Group of Prehistoric Fish

Prehistoric fish are various groups of fishes that lived before recorded history. A few, such as the coelacanth still exist today and are considered living fossils.

The first fish and indeed the first vertebrates, were the ostracoderms, which appeared in the Cambrian Period, about 510 million years ago, and became extinct at the end of the Devonian, about 350 million years ago. Ostracoderms were jawless fishes found mainly in fresh water. They were covered with a bony armor or scales and were often less than 30 cm (1 ft) long. The ostracoderms are placed in the class Agnatha along with the living jawless fishes, the lampreys and hagfishes, which are believed to be descended from the ostracoderms.

The first fish with jaws, the acanthodians, or spiny sharks, appeared in the late Silurian, about 410 million years ago, and became extinct before the end of the Permian, about 250 million years ago. Acanthodians were generally small sharklike fishes varying from toothless filter-feeders to toothed predators. They were once often classified as an order of the class Placodermi, another group of primitive fishes, but recent authorities tend to place the acanthodiaes or that both groups share a common ancestor.

The placoderms, another group of jawed fishes, appeared at the beginning of the Devonian, about 395 million years ago, and became extinct at the end of the Devonian or the beginning of the Mississippian (Carboniferous), about 345 million years ago. Detailed anatomical studies of fossil remains by the Swedish scientist Erik Stensiö strongly suggest that the placoderms were closely related to sharks. Placoderms were typically small, flattened bottom-dwellers, however, many, particularly the arthrodires, were active midwater predators. Dunkleosteus was the largest and most famous of these. The upper jaw was firmly fused to the skull, but there was a hinge joint between the skull and the bony plating of the trunk region. This allowed the upper part of the head to be thrown back, and in arthrodires, this allowed them to take larger bites.

The cartilaginous-skeleton sharks and rays, class Chondrichthyes, which appeared about 370 million years ago in the middle Devonian, are generally believed to be descended from the bony-skeleton placoderms. The cartilaginous skeletons are considered to be a later development.

The modern bony fishes, class Osteichthyes, appeared in the late Silurian or early Devonian, about 395 million years ago. The early forms were freshwater fishes, for no fossil remains of modern bony fishes have been found in marine deposits older than Triassic time, about 230 million years ago. The Osteichthyes may have arisen from the acanthodians. A subclass of the Osteichthyes, the ray-finned fishes (subclass Actinopterygii), became and have remained the dominant group of fishes throughout the world. It was not the ray-finned fishes, however, that led to the evolution of the land vertebrates.

The ancestors of the land vertebrates are found among another group of bony fishes called the Choanichthyes or Sarcopterygii. Choanate fishes are characterized by internal nostrils, fleshy fins called lobe fins, and cosmoid scales. The choanate fishes appeared in the late Silurian or early Devonian, more than 390 million years ago, and possibly arose from the acanthodians. The choanate fishes include a group known as the Crossopterygii, which has one living representative, the coelacanth (Latimeria). During the Devonian Period some crossopterygian fishes of the order (or suborder) Rhipidistia crawled out of the water to become the first tetrapods.

The story of vertebrate evolution started in the seas of the Cambrian period, when jawless, toothless, soft-bodied fishlike creatures wriggled through the water, sucking up microscopic food particles. Only after tough, non-decaying bone was developed (initially as a scaly outer covering and later within the body) did fossils form and become preserved in the rocks. And only then could paleontologists take up the story with any certainty.

The earliest traces of bony scales are found in rocks of the Late Cambrian period, and the first recognizable vertebrate fish has been found in Australian rocks of Early Ordovician age. So, the first chapter in the vertebrate evolution starts with the ancient Arandaspis, a fish about 6in/15cm long with no jaws, no teeth and no fins other than a tail. It did, however, have gills and a stiffening rod of cartilaginous material (the notochord) that served as a backbone.

Indonesian coelacanth Make Scientists be Exciting

Ronan Bourhis said :

French experts equipped with sonar and GPS try to reconstruct trough asked an Indonesia (Manado) Fisherman how to catch a rare coelacanth fish, an awkward-swimming species among the world's oldest. This Full Article can read in Yahoo Tech News



A very rare coelacanth fish as Indonesian, Japanese and French specialists (unseen) carry out an autopsy of in Manado, North Sulawesi, in June. Coelacanths are among the world's oldest fish species. Their fossil records date back more than 360 million years and suggest the animal has changed little in that time.(Photo credit : AFP/File/ Ronan Bourhis)





Second Indonesian coelacanth known to science, later to become holotype of new species, Latimeria menadoensis. Photograph by Mark V. Erdmann, July 1998





Relate Article :

• The Coelacanth: More Living than Fossil (http://www.mnh.si.edu/highlight/coelacanth/)
• NOVA's "Ancient Creature of the Deep" site: http://www.pbs.org/wgbh/nova/fish/
• A general information site about the coelacanth: http://www.dinofish.com/
• South African deep water dives and the coelacanth: http://www.coelacanth-diver.co.za/

Sea Lice ; Parasite found on fish world wide

What Sea Lice are ?

Sea lice are a parasite found on fish world wide.

