Tunas
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Tunas
Tunas are the most important food fishes of tropical seas. The skipjack tuna is the world's most important fishery species with annual catches reaching six million tons.
Eight kinds of tuna have been reported from Guam. Skipjack tuna is the most abundant, followed by yellowfin tuna, and kawakawa, all of which are caught by trolling. Dogtooth tuna live near reefs and are caught primarily by bottom fishing. Frigate tuna and double-lined mackerels are rare visitors, and albacore and bigeye tuna stay in deep offshore waters.
Guam is the home base for a large fleet of purse-seiners and the world's largest fleet of longliners. These vessels fish primarily south of Guam in the Federated States of Micronesia. The purse seiners target skipjack and yellowfin tuna and can scoop several tons in a single set. Most of their catch is transhipped to foreign canneries. The longliners target large yellowfin and bigeye tuna from water as deep as 825 feet (251 m). Most of their catch is air-flown to Japan for the fresh-fish sashimi market.
Most tunas are highly migratory, high-seas fishes that feed on a variety of smaller fishes, squids, and crustaceans. They grow rapidly and live for only a few years. Most tunas are "warm-blooded." As they increase in size, their core body temperature gets progressively higher than the temperature of the surrounding water. To avoid overheating, they must move to cooler waters as they grow, either by migrating to subtropical or temperate regions, or by remaining in deep water if they stay in the tropics. For this reason, large tunas of most species cannot be caught by trolling in surface waters near Guam.
Skipjack Tuna / Bunita
Skipjack tuna is the most abundant and easily-caught fish by trolling. Recent Guam annual landings have ranged from 37 to 124 tons (34 to 112 MT). However, skipjack tuna have a low market value so many fishermen try to catch other species instead. Therefore, in some years, the catch of skipjack tuna is exceeded by that of mahimahi or wahoo. Skipjack tuna reach a weight of 42 pounds(19 kg), but the largest from Guam are about 20 pounds (9 kg).
Yellowfin Tuna
Image from Coral Reefs CD
Yellowfin tuna is highly prized for the local sashimi market. However, it is not as abundant as skipjack tuna; recent annual landings by trolling are almost always lower, ranging from 17 to 68 tons (16 to 62 MT). Catch rates and the abundance of 50 to 150 pound (23 to 68 kg) fish seem to be declining. This may be an indication of overfishing by purse-seiners and longliners.
Yellowfin tuna reach a weight of 388 pounds(176 kg), but the largest caught by local trollers are about 160 pounds (73 kg).
Kawakawa
Dogtooth tuna
Gymnosarda unicolor
Guam Comprehensive Wildlife Conservation Strategy, 9/27/2005
