Skipjack tuna

Skipjack tuna or Katsuwonus pelamis have been harvested in the eastern Pacific by commercial bait boats since the early 1900s, and later by commercial purse seine, gilinet, troll fisheries and recreational fisheries. It is one of the most abundant pelagic tuna species.

Skipjack - leaner than albacore tune; it is the most commonly used tuna for canning.

Skipjack tuna occur throughout the tropical, subtropical waters and warm temperate waters of all oceans. They are two stock structures hypothesized for Pacific skipjack tuna, a single stock with isolated subgroups two or more different stocks.

Katsuwonus pelamis

They are common throughout the tropical Atlantic south to Argentina and may range as far as Cape Cod, Massachusetts, in summer months.

Skipjack tuna can attain a maximum of 40 to 45 inches in length but are commonly between 16 and 28 inches long and weigh for 5 to 15 pounds. Skipjack tuna feeding is opportunistic on fish, crustaceans and cephalopods.
Skipjack tuna

Tuna fish canning

At the processing plant, the fish are thawed in holding rooms at ambient temperature or in tanks with running water.

When thawed, the fish are eviscerated and washed. They are then cooked in steam, under pressure, and then cooled.

Precooking removes most of the strong flavored oils. The strong flavor of dark tuna flesh affects the delicate flavor of white flesh. When cooled, the heads and skins are removed.

The fish then cut longitudinally after which all bones and the dark meat are removed.

The white meat is shaped, mechanically into a cylinder, feed into cans and cut to length. To pack chunk style tuna, pieces are filled into cans with adjustable filler.

Vegetable oil or a broth containing hydrolyzed vegetable protein in water is metered into the cans, are then heated in steam, sealed, heat-processed. The sterilized cans are cooled in ruining water, wiped and kept in a cool place 10-15.5 °C. The cans then are labeled and stored.
Tuna fish canning

Frozen tuna aboard the boat

Most tuna fish fishing boats make trips lasting for several months and for this reason, the fish are usually frozen aboard the boat.

The freezing process depends on the type of tuna. For bluefin tuna as an example, fisherman first cut the tail and gills, then gut bled and freeze it t -65 C for 35horus before placing them in to the fish hold at -60 C.

Normally in freezing, the whole fish are cooled in large well with refrigerated sweater circulated through it at 28 F (-2.2 C). Once the fish are cook led, the refrigerated seawater is pumped out of the well, and it is replaced with refrigerated bone at 10 F (-12.2 C) or lower.

When the fish are frozen, the brine is pump out of the well, and the fish are kept frozen in the dry well by circulating mechanically refrigerated air.

In one system brine is sprayed on refrigerated pipe coils located in the hold of the vessels until a coating of ice one foot thick or more is frozen. The compartment is then filled with fish and is flooded with brine. Accumulated ice provides refrigeration capacity needed to chill the brine and freeze the fish.

They remain there until the boat arrives at port.
Frozen tuna aboard the boat

Fishing tuna

At one time, fishing for tuna was carried out exclusively with pole lines. The pole lines are the traditional method and a cotton line with a barbless small fish-shaped hook attached to it is used.

Live bait is carried in a big tank on deck and these small fish are thrown overboard to attract schools of tuna when on the fishing grounds. Once tuna begin to strike, the crew starts fishing with poles and lines using a feather lure that contains a barbless hook.

Today tuna are mainly caught with purse seines which, due to the size of the fish, are made with heavy twine.

Catching tuna with purse seines is the most efficient method currently available. The catches of tunas by purse seines have increased rapidly since the early 1980s and large part of this increase has been due to increased used of fish –aggregating devices.

Some tuna may still be taken with pole lines and some with troll lines. In the Pacific, about 70 percent of the catch of principle market tuna is taken by purse seiners, 10 percent by pole and line and 8 percent by long-lines. In the Indian Ocean, these values are 45, 15 and 20 percent.
Fishing tuna

Light tuna

Skipjack - leaner than albacore tune; it is the most commonly used tuna for canning. Skipjack tuna are highly migratory and have been fished by any different countries such as the US, Mexico, Ecuador, France and Spain.

Skipjack tuna

Yellowfin – larger and leaner than albacore; it has pale pink flesh and is the second most popular species of tuna used in canning.  It is found throughout the world’s tropical and subtropical seas, except the Mediterranean.

