Tuna on the fly Thunnus

Special Physiology
All tunas are able to maintain the temperature of certain parts of their body above the temperature of ambient seawater. For example, bluefin can maintain a core body temperature of 25–33 °C (77–91 °F), in water as cold as 6 °C (43 °F). Tuna achieve endothermy by conserving the heat generated through normal metabolism with the rete mirabile. A rete mirabile (the “wonderful net” in latin) is a complex of arteries and veins lying very close to each other, found in some vertebrates. It utilizes countercurrent blood flow within the net & exchanges heat, ions or gases between vessel walls. The “wonderful net” of veins and arteries in the body’s periphery, transfers heat from venous to arterial blood thus decreasing or eliminating the effects of surface cooling. This allows the tuna to elevate the temperatures of the highly-aerobic skeletal muscles, eyes and brain, which supports faster swimming speeds and reduced energy expenditure, and which enables them to survive in cooler waters over a wider range of ocean environments than those of other fish. Also unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red muscles derive their color from myoglobin, which tuna express in quantities far higher than most other fish. The oxygen-rich blood further ables energy delivery to their muscles In all tunas, however, the heart operates at ambient water temperature as it receives cooled blood & coronary circulation directly from the gills.

Yellowfin Tuna
Distinctive features & Description Other common names around the world include A’ahi (Tahiti), Ahi & maha’o (Hawaii), kihada (Japanese), te baibo (Kiribati), thon jaune (French), tonnos macropteros (Greek), yatu (Fiji) thunfisch (German), tonno albacora (Italian), Rabil (Spanish), albacora (Portugual). Yellowfin tuna (Thunnus albacares) The yellowfin is a large tuna and has the typical fusiform body of tuna species. The body is metallic blue in color and changes to a silver at the belly. It has two dorsal fins and in adults, the second dorsal fin is longer than the first, as is the anal fin, which sits directly below the second dorsal. The anal and second dorsal in adult fish can sometimes extend to the tail. Whatever the size of the yellowfin tuna, its yellow fins are always visible. The yellow fins are the anal fin and the second dorsal fin. They also have even to ten dorsal and ventral finlets. These small finlets situated between the tail and the fins are also yellow. The eyes are large. They do have teeth but they are small and conical primaily used for grasping prey rather than cutting them in half. Reported sizes have reported catched as large as 95 inches (235 centimeters) in length and 440 lbs (200 kilograms) in weight. A 15-40 lb (7-19 kg) yellowfin is a good catch and seems to be about the most common size fish caught on the fly. The current IGFA record for this species stands at 388 pounds (176 kg) for a fish caught in 1977 near San Benedicto Island in Mexico. In 2010 a 405 pounds (184 kg) yellowfin was caught off Cabo San Lucas, Mexico measuring 86-inch (2,200 mm) long with a girth of 61 inches (1,500 mm). In 2012, a fisherman in Baja California caught a 427 pound yellowfin. The later 2 catches have not yet been verified.
What Yellowfin Eat The yellowfin diet consists of squid and small fish. They chase after mackerel, sardines, saury and flying fish. Their natural predators are the wahoo, marlin, shark, seabirds and other large tuna. Other predators include the great white shark, the mako and sailfish. Despite the large size of the yellowfin tuna, it has not been able to escape overfishing. As a result, its population has been dwindling. Just like other threatened fish species, there are now efforts to curb fishing and increase its population. As always we encourage catch and release.
Distribution & Habitats Yellowfin tunas are found worldwide in tropical and subtropical waters, from latitudes of approximately 40°N to 35°S. They are not found in the Mediterranean Sea. The yellowfin tuna is highly migratory. The yellowfin tuna is both an epipelagic/pelagic species. This means they live above and below the thermocline, at temperatures of 65 to 88°F (18-31°C). It is generally found in the upper 330 feet (100 m) of the water column. Yellowfin are strong schoolers. Their tendency to school with organisms of the same size is stronger than the tendency to school by species. They often found swimming in mixed schools of skipjack, bigeye, and other tunas. In the eastern Pacific Ocean, larger yellowfin frequently school in association with dolphins, particularly the spotted dolphin, spinner dolphin, and common dolphin. Yellowfin will commonly school under drifting objects such as driftwood, patches of seagrass, boats, or dead marine mammals. Yellowfin may be attracted to the object to feed on smaller prey which are foraging on the structure. The drifting object provides shade and shelter from predators. Yellowfin tuna may use the object as a substrate on which to lay their eggs or as a “cleaning station,” where parasites are removed by other fishes.

Bluefin Tuna
Pacific bluefin tuna Thunnus orientalis is a migrating, predatory species of tuna found widely in the northern Pacific Ocean. It is almost identical to the Thunnus thynnus or the Atlantic bluefin tuna. Migrations are based on where the food is and dictated by following the baitfish. They have been found as far south as the South Pacific. They can be large and reach It may reach a length of almost 10 ft (~3 m) and over 990 pounds (450 kg) (990 lb). Pacific bluefin is a commercially valuable species and several thousand tonnes are caught each year, it is overfished and becoming more concerning to conservation groups. The appeal comes from bluefin being the most desired species for shushi and fetches huge dollars at the Tokyo Fish Market. Monterey Bay Aquarium have placed all bluefin tunas on the “Avoid” list, and they are also placed on the Greenpeace Red List. The tuna’s ability to maintain body temperature (mentioned in the general information section) has several definite advantages over other sea life. It does not need to limit its range according to water temperature, and it almost completely unaffected by climatic changes. The additional heat supplied to the muscles also results in extra speed & power. Bluefin tuna have been clocked in excess of 40 miles per hour (~50 km/h) during bursts & sprints. This allows tuna it to hunt squid, herring, mackerel, sardines and other species that slower predators cannot catch. The Pacific bluefin tuna is mostly a Northern Pacific species but range from the East Asian coast to the west coast of North America. Tuna likes colder waters and are a pelagic species found in temperate oceans, but it also ranges into the tropics and more coastal regions. It is typically seen from the surface to 660 ft (200 m),but has been found as deep as 1800 ft (550 m). Spawning occurs in the northwestern Philippine Sea near Taiwan and in the Sea of Japan. A proportion of these fish will migrate to the East Pacific and return to the spawning grounds after a few years.
What Bluefin Eat Bluefin Tuna eat a variety of baitfish including Sardines, Mackerels and flying fish. They also eat squid. The size of the prey fish is usually anywhere from 2 inches to 12 inches long.