Working worldwide to advance the conservation of Billfish & associated species to improve the health of oceans & economies.

Did You Know?



Welcome to our Did You Know blog! Billfish and related species, like tuna and swordfish, are amazing creatures and set themselves apart from other fish. Every week, The Billfish Foundation would like to share some of the most interesting facts and stories involving these fish. What some of the things that surprised you about these magnificent animals? #didyouknow

August 30, 2017 – Managing (And Sharing) A Global Fish

Considering the vast distances they can traverse, billfish are known as highly migratory species (HMS). Other fish such as tuna and sharks are also considered HMS, and all have particular considerations for management.  Because of their migratory nature, these fish do not respect national boundaries and instead travel between nations and even continents. Unlike fishery management plans for snapper in the Southeast or lobster in Maine, plans for billfish have to consider many other countries.

There are several Regional Fishery Management Organizations (RFMOs) for the world’s oceans, and these bodies are responsible for deciding plans for HMS, including billfishNations as well as stakeholders such as commercial fishing interests and environmental organizations are members to such bodies. TBF is a part of several advisory committees to RFMOs, and TBF President Ellen Peel recently served as the recreational commissioner for ICCAT. These RFMOs conduct their own research and stock assessment of species, and then determine the best management route based on the science. This includes setting total catch limits which are then divided among contracting parties. Sometimes the allocation is equal, other times select nations are given more quota than others or a country that does not catch much of a particular species may trade with one who does.

Once the quota is disbursed, each nation is then responsible for implementing relevant regulations to keep harvest of a species within their allotted quota, described as total tonnage or number of individual fish. The quota may be used to account for bycatch—when a species is caught unintentionally—in industrial fishing like longlining, it may be used for the recreational sector to allow harvest of a certain number of marlin, or it may be used by the commercial fishing sector in some countries where billfish are targeted. The allocation of quota depends on the voice from each sector.

This White marlin traveled from the U.S., where it was tagged off of Montauk, to Brazil where it was recaptured.

For instance, the International Commission for the Conservation of Atlantic Tuna (ICCAT) decided in 2015 to maintain reduced quota that was established in 2012 for several billfish species, setting the limit for blue marlin at 2,000 tons each year, and the limit for white marlin and spearfish at 400 tons each year through 2018. The tonnage was then distributed to member nations. When it comes to blue marlin, Brazil is limited to 190t, The EU limited to 480t, Ghana limited to 250t, Japan limited to 390t, and several more. In this same measure, the United States’ landings were limited to 250 recreationally-caught Atlantic blue marlin and white marlin/spearfish combined annually. And what happens if you exceed your allotted landings quota? Well the overage is then subtracted from next year’s allowance.

Beyond setting the limits, the international RFMOs also publish recommended management measures for billfish, including promoting safe handling practices, requiring minimum sizes, observer coverage, and regulations on sale of billfish products. It is, however, up to the member nation to take these recommendations home and create domestic law.

On the global playing field, the U.S. commercial fishing industry is by far the leader when it comes to fisheries conservation measures. The U.S. has passed several laws regarding billfish and the sale of Atlantic billfish has been prohibited since 1988. Most recently the Billfish Conservation Act passed in 2012 making it illegal to sell billfish and billfish products, with the exception of billfish caught in Hawaii or American Pacific areas where there is a billfish fishery.


August 16, 2017 – Who Would Prey on the Apex Billfish?

Commercial fisherman Jason Moyce was surprised to catch a mako shark with a marlin bill stuck through its body

Billfish such as sailfish and marlin are predators themselves, but that’s not to say they aren’t vulnerable to predation. Naturally billfish are most susceptible to becoming prey as juveniles, eaten by tunas, wahoo, dolphinfishes and even larger billfish.

At the adult stage, when a billfish is a fully formed apex predator, there are fewer fish capable of taking aim. For starters, sailfish are one of the fastest fish in the world, reaching upwards of 60 miles per hour. Then there’s the bill to consider if you’re a predator, and billfish rostrums, as they’re referred to, have been recorded stunning, slicing and impaling not only prey fish but also oil rigs and the occasional angler.

Mako bite marks on a swordfish (credit: Chad Macfie, FL Museum)

So who could possibly hunt the full grown sailfish or marlin? The only answer is a large, pelagic shark, such as the shortfin mako or great white.


Great white sharks have developed a vertical predation pattern that works well in surprising prey, and will feed on most anything caught on a longline, such as a billfish. Mako sharks are one of the other fastest fish in the sea, and are known to feed on swordfish. In fact, there have been shortfin makos captured that bear scars apparently due to encounters will billfish, and one mako was even reported impaled through the eye with the bill of a swordfish.


