Bigeye tuna is an important edible fish which belongs to the Scombridae family. It is closely related to the yellow-fin tuna. Some people believe that the Bigeye tuna has evolved from yellow-fin tuna. In Hawaii, Bigeye tuna as well as the yellow-fin tuna are referred to as ‘Ahi’. This species is counted among the great swimmers in the ocean. Their adaptation quality makes them an efficient predator of small fishes.
Size and Weight: The Bigeye tuna is a metallic-colored fast-swimming fish. The size of a full grown fish is around 250 cm in length and weighs around 300 to 380 pounds.
Color: The first dorsal fin is dark yellow and the second one is pale yellow. The finlets are bright yellow in color with narrow black edges.
Head and Eyes: Their head is pointed and eyes are relatively big compared to the body. They do not have any special marking on their body.
Bigeye tuna are found in all tropical and sub-tropical oceans across the world except the polar seas.
Bigeye is found between 50° North to 45° South in the Atlantic Ocean. In the western part of the Atlantic Ocean, they are found from Canada to Argentina that includes the Gulf of Mexico as well. In the Eastern Pacific, they are found from 40° North to 30° South. In the western part of the Pacific Ocean, they range from Japan to Mexico.
Habitat
This fish is not a deep water species. They are found at the ocean surface going as deep as 800 to 1000 feet. During the daytime, Bigeye is hardly spotted on the water surface as they tend to swim deeper into the water than other tuna species. The Gulf of Guinea is one of the major nursery grounds of this species.
Behavior
While the adults are found in deeper waters, young and juveniles tend to swim at the surface of the ocean. This species is highly migratory. Bigeye tunas loiter in groups and sometime go down more than 1000 feet from the sea surface.
Diet
The diet of this fish includes mullet, small mackerels, sardines, squid, crustaceans and other small deep water species.
Reproduction
A young fish grows relatively fast and reaches its sexual maturity at the age of three to four years. When the environment is favorable, females lay around 3 million – 6 million eggs at a time in tropical water.
In the North-west tropical Atlantic, the Bigeye tuna spawn around June and in the Gulf of Guinea spawning takes place around January – February. Spawning has been noticed throughout the year in the east Pacific region from 10° north to l0° south.
Life span
This species lives longer than any other tuna species. They are known to live around 9 – 10 years, though there are dispute regarding the life span as some believe that this species can live for more than 15 years.
Predator
Shark is the main predator of this species. Apart from sharks, toothed whales and large billfish are counted among its predators.
Interesting Facts
Here are some interesting facts related to Bigeye:
Greenpeace added this species in its seafood red-list in 2010.
There are no international laws to stop fishing using longlines. Therefore, along with this species the population of other threatened and endangered species is also decreasing.
Except for its commercial interest, Bigeye is a very popular game fish.
The largest Bigeye caught in the Atlantic Ocean weighed 392 pounds.
The majority of this species comes from the Pacific Ocean.
The heart of this species are relatively larger as compared to other fishes.
They can’t pump water over the gills. Instead, they swim with their mouth open which helps to push the water into their gills.
Fishing
Bigeye is highly popular in big restaurants around the world. Therefore, it is exported in large numbers. This fish is primarily caught by big industrial fisheries. They are generally caught in tropical deep ocean water throughout the year by using a variety of fishing instruments, but the most common method is longline fishing. However it results in large bycatch, which includes other endangered or threatened species like seabirds, sharks and sea-turtles. A large population of this fish is depleting due to longline fishing.
Nutritional Facts
It is an excellent source of protein, phosphorus, thiamin, selenium, vitamin B12 and vitamin B6. It is also provides magnesium and iodine. This fish is low in sodium and saturated fat.
Recipes
This fish is used to make sushi, sashimi and other popular carpaccio dishes. Smoked tuna is another very popular dish.
Conservation Status – Vulnerable
Overfishing in some regions is really a challenge for this fish. Commissions have been formed in all the major oceans (Indian, Atlantic and Pacific) across the world for its conservation. According to the International Union for Conservation of Nature (IUCN), this species is considered as a vulnerable species.
