Norwegian marine researchers have discovered that big quantities of mackerel pressed together in a fish net can affect the fish quality. Photo: Norwegian HI

Norwegian marine researchers have discovered that big catches of mackerel pressed together in a net leads to stressed and poor quality fish. Photo: Norwegian HI

Marine researchers with the Norwegian Institute of Marine Research have discovered that large quantities of mackerel pressed together in a fish net can affect the fish’s quality.

A new study from the Institute of Marine Research (HI) shows that fish vitality is a good measure of welfare. The marine scientists found this out by combining several practical investigations.

“When you fish for mackerel with a purse seine, the catch is “snared” tightly together in large quantities, to make it easier to pump the fish on board the boat,” explains HI researcher Neil Anders.

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“We wanted to find a way to measure how the fish feels when it is pressed together like this,” says research colleague Michael Breen.

Checked the “shape” of individual fish

First, the marine scientists “recreated” how the fish can feel outside in a fishing net, by cramming mackerel together in breeding cages.

Afterwards, the researchers tested the “shape” of the fish, through various tests, to find out which physical and behavioral stress responses it showed.

Together, the results gave a measure of the vitality of each individual fish.

The marine researchers then took their experience and methods from the cage to a commercial purse seine boat. There they also examined the stress response, blood tests and general condition of individual fish from the catch.

Larger catches and longer pumping times resulted in poorer conditions

The results were clear: Animal welfare in the catching process was negatively affected when large catches had to be pressed together to be pumped into the boat.

“It was clear that larger catches result in longer pumping times, which increases the negative consequences for welfare. We saw that vitality deteriorated, and in the blood samples we could measure that fish from large catches had been very stressed,” says Breen.

“The study provides a good indication of how animal welfare can be improved in the trapping process,” Anders believes. “For example, by going after the smaller shoals. If the catches are smaller, the time it takes to pump the fish on board is shorter, and then welfare is better.”

Important progress to monitor animal welfare in fisheries

The most important thing for the marine scientists, however, is the new method they have developed.

“Being able to measure welfare through the fish’s vitality is an important tool for being able to monitor, and further improve, fish welfare during the catching process,” concludes Breen.

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Research finds big catches means stressed and poor quality fish

by editor time to read: 6 min