August, 8 2017- Throwing Out, Not Throwing Up

Most fishermen that bring a billfish to the boat with its stomach hanging out of its mouth would think they’ve gut hooked it and destined their catch to a painful death. Luckily, this is typical behavior and is not a sign of any damage caused to the fish!

The visibly expelled stomach of a sailfish looks far more gruesome than it actually is, a natural process for billfish. Photo Credit: Sport Fishing Magazine

Billfish, just like humans, regurgitate their stomach contents when they are having trouble digesting or want to expel unwanted objects from their digestive tract. However, instead of throwing their stomach contents  “up” and out their mouth like humans and many other land animals do, many fish and shark species expel their entire stomach organ inside out from their mouth, emptying the contents within. The scientific term for this seemingly grotesque behavior is gastric eversion and is an essential feature in the digestive system of these animals. Large bones, spines, and shells are difficult and even somewhat dangerous to digest, so many large predators have developed this ability to avoid processing troublesome parts.

Fishermen can often witness this behavior when catching sharks or billfish, like the sailfish pictured above or in this video of a hooked shark. Man-made hooks are new to these species, as they have existed for millions of years. Often, their instinct is to treat a hook much like a bone or spine lodged in their mouth or throat, using gastric eversion and, more commonly seen, head shaking to dislodge the unwanted item.

So, going forward, remember that a protruding stomach does not necessarily mean death. As long as your hook is where it’s supposed to be, (its mouth) a stomach exhibiting billfish has suffered no internal injury should be treated no different than usual!

August 1, 2017- Mimicking Nature

Oceanic ecosystems are some of the oldest in the world. According to the Smithsonian, marine animals have existed for over 500 million years, while land animals have “only” been around for 300 million years. These hundreds of millions of years in evolutionary time have shaped the animals we know today into near perfect specialists of their environment. Every physical and behavioral feature they possess is meant to maximize their ability to benefit from their surroundings.  Biomimicry is the practice of utilizing nature’s highly adapted and efficient designs as a template for modern innovations. Check out a few of the most interesting products and designs inspired by pelagic species.

Sailfish Speed  

The sailfish-inspired McLaren P1 racing down a track in England. Photo Credit: Top Gear

In today’s supercar industry, hi-end auto manufacturers are competing to make the fastest and best looking cars in the business. McLaren found their inspiration for both speed and beauty in the fastest fish in the ocean- the sailfish.

Sailfish using its speed to propel itself out the water. Photo Credit: Chris Sheeder

According to the BBC, McLaren’s design director, Frank Stephenson, was on holiday in the Caribbean and noticed a sailfish mounted on the wall of the resort he was staying at and was lucky enough to meet the man who caught it. During their discussion, the man mentioned that it is an amazing feet to catch a sailfish, due to their record breaking speed- and the moment he heard “speed,” the light bulb went off in Stephenson’s head. The moment he returned to headquarters in London, Stephenson and his team began researching what features allow sailfish to reach such high speeds. They found that the small scales found on sailfish skin create microscopic vortexes as water flows over them, reducing drag considerably. Stephenson and his team texturized the air ducts leading into the engine, mimicking sailfish skin, which increased airflow to the engine by nearly 20 percent, according to the BBC. In addition they styled the car’s exterior around the sailfish hydrodynamic profile. You can even see how the raised “fin” on the car’s roof takes after the small fins behind the sailfish main sail. These maximize airflow and help stabilize the car at high speeds.

Heating Like a Tuna

A tuna’s internal heating system can be translated to building design in order to maximize heating efficiency. Photo credit: Building Services Blog

Tuna’s teardrop body shape and retractable fins make them some of the most efficient swimmers in the ocean, and they need to be. Tuna, like the bluefin and yellowfin, often make very long transocean journeys. It isn’t unlikely that a bluefin tuna born in the Gulf of Mexico could one day be caught off of the coast of Italy. A less well known physical feature that allows tuna to make these long journeys while catching prey and avoiding predators is their internal heating system. As the cross section of the tuna above demonstrates, tuna have two noticeable types of muscle. A darker, denser muscle at the core and a more light muscle surrounding the rest of the fish. Tuna have one of the most efficient heating systems in the ocean, allowing them to swim fast and maintain a high body temperature in colder waters. The darker muscles at the center provide the main propulsion for swimming and operate at a very high metabolic rate when in motion that produces large quantities of heat.  As these muscles work, they radiate the large quantity of heat outwards, efficiently heating the tuna’s entire body. Because of its efficiency, building engineers have started to utilize similar designs when planning entire building blueprints by placing office spaces and heating systems in the interior and open passageways around the exterior. For example, the headquarters for Siemens-Gamesa Renewable Technologies in Spain mimics a tuna’s cross section with its cylindrical exterior and internally situated offices, meeting rooms, and heaters.

