be some sort of defense.

They decided to investigate the anti-predator benefits of the
animals' wave action. Their studies confirmed that the fish engaged
in surface waves that were highly conspicuous, repetitive, and
rhythmic. Experimentally induced fish waves also doubled the time birds
waited until their next attack to substantially reduce their attack
frequency.

For one of their bird predators, capture probability, too, decreased with
wave number. Birds also switched perches in response to wave displays
more often than in control treatments, suggesting that they'd decided
to direct their attacks elsewhere.

Taken together, the findings support an anti-predator function of
fish waves.

The findings are the first to show that a collective behavior is
causally responsible for reducing an animal's predation risk. As such,
the researchers say that this discovery has important implications for
the study of collective behavior in animals more broadly.

"So far scientists have primarily explained how collective patterns arise
from the interactions of individuals but it was unclear why animals
produce these patterns in the first place," Krause said. "Our study
shows that some collective behavior patterns can be very effective in
providing anti-predator protection." It's clear that the fish's waving
reduces birds' chances of carrying out a successful attack on sulphur
mollies. What's not yet clear is exactly why that is. Do the birds
get confused? Do the waves tell them they've been noticed and are less
likely to succeed in capturing their prey as a result? In future studies,
the researchers plan to explore such questions.

========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Carolina Doran, David Bierbach, Juliane Lukas, Pascal Klamser, Tim
Landgraf, Haider Klenz, Marie Habedank, Lenin Arias-Rodriguez,
Stefan Krause, Pawel Romanczuk, Jens Krause. Fish waves as emergent
collective antipredator behavior. Current Biology, 2021; DOI:
10.1016/ j.cub.2021.11.068 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211222153134.htm

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