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Commercial Fisheries News
Volume 33 Number 12
August 2005
Where do bluefin spawn? Another point of view
I have to come out of retirement to rebut what I feel is misleading information on bluefin tuna spawning. Scientist Barbara Block, after many years of tagging large bluefin tuna with satellite tags and archival tags, came to the same conclusion that bluefin tuna researchers at the National Marine Fisheries Service (NMFS) Southeast Fisheries Center in Miami Beach reached in the 1960s:
“The only known bluefin tuna spawning ground in the western Atlantic is in the Gulf of Mexico and the smallest bluefin using the spawning ground are about 300 pounds and 78" long (age 10).” – Luis R. Rivas SCRS 1975
What they didn’t know at the time was that a 10-year-old bluefin weighs 500 pounds. Even after the tuna seiners caught, measured, and tagged about 13,000 small bluefin, then recaptured hundreds of tagged fish every year for many years, revealing how fast bluefin grew through about 20 years of life, the NMFS people still haven’t accepted their true ages. They continue to divide 20-year bluefin life spans into 30 years.
Barbara Block tagged most of her giant bluefin off the Carolinas. I seined bluefin of all sizes – ages 1 to 20 and weighing 10 to 1,100 pounds – from Portland, ME to Cape Hatteras, NC. Most of them were residents of the Northwest Atlantic Ocean.
Tropical stock component
It is my firm belief that the bluefin below Cape Hatteras are tropical bluefin. These are warm-water fish that winter off Brazil and, in the springtime, swim west in the Caribbean current along the Venezuelan coast. Some swim through the Caribbean Sea and spawn in the Gulf of Mexico, while the main body follows the Antilles current and spawns east of the Bahaman Islands and southwest of Bermuda, east of the Gulf Stream.
Here are some scientific notes that back me up.
“Rumors of a run of giant tuna along the outside of the Bahamas have been persistent but unsubstantiated. Crawford caught them in nine out of 10 sets between San Salvador and the northern end of the group, some close to shore and others up to 100 miles out, confirming their presence in considerable numbers over a vast area. Ovaries of bluefin taken east of the Bahamas contained more eggs than any previously examined and were the largest yet encountered. Some ovaries weighed up to 25 pounds.”
–R/V Crawford cruise, April 19 to June 8, 1961, Frank J. Mather, chief scientist, Woods Hole Oceanographic Institution
“Of particular interest was the fact that all of the bluefin tuna captured south of station 2 were of the giant category with weights near or over 500 pounds. Some of the tunas captured were tagged and released. Of those landed for examination it was noted that the gonads of the bluefin examined were in an advanced near-spawning condition.”
–Crawford cruise heading south, April 1961, making longline sets about southwest of Bermuda and east of the Gulf Stream, Warren F. Rathjen, longline gear specialist, NMFS
“Hundreds of larval tuna were taken to form one of the most extensive collections of young tuna ever assembled.”
–John Elliot Pillsbury (owned and operated by the Institute of Marine Science, University of Miami) cruise to Bermuda and the northeastern Bahamas, July 24-Aug. 14, 1964.
Those cruises were a long way from the Gulf of Mexico spawning area.
Northwest Atlantic bluefin spawn east of the New England continental shelf and off Cape Hatteras in April, May, and June, according to several R/V Delaware cruises. Unpublished data recorded June 8-14, 1957 reports the catching of bluefin as small as age 4 with well-developed eggs approaching ripe, some loose.
According to Frank Mather, the medium sized tuna, 115 pounds to 300 pounds, remain in the Northwest Atlantic year-round, so if they do any spawning, it is north and west of the Gulf Stream.
I know that giants native to the Northwest Atlantic remain in the cooler waters off Maine to the Gulf of St. Lawrence and Newfoundland until late November and then move southeast to the warmer waters adjacent to the Gulf Stream.
Those Barbara Block giants are a different breed of bluefin. Our giant bluefin wouldn’t be caught dead in 80° water. Small bluefin can stand warmer water but balk at water in the 60s. That is why you have to search north of school bluefin to find the giants.
I have seined tons of 20-pound bluefin a mile north of Cape Hatteras in early June but never caught a 10-pounder below Delaware Bay.
In 1966 when we were struggling to find school fish, a dragger called us on the radio and reported large schools of football tunas (10-pounders) near Block Canyon. We steamed out to the edge of the shelf and loaded the boat. They were swimming in from the east.
Late in September, age zero bluefin swam to the Jersey coast from the east, indicating they were spawned east of our continental shelf. I do not believe that the juvenile bluefin that are spawned east of the Bahamas cross the Gulf Stream to the Northwest Atlantic.
I tagged a small bluefin off the Jersey coast that was recaptured on the other side of the Atlantic in the Bay of Biscay when it was a 20-pounder. I also caught a 20-pounder that had been tagged in the eastern Atlantic when it was a 10-pounder. There is a constant interchange of stocks.
Spawning with skipjack
I believe that our bluefin spawn in the same offshore areas as do the skipjack tuna. Oceanic Bonito, as they are known, show up in gargantuan schools east of Block Canyon off the continental shelf in July.
I seined them on one trip in 1,100 fathoms of water. There were millions of them. I was fortunate to stop about 60 tons of them. They had a habit of diving down and swimming under the leadline of our net. They were mixed with small bluefin tuna. To intermingle at such an early age, they must have shared a common spawning ground.
Eastern Pacific skipjack spawn in the central Pacific, far away from predators. The larvae, after they are hatched, thrive on plankton until they are large enough to swim to the feeding grounds. Thus, the survival rate of tunas is increased by spawning far from the feeding grounds.
I believe the bluefin tuna act the same way, and Dr. Molly Lutcavage of the University of New Hampshire has a good shot at finding that spawning ground, which is where her satellite tagged bluefin spend March, April, and May.
I would like to quota from a paper delivered by Frank J. Mather in 1962.
“Thunnus thynnus, the bluefin tuna, is scattered over a wide range at birth owing to the vast extent of its spawning grounds. Juvenile T. thynnus tend to concentrate in northwestern Atlantic coastal waters during their first year of life.”
Finally, if I was in charge of tuna management, I would grant Mid-Atlantic fishermen their own quota to fish on the southern bluefin stocks that winter below Cape Hatteras and to continue the historical quotas for the Northwest Atlantic tuna fishermen.
Frank Cyganowski, 84, ran the purse seiner A. A. Ferrante from 1962 to early 1983. Over the course of his seining career, Cyganowski estimates he caught 6,000-7,000 tons of bluefin, 600-700 tons of skipjack, several thousand tons of herring, and 1,000 tons of mackerel.
He also worked side by side with the many scientists who came out on his boat, weighing, measuring, and tagging bluefin, recording his observations, and reading and saving just about every scientific report ever written on the big fish. Cyganowski lives in Fairhaven, MA.
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