May 21, 2010

Guy Harvey On Yellowfin Tuna

by Guy Harvey
Yellowfin tuna are prized by anglers for both their challenging fight and good taste

Yellowfin tuna are prized by anglers for both their challenging fight and good taste

We are fortunate in the Cayman Islands to have several tuna species here, available all year round, but it is the yellowfin tuna that is preferred by anglers and commercial fisherman alike.  Our preferred method of fishing them is to drift with cut bait gently sinking in the current accompanied by a lot of chum in the water.  The smell of the chum brings the tuna and other game fish closer to the surface.  Trolling using lures or rigged ballyhoo works well where tunas are not concentrated in one spot.

The yellowfin tend to congregate near undersea ridges.  Here in the Cayman Islands this means they are found at East End, NW and SW points, and around 12-mile Bank.  They are found further offshore around other oceanic seamounts such as 60-mile Bank, and Pickle Bank as well as the Sister Islands.  Preferring the deep water, they linger where the current meets these obstructions and wait for baitfish to be pushed past them.  Hence when fishing for yellowfin tuna, the fishermen are generally spread out on the up-current side of the bank.  To see the tunas chase flying fish at the surface, frigate birds over head, will get any angler’s pulse racing.

The yellowfin tuna is the most brilliantly coloured of all the tunas with a broad stripe of golden yellow on its flanks, and bright yellow on all of its fins and finlets.  The lower sides have vivid white spots and vertical streaks.  I love to paint yellowfins, because of their bright colours, and wide eyed look in predator/prey interactions.

The Atlantic and Pacific forms of yellowfin have been called separate species, but all yellowfins are now considered to be a single species, found in tropical and subtropical waters around the world.  Large individuals with exceptionally long second dorsal and anal fins have been called Allison tuna — but these are just variations.

Yellowfin tuna grow to a fairly large size reaching 400 lbs., with most here being in the 20-120 lbs. size range.  The Cayman record is a respectable 189 lbs. fish caught back in 1989.  The IGFA all tackle record is 388 lbs.  My daughter Jessica, has a current IGFA Junior Angler (girls) record of 198 lbs., caught in Panama in 2002.

The Yellowfin tuna is the tuna of choice in the Caymen Islands

The Yellowfin tuna is the tuna of choice in the Caymen Islands

I have spent a lot of time in Panama working on yellowfins, as some of the greatest concentrations of this species are found in the productive waters of the eastern tropical Pacific. There is a marine lab in southern Panama at Achotines, where most of the research work on yellowfins has been conducted. Adults are kept in captivity, and have been found to spawn daily as long as the water temperature is above 24°C.  The production of eggs and larvae in captivity have allowed for extensive research on early life history and growth rates.  This knowledge is very important when it comes to managing the fishery, particularly as the tunas migrate through the EEZ of many countries, and are fished offshore in international waters by fleets from many more countries.

Yellowfin tuna and big-eye tuna readily associate with spotted dolphins and spinner dolphins, in a unique relationship between a fish and a mammal.  It has been suggested that the tunas take advantage of the dolphin’s food finding capabilities and tag along for the hunt.  Once the bait schools are located the tunas and dolphin corral the bait, and then plunder the masses of fish.  I have been fortunate enough to film these feeding episodes under water for my TV series, “Portraits from the Deep”.

Unfortunately many dolphins got killed in the purse seines set around them for the tuna swimming below.  Purse seining was a very effective way of catching large numbers of adult tuna, with no bycatch, apart from the dolphins. Following the outrage of published numbers of dolphins dying using this method, two things happened. Firstly, those boats setting on the dolphin schools, had to free the dolphins, alive, and often used divers to accomplish this, successfully reducing dolphin mortality to almost zero.
 
Secondly, but tragically, the tuna boats would set purse seines on floating objects (natural and man-made) as tuna were known to associate with flotsam. As it turned out, this “flotsam fishery” caused an ecological disaster. But because it was carried on far offshore, and did not involve dolphins, the news of this destruction did not reach the consuming public’s attention. Being “dolphin safe” caused problems infinitely more serious for other species living in the open ocean.

Flotsam provides an oasis in the vast ocean under which juvenile tunas congregate, some adults, but also thousands of tons of other non-targeted fish such as mahi-mahi, many species of sharks, billfish, wahoo, jacks, sunfish, triple tails, turtles, manta rays, and juveniles of many reef species. All these, plus the juvenile tuna, ended up as bycatch and were unusable in this fishery.  Thousands of tons were shoveled overboard, resulting in the unnecessary destruction of important game fish species, and the annihilation of the juvenile tunas that would in a few years have been the adults and the brood stock for the future.

It is our collective responsibility to be concerned with the resource issues facing the marine creature we target as seafood, and ensure the continued biodiversity of marine ecosystems and the survival of all marine creatures.

Guy Harvey

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One Response to “Guy Harvey On Yellowfin Tuna”

  1. John LoGioco says:

    Great post Guy! Yellowfin tuna are amazing and need to be looked after carefully. Here in the Northeast, for the last 2 fishing seasons, the numbers of yellowfin and bigeye tuna were drastically down. This year, every canyon fisherman is waiting with high anticipation for a change this season – which starts right about now. There are folks here on the East coast trying to figure out what the problem might be. Early signs are pointing to the over harvest of yellowfin and bigeye tuna in the Gulf of Guinea. So like the bluefin, the next major front for tuna conservation here in the Atlantic will likely be addressing the harvest in this region and its connectedness to other areas of the Atlantic.

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