There are two species of sea lice commonly found on cultured salmonids,

• Caligus elongatus Nordmann, which infests over fifty different species of marine fish, and
  
• Lepeophtheirus salmonis Krøyer, which infests only salmon and closely related species such as rainbow trout.

What effect do sea lice have?

Sea lice are regarded as having the most commercially damaging effect on cultured salmon in the world with major economic losses to the fish farming community resulting each year.

They inflict damage to their hosts through their feeding activity on the host's body. Sea lice affect salmon in a variety of ways; mainly by reducing fish growth; loss of scales which leaves the fish open to secondary infections; and damaging of fish which reduces marketability.

Sea Lice

Sea lice monitoring annual Report

The Marine Institute is charged with carrying out regular inspection of sea lice levels around the country in accordance with the Department of Marine and Natural Resources

Catch-and-Release Fishing

By Erik Williams and Malia Schwartz

Every recreational angler in every part of the country must at one time or another release fish. Minimum size regulations require many anglers to release sub-legal-sized fish or "shorts." Rivers, lakes, and reservoirs are areas where catch and release are particularly important. The increasing popularity of recreational fishing has led to the problem of too many people, too few fish. In some areas, only catch-and-release fishing is allowed. The increase in recreational anglers is not just limited to inland fisheries. Marine recreational angling is having a great impact on certain fish stocks as well. One of the primary means of allowing all these anglers to continue fishing and maintain healthy fish stocks is catch and release. Catch and release, whether it is voluntary or required, must be done properly if it is to succeed in having the fish survive. This fact sheet should help anglers to release fish properly to increase the likelihood that the released fish will survive.

Why Catch and Release?

With the cost of a typical fishing trip, the uncertainties of success, and the appeal of a fish dinner, why should anglers want to adopt the practice of catch and release? Aside from certain regulations, such as bag limits or size limits, there are a number of good reasons for releasing a portion of the catch alive.

First, catch and release offers a sensible way to extend the fishing trip after a reasonable or legal catch limit has been reached. If the trip involves a guide or charter service, catch and release can prolong an enjoyable recreational opportunity, giving anglers more value for their money.

Second, several recent studies have suggested that as anglers gain expertise in a particular fishery or fishing technique, they often develop an interest in "limiting their kill instead of killing their limit."

Why Do Hooked Fish Die?

Fish that are caught and released may die for several reasons, but the two primary causes are stress and wounding. Stress results from the fish fighting after being hooked. Internally, the physical exertion causes an oxygen deficit in the tissues, forcing the muscles to function anaerobically (without oxygen). This causes lactic acid to build up in the muscle tissue, and then to diffuse into the blood. Lactic acid acts as an acid in the blood, causing the pH of the blood to drop. Even slight changes in pH can cause major disruptions of the metabolic processes, ultimately killing the fish. If the fish is quickly released, its blood pH usually returns to normal and the fish will be unaffected. Some fish, after a long tow, may appear to live once released, but the imbalance in the blood chemistry may kill them as late as three days after being caught. In most cases, the means of preventing this type of mortality is to not keep the fish in action for a long period of time, unless the intent is to keep it.

The other primary cause of mortality is wounding by the hook. Injuries caused by hooks can range from very minor to lethal. The degree of injury is dependent on the location of the hook wound. Higher mortalities will occur in fish that are hooked in the gill or stomach areas, while lower mortalities occur in fish that are hooked in the lip, jaw, or cheek areas. Baited hooks are more likely to result in a gill or stomach hooking that artificial lures. Treble hooks, for obvious reasons, will result in more puncture wounds and subsequently higher mortalities. Barbless hooks facilitate release and decrease "out-of-water" time, but for reasons yet unclear, may not significantly reduce mortality, especially when used with bait.

There are other kinds of physiological stress that can lead to higher mortalities in released fish. Fish may not be able to adjust to changes in pressure or to higher surface water temperatures. Also, when a fish is handled or comes in contact with dry surfaces, such as landing nets or dry hands, its mucous layers – commonly called slime layers – may be partially removed, presenting an opportunity for bacteria or pathogens to invade the skin.

Burping and Puncturing

When certain fish are brought up from depths greater than 40 feet too quickly, their swim bladders, which normally control buoyancy, can overinflate from rapid depressurization. Burping is a technique used on a fish with an overinflated swim bladder. The fish is massaged in the belly region in an attempt to release the excess air in the swim bladder. Puncturing involves using a needle or ice pick to poke a hole in the fish’s exposed swim bladder. Both of these techniques are currently being advocated in other parts of the country. However, if the procedure is not carried out correctly, more damage than good may be done to the fish.

The success of burping depends on the species of fish. Some fish, such as largemouth bass, perch, striped bass, cod, hake, and black sea bass, do not have a connection from their gut to their swim bladder. If a fish’s gut is not connected to its swim bladder, then burping is impossible. Puncturing is a very controversial technique. To date, there is no evidence that puncturing will increase a fish’s chance of survival.

The best advice for releasing fish with overinflated swim bladders is to let them go as quickly as possible.

NEVER ATTEMPT TO BURP OR PUNCTURE A FISH WITHOUT KNOWING WHAT TO DO!

