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Tuna Triva

I love tuna! A powerful fighter, great tasting and a sleek, voracious predator that defines the term "gamefish". But besides all that, they are every bit as fascinating as they are fun to catch. There are literally hundreds of articles written on how, where and when to catch this magnificent fish. So, thereís not a whole lot I could tell you that you donít already know or havenít read. If your looking to read a "how to" article, you can stop now. Instead, this article focuses on the physiology and habits of yellowfin, with a little trivia thrown in for good measure. However, learning about the life, habits and physiology of the yellowfin will certainly aid you in putting more of them in the fish lockers.†

There have been some wonderful, scientific papers published that shed a great deal of light on the mysteries of yellowfin. Unfortunately, these reports are written by scientists for scientists, and do little to enlighten the scientifically impaired. So, if you donít have a PH.D. in ichthyology, they are of little practical use. But fortunately for the curious, I have managed to wade through the mounds of scientific data and discover some very interesting facts and theories relevant to the angler.

Donít get me wrong. Im not claiming to be a nuclear physicist. In fact, the only thing Einstein and I have in common is the inability to keep our hair in place. I am, however, intrigued with the oceans and the creatures that live in it. When I was a young boy, every fish I caught had to be subjected to the indignities of a complete autopsy. My fascination with fish and how they work led me to research scientific data, where I discovered that gaining insight into fish physiology, translates into more hook-ups. It increased my angling skills considerably. But more on that later. First, a little tuna trivia.

Manís interest in the yellowfin is an ancient one: Research on the tunaís migration, feeding and spawning practices was begun in the sixth century B.C. by the Greek fishermen that prized their delicate flesh. Twenty-four centuries later, modern researchers are beginning to gain some insight into what many believe to be the most fascinating fish in the sea. The yellowfin tuna is so sophisticated in design and so well adapted to its environment , that it has attracted the attention of biologists ranging from biochemists to physiologists to ecologists.

The yellowfin is a member of the mackerel family and the most brilliantly colored of the tunas. Their bodies are designed for extreme speed with the lines and shape similar to those of missiles. When cruising, the forward dorsal, ventral and pectoral fins extend outward, making the fish capable of executing extremely tight maneuvers. When sprinting however, all forward fins fold into slots with only the tail fins and two rows of turbulence reducing finlets - which also double as stabilizers - protruding from its sleek frame. This advanced design enables the yellowfin to cruise at ten miles per hour, with bursts of speed that have been clocked in excess of 40 mph. It can weigh as much as 450 lbs., and many anglers consider it to be pound for pound one of the hardest fighting fish alive. In Hawaii, the commercial fisherman call the yellowfin ahi, which is the Hawaiian word for fire. This is a result of too many Hawaiian anglers, both hand line and rod and reel, burning themselves on fishing line during one of the yellowfins sizzling runs.

For such a noble fish, the yellowfin is born in a† humble manner. Although mating practices are not well known, the parents do not appear to care for their young. A male and female will separate from the school, release eggs and sperm into the water and then either rejoin the school or swim off their separate ways. During this spawning a female releases one to several million BB-shot sized eggs. Each egg contains an oil drop that causes it to float near the surface, where it hatches after thirty hours. Like most births of this type, the first few days of the larval yellowfinís life is critical. The larva lives off the egg of its yolk until its digestive system has developed to the point where it can hunt for food.†

The chances of the larval tuna surviving its first few weeks are not very promising. Some will simply starve to death , while the majority will be eaten by other fishes, sea birds, or their cannibalistic relatives. This can be evidenced by the fact that what little is known about the early development of yellowfins is by the examination of the contents of larger fishesí stomachs.

Yellowfins grow quickly, attaining the weight of eight pounds by their first birthday. These young tuna congregate with survivors of other spawnings and form protective schools until they are about four years old and weigh one hundred and forty pounds. Then, for some unknown reason, they abandon the school and become solitary swimmers for the rest of their lives, which can last for an additional fifteen years. Their age can be determined by counting the rings that develop in the otoliths (inner ear bones), similar to the way one counts growth rings on a tree.

The yellowfin inhabit vast areas of the earthís ocean. They are warm-water fishes and are usually found in waters with temperatures between 60 and 80 degrees Fahrenheit. Hence, its range extends from point conception southward, through the Gulf of California and along the Mexican Coast to the Galapagos. They can also be found in the waters of Hawaii, Japan, the Dutch East Indies, India, the Red Sea, and on the southeast coast of North America, where they are usually found within a few miles of the mainland, or around islands, underwater sea mounts and banks. The yellowfin does not travel as long or as far as other tunas, because they do not undertake a spawning migration. Tagging has shown that they tend to stay in the same geographical area throughout their lives, seldom, if ever, mixing with populations from different regions.

The yellowfin is a voracious predator living in the open sea, which is analogous to a vast biological desert. Although they do have teeth, they usually gulp and swallow their prey whole, which consists of smaller fishes such as flying fish, anchovies and sardines, along with copepods, shrimps, and the larvae of crustaceans. From a regional stand point, they can also be quite fond of mollusks lacking a protective shell, with various squids topping the list. Since food is scattered here and there in the form of dense schools, the yellowfins job is to find them. In order to accomplish this, it cruises continuously at eight to ten miles per hour searching for food, a duty it was designed perfectly to fulfill. Their life is a continual pursuit for energy, which requires a steady food source. Since they are warm blooded, they have much greater power than other fish and their body is designed for the high-speed searching and tracking of baitfish.

One way the yellowfin has helped to overcome this food finding problem is to enlist some help from mammals. In the Pacific, yellowfin tuna and dolphins swim in mixed schools. The reason for this is that dolphins and tuna compete for the same widely scattered schools of baitfish and squid, but the dolphins are thought to be better at finding them. By tagging along with the mammals, the tunas take advantage of their fish finding superiority.

