Crafty haddock learn to swim through fishing nets

Source - ICES

When a fishing boat tows a net along the seabed the way it’s supposed to work is that the small, younger fish escape through the mesh and leave the bigger fish behind. The reality is that nets are often bulging with a mixture of both adult and immature fish as the younger ones often seem reluctant to break-out.

But some young fish do escape and scientists at the Aberdeen Marine Laboratory wondered whether these fish remember what to do the next time they are jostling along inside a trawler’s net.
Do haddock remember how to escape from fishing nets?

To find some answers the scientists caught 10 young haddock and put them through their paces in a 6-metre long pool at the Marine Laboratory’s Fish Behaviour Unit.

First the young haddock were taught to race across the pool for a food reward.

Then once the fish trainees had got the hang of racing, the scientists suspended a net across the middle of the pool and recorded their reaction on video cameras.

The effect was immediate: on cue the fish raced across the pool but stopped in their tracks at the net and swam round in circles at a wary distance.

And although the 20 cm holes in the net were several times larger than the width of the fish, they kept their distance from it for the next four races.

But then, by the sixth race, a couple of haddock had the nerve to swim through and they got to the food.

The others appeared to have observed their bolder schoolmates, as more and more fish then dared to swim through, and by the end of the fifteenth race all ten fish were confidently swimming straight through the net.
"... by the end of the fifteenth race all ten fish were confidently swimming straight through the net.”

The scientists then made it a bit trickier: they replaced the 20 cm mesh net with a much smaller 10 cm mesh net.

This set the fish back a bit. For the first two races only a couple of haddock squeezed through the smaller opening. But this time they learnt more quickly and already by the third race all ten fish successfully broke through the net.

So it seems that haddock can not only learn to swim through nets and remember for the future but their behaviour is also copied by other fish in the school.

This raises the interesting question as to whether there are “veteran” haddock in heavily trawled areas—such as the North Sea—that are both harder to catch and that also show the other less-experienced fish how to escape.

This and other papers on fish behaviour from a recent ICES Symposium will appear in “Fish Behaviour in Exploited Ecosystems”, ICES Journal of Marine Science Vol. 61 due out in October 2004.

This research was completed by:
Huseyin Ozbilgin, Ege University, Fisheries Faculty, Bornova, 35100, Turkey.
Chris Glass, Manomet Center for Conservation Sciences, 81 Stagepoint Road, P.O. Box 1770, Manomet MA 02345, USA.

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