Family: Scombridae (Mackerels and Tunas)
Genus and Species: Thunnus obesus
Description: The body of the bigeye tuna is cigar-shaped (tapered at both ends). The head is pointed and the eye is relatively large. The color is dark metallic brownish blue to dark yellow on the back becoming gray or whitish below. There often is a bluish stripe on the side. In most individuals, the length of the pectoral fins should enable one to identify the species properly. Both bigeye and yellowfin tuna look similar, but bigeye tuna have pectoral fins which extend well past their anal fin, while yellowfin tuna have much shorter pectoral fins. Tuna which cannot be distinguished by external characteristics can be positively identified by liver characteristics. Bigeye tuna livers are striated (covered with blood vessels) along the trailing edges, while yellowfin tuna livers are smooth. Small bigeye tuna also may be distinguished from albacore by the characteristics of the liver. The liver is heavily striated in the albacore while the bigeye tuna liver is only striated along the trailing edges.
Range: Bigeye tuna occur worldwide in warmer seas. In the eastern Pacific these tuna range from Peru to Iron Springs, Washington. They are occasional visitors to California, entering our fishing grounds in June and remaining until November. These fish prefer temperate water in excess of 70° F, but significant catches have occurred in water as cool as 65° F.
Natural History: The diet of bigeye tuna includes fishes, squid, and crustaceans. Like most other tunas, they feed on what is most abundant in the area. Bigeye tuna do not spawn in waters off California, but spawn further south in the Pacific. Bigeye tuna are approximately 3 years old at first spawning. In the equatorial regions of the Pacific, the peak spawning is between April and September. A bigeye tuna weighing 159 pounds will produce an estimated 3.3 million eggs per year. The young are fast growing and weigh about 45 pounds when they first mature. They live 7 or 8 years.
Fishing Information: Bigeye tuna generally are not accessible to recreational anglers because they travel far below the surface during the day. Only rarely are they seen on the surface, and then, only momentarily while feeding. This makes the fish hard to locate since they leave no telltale surface signs nor can they be easily located by trolling. Most bigeye tuna are taken incidental to albacore or marlin fishing. The best way to fish for them is to troll marlin lures in an area where the fish are known to occur. Most bigeye tuna taken in southern California weigh 50 to 100 pounds,
with an occasional 150 to 200 pounder landed.
Other Common Names: gorilla, tuna, patudo.
Largest recorded: 80 inches; 435 pounds; 215 pounds (California).
Source: Marine Sportfish Identification, California Department of Fish and Game, 1987
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