Norwegian Institute of Marine Research tests new gun-type stunner for handling Atlantic bluefin tuna that enter aquaculture pens

The Norwegian Institute of Marine Research (HI) announced this week that researchers, working with fishermen, successfully carried out a controlled kill of live Atlantic bluefin tuna using a specially developed pole-mounted stunner. The trials took place this year, and project leader and HI researcher Odd Børre Humborstad said the technical operation of the killing step went "very smoothly."

The tool was developed by the institute in collaboration with gunsmith Alf Holmaas Helland. Helland handled the manufacture of the production-approved lupara firearm as well as the technical development of the gun. According to Humborstad, the stunner is mounted on a long pole and fires a single shot when the barrel is pressed against the tuna's head; hitting the brain region should render the fish immediately unconscious and subsequently dead. The trials showed that free-swimming tuna can be killed one by one in a controlled manner, but the researchers are not yet making absolute claims about the conclusions.

Humborstad also stressed that the device is not yet commercialized. Before it can be put into routine use, it must be further developed in line with strict technical design and safety requirements, and because it is a firearm, corresponding training and occupational health and safety (HMS) systems must be established. Another unresolved issue is regulatory jurisdiction: current Norwegian Directorate of Fisheries guidelines recommend using weapons and ammunition suitable for large game, whereas the lupara developed in this project uses 12- and 20-gauge shotgun shells, so clarification is still needed on the use of such weapons under current regulations.

Atlantic bluefin tuna entering aquaculture pens is no longer a rare phenomenon in Norway. Humborstad told iLaks that tuna are reported entering aquaculture pens every year; the fish can reach three meters in length and weigh more than 500 kilograms, and besides potentially causing holes in the netting—which can then lead to escapes of salmon and trout—removing it from the pen is itself very difficult. According to statistics from the Norwegian Directorate of Fisheries, between 2023 and 2025 such incidents were reported 6 to 8 times per year. As recently as last month, Lerøy reported that an Atlantic bluefin tuna had entered a submersible pen in Nordmøre, and the company had to raise the netting and kill and remove the fish.

Under current recommendations, if the tuna is still alive it should first be contained with a seine net and then killed with a firearm. Humborstad noted that this process involves a good deal of handling, and the isolation and killing operations may also stress the farmed fish.

At the population level, Humborstad said the Atlantic bluefin tuna stock has grown substantially in recent years, and the Norwegian Directorate of Fisheries has recorded more intrusions at aquaculture facilities than before. He declined to assert that this trend will continue, but sees a possible connection: "There is reason to assume that a growing Atlantic bluefin tuna population could lead to more such incidents, but we currently have no basis for making a definitive judgement about how this will develop." He also noted that the Directorate of Fisheries' statistics show reported incidents have been increasing since 2015.

The researchers are also studying preventive solutions. Humborstad said that in follow-up work on live holding (levendelagring), the team is also examining feasible devices for catching tuna associated with fish farms; such fishing devices might help to lure tuna away or keep them from approaching aquaculture facilities, thereby reducing the likelihood of them swimming into pens.

Meanwhile, the underwater drone project previously reported by iLaks is still moving forward. Humborstad said the underwater drone remains relevant, especially for Atlantic bluefin tuna that have already entered aquaculture pens; with such solutions it might be possible to kill the tuna without hauling up the seine net, thereby reducing the handling required for the farmed fish. HI made the lupara trials a priority this year, but is continuing to advance further development of the underwater drone.

Humborstad also said the institute is in dialogue with aquaculture companies concerned about the tuna-in-pens issue, and that these companies have shown interest in taking part in follow-up work; however, the technology itself has not yet been discussed in depth outside the project group.