Catch-and-Release Guidelines

These guidelines provide basic information on the most beneficial catch-and-release methods for most small- to medium-sized freshwater and marine fish:

1. If you plan to fish with artificial lures, such as plugs and spoons, consider replacing treble hooks with single hooks. Single hooks are quicker and easier to remove, especially when dealing with such predatory fish as bluefish and northern pike. Consider pinching the barb on your hooks, since this will make releasing the fish much easier.
2. Plan your release strategy. Decide whether to keep or release any fish prior to angling or at least before removing the fish from the water. Familiarize yourself with any regulations in effect for the species targeted, and gather any items that will facilitate handling and releasing the fish.
3. When a fish is hooked, use a steady, deliberate retrieval technique. This can reduce the amount of stress a hooked fish undergoes when pulled up from the depths too quickly, or when physically exhausted from an overly slow retrieve.
4. Once you have decided on releasing the fish, avoid netting or even removing it from the water if possible. Use needle-nosed pliers to pry the hook from the fish while it is still in the water. Fish that can be lifted by the leader – the short length of line used to attach the end of the fishing line to the lure or hook – can easily be released over the rail using a "dehooker." These devices, whether homemade or purchased, are gaining in popularity in the bluefish industry – to avoid the fish’s nasty teeth – and are useful for releasing a number of other species. A dehooker may simply be a metal rod with a handle at one end and a small upturned hook at the other end. If live bait or a lure is deeply embedded in the fish’s gullet, cut the leader close to the fish’s mouth and let the fish keep the hook. Studies have shown that fish can get rid of the hook up to 120 days later.
5. When landing the fish, it is important to minimize out-of-water time and any fish contact with surrounding surfaces or objects.

• Avoid using landing nets if possible. If a landing net must be used, one with a neoprene bag rather than natural twine should be used. Neoprene removes less of the fish’s mucous coat.

• Do not use a gaff!

• Keep hands moistened. This helps prevent removal of the fish’s natural protective mucous layer, and reduces the chance of subsequent infections in the fish’s skin.

• Minimize handling, particularly of the gills and soft underbelly. Gently prevent the fish from battering itself on surrounding hard surfaces. Place the fish on an old piece of foam cushion and place a wet rag or gloved hand over the fish’s eye. These two actions can do much to subdue even unruly tuna and bluefish.

1. Return the fish to the water headfirst. In most cases, it is best to point the fish’s head straight down and allow the fish to plunge down into the water.

Sources:

Klauber, A. 1992. Catch & Release. In: Nor’easter: Magazine of the Northeast Sea Grant Programs. Fall/Winter 1992.

Malchoff, M.H., M.P. Voiland, and D.B. MacNeill. 1992. Guidelines to Increase Survival of Recreational Sport Fish. Cornell Cooperative Extension Fact Sheet.

Striped Bass

by Amanda Argentieri

The striped bass, Morone saxatilis, has long been one of the most important commercial and recreational species found along the Atlantic coast. Also known as the striper, rockfish, linesider, and roller, the striped bass has been a sought-after finfish since the colonial era. New England Indians and European settlers caught and dried the fish in abundance. Along with cod, striped bass was one of the first natural resources to be regulated by early conservation measures. For example, in 1639, the Massachusetts Bay Colony passed a law that neither species could be sold as fertilizer. By 1776, New York and Massachusetts prohibited all sales of the fish in the winter months. Continuous harvesting of striped bass continued into the 20th century, but a severe decline in total landings experienced in the 1970s resulted in the development of increased regulation and conservation actions. Today, the striped bass is still a popular species fished both commercially and recreationally. However, preservation and protection remain primary issues in the management of this fishery.

Physical Characteristics
The adult striped bass, known for its size and fighting ability, weighs on average 4 to 7 kilograms (kg) (8 to 15 pounds (lbs)). However, bass exceeding 23 kg (50 lbs) are caught every year. The length of the fish also varies considerably from 46 to 140 centimeters (18 to 55 inches (in)). Its coloring can be light green, olive, steel blue, black or brown, with a white or silver iridescent underside. This stout-shaped fish also can be identified by its seven to eight continuous horizontal stripes on each side of the body from gills to tail.

Distribution
The striped bass is found along the western Atlantic coast from the St. Lawrence River in Canada to the St. Johns River in Florida. The species also inhabits the waters west of the Swanee River, Fla. to Lake Pontchartrain, La. In addition, striped bass has been successfully introduced along the Pacific coast and to inland reservoirs and lakes nationwide. Striped bass is classified as an anadromous fish, meaning it migrates from salt water to fresh water during the spawning season. North of Cape Hatteras, some striped bass stocks participate in coastal migrations—north in the summer, and south during the late fall and winter.

Habitat
Striped bass prefer large bodies of deep, clear water with a temperature between 65F and 70F (18C and 21C). Mature bass can be found in a variety of inshore, estuarine, and freshwater habitats depending on the location and season. Most striped bass remain in inshore waters, and are not usually found more than eight kilometers (five miles) from the coast. Young bass are typically found in river systems and estuaries, which are critical spawning and nursery grounds for the species.

