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Seals that empty trap nets are specialists

Linda Calamnius

“My research is aimed at helping coastal professional fishers and seals to coexist,” says Linda Calamnius, researcher at the University of Gävle.

Seals that empty trap nets are specialists

“My research is aimed at helping coastal professional fishers and seals to coexist,” says Linda Calamnius, researcher at the University of Gävle.

Linda Calamnius lives in Hudiksvall and has worked with seal-proof trap nets since 2009. She is a marine biologist and now carries out her PhD studies in a collaboration between the University of Gävle and the Swedish University of Agricultural Sciences (SLU).

Earlier, she carried out part of her research at a small business in Stocka outside Hudiksvall, Harmångers Maskin och Marin, which manufactures a completely new type of seal-proof trap nets. Nowadays, she is employed by the University of Gävle and works closely with the manufacturers of the trap.

“When you improve the traps, the seals find new ways of getting at the fish. I would like to study how seal and fish behave around these seal-proof pontoon traps. My aim is to stop the behaviour by preventing the seals from getting at the fish,” Linda Calamnius says.

A huge problem for fishing

The seals are a huge problem for the coastal fishers, as the seal population of, above all, grey seal and ringed seal has increased so much in the Baltic Sea and the Bothnian Sea.

This is a positive fact as it is a sign of good, healthy environment. In the seventies, there was a crisis for the seals; at this time, they were an endangered species because of environmental contaminants like DDT and PCB.

“They have recovered and the population is growing considerably. Now, we have a healthy population of grey seal. The negative aspect of this population growth is that there are more conflicts with coastal fishers.”

The seal gate

Net traps have been around for a long time and the principle remains the same: you guide the fish into smaller and smaller chambers to make it impossible for fish to find their way out again.

“I have played a part in the construction of a seal gate, which we put at the next-to-last chamber, to prevent the seal from reaching the final part of the trap. We would now like to study what happens to the catch; should it affect the catch, the fishers would not want to use it.”

During tests, observations showed that the trout was affected, but not the salmon. They then changed the way the gate was placed and as a result both big trout and salmon could get in.

“We have to look at the behaviour in both seal and fish. When we filmed a herring trap during two months, we had 1400 seal visits by 12 individuals. It’s the best sweet shop of the world for the seals.”


The whole system of traps can be 80 x 120 m wide and ends with the so-called fish house. This is the final part, where fish gather and are fished up. In the photo, this is the small part pointing towards A.
Film showing how the trap is emptied

12 specialists

“I have studied these films and identified 12 individuals. It’s quite fun to find names for them and I think I have discovered certain patterns.”

Linda explains that the seals that empty the traps are specialists. She also has a theory: most often, it is the males, but not all the males in a seal population.

“If you take the example of boys who take their mopeds to the kiosk to show off and be tough, they are a special kind—not all boys do that. It has something to do with testosterone, I think, but it is unproven.”

Bingo—a specialist among specialists

Sälen "Bingo"

Linda calls him Bingo, since he won the bingo every time he swam into the herring trap. Bingos was the most frequent visitor and he alone made 361 visits of a total of 1400, which 12 individuals made during two months.



“You can see how Scarneck here cranes his neck. It is exactly like birds; he is a bit curious.”

Seals are clever

“They are clever, proactive predators; all the time they push the limits and try new things. They have to get in all the way, and if they can’t find their way out again, it is not going to end happily for them. It is about helping the fishers and the seals to co-exist. I also help the seals, so they do not get stuck in the gear and die.”

She tells us that on average the seals are in the trap for two minutes, but they can hold their breath for much longer. One seal, Pirate, was in there for 26 minutes. But he was frightened off and never went back in.

“Once, I was the ‘seal-nanny’ for a seal pup a fisher had taken care of. Even though she had such a limited environment in her tub, the water hose and the herring, she found new ways to do things all the time. It was amazing to watch.”

Linda tries to write a character log book for all the individual seals; she looks closely at their behaviour and studies their personalities. What drives them? How do they act when they are inside the trap, for example when two individuals are there at the same time?

“I wish my research could contribute to finding a new method which keeps seals out of fishing gear and fish farms. Fish farms in, for instance, Chile and Norway have great problems with the seal and also with sea lions,” says Linda Calamnius.


Linda Calamnius has carried out five project in collaboration with Länstyrelsen, the county administrative board, during her PhD studies.

One EU project focused on enhancing a trap for perch, whitefish, salmon and herring; it only catches the bigger perch, while sorting out the smaller ones by making it possible for them to get out. In this manner, the trap contributes to sustainable fishing.

“These tests have been carried out with professional fishers in Gävleborg, the north of Uppland and west Norrland. The collaboration with the fishers is very close and a lot of fun. The world’s best job ever!”


For more information, please contact:
Linda Calamnius, researcher at the University of Gävle.
Phone: 070-3326756
Mail: Linda.Calamnius@hig.se


Text: Douglas Öhrbom
Photo: Privat

Published by: Douglas Öhrbom Page responsible: Anders Munck Updated: 2017-09-25
Högskolan i Gävle
Box 801 76 GÄVLE
026-64 85 00 (växel)