It is canned and marketed as light tuna, but it is also an important component of sushi and sashimi.

Bigeye – similar to yellowfin; it has a milder flavor than skipjack or yellowfin and is frequently used in canning. It is a tropical and subtropical species with separate stocks in the Atlantic, India, Western and Central Pacific and Eastern Pacific Oceans.

Together yellowfin tuna and skipjack tuna account for most of the world’s canned light tuna, but chunk light tuna may refer to a number of species: bigeye, yellowfin, skipjack or tongol tuna.
Light tuna

White tuna

American demand for fresh tuna grew tremendously toward the end of the twentieth century, and fisherman scoured the seas, searching for the finest tuna.

Tuna is canned solid and in chunks. About ten different species of tuna are canned, but labels usually distinguish only between ‘white tuna’ and ‘light tuna’.

Albacore
Albacore is high in fat and rich in EPA/DHA; it has the whitest flesh and is typically referred to as white tune; it is eaten both canned and fresh.

It is a member of the Scombridae family of tuna and mackerel. The albacore is an excellent light-tackle gamefish.

The average weight for albacore is between 1-0 and 25 pounds. Albacore generally contain more methylmercury than other types of tuna and may also contain more lipophilic compounds.

Northern Bluefin 
The Northern Bluefin tuna occurs in commercial quantities in the Atlantic and Pacific Oceans, from 70 °N to 25 °N and to a smaller extent south of the equator in the Pacific. The fish is high in fat and EPA/DHA; it is a slow-growing and thus rarer species than albacore and has a very high-quality meat; its major market is Japan where it is used for sashimi.

Southern Bluefin 
Stocks are in decline and thus it is harder to obtain than other tunas. It is the most expensive fresh tuna. They are distributed only in southern hemisphere and mainly inhabit cold waters around 40 °S.

This is unique species of tuna, in that one stock is distributed throughout the three major oceans, Pacific, Indian and Atlantic.
White tuna

Canned tuna fish

The suborder Scombroidei is usually referred to as tuna and tuna-like species. It is composed of tunas, billfishes and other tuna-like species.

Tuna is the most popular fish used for canning and is the second most consumed type of seafood in the United States, Japan.

The tunas (Thunnim) is include the most economically important species referred to as the principal market tunas because of the global economic importance and intensive international trade for canning and sashimi. 

Canned fish is an excellent way to have fish available at any time. The best are canned tuna fish. Six species of tuna are canned and sold: yellow-fish, skipjack. Bluefin, Oriental tuna, little tuna and albacore.

Canned tuna labeled ‘white meat’ comes from albacore and is the most expensive. Canned albacore tuna has the most omega-3 fatty acid. The other species are labeled light meat.

Canned tuna are available packed in oil, water and brine. When fish is canned, processers often add fat in the form of vegetable oil. This added oil usually doubles the calories in the fish and adds up to ten time more fish.
Canned tuna fish

Tuna distribution

The major commercial tuna species are albacore, bigeye Atlantic, northern and southern bluefin, skipjack and yellowfin tunas.

The yellow fin tuna is found on the West Coast from Southern California to Southern Chile. Yellow fin tuna are caught by various gears such as purse seines, longlines and baitboats.

Until the development of the purse –seine fishery, most of the catches were made by longlines, which take medium to large-sized fish, as one of the main target species.

Southern bluefin tuna are distributed only in the southern hemisphere and mainly inhabit cold waters around 40 degree S. However, their spawning grounds are in tropical waters.

Bluefin tuna range from Nova Scotia to Brazil on the East Coast and from Southern California to Northern Mexico on the West Coast.

Skipjack is one of the most abundant pelagic tuna species, inhabiting of tropical waters. Skipjack tuna are cosmopolitan and subtropical seas, usually in deep coastal and oceanic waters. The skipjack is found in the Pacific Ocean from Southern California to Central and Southern America.

Albacore is a member of the Scombridae family of tuna and mackerel. It is an excellent light-tackle gamefish. Albacore is best known as Americas highest grade, ‘white meat’ canned tuna.

The albacore ranges from Puget Sound to lower California. The yellow tail is found in Pacific waters from Southern California to the coast of Mexico.

Several other species of tuna found elsewhere, especially in the Eastern Pacific Ocean.
Tuna distribution