Reproduction
The spawning activities of striped bass are triggered by an increase in water temperature, and occur near the surface in fresh or slightly brackish waters. Depending on the latitude, adult striped bass travel inland to their natal rivers to spawn during the late spring or early summer. Male bass reach sexual maturity at two years, while females usually do not spawn until age four. During the spawning process, the female releases her eggs into the water column to be fertilized by the males. The fertilized eggs must remain in the water column—any that settle to the bottom are smothered and killed. Depending on the water temperature, the eggs can hatch 25 to 109 hours after fertilization. The larvae are 2.0 to 3.7 millimeters (0.08 to 1.5 in) at hatching. The duration of the larval stage is 23 to 68 days, depending on water temperature. The larvae begin feeding after 6 to 8 days. By day 30 to 50, the larvae have transformed into juvenile fish, taking the body shape of an adult bass.

Diet
Striped bass are nocturnal feeders. Larval striped bass feed on zooplankton, while the diet of juvenile bass consists of insect larvae, small crustaceans, mayflies, and other larval fish. Adult bass are considered piscivorous (fish-eating). They eat almost any kind of small fish as well as several invertebrates, particularly crabs and squid.

Fishery
Striped bass are caught commercially using gill nets, pound nets, hook-and-line, and haul seines. Both the commercial and recreational striped bass fisheries rely heavily on the production from populations spawning in the Hudson, Delaware, and Roanoke rivers, and the Chesapeake Bay system. Historically, Chesapeake Bay has produced the majority of the striped bass found along the Atlantic coast. However, poor juvenile production in the 1970s and 1980s caused a severe decline in commercial and recreational landings. The cause of this sudden decline has been attributed to several factors, including overfishing, poor water quality in spawning and nursery areas, contaminants, natural stresses, and pollution.

Protection & Management
The rapid deterioration of the striped bass fishery was addressed at both the state and federal level through legislation and management plans. In 1984, Congress passed the Striped Bass Conservation Act, which allowed the Atlantic States Marine Fisheries Commission to develop an Interstate Fisheries Management Plan for Striped Bass. Under the plan, states along the eastern seaboard were required to comply with certain size limits, seasonal closures, recreational daily bag limits, and annual commercial catch quotas to help rebuild the stocks. In 1995, Atlantic striped bass was officially declared a restored stock, and the strictest regulatory measures were relaxed.

Other methods of conservation include water pollution control, artificial stocking, and the use of hormones to promote female ovulation. Also employed are fishways, a device that allows striped bass to swim past dams and other obstructions while migrating upstream to spawn. In addition, scientists and aquaculturists have successfully crossed the striped bass with white bass to create a silvery hybrid with dark, broken lines. This hybrid is raised in fish farms and sold in fish markets.

The striped bass fishery is thriving once again, but under tight regulation. Scientists, fishermen, and state and federal governments continue to examine methods to protect this species by improving conservation techniques and enforcing proper management measures.

References

Collette, B.B., and G. Klein-MacPhee (eds.). 2002. Bigelow and Scroeder’s Fishes of the Gulf of Maine, Third Edition. Smithsonian Institution Press, Washington.

Groman, D.B. 1982. Histology of the Striped Bass. American Fisheries Society, Bethesda.

Setzler, E.M. et al. 1980. Synopsis of Biological Data on Striped Bass, Morone saxatilis (Walbaum). Dept. of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Washington.

Wirtanen, L.J., and R.H. Ray. 1970. Striped Bass Morone saxatilis (Walbaum): 1970 Report on the Development of Essential Requirements for Production. U.S. Dept. of the Interior, Fish and Wildlife Service, Bureau of Sport Fisheries and Wildlife, Division of Fish Hatcheries, Atlanta.

Websites

NOAA Fisheries Northeast Fisheries Science Center

Chesapeake Bay Program: Striped Bass

Swordfish

By : Malia Schwartz, Deborah Grossman-Garber, and Henry Milliken

The swordfish (Xiphias gladius Linnaeus 1758), also called the broadbill, is the only member of the family Xiphiidae. As its name implies, this magnificent fish is characterized by an upper jaw that extends to form a flat, sharp-edged "sword." Swordfish are impressive jumpers and powerful fighters—thrilling for anglers and boaters alike.

Physical Characteristics

The swordfish has a stout, fairly rounded body and large eyes. The first dorsal fin (rising from the back of the fish) is tall and crescent-shaped. The second dorsal fin is quite separate from the first and very small. Both are soft-rayed—having thin, bony rods that extend from the base of the fin and support the fin membrane. The anal fins approximate the shape of the dorsal fins, but are noticeably smaller. Ventral fins, found on the underside of fish, are absent. There is a strong, longitudinal keel, or ridge, on either side of the caudal peduncle (the base of the tail where the tail fins project from), which leads to a broad, crescent-shaped tail. Adult swordfish have neither teeth nor scales.

The swordfish snout elongates into a true sword shape. Measuring at least one-third the length of the body, it is long, flat, pointed, and very sharp. The lower jaw is much smaller, though just as pointed, ending in a very wide mouth.

The bodies of swordfish fry (recently hatched fish larvae) are quite different form those of the adults. Their upper and lower jaws are equally prolonged; bodies are long, thin, and snakelike; they are covered with rough, spiny scales and plates; tails are rounded; and they have just one long dorsal and anal fin.

Swordfish coloration varies greatly among individuals. The dorsal side can range from dark brown to grayish-blue. This dark shading can extend anywhere from halfway down the side to almost the full extent of the body. The remaining area of the skin is tinged silvery white.

