Calling it an ‘very unusual and positive event’, chief fisheries and conservation officer Tim Dapling said it was the first time tuna had been seen up close in Sussex.
Following a report of a ‘large stranded dead fish’ at Thorney Island Sailing Club, the Chichester Harbour Conservancy staff located and recovered it and sought help from the Sussex Inshore Fisheries and Conservation Authority.
Fortunately, the authority was conducting a sea patrol within the harbour at the time with fisheries patrol vessel ‘Watchful’.
The fish was transferred to the deck of Watchful with a davit and winch, where it was identified as the tuna species Atlantic Bluefin.
It was then transported back to Shoreham-by-Sea where the fish was landed ashore and stored overnight at fisheries wholesaler and retailer Monteums Ltd.
IFCA officers Dr Jen Lewis and Nick Rogers conducted sampling work on the carcass, collecting key measurements and tissue.
The fish showed no immediate signs of damage, or any evidence that it had encountered any fishing gear causing its death.
It was also evident the fish had only recently died, given its condition and lack of damage or decomposition.
Given that the cause of death was unknown the carcass was properly disposed of once all samples had been collected.
The Eastern Atlantic Bluefin tuna went from ‘endangered’ to ‘near threatened’ in 2015 showing numbers had improved but the continued need for a cautious approach to their management.
Currently the UK holds no quota for Bluefin tuna and no commercial UK fishing vessels are allowed to catch the species.
Any Bluefin tuna caught by any UK vessel must be returned to the sea, alive and unharmed.
Atlantic Bluefin tuna, (Thunnus thynnus), are the largest tuna species reaching up to three metres in length and weighing over 600kg.
The species is highly migratory throughout the North Atlantic, with spawning areas in both the Gulf of Mexico and the Eastern Mediterranean.
Historically bluefin tuna regularly frequented UK waters, feeding upon plentiful prey fish species such as herring and mackerel, however global fishing pressure due to high demand and prices caused bluefin numbers to drastically decline over the past century, to the point that they were classified as an endangered species by the IUCN.
Tim Dapling said: “This is a very unusual and positive event in terms of fisheries the marine environment and the presence of a key species.
“Although it is a pity the fish was not alive, it is first time we have an encountered at close quarters a Bluefin tuna specimen in Sussex coastal waters.
“There are various reports of Bluefin tuna in the wider channel area and we know they are regularly sighted further to the west off Devon and Cornwall.
“It was a quite remarkable and impressive fish, why it was in Chichester Harbour or came ashore may never be clear, but we do know species such as mackerel and bass are present in numbers within the harbour and perhaps it entered the harbour to feed and became disorientated.
“Presently we have spring tides, and at low water the channels of the harbour can be relatively shallow and narrow.
“A fish of this size and species is used to open sea areas where it can swim unconstrained to hunt prey.
“The adult Bluefin tuna are at the top of the marine food chain and the increasing presence of top predators typically indicates the improving health of ecosystems. Of course, this was just one fish, however I’d be surprised if it was the only one in Sussex waters.
“Working together with both colleagues in other organisations and the support of Monteums Ltd we were able to ensure benefit from the situation.
“The essential biological information collected will in a small way feed into strategic research on Bluefin tuna in the northeast Atlantic.”