Wild Fish Can Tell Human Divers Apart Based on Their Outfits, Study Suggests
Using visual cues, including colors on wetsuits, seabream in the Mediterranean learned to identify researchers that would feed them
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While diving in the Mediterranean Sea, a team of scientists noticed something curious: Every field season, groups of local fish called seabream would follow them around, stealing food intended as rewards for other fish in their experiments.
The seabream seemed to recognize the divers and even appeared to know which individual humans were most likely to be carrying food. Not even decoy divers threw them off. To the scientists, the swarming seabream were “really very annoying,” as Maëlan Tomasek, a researcher at the Max Planck Institute of Animal Behavior, tells the London Times’ Tom Whipple.
So, the team designed another study, published Wednesday in the journal Biology Letters, with the seabream as “willing volunteers who could come and go as they pleased,” as Katinka Soller of the Max Planck Institute of Animal Behavior, who is a co-lead author of the study alongside Tomasek, says in a statement.
In the first experiment, Soller spent 12 days training wild saddled seabream and black seabream to follow her around. At first, she wore a bright red vest and fed the fish as she swam for about 164 feet. But in repeated trials, she gradually transitioned to wearing more plain diving gear and only fed the seabream that followed her for the full distance.
“Once I entered the water, it was a matter of seconds before I would see them swimming towards me, seemingly coming out of nowhere,” Soller says in the statement. The same fish would join her repeatedly, and she recognized them. “There was Bernie with two shiny silver scales on the back and Alfie who had a nip out of the tail fin.”
But in the second phase of the experiment, the team wanted to find out if the seabream recognized her, too. To test this, Tomasek joined Soller in the water, wearing differently colored gear. On the first day, the fish followed both Tomasek and Soller equally. But the fish slowly realized that Tomasek never fed them, and more of them started to follow Soller.
To confirm that the fish were really learning to recognize each diver, the scientists narrowed down their focus to six individuals. They found that four of them became better at choosing which diver to follow over time.
“This is a cool result, because it shows that fish were not simply following Katinka [Soller] out of habit or because other fish were there,” says Tomasek in the statement. “They were conscious of both divers, testing each one and learning that Katinka produced the reward at the end of the swim.”
When the divers wore identical gear, however, the fish were seemingly unable to tell them apart. The researchers say this is evidence that the fish were using visual cues, like the color of wetsuits and flippers, to differentiate between the scientists. “They are just using simple mechanisms that they use every day in their lives, and they adapt it to [recognize] humans,” explains Tomasek to Nicola Davis at the Guardian.
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Senior author Alex Jordan, also a researcher at the Max Planck Institute of Animal Behavior, says in the statement that humans underestimate the abilities of fish, based on the team’s findings. “It really shows that we have strong misconceptions of fish cognition,” Tomasek adds to the Times. “We always think that they’re dumb.”
Tomasek hopes the study could make humans reconsider the way they treat fish. “It’s very human to not want to care about them, but the fact that they can care about us, maybe it’s time that we can care about them, too,” he says to the Guardian.