In Northeast waters, only the spearfish bears any resemblance to the swordfish. It is distinguished from the swordfish by its rounded sword, small teeth, a long, continuous dorsal fin, and ventral fins.

Size

Swordfish are very large fish. Today, the average fish caught in the commercial fishery weighs between 90 and 150 kilograms (1 kilogram equals 2.2 pounds). While fish over 200 kg are unusual, the largest recorded in the North Atlantic ocean weighed 550 kg. The largest fish to be caught on a tackle weighed 274 kg. These larger fish measure approximately 4.5 meters in length (1 meter equals 3.3 feet)—with a 3 meter body and a 5 meter sword.

Female swordfish grow faster, live longer, and are proportionally heavier than their male counterparts. Research shows that by 1 year of age, the female is already almost 4 kg. During the next 2 years, she triples her weight of the previous year. By age 4, the female is likely to weigh 70 kg, and at age 5, 110 kg. Similar data for males and older swordfish are inconclusive.

Longevity

Swordfish reach sexual maturity at about 2 to 3 years of age, and live for at least nine years. While they may survive longer, no such documentation exists. The majority of swordfish caught in the North Atlantic sport fishery are thought to be 4 to 5 years old.

Distribution

Swordfish are pelagic fish—living within the water column rather than on the bottom or in coastal areas. They are typically found at depths of between 180 meters and 580 meters, and are found worldwide in temperate and tropical waters. They are believed to prefer waters where the surface temperature is above 15°C (58°F), although they can tolerate temperatures as low as 10°C (50°F). There seems to be some correlation between larger size and the ability to tolerate colder temperatures. Few fish under 90 kg are found in waters less than 18°C (64°F).

Swordfish are summer and fall visitors to New England waters, entering the warming Atlantic coastal waters from far offshore in the Gulf Stream around June and departing in late October. Evidence suggests that such onshore-offshore seasonal migrations are more prevalent than are migrations between the northern feeding areas off Cape Hatteras and the southern spawning grounds off Florid and the Caribbean.

Behavior

Swordfish are not schooling fish. They swim alone or in very loose aggregations, separated by as much as 10 meters from a neighboring swordfish. They are frequently found basking at the surface, airing their first dorsal fin. Boaters report this to be a beautiful sight, as is the powerful jumping for which the species is known. This jumping, also called breaching, is thought by some researchers to be an effort to dislodge pests, such as remoras or lampreys. It could also be a way of surface feeding by stunning small fish as they jump out of the water, making the fish more easily captured for food.

Swordfish feed daily, most often at night when they rise to surface and near-surface waters in search of smaller fish. They have been observed moving through schools of fish, thrashing their swords to kill or stun their prey and then quickly turning to consume their catch. In the western North Atlantic, squid is the most popular food item consumed. But fish, such as menhaden, mackerel, bluefish, silver hake, butterfish, and herring also contribute to the swordfish diet.

Swordfish are vigorous, powerful fighters. When hooked or harpooned, they have been known to dive so quickly that they have impaled their swords into the ocean bottom up to their eyes. Although there are no reports of unprovoked attacks on humans, swordfish can be very dangerous when harpooned. They have run their swords through the planking of small boats when hurt.

The adults have few natural enemies, with the exception of large sharks and sperm and killer whales. They are easily frightened by small boats, yet paradoxically, large craft are often able to draw very near without scaring them. This makes swordfish easy to harpoon.

Fisheries

Today, swordfish are caught in gill nets, with harpoons, and, most successfully, on longlines consisting of a main line, usually several miles long, which is supported in the water column by floats and from which baited hooks are suspended. In addition, swordfish are often an incidental catch in the tuna fishery.

The sport fishery normally fishes for swordfish by trolling and drift-fishing, using rod-and-reel gear. The catch rate has increased considerably since fishermen began in the mid-1970s to fish for swordfish at night using drifting baited lines.

Once almost unsalable, swordfish meat gained in popularity during World War II and continued through the early 1970s. In 1971, the U.S. and Canadian swordfish fishery was essentially terminated following U.S. Food and Drug Administration (FDA) restrictions imposed on the sale of swordfish found to have levels of mercury in the flesh higher than 0.5 parts per million (ppm).

But gradually, the U.S. fishery began to rebound. In 1979, the FDA raised the acceptable mercury level to 1.0 ppm, based, in part, on a National Marine Fisheries Service study, showing that a 1.0 ppm action level would adequately protect consumers. Finally, in 1984, the FDA switched from enforcing the mercury action level based on total mercury concentration to methyl mercury concentration. This change occurred for two reasons: (1) It was determined that methyl mercury was the toxic component of the total mercury concentration, and (2) a test specific for methyl mercury became available. Since then, both catch and fishing effort have been exceedingly high in the Atlantic Ocean, with swordfish meat commanding top prices in the marketplace.

