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BLUEFIN TUNA
Thunnus thynnus
The bluefin tuna is the largest species in the family Scombridae (the mackerels)
and can reach a length of over three metres and weigh in excess of
500kg. This is the family which includes our summer favourite, the mackerel,
as well as the rather less common Bonito, which has appeared off the West
Coast of Sweden in recent years. There are two populations of bluefin tuna
in the Atlantic, one which spawns in the Gulf of Mexico and the other in the
Mediterranean. It is a protected species, so targeted sports fishing for bluefin
tuna is not permitted. An exception to the prohibition is that fish may be
caught, tagged with a transmitter and released for the purpose of scientific
research.
On 9 September 2017, Swedish sports fishing history was made when the first
rod-caught tuna in over 50 years was taken in our waters. The population had
been fished to extinction and had disappeared from our waters in the mid-1960s.
Bluefin tuna were once again sighted off the Swedish coast a couple of years
ago, and the catch was part of a unique tagging project, involving a collaboration
between the World Wide Fund for Nature WWF, the Swedish University of
Agricultural Sciences Department of Aquatic Resources (SLU Aqua) and its Danish
counterpart, DTU Aqua, Sportsfiskarna [the Swedish Association for Sports
Fishing and Fish Conservation] and a number of expert sea-angling teams.
The tuna fish project, which was financed by ICCAT (the International Commission
for the Conservation of Atlantic Tunas) was exceptionally successful. In total,
18 tuna were tagged and released over a period of one and a half weeks, 14
of them in the Swedish part of the project. The result was extremely positive, and
it will hopefully provide a large amount of useful information for the scientists.
The purpose of the tagging was to increase our understanding of tuna fish and
their living habits, and also to study their patterns of movement. Where do they
travel to during the year? The tuna is one of the ocean’s real long-distance swimmers,
which can cover vast areas in the hunt for food. In our waters, mackerel are
far and away their favourite food.
Photo:
Martin Falklind/
Fiskejournalen
During the tagging process, when a transmitter was attached to the second dorsal
fin, tissue samples were also taken from each fish to establish which population
the fish belonged to. The tagging was carried out by SLU and scientists
from the Spanish technology research centre, Azti Tecnalia, who were in an escort
boat in the area in which the fishing took place. When a boat caught a fish,
the escort boat came alongside to tag the fish and take samples. Not exactly the
easiest of projects, when you are dealing with an absolute powerhouse of a fish,
weighing at least 200-300kg and able to swim at almost 70 kmh.
4 | FLADEN FISHING - 2018
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