Does remember the fish being caught by fishing?

When fishing in rivers, oceans, and reservoirs, you may occasionally encounter fish that don’t even bother to bite the bait, even though they are actually numerous and active. This can often lead you to conclude that the fish are either becoming more wary or their numbers have decreased.

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In response to these questions that anglers have, there have been two theories that have been passed down for over 50 years: one is that fish that have been caught at least once remember the hook and have learned from it, so they are not easily caught; the other is that some fish are inherently good at catching. Recently, the results of an experiment that combined these two theories have been published.

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There is “Beukema’s learning theory” that fish remember the experience of being caught by fishing, and “Martin’s hypothesis” that there are individual fish that are good at catching. Today, we will first learn about “Beukema’s learning theory”.

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Dr. Jan J. Beukema of the Royal Netherlands Marine Institute published a paper in 1970 that could be translated as “Decreasing catchability through one-trial learning.”

For his experiment, Dr. Beukema placed carp that had never been caught by fishing before in a test pond and had 800 people fish every day for two weeks, using whatever equipment and bait they wanted.

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However, any carp caught had to be tagged and released, and fishing time per person was limited to four hours per day.

According to the experimental results, the best catch per person was on the first day (average 1.24 fish), and it started to decline from the second day, and on the fifth day, it was about a quarter of the first day’s catch. In other words, the fact that it became increasingly difficult to catch carp even though there was always the same number of carp in the pond led me to think that the carp might be avoiding the bait attached to the hook after learning from the experience of being caught on the hook. To verify this, I used two methods.

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The first one predicted and actually observed that whether or not a carp without learning effect would be caught would be determined randomly and that the number of times it was caught would match the “Poisson distribution.”

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However, the experimental results were significantly different from the Poisson distribution, contrary to the predictions, and the number of carp caught for the first time was much lower than predicted.

The second verification method was to see what percentage of the carp caught that day had been previously caught by fishing. From day 1 to day 4, 20-30% of the carp that had never been caught before were caught by fishing, confirming that the carp that had been caught by fishing before were more likely to be caught than the 5% that were caught again.

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However, from the 5th day onwards, regardless of whether they had experience catching fish or not, they only managed to raise the catch rate by 5%. Based on this, Dr. Beukema concluded that this was due to the learning effect that most of the carp in the pond had already been hooked at least once after 4 days since the start of the experiment.

Dr. Beukema also announced that the fish’s learning effects persist even after a year. How is Dr. Beukema’s theory currently being accepted? And can it be validated simultaneously with “Martin’s hypothesis,” which we’ll discuss next time, that certain fish are particularly good at catching?

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If you’re curious, please look forward to the next episode^^