While swordfish sold on commercial markets is closely monitored to make sure that methyl mercury levels remain below the 1.0 ppm action level, most experts urge those concerned about chemical contaminants to take certain precautions:

1. Eat a variety of different fish; don’t restrict yourself to swordfish.
2. Avoid eating excessive amounts of any single type of fish.
3. Avoid eating the internal organs of the fish—they typically contain higher contaminant concentrations than the flesh.
4. When catching your own swordfish, check and follow all applicable health advisories.
5. High-risk individuals—pregnant women, women of childbearing age, and children under age 15—should limit their consumption of swordfish. Pregnanat or nursing mothers should limit their consumption to once a month.
6. If you choose to eat a sport-caught swordfish that may contain elevated levels of contaminants, trim away fatty areas and use cooking methods like baking or broiling, to allow fats and juices to drain away.

Fish Schooling

By Prentice K. Stout

Schooling of fish has very little to do with their education. It does have much to do with their ability to survive and reproduce in sufficient numbers. Schools are composed of many fish of the same species moving in more or less harmonious patterns throughout the oceans. A very prevalent behavior, schooling is exhibited by almost 80 percent of the more than 20,000 known fish species during some phase of their life cycle. Many of the world's fishing industries rely on this behavior pattern to increase their catch size, especially for species such as cod, tuna, mackerel, and menhaden.

Aristotle, over 2,400 years ago, observed this behavior in fish. Perhaps he sparked the interest humans have had in this fascinating trait of certain fishes.

Why school? For one, there are ecological advantages. Some species of fish secrete a "slime" that helps to reduce the friction of water over their bodies. Also the fish swim in fairly precise, staggered patterns when traveling in schools, and the "to-and-fro" motion of their tails produces tiny currents called "vortices" (swirling motions similar to little whirlpools). Each individual, in theory, can use the tiny whirlpool of its neighbor to assist in reducing the water's friction on its own body.

Another advantage is the safety factor against predators. A potential predator breeding hunting for a meal might become confused by the closely spaced school, which can give the impression of one vast and frightening fish. Additionally, there is the concept of "safety in numbers"—a predator cannot consume and unlimited quantity of prey. The sheer number of fish in a school allows species to hide behind each other, thus confusing a predator by the alteration of shapes and colors presented as the school swims along. Of course, those on the outside edges of the school are more likely to be eaten than those in the center. Predatory fish also gain from schooling because it gives them the ability to travel in large numbers in search of food. Bluefish (Pomatomus saltatrix) in pursuit of menhaden are a good case in point.

Schooling fish respond quickly to changes in the direction and speed of their neighbors. Anyone who has swum in a school of fish can attest to their ability to change direction swiftly while still retaining their closely knit swimming pattern. They can move from one configuration to another and then regroup almost as one unit.

When young, most fish species do not exhibit the schooling pattern. As they mature, they begin to swim in pairs and then in larger and larger clusters until they attain the classic parallel pattern. Thus, schooling can be said to be a formed behavior pattern imprinted on the genetic material. Research leads us to believe that as the sense organs of the young mature, their schooling behavior strengthens. The first sense used is that of sight, which begins to function immediately after birth to allow for feeding. Fish eyes cannot focus directly forward because they are located on the sides of the head. This placement does, however, permit the eyes to be especially sensitive to lateral movement—a very helpful attribute in schooling. The fish can see what other members of the school are doing in relationship to themselves and respond accordingly.

Of interest is the acoustico-lateralis, the much-studied lateral line system on the sides of some fish. This is a line of special neuromast cells that runs down either side of a fish body. The scientific name for these lines gives us a clue to their function: "acoustico" means sound, and sound waves produce pressures; and "lateralis" alludes to the sides of the fish's body. These two lateral lines are highly sensitive to movements and the displacement of water as the fish swims close to its neighbor. They aid in keeping the fish in a neat, orderly pattern. Some fish do not have lateral lines, nor the sensitive cells, and thus rely on their eyesight. Research suggests that if fish are blinded and their lateral lines cut, schooling does not take place; but if the lateral lines are left in place, the fish are still able to school. The lateral lines are especially important to fish living in the highly murky waters of the estuarine environment where sight is not particularly useful. The silver strip of the Atlantic silversides (Menidia menidia) affords us a good representation of the lateral lines of a typical species.

We are now ready to attempt a definition of schooling—no easy thing to arrive at. An accepted version could be a "grouping of fish based on mutual attraction and exhibiting a geometrical relationship." We say "mutual attraction," for fish of different species are almost never found intermingled. Fish stay with their own kind in a schooling configuration.

Schooling has some other interesting aspects. In the spring along the New England coast the alewife (Pomolobus pseudoharengus), in response to an ancient biological urge to reproduce, begins to form in large schools. They begin just where the rivers pour into estuaries and then, seemingly without a central signal, they migrate up the rushing currents. So large are their numbers that the bottom of the stream cannot be seen, and the whole picture is one of wriggling, bluish bodies swimming against the current. Alewives are "anadromous" fish that, much like salmon and shad, mature in salt water but spawn in fresh water. (Eels, on the other hand, are "catadromous," meaning just the reverse—they grow in fresh water and spawn in the sea.) the shad (Alosa sapidissima), first cousin to the alewife, also schools in large numbers in the spring. They are the source of the highly prized "shad roe," the millions of eggs that will not reach maturity because they are frying in our breakfast pans.