Using mathematical calculations, scientists have shown that dolphin and tuna have identical hydrodynamics and therefore the same energy costs of swimming, making them perfectly compatible in their journeys.
Serious research of the yellowfin began in the 1950's when ichthyologists began studies in an attempt to help improve the declining tuna catch. But after scientists realized what an extraordinary fish the yellowfin was, the research headed a different direction and took on a life of its own. There is a consensus among many scientists that the tunas are so well suited to their environment that it would be next to impossible for nature to make improvements on their design. The proof of this evolutionary adaptation is that the yellowfin, along with other species of advanced tunas are warm blooded.

At a casual glance, body warmth in a fish may sound like a curious bit of trivia, but in fact, it is one of natureís ultimate challenges in biological engineering. Virtually all laws of thermodynamics are stacked against it. For one thing, water absorbs heat up to fifty times faster than air. To offset this energy loss to water, the body must generate more heat, and this requires oxygen; but water contains just 2.5% the oxygen of air. A fish can compensate by processing more water with its gills, but in order to do so, it must swim with its mouth open and process a large volume of water. This, however, creates a problem because water is eight hundred times denser than air, and the faster a fish swims, the more resistance the water produces and the more energy and oxygen the effort requires. Despite all these factors stacked against him, the yellowfin manages to keep its body temperature up to 35 degrees Fahrenheit warmer than the surrounding water temperature.†

Evolution has overcome the problems of warming a yellowfinís blood through an ingenious and unique system of heat exchangers created in the vascular system . Cold blood carrying oxygen back from the gills is routed near the body surface; hot blood going towards the gills is also routed on the body surface. These vessels of hot and cold blood are interwoven in such a way that it creates a net. In this net the warmth held in gill-bound deoxygenated blood passes into the cold , oxygen-filled blood returning to the body and is carried back to the body core. Scientists believe that this elevated temperature helps the tunaís eyes and brain to perform more efficiently. This is extremely important because tunas locate their food primarily by sight. Their higher body temperature may also enable them to convert food more rapidly into energy, which they need for constant movement, respiration, and rapid bursts of speed in order to pursue prey and escape predators.†

Inherent to the tuna clan is its modified gill structure which has transformed from ordinary gills into "ram-gills." The fish swims with its mouth partially open, which forces water over the gills and the faster the movement, the more water processed and the more oxygen extracted. So complete was this adaptation that the gills of a tuna operate only when the fish is moving; unlike most fish, it cannot survive by lying still and gulping water.
Yellowfin need to use physical exertion to regulate their body temperatures, lacking the high resting metabolism of birds and mammals. This explains why the yellowfin cruise at a high rate of speed in colder waters and slow down considerably while in the tropics.

Despite their inherent high speed design, the yellowfin is capable of swimming at a much slower pace than theoretical modeling or speculation previously believed. Yellowfin have been observed using techniques like turning over on their sides at a 45 degree angle and using their bodies as a hydrofoil, to obtain speeds previously thought impossible. Earlier thinking theorized that tunas, which are heavier than water, would sink at low speeds.†

Another oddity among yellowfin is that they have a magnetic sensing organ located in the ethmoid region of their skull. Some scientists hypothesize that this magnetite-based magneto reception system in the yellowfin is sensitive enough to resolve the earthís magnetic field direction within two seconds of arc. This is especially puzzling because other tunas, most of which are far more migratory in nature lack such an organ.
Most importantly, tagging studies and scientific data have revealed the following information which the savvy angler can use to catch more yellowfin:

* Yellowfin remain 180 to 330 feet below the surface 80% of daylight hours. They spend only 6% of their time within 90 feet of the surface during this time frame.
* They travel and feed in waters as cold as 60 degrees and warm as 80 degrees.†
* Yellowfin change colors when aroused; whether it be fighting at the back of a boat, feeding, or mating.
* Yellowfin do not show a definitive temperature preference as long as water temperatures were within their comfort range of 68 to 75 degrees F.
* They swim faster in cold water and slower in warm water.
* Yellowfin swim closer to the surface at night then they do during the day.
* They average an hourly swimming speed of 8.4 feet per second. Their average sustained†† swimming speed (4 to 10 hour measurements) is 4.1 feet per second.
* Scientific theory suggests yellowfin move up and down in the water column searching for odor trails of baitfish and to help regulate their body temperature.†
* Migratory yellowfin make fewer vertical movements and maintain lower depths than feeding fish.
* They demonstrate predictable swimming patterns that differ between night and day.
* Yellowfin can navigate via a magnetic based sensing organ located in their skull.†
* They are able to know their exact position relative to fixed objects or topography 10 miles away.
* During daylight hours, they associate with topography; banks, ridges, seamounts, FADS, etc.† Late in the afternoon, they move away from their reference point or landmark and begin a circular and sometimes twisting searching pattern at an average of 5 knots from their starting† point. By dawn, they are already at, or enroute to their starting point or landmark.
* Yellowfin have an internal clock. Migratory patterns show that at 2:00am.
* Their eyesight and sense of smell are well developed and superior to most fishes.
* They respond well to splash, low frequency vibration, and visual stimulus.†
* Yellowfin are both trainable and smart.

Thanks to increasing improvements in underwater research capabilities, computers, transmitters, and other state-of-the-art equipment, the next few years promise to be very productive for those who are committed to understanding the complexities of these incredible fishes. There are still many unanswered questions, speculations, and hypothesis that need to be answered and proven. Eventually, this work will help assemble a scientific understanding of how these masters of their environment, a veritable checklist of adaptations to life in the ocean, are able to cope so dramatically with a world we can barely begin to understand. Oh yeah, besides all that, this research will also help me catch more fish.

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