Photo credit: Kim Birnie-Gauvin
Written by: Hilde Johannesen
A few years ago, the iconic Atlantic Bluefin Tuna (Thunnus thynnus; ABFT) returned to Scandinavian waters after being absent for approximately half a century. Due to the species’ high economic value worldwide, the fishing pressure has largely exceeded that of a sustainable catch in recent decades, resulting in overexploitation. After a persistent decline was observed, a plan to recover the stock was implemented, which significantly restricted the fishery. The return of the ABFT in Scandinavian waters illustrates the positive effects of fishery management. Currently, scientists from DTU Aqua, together with SLU VFM, ICCAT, and recreational fishers, are leading a tagging project to investigate the characteristics of this large fish species and identify necessary measures to develop and secure the stock.
There are mainly two ABFT stocks divided between the spawning grounds in either the Gulf of Mexico (West Atlantic stock), or the Mediterranean (East Atlantic stock). These two stocks do experience some mixing in the northeast Atlantic. The stock of ABFT that is present in the Scandinavian waters is most commonly from the west Atlantic stock, which undergoes vast migrations from the spawning site and further north to feed. These extensive migrations truly highlight the importance of collaborations across borders to be able to create receiver networks that could possibly collect data from all stages of the ABFT migration from the tagged individuals.
The development of electronic tagging methods was not employed until after the 1960s, and as a result, none of the data obtained from this kind of technology was recorded prior to the ABFT stock crash. Now that the ABFT has returned to Scandinavian waters, it is vital that we utilize newer technology, such as acoustic telemetry, to study the behavior of the species, make informed management decisions, and ensure their persistence.
“We are SUPER excited for the upcoming season so we can continue to track these giants as they migrate in and out of our waters and beyond. Our goal is really to acquire the necessary knowledge about their biology and ecology, including behavioral patterns, habitat use, migration routes, and how they respond to stressors and environmental parameters. This knowledge will enable us to protect and manage them to the best of our ability, ensuring their continued presence in our waters.” – Kim Birnie-Gauvin, DTU
Thanks to the European Tracking Network, ABFT has already been detected all around Europe using our Thelma Biotel TBR 800 receivers, the older TBR 700 and in effective combinations of receiver grids from other manufacturers! In total, over 400 ABFT were tagged with Thelma Biotel transmitters (16 mm), and they will continue providing data for the next decade as they pass through compatible receiver networks.
There is no doubt about the value of the commercial and recreational fisheries of ABFT before the collapse in the 1960s. The significance of ABFT’s return is evident, and the goal is to grow and sustain the stock at a level where it can become a valuable and sustainable resource.
To read more about the first results from the tagging efforts of the ABFT, an article has been published here.
To read about the economic expenditures by recreational anglers on ABFT, an article has been published here.
Additionally, the most recent video published by the European Tracking Network contains its own section concerning The Atlantic bluefin tuna from 2:43.