In many ways fish schools are much like herds of land animals or flocks of airborne birds. There is that undefined need to stay together. In some instances this herding has been the undoing of certain species. The now-extinct passenger pigeon flocked in such staggering numbers that it was rather a simple task in the predawn hours to take a club and sweep a branch of roosting birds into a sack for future eating. There are stories of the sky being darkened by the passage of these relatives of today's mourning doves. For centuries, wildebeest and antelope have formed huge herds that have crossed the endless African plains in search of greener pastures or to migrate to their ancestral breeding grounds. Indeed, if one looks at the huge cities of today's society one wonders if we humans are not prone to schooling. We live and move in vast numbers controlled by the technology of our society.

TUNA

By Elizabeth Gibbs

Tuna are finfish belonging to the tribe Thunnini, a sub-grouping of the mackerel family (Scombridae), which also includes the mackerels, bonitos, and the skipjacks. Species of tuna found in Northeast waters include albacore (Thunnus alalunga), yellowfin (Thunnus albacares), blackfin (Thunnus atlanticus), bigeye (Thunnus obesus), northern bluefin (Thunnus thynnus), and skipjack (Katsuwomus pelamis).

Physical Characteristics

The tuna is a streamlined fish, stout in the middle and tapering to points at either end. Two closely spaced dorsal fins rise from its back. The first is depressible–it can be laid down, flush, in a groove along the fish’s back. The second dorsal fin and corresponding anal fin are long and pointed, resembling a sickle. Seven to 10 yellow finlets run between these fins and the tail, which is lunate–curved like a crescent moon–and tapered to pointy tips. The caudal peduncle, to which the tail is attached, is very slender, with three stabilizing keels on each side. The tuna’s dorsal side is generally a metallic dark blue color, while the ventral side, or underside, is silvery or whitish.

Size

Atlantic tunas vary greatly in size, from the skipjack and blackfin, which rarely exceed three feet (90 cm) in length, to the northern bluefin–the world’s largest living bony fish–which can attain a length of over 10 feet (300 cm) and weigh well over half a ton. The largest bluefin ever caught on a rod and reel–in Nova Scotia in 1979–weighed in at 1,496 pounds. Common sizes for the bluefin range from 15 inches to roughly 6.5 feet (40 to 200 cm), but the "giants" of this species, which live in the Atlantic, are longer than 77 inches and weigh over 310 pounds. Yellowfin and bigeye tunas reach a maximum length of about six feet (190 cm), while albacore generally grow no longer than four feet (120 cm).

Reproduction and Longevity

The age of tuna at sexual maturity ranges from about three to five years, depending on the species. A spawning female may release as many as 100,000 eggs per 2.2 pounds (1 kg) of body weight. This means that a 100-kg female would produce as many as 10 million eggs in a spawning season. After about 30 hours, the eggs are ready to hatch, but very few survive to adulthood. Tuna grow rapidly and are long-lived. Bigeye and albacore, for instance, have been estimated to live nine or more years, while bluefin are thought to reach an age of over 30 years.

Distribution

Tuna are considered epipelagic-to-midwater fish, inhabiting the upper and middle layers of ocean water, to a depth of 1,600 feet or more (500 m), depending on size and species. They are found in oceans the world over, except in polar seas. They roam long distances, following extensive north-south and even transoceanic migration patterns. Scientists and international organizations have tracked these patterns by the use of tagging. Fish tagged in the Bahamas have been recovered in Norway and even Uruguay. Others tagged in the Northeast have appeared off the coast of Europe. Tagged bluefin tuna have been known to travel over 4,800 miles (7,700 km) across the Atlantic in just 119 days—an average, assuming the fish swam in a straight line, of over 40 miles (65 km) per day. While yellowfin tuna seem to make less extensive journeys–most have been recaptured within 1,000 miles (1,600 km) of tagging–they have been known to travel over 3,100 miles (5,000 km).

Tuna migrate on a yearly cycle. Northern bluefin, for example, arrive in waters off the coast of the Northeast by June of each year and depart in late autumn. The species may be found as far north as Newfoundland in the summer, and travels as far as 40 degrees south of the equator during the winter. Northern waters provide the fish with rich feeding grounds, where they can grow and store fat as an energy source for migration. They then return to their specific spawning grounds–the Caribbean region in the case of the bluefin–each year. Some researchers suspect that there are two separate populations–eastern Atlantic and western Atlantic–of the northern bluefin, although others believe that there is only one population, which commonly migrates across the Atlantic.

Physiology and Behavior

Tunas have a circulatory and respiratory system that is unique among fish, enabling them to maintain a body temperature slightly higher than the surrounding water. This additional heat, when transmitted to oxygen-rich blood, gives an extra boost to already powerful muscles, permitting the bluefin tuna, for instance, to reach speeds of over 40 miles per hour for short distances. The tuna’s steady, powerful swimming sustains a uniquely high metabolic rate, which permits its extraordinary growth rate. This also places a large oxygen demand on the fish, requiring tuna to swim continuously in order to meet that demand. Tuna must swim at a rate of at least one body length per second to pass enough oxygen over their gills.

Tuna normally travel in small schools ranging from six to as many as 40 fish, all of the same size but often including several species. The very large tuna, over 500 pounds (225 kg), are usually solitary.