The headquarters of Siemens-Gamesa Renewable Technologies in Spain utilizes an ultra-efficient heating design much like that of the tuna. Photo credit: AECCafe










Swimming with Shark Skin

Speedo replicated the denticles found on shark skin to help reduce drag in their Olympic swim suites. Photo Credit: Science In The news

Speedo took an up close look to a shark’s sandpaper like skin when designing their new Fastskin Series swimsuit. A shark’s skin is covered by tooth like teeth called denticles. Apart from protecting the shark from abrasion and penetration, these tightly knit denticles help propel the shark forward. As water moves over the denticles, small vortexes are formed behind and beneath the structures. The high pressure formed by the vortexes produces an almost reverse-vacuum effect that propels the shark forward. These swimsuits significantly enhanced swimmers’ performance- over 80 percent of the medalists at the 2000 olympic games were wearing the shark inspired suite.

Other Examples of Biomimicry:

July 25, 2017- Hunting Tool or Weapon?

Did you know that in 2010 a single blue marlin cost British Petroleum (BP) 100 million dollars in damages? The same features that make marlin one of the most desired fish to catch- their size, speed, and strength- makes them a very dangerous weapon when combined with their very strong and sharp bill. According to Bloomberg, a blue marlin punctured one of the highly protected, ultra thick main pipelines leading to BP’s Plutonio field storage barge off of the west coast of Angola, preventing 900,000 barrels of oil from being exported for sale and over 100,000 million dollars in losses. Thankfully, very little oil was leaked into the water.

The bill of a blue marlin that punctured this ultra-thick BP oil pipeline, costing BP over 100 million dollars. Photo Credit: Africa Travel Channel


Here are some more strange, gruesome, and unexpected instances where billfish (and swordfish) got wild with their bill.

A commercial fishing trip off the coast off Bermagui, Australia caught a large mako shark (below). Upon inspecting the shark and getting it ready for processing, the crew noticed that it had an object protruding from both sides of its body. It quickly became apparent that it was the bill of a large marlin that had penetrated through the shark just under the dorsal fin and broken off. The bill had started growing barnacles, signifying that the shark had been carrying the burden for quite some time. As far as scientists are aware, billfish and swordfish primarily utilize their bills to kill or stun smaller prey, not to attack larger animals. There have been a surprising amount of instances, however, like this one, that prove these fish aren’t scared to go on the offensive.

A mako shark was lucky to survive being impaled by a large marlin and had lived for quite some time with the bill in its back. Photo Credit: Narooma News Online



Some of the craziest documented attacks have been carried out by swordfish in the deep. In the first picture, a camera catches the instant a small swordfish penetrated a deep diver’s welding gear just above their oxygen tank- Click here to watch the full video. The footage clearly shows the swordfish singling out the diver, charging sword-first at speed. The second photo shows a swordfish lodged into the hull of Alvin, a deep sea Navy submarine. The Alvin is famous for voyage missions to survey hydrothermal vents, decommissioning sunken WWII bombs, and exploring the wreck of the Titanic. According to the Smithsonian, in 1967, Alvin was exploring deep sea corals in 2000 feet of water off the coast of Florida when a swordfish attacked and got stuck to its hull. The swordfish was just under 200 pounds and hit the sub so hard the majority of its head was jammed into a small gap in the sub’s exterior and was brought to the surface.

A deep sea welder is charged and his gear impaled by a swordfish, luckily the sword just missed the oxygen tank. Photo credit: Luis Nascimento

The famous U.S. Navy Submarine, the Alvin, was impaled by a swordfish in 2000 feet of water off the coast of Florida. Photo Credit: Woods Hole Oceanographic Institute

More common instances of billfish impalement are those associated fishing. There have been many instances of billfish impaling boat hulls and transoms, as well as the anglers themselves, sometimes even causing fatalities. In 2008, a young man off the coast of Panama was bringing in what looked to be a tired 600 pound black marlin when it suddenly jumped bill first into the boat. According to the Travel Channel, the marlin’s bill penetrated through the man’s mouth and lodged into his throat. Thankfully, he survived the encounter.

