How do you tag a big fish weighing over 200 kg? This was the challenge given to the Norwegian scientist Johannes Hamre. In the 1950′s fishing for bluefin tuna became an important fishery for many Norwegian fishermen. Tagging tuna should give the scientists more information about the bluefin tuna, its growth and its migration pattern.
The tuna is depended on a constant flow of water over its gills in order to get enough oxygen. While caught in a seine, the tuna will die as the seine is hauled in – preventing it to swim. Tagging tuna was therefore a difficult task; both to place the tag and then releasing the tuna before it died.
A Norwegian bluefin tuna seiner with a catch in 1959. Johannes Hamre has left his small rowboat. He is here aiming for a fish with his tagging-stick. The tuna is panicking and it was not easy to place the tag and then releasing the same fish.
A bluefin tuna is tagged and released. The lack of oxygen while caught in the seine has made the fish dizzy. 42 bluefin tuna were tagged in 1959. Some of the tunas tagged in 1957, 1958 and 1959 were later caught in foreign waters; outside Spain, Portugal, Denmark and Morocco. Most of the tagged fish were though caught by Norwegian fishermen outside Norway.
The scientific work done by Harme also included biological samples and collecting data from the fishery. His work on the bluefin tuna represents the best data we have of the bluefin tuna stock in the 1950′s. Even today his work is studied to learn more about this big fish – now suffering from decades with overfishing.
All photos: The Norwegian Institute of Marine Research. Related posts:
The basking shark (Cetorhinus maximus) is the second largest fish in the world. Only the whale shark is bigger. A grown basking shark has usually a length between eight and ten meters, but it can be at least 13,7 meters long, weighing several tons.
In spite of its size the basking shark is a harmless shark. It feeds on plankton and other small fishes and creatures floating near the surface. While feeding the shark swims with its mouth open, using its gills to filter the seawater. This huge shark has a worldwide distribution and can bee observed alone or in shoals. In spring and summer the basking shark is often seen feeding in the surface but the basking shark seeks to deeper waters in the winter.
This short video shows a basking shark feeding. You can see some photos of former hunt for basking shark on this page.
It is not much you need to be afraid of while spending time by the coast of Norway. No bears, no wolfs and no dangerous sharks outside the beaches. I guess stinging jellyfish and sea urchins are what most people fear the most, though you should not play with the teeth of the porbeagle or the wolf fish – nor shaking hands with crabs and lobsters. The most dangerous fish in Norwegian waters must be the weever fish – greater weever. Not because of its size, but by the fact that it is poisonous.
You don’t die if you get poisoned by a weever fish, but it is very painful. The injury also qualify to visit a doctor. Most people never get to see a weever fish, but in some areas along the Nowegian coast it is quite common. In Norway you may catch greater weever on shallow waters using baited hooks (or long lines). If you some day get a weever fish on the hook, then handle it with care. Most injuries occure while handling the fish. Remember that the weever fish has two poisonous spines on the frontal dorsal fin and one on each side of the gills.
The halibut has always been a popular fish in Norway. We know that man has fished halibut since the stone age. Illustrations of halibuts were engraved into stone by proud fishermen. The big halibut was a fish surrounded by mystery and superstition. In those days it is likely to believe that the halibut was caught by using harpoons. They may also had used hooks made of bone.
Except from the spawning period, big halibuts can bee found in shallow waters. A big halibut gives the fisherman an unforgettable fight and one fish is enough to feed several families. Fishermen used hooks (on lines and long lines) and harpoons for hundreds of years, but in the 1930′s a new fishing gear was introduced to the fishermen in the northern part of Norway.
In 1936 the first Norwegian halibut-nets were made. The Norwegian government paid the costs for making and trying out ten nets. The nets were set on deep water in Lofoten and the result was outstanding. During the autumt the same year 60 vessels participated in this fishery. The catches were very good, but by the end of the year the halibut “disappeared” from the fishing ground. The fishermen moved their nets to other fishing grounds. It was a success. Equipped with their new nets, the fishermen set their gear on every known spawning ground. The increase in the catches were unbelievable. Using nets for one month gave a better result than fishing with long lines for a whole year. Nothing lasts forever, and the adventure in the north lasted only for a few months. The halibuts were gone. Where did they go? The halibuts had not gone anywhere – the fishermen had taken them all. Norwegian scientists and the government responded quickly. In 1937 a minimum size limit was introduced and it was not allowed to fish with nets in the spawning period. The catches in 1937 were depressing. The number of halibuts entering the spawning grounds were low. The grown halibuts – seeking the limited spawning grounds by instinct – had been an easy prey for the fishermen. Some fishing grounds were “dead”. In other spawning areas only a few halibuts spawned. A halibut is about 10 years old the first time it spawns. You don’t have to be a scientist to figure out that it took decades to rebuild the stocks.
Even today, 70 years later, the stocks – both in the north and especially in the south of Norway – are too small. Some halibuts in the south is caught to be tagged. Every year the scientists learn more about the halibut. Knowledge is essential to make us understand the halibut and how the stock respond to the pressure from fishing and changes in its environment.