Tunas are agile predators, often feeding on smaller, particularly schooling, fishes. The species of prey depends on what is locally available at the time, but common species include herring, menhaden, hake, cod, bluefish, whiting, and mackerel, as well as squid and crustaceans such as shrimp.

Because of their size, large tuna have few predators besides billfish, some sharks, toothed whales such as orcas and pilot whales, and humans.

Fishery

Among the world’s most valuable commercial species, tuna are fished in over 70 countries worldwide, and marketed in fresh, frozen, or canned form. The most important commercial species caught in the Northeast are yellowfin, bigeye and bluefin tunas.

Japan and the United States are the largest consumers of tuna, using about 36 percent and 31 percent, respectively, of the world’s catch, although U.S. consumption of canned tuna has declined somewhat since the "dolphin safe" controversy beginning in 1990.

Methods of Catch

The majority of tuna are harvested using one of three methods: pole and line, longlining, and purse seining. The method used varies locally and among species. Pole and line fishing from baitboats is the technique used for over 40 percent of the world’s catch. Longlining, as the name implies, involves the setting of a line at the surface that stretches for as many as 80 miles (130 km). Baited hooks, set at depths of 180 to 500 feet (55 to 150 m), are suspended at intervals along the line. Purse seines are large nets–as much as a mile (1.6 km) long and 600 feet (185 m) deep–that are set in a circle around a school of fish, then drawn closed at the bottom, like a draw-string purse. All three of these are among the methods used in the Northeast.

The Dolphin-Tuna Issue

In recent years, the consumption of tuna became an issue of conscience as well as taste, as attention has focused on tuna fishing-associated deaths of dolphins. Yellowfin tuna have been caught using the highly efficient method of "dolphin fishing." Yellowfins swim closely with several species of dolphin. When the dolphins surface to breathe, fishing boats set their nets around both tuna and dolphin, sometimes drowning the dolphins. International efforts to cut dolphin kills during tuna seining reduced the number of dolphins killed from over 400,000 per year in the 1960s to 2,500 in 1996. On August 15, 1997, President Clinton signed a bill that redefines "dolphin safe" tuna. Prior to this law, "dolphin safe" meant that tuna was not taken in association with dolphins. As a result of the law, "dolphin safe" now means that no dolphins were harmed during the catch. Labelling changes took place in 1999.

Bycatch Reduction

Dolphins are not the only marine animals that have been harmed in the process of catching tuna. Other animals, such as whales, sharks and sea turtles, have been adversely affected by tuna and other pelagic fishing. Take reduction plans mandated by the amended Marine Mammal Protection Act are designed to reduce bycatch significantly.

Sportfishing

Sportfishing for tuna is also popular, especially on the East Coast, where giant bluefin are much in demand although increasingly rare. The peak season for the sport fishery in this region is late August through October. The annual Rhode Island Tuna Tournament, incorporated in 1958, became one of the world’s largest such events in the late 1960s and early 1970s. It continues today, but with a 50 percent drop in participation from its heyday due to a reduction in the numbers of tuna to be found off the Rhode Island coast. Increasingly, emphasis is being placed on "tag and release" fishing, both in the tournament and in sportfishing for tuna in general.

Conservation and Management

Conservation and management efforts are the primary responsibility of international organizations such as the International Commission for the Conservation of Atlantic Tunas and the Inter-American Tropical Tuna Commission, which set catch quotas on tuna catch and operate research and conservation programs. In the United States, the National Marine Fisheries Service (NMFS) produced the Final Fishery Management Plan for Atlantic Tunas, Swordfish, and Sharks in 1999 to regulate the U.S. tuna fishery.

The bluefin has been under management, including catch quotas, in the western Atlantic since the 1980s as a means for rebuilding its stocks, yet there is much controversy over whether the quotas are sufficient to stem a continued drop in numbers. To better understand the dynamics of the Atlantic bluefin tuna fishery in the United States, the NMFS has instituted an automated catch reporting system for recreationally caught bluefins, as well as a large pelagic survey. These efforts will help monitor quotas.

Additional Reading:

Bigelow, H.B. and W.C. Schroeder. Fishes of the Gulf of Maine. United States Department of the Interior, Fish and Wildlife Service, Fishery bulletin 74, Vol. 53. Washington, D.C.: 1953.

Freeman, B.L. and L.A. Walford. Anglers’ Guide to the United States Atlantic Coast: Fish, Fishing Grounds and Fishing Facilities, Section II, Nantucket Shoals to Long Island Sound. Seattle, Wash.: 1974. For sale by the Government Printing Office, Washington, D.C.

Joseph, J., W. Klawe and P. Murphy. Tuna and Billfish: Fish without a Country. La Jolla, California: Inter-American Tropical Tuna Commission. 1988.

Miyake, Makoto. Field Manual for Statistical Sampling of Atlantic Tunas and Tuna-like Fishes. International Commission for the Conservation of Atlantic Tunas, Madrid, Spain. 1990.

NMFS website. http://www.nmfs.noaa.gov

National Oceanic and Atmospheric Administration. Final Fishery Mangement Plan for Atlantic Tuna, Swordfish, and Sharks. Prepared by: Highly Migratory Species Management Division, Silver Spring, Maryland.

NMFS Fishery Market News