Billfish bone has a density and strength much closer to that of large mammals like horses than it does to most fish bone. This strength is accompanied by a dangerously sharp tip, which is why indigenous peoples around the world used bills and (swordfish) swords as daggers and spears. A 500 pound animal wielding this sort weapon is part of what makes these fish some of the most exciting fish to pursue but also some of the most dangerous. It’s important that anglers, divers, and even submarines never let their guard down around these incredible, powerful fish.

July 18, 2017- From Cat Food to Million Dollar Fish 

Did you know that the bluefin tuna sold for 1.8 million dollars in 2013 at the famous Tsukiji Fish Market in Tokyo would have probably been used for cat food prior to 1970? The tuna was sold in the traditional new year auction that is famous for attracting astonishingly high bids for bluefin. The buyer, Kiyoshi Kimura, has won the coveted tuna auction since 2011; and, although not rivalling 2013’s exorbitant price, has spent around half a million dollars on multiple other fish. Bluefin meat (maguro), more specifically the fatty meat around the belly (toro), is of the most desired meats by sushi chefs and consumers worldwide; but believe it or not, just  50 years ago bluefin meat was considered nearly worthless.

A flesh sample being taken from a bluefin tuna at the Tsukiji Fish Market in Tokyo on the first Saturday of 2013 – It would eventually be sold for 1.8 million dollars

According to the Smithsonian, during the 40’s, 50’s and 60’s, when tuna sportfishing was becoming exceedingly popular, bluefin were sought out by anglers due to their massive size –  measuring larger than 14 ft and weighing more than 1500 pounds. During that period, however, tuna were perceived to have little to no food value for the human consumer. They were often weighed, pictured, and then dumped back into the ocean or ground up for cat and dog food. The drastic turnaround from pet food to million dollar sushi meat began in the 1970’s when a palate shift occurred in Japan. Rather than favoring only light, white meat fish, an increase in beef consumption around the same time shifted Japanese palates toward the dark, rich meat of the bluefin. Once the appreciation for bluefin as a raw delicacy spread to the U.S. and Europe, the bluefin became one of the most sought after fish in the world.

An Atlantic bluefin tuna feeds in the cold waters off of the coast of Canada

Commercial fisherman utilizing large, encircling purse seine nets began targeting the giant schools of North Atlantic bluefin to sell to Japan. Intense overfishing has led to a severe depletion of bluefin stocks worldwide, where populations of the three bluefin species are less than 10 percent of their levels prior to the 1970’s. Although currently considered endangered, a high demand still exists.


A bluefin tuna tagged by Captain Eric Stewart near Cape Cod, Massachusetts migrated 5,000 miles before being re-captured off of the island of Malta in the Mediterranean Sea

On the bright side, over the last 20 years, there have been some strong conservation efforts worldwide trying to halt overfishing. The United States has been a standout leader in conservation efforts, establishing rigid regulations and low catch quotas for both commercial and recreational bluefin fisherman. However, conservation has proven difficult due to the bluefin being a highly migratory fish, often making multiple trans-Atlantic trips in its lifetime. In order to help synchronize efforts, much research is needed in order to understand where these fish migrate, breed, and feed. TBF is proud to collaborate with the Large Pelagics Research Center in their quest to gather this vital data through large scale tagging operations. Hopefully efforts such as this can help in preserving these incredible fish for years to come.

July 11, 2017 – Billfish Eye Heaters

Did you know that billfish, although cold blooded, can heat up their eyes to help them see better? Billfish and tuna are considered some of the ocean’s most athletic apex predators- and they have to be. Picking off small, agile baitfish from a dynamic school in the open ocean requires extreme speed, precision, and agility. Recent science has revealed one of physiological adaptations that gives these fish a major advantage over their prey- an internal eye and brain heating system.

The ability to heat their eyes allows billfish and tuna to react to visual cues much faster than their prey

Fish are ectotherms (cold blooded), meaning that their body heat is heavily dependent on the ambient water temperature. But billfish, swordfish, tuna, and most sharks possess the unique ability of heating their eye muscles and certain parts of their brain. According to a 2005 study, these fish have muscles tucked behind their eyes and adjacent to ocular nerves that vibrate to create heat. By heating their eyes 10-15 degrees celsius above the ambient water temperature, these fish significantly enhance their ability to detect and respond to motion. The same 2005 study found that fish with these heating muscles can pick up and react to visual cues up to ten times faster than fish whose eyes are the same temperature as the surrounding water