Ireland is co-operating with scientists from the US in tagging, releasing and tracking the elusive bluefin tuna, writes Lorna Siggins, Marine Correspondent.
Irish and US marine scientists have tracked the transatlantic progress of several bluefin tuna which were tagged off the Irish west coast as part of a joint research project.
Data from the tagged fish suggest that Ireland may be a feeding location for fish of both western and eastern Atlantic origin. "What's really interesting is that the size of the fish in Irish waters, compared to the stock off the US east coast, is quite remarkable," says Chuck Farwell, one of the US researchers from Monterey Bay Aquarium.
Since the project began over a year ago, six bluefin (Thunnus thynnus) have been tagged and released by the team, in cooperation with skippers of west-coast-based sea angling vessels who are involved in a developing sport fishery for the bluefin. Two of the three "pop-up" satellite tags fixed on fish off Donegal and Mayo last year have been released automatically.
The data shows that one of the fish moved from the west of Ireland and the Celtic Sea area in November/December of last year to the west Atlantic in January. It crossed the Atlantic and its tag popped off in a known spawning area north of the Bahamas in late March of this year, according to Ronan Cosgrove, coordinator of the BIM Bluefin Tuna Tagging Programme.
The second fish moved to the mid-Atlantic ridge area where it remained throughout December and January, before returning east. Its tag popped up west of Portugal in mid-April of this year.
The pop-up archival transmitting (PAT) tags are designed to track large-scale movements and behaviour of pelagic fish and other animals, Cosgrove explains. They can store summaries of depth, temperature and light-level data while being towed.
The tag doesn't have to be retrieved to download this information. It transmits it via the Argos satellite system when it is released and floats to the surface at a specified time and date. The results provide the migration path, depth and temperature preferences of the animal being studied, as well as other oceanographic information.
So far, the information points to three patterns of migration for the fish, according to Farwell - from North Carolina to New England and back to North Carolina in the US; from North Carolina to New England and further offshore; and from North Carolina across the Atlantic to Ireland.
"Some of the fish tagged before have turned up in the Mediterranean and also in the Gulf of Mexico, but it certainly looks as if the European population spend a fair amount of time on the US east coast and only return when they reach a certain size and age," he says. "We are trying to find out how long they spend over here off Ireland, and whether they also swim up as far as Norway."
This autumn, another three fish were tagged during a series of trips off the west coast harbour of Cleggan, Co Galway, using several different methods of angling. "We've even tried kite-fishing," Dr Peter Tyndall of BIM in Galway says.
One of the "hot spots" identified for the bluefin was south-west of the Bills Rocks off Clare island, Co Mayo - when the team also saw a pod of up to half a dozen fin whales, the world's second largest cetacean.
Bluefin have been recorded as an accidental by-catch in Irish waters since the late 1970s, and the first one caught by rod and line was taken in September, 2000. Last year, the US scientists involved in the joint programme with BIM recommended that Ireland declare a 200-mile conservation zone for the bluefin, given that this country may be providing the fish with one of its last sanctuaries.
The fish can fetch up to $35,000 (€27,000) fresh on the Japanese fish market, and is regarded as a stock under severe pressure.
A sustainable sport fishery has already been developed in North Carolina since substantial bluefin stocks were identified there in the mid 1990s.
The Irish west coast is now developing a reputation along with Kenya, the Cape Verdes and Madeira, as a destination for high spending sport anglers who want to try their hand at the bluefin during the autumn period from September to November. Average size is around 200 kgs or 440 lbs.
The research programme run by Bord Iascaigh Mhara (BIM) in conjunction with Stanford University, California, has encouraged members of the Irish Game Fish Association to adopt a voluntary catch and release approach for the fish.
The BIM/Stanford University research team hopes to continue tagging next year, and expects to receive information from the three new tags over the coming months.