A new way of measuring fish welfare in wild-capture fisheries
When you fish for mackerel with a seine net, the catch is crowded tightly together in large quantities to make it easier to pump the fish on board the boat. The scientists wanted to find a way to measure how the fish respond to that.
Photo: Institute of Marine Research Norway (IMR)Published: 24.01.2023
Today, there is little research into animal welfare in fisheries.
It is also a difficult area to research. How do you measure how a fish is coping in a stressful situation?
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.
The mackerel is crowded together in large quantities
– When you fish for mackerel with a seine net, the catch is crowded tightly together in large quantities to make it easier to pump the fish on board the boat, explains HI researcher Neil Anders.
– We wanted to find a way to measure how the fish respond when they are pressed together like this, says research colleague Michael Breen.
Checking the "vitality" of individual fish
First, the scientists recreated what the fish experience inside a fishing net, by crowding mackerel together in an aquaculture cage.
The researchers tested how individual fish coped, using various tests to find out which physiological and behavioral stress responses they 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 welfare
The results were clear: animal welfare in the catching process was negatively affected when large catches were crowded 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 capture process, Anders believes. – For example, by going after the smaller schools. If the catches are smaller, the time it takes to pump the fish on board is shorter, and then welfare would be improved.
Important progress to monitor animal welfare in fisheries
One of the most important results 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 capture process, concludes Breen.
Reference
Anders, N., Hannaas , S., Saltskår, J. et al. Vitality as a measure of animal welfare during purse seine pumping related crowding of Atlantic mackerel ( Scomber scrombrus ). Sci Rep 12, 21949 (2022).