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By Staff | Jul 13, 2017

Capt. Rob Cosgrove (left) and Capt. Jonny Keiley with their 136.6- and 126.6-pound “Allison” yellowfin tuna. PHOTO BY DONNELL TATE.

Call it “Ahi Fever,” “Yellow Fever” or “Money Fever.” Like Spring Fever, it’s an affliction caused by a strange virus that infects all boat fishermen starting in the early month of May. Multiple symptoms: Argumentative, grumpy, daydreaming, restlessness, inability to think and work, an overwhelming feeling of anticipation, to procrastinate everything that’s important in life, anxiety for fishing. Just the mention of sashimi can trigger an attack.

With only four ahi over 100 pounds landed heading into the summer season, was it going to be a non-ahi year again? Both 2015 and 2016 only had five 100-pound ahi for the entire year; 2014 was a lot better, with 19 for the entire year.

Starting the second week of June, the “Buoy” boats Action and Die Hard 2 started to find the 100-pound ahi off the Halawa end of Molokai. During the last 22 days of the month, they landed 18 ahi over 100 pounds from the area. The largest was 145.0 pounds, with a 144.0 a close second. At least a dozen in the 80- to 99-pound range were also weighed.

June was also the best June for big ahi and third best month since 1988. June of 2014 was a record month with 16 ahi weighed. I had to go back to 1994 to find a better month, with July of that year producing 40 ahi of the 64 for the year. The best month for ahi since 1988 was also July in 1995, with 56 100-pounders weighed of the 63 for the year.

There are actually many different races of “Allison” yellowfin tuna, which seem to migrate in overlapping circles across the Pacific. The various strains differ in the relative size of the eye, length of the fins and robustness of the body. The yellowfin tuna (Thunnus albacares) – specifically the larger adults with long, sickle-shaped anal fins called “Allison” yellowfin tuna – were formerly regarded as a separate species (Thunnus allisoni) originating in the 1920s. Its earliest usage was found in The National Geographic, from the name of James A. Allison, United States entrepreneur and founder of an aquarium at Miami Beach, Florida.

Here are a few interesting facts about yellowfin tuna.

After attaining maturity at around two years, female yellowfin can spawn repeatedly every day for long periods and will release millions of eggs per spawning. Actually, spawning occurs at night, usually between the early evening and the early morning hours.

The eggs “hydrate,” or expand rapidly, by taking on water in the late afternoon prior to the evening spawning. The hydrated egg sacs swell noticeably and may be around 8-12 inches long and over three inches in diameter. The eggs are approximately 1.0 millimeter in diameter and are fertilized in the open ocean, where they float with the plankton until hatching, known as “broadcast spawning.”

Some spawning occurs all year long along the Equator, where surface water temperatures are always above 81 or 82 degrees Fahrenheit. An abundant food source and active feeding activity is coincident with daily spawning cycles.

In Hawaiian waters, yellowfin concentrations close to the islands apparently increase at the onset of the spawning season in April and May with rising surface water.

Yellowfin in Hawaiian waters also exhibit near daily spawning frequencies during the peak of the summer spawning season, with spawning ceasing around September and October. The active feeding required to fuel this reproductive activity increases their vulnerability to surface trolling gear, shallow set longline gear and ika shibi handlines. During the spawning season, all three fisheries are in direct interaction with each other for mature, reproductively active yellowfin.

The high spawning rates and tremendous egg production by the species is a great advantage to yellowfin stocks. Obviously, only a small fraction of the eggs survive to produce adult fish, while the rest are consumed by other fish or zooplankton. Their approximate longevity is around ten years.

Hawaiian yellowfin tuna appear to be mainly a product of a localized spawning population, with a smaller immigration component coming in from south of Hawaii. These tuna tend to remain in Hawaiian waters throughout their lifetime with low exchange rates between Hawaii and other regions of the Pacific.

Estimated growth rates of Central and Western Pacific yellowfin tuna are: 30 days, length six inches, weight 1/4-pound; four months, 14 inches, two pounds; one year, 23 inches, eight pounds; two years, 35-40 inches, 30-45 pounds; three years, 45-52 inches, 65-85 pounds; four years, 55-60 inches, 100-125-pounds; five years, 60-62 inches, 135-150 pounds.