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Two mirror carp (Cyprinus carpio) surrounded by a school of rudd in a lake in Bavaria
Photo: A. Hartl / blickwinkel / IMAGO
SPIEGEL:
As a co-author of an article published on Thursday in the scientific journal Science, you proclaimed the age of high-resolution “exercise ecology”.
What do you mean by that?
Arlinghaus:
We are currently witnessing a revolution in the study of animal movement and migration.
This opens up completely new insights into behavior.
With the help of sensors attached to animals, which emit either radio waves on land or ultrasound under water, researchers can track animals, sometimes to the second with very high spatial resolution: eagles, bats, wolves, fish.
There are now huge databases of animal movement patterns.
This location data is then evaluated using Big Data methods.
SPIEGEL:
Is that more than a fashion?
Arlinghaus:
Yes, the new high-resolution methods are a huge step forward because you can now understand the interrelationships between individual animals.
So far, a large part of behavioral research has inevitably taken place in the laboratory, but that can never depict the ecological concert.
Now we can track the exact hunting and social behavior of animals in their natural habitat for days, weeks or even years!
SPIEGEL:
Has the new positioning technology changed your perspective?
Arlinghaus:
Yes, for example, we equipped an entire lake with a fish tracking system for different species at the same time.
Our research lake has become a natural aquarium, so to speak.
Since then, I've seen fish, some of which I've been researching for decades, with completely different eyes.
Carp, for example, like to stay in smaller groups.
That was known.
But it was an unbelievable surprise that individual animals like to swim around with very specific conspecifics, almost cultivating loose “friendships”.
In winter, these stable relationships break up, and the carp are more likely to be out in the open water in schools, almost like a school of herring.
Up until now, experts have tended to assume that carp, as warmth-loving animals, retreat to deep lake regions and hibernate.
But they don't.
Catfish, on the other hand, do.
SPIEGEL:
A few years ago you caused a stir by saying that fish hardly feel any pain.
And now they are even supposed to cultivate "friendships"?
Arlinghaus:
That is now very colloquial and also expressed in an abbreviated way, of course these are not necessarily emotional affinities like in humans, we biologists call them somewhat drier “proximity-based social networks”.
What is going on in the fish brains when the animals seek mutual proximity, and whether emotions are associated with this, we cannot currently answer seriously.
However, the active social behavior does not contradict the finding that fish probably have a different perception of pain than humans.
Social behavior and pain are simply two very different phenomena.
»Fish have something like individuality, some researchers even speak of personality.«
SPIEGEL:
Were there any other surprises?
Arlinghaus:
A lot.
For example, fish of one species behave very differently, some are curious and active, others are lazy and shy.
Fish have something like individuality, some researchers even speak of personality.
We are dealing with "intraspecific diversity of behavior" in a somewhat less humanized way.
This individuality of fish also has a major impact on catchability in fisheries.
SPIEGEL:
You have to explain that.
Arlinghaus
: With pike, for example, it is the case that the animals that swim a lot go to the fishing rod or into the net.
Daredevils end up in the pan more often.
That has consequences.
As a result, anglers and fishermen exert selection pressure, so we unintentionally select the less active, almost »shy« fish, because they are more likely to survive.
This can also have ecological consequences.
On coral reefs heavily affected by spearfishing, the greater shyness of algae-grazing fish species has meant that the increased amount of algae has further afflicted the corals.
Such phenomena, which relate to the interaction between predator and prey, have so far remained largely hidden under the water surface.
SPIEGEL:
Satellite navigation doesn't work underwater.
How do you proceed?
Arlinghaus:
We submitted animal-experimental research applications and, after approval, implanted acoustic transmitters in the abdominal cavity of the fish.
We placed several hydrophones under water in the lake.
The ultrasonic signals from the fish transmitters are then received and stored at the hydrophones.
We then go out to the lake every few weeks, pull the hydrophones on board and read out the data.
The fish positions are then calculated on the computer.
SPIEGEL:
Can't fish hear these acoustic signals?
Arlinghaus:
No, our freshwater fish, for example, are »deaf« to the ultrasonic frequency of 200 kilohertz that is used.
But in the sea there are also species such as marine mammals or seals that can hear ultrasound.
A "chirping" fish can also be eaten by seals.
The transmitter continues to run - but from the seal's stomach, the movement pattern is then completely different.
In order to correct such errors and constantly improve the location methods, we need close cooperation with electrical engineers, statisticians and computer scientists.
"We hope to include more and more voices in the Orchestra of Species."
SPIEGEL:
What's next?
Arlinghaus:
We hope to include more and more voices in the orchestra of species: more species of fish, more habitats, maybe even the interactions between terrestrial and aquatic animals or between cormorants, seals, white-tailed eagles and fish.
So far, many teams have been researching separately and the data is not necessarily exchanged.
But there are approaches to cooperation here.
In the future, for example, we could try to use coordinated experiments to understand global factors such as the effects of climate change or environmental pollution on animal behavior and animal populations.
SPIEGEL:
Will there ever be apps for anglers that reveal exactly where you can catch which fish?
Arlinghaus:
As an angler, that would of course be of great interest to me.
However, the fish is still ahead of us here.
We could say roughly where the fish are likely to be and when, but we don't know if the fish then want to bite.
These kinds of predictions don't work.
Because fish are intelligent, as our experiments have also shown.
Carp, for example, are particularly capable of learning, they often swim around the fishing lure, but they know pretty well what to do with the lure that also has a hook in it.
Our camera recordings showed that the carp were able to immediately spit out the hooked bait.
Experienced carp anglers can sing a song about it.
One thing is clear: you should never underestimate Pisces.