Atlantic bluefin tuna have returned to UK waters and can again be seen during the summer and autumn months.
Their number seems to be increasing, following a long period of absence linked to the decline of the population, according to research carried out by Cefas and the University of Exeter.
Marine scientists from the United Kingdom and Ireland analyzed several datasets, spanning a period of 16 years, to document the increase in bluefin tuna, which arrives in the waters of Celtic seas and off the south-west of England, the Isles of Scilly and North West Ireland for late summer and fall feed.
The research is part of the “Thunnus UK” research project funded by Defra.
Thunnus UK was created to improve knowledge of this species, an essential first step in securing a positive future for Atlantic bluefin tuna around the UK.
A concerted effort to share and combine important data on where people have observed Atlantic bluefin tuna is central to the success of the project.
This will help identify where and when these fish are found in UK waters.
Almost 1,000 unique observations were recorded between 2013 and 2018 by citizen scientists, scientists, fishermen and ecotourism managers.
The researchers found that the Atlantic bluefin tuna began to arrive in May and stay until January.
However, peak figures have been recorded between August and October each year.
The research draws on five key data sources:
- The general public: a total of 80 observations recorded by the public and submitted to http://www.thunnusuk.org
- Ecotourism: Three ecotourism vessels collecting data on more than 1,600 boat trips off the southwest coast of England between 2008 and 2018.
- Opportunistic scientific investigations: 40 days of investigations with more than 2,500 km of effort carried out by experts from Cefas and the University of Exeter off the north-west coast of Ireland and the south-west of the ‘England in 2016 and 2018.
- Independent fishery surveys: (1) data collected by MarineLife during the Cefas Peltic survey between 2013 and 2015, and (2) data collected by the Irish Whale and Dolphin Group during the acoustic survey on herring in Celtic Sea from the Irish Marine Institute between 2014 and 2018
- Bycatch in commercial fisheries: Bluefin tuna was accidentally caught (bycatch) in the Irish commercial albacore fishery between 2003 and 2017.
Lead author Tom Horton, University of Exeter, said: “Atlantic bluefin tuna are again a feature of coastal waters off the UK and Ireland.
“We were able to document this story using data from a wide variety of sources.
“We must work together to secure a future for the Atlantic bluefin tuna, both in the UK and Ireland and more broadly in its range in the Atlantic Ocean.
“This is a really exciting study and the return of these fish suggests an important role in the UK ecosystem.”
Jeroen van der Kooij, Senior Scientist and Head of the Peltic Survey, Cefas, said: “The unique data collected during our annual survey of the pelagic ecosystem of South West England waters is fundamental to this research. .
“MARINELife’s marine animal observers aboard our research vessel have recorded not only the arrival but also a year-over-year increase in bluefin tuna sightings in the region.
“We will continue to collect this information, which, in combination with data on their prey and habitat collected in the same survey, will hopefully increase our knowledge of these exciting but enigmatic animals.
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