Just bringing up the word tuna in a sentence is usually enough to get most game and sport fishing enthusiasts excited and eager to talk.
The different types of tuna, bluefin, yellowfin or dogtooth are among the largest, fastest, and most beautifully colored of all the world’s fishes and are an exciting catch. Their torpedo-shaped, streamlined bodies are built for speed and endurance. Their coloring—metallic blue on top and shimmering silver-white on the bottom—helps camouflage them from above and below. And their voracious appetite and varied diet pushes their average size to a whopping 6.5 feet in length and 550 pounds, although much larger specimens are not uncommon.
Unfortunately, tuna meat also happens to be regarded as surpassingly delicious, particularly among sashimi eaters, and overfishing by Japanese fisherman is an issue nowadays. The first tuna of the year has already been sold for over $1.75 million! But already Romans and Greeks where fascinated by this fish and even as far back as the stone age era, there has been an indication of interaction between fisherman and tuna species
Interesting Facts about the Tuna
These fish have several interesting traits and adaptations that make them unique.
- There are Eight “True” Tunas
- The eight species in this group are the albacore, southern bluefin, bigeye, Pacific bluefin, Atlantic bluefin, yellowfin, blackfin, and longtail Tuna. Here in Tanzania we catch mostly yellowfin tuna.
- Self-Regulation – Researchers recognize this group as one of the few fishes that can maintain their body temperature in a way like mammals. This allows them to maintain their body temperature in chilly waters, letting them hunt in deep water without losing strength or speed.
- Tuna Farming – People in some areas have attempted raising these fish in an aquaculture, or farming, setting. In Australia, “ranchers” build offshore pens to raise fish. They catch juvenile fish and transfer them to the pens, where they raise them to their adult size and sell them.
- Some are Endothermic
Most other fish cannot regulate their body temperature, but the tuna have an endothermic circulatory system. This means, just like mammals, they can regulate their body temperature. The ability to maintain their body temperature allows these fish to swim in colder waters, such as subarctic regions or deep beneath the surface, without losing speed or strength.
- Fishing Pressure – All species in this group face some level of fishing pressure that causes decline in their populations. The IUCN lists the Pacific species as Vulnerable, the Atlantic species as Endangered, and the Southern species as Critically Endangered.
Habitat & Migration of the Tuna
While each species has its own specific habitat preferences, all eight true tunas have pelagic lifestyles. This means that they live in open water and do not stay on the sea floor. Their depth preference varies by species, some live in deeper waters than others.
Each species has its own specific distribution and range, but all of them have cosmopolitan distribution. The southern species lives across the globe in waters just north of Antarctic polar regions. As their names suggest, the Pacific and Atlantic species utilize tropical and temperate waters in the Pacific and Atlantic oceans.
Fight and Speed of Tuna
They are prized among sport fishers for their fight and speed, shooting through the water with their powerful, crescent-shaped tails up to 43 miles per hour. They can retract their dorsal and pectoral fins into slots to reduce drag. And some scientists think the series of “finlets” on their tails may even serve to reduce water turbulence.
Diet of Bluefin Tuna
Tunas attain their enormous size by indulging themselves almost constantly on smaller fish, crustaceans, squid, and eels. They also filter-feed on zooplankton and other small organisms and have even been observed eating kelp. The largest tuna ever recorded was an Atlantic bluefin caught off Nova Scotia that weighed almost 700kg.
As each species lives in a different region, they each prey on different species of fish and squid. Larger species prey on larger fish, while smaller species and individuals target smaller prey. All three species have carnivorous feeding habits, which means that they eat other animals. They have primarily piscivorous diets, as they feed mostly on fish and squid.
Humans have eaten tuna for centuries. However, in the 1970s, demand and prices for large bluefins soared worldwide, particularly in Japan, and commercial fishing operations found new ways to find and catch these sleek giants. As a result, bluefin stocks, especially of large, breeding-age fish, have plummeted, and international conservation efforts have led to curbs on commercial takes. Nevertheless, at least one group says illegal fishing in Europe has pushed the Atlantic bluefin populations there to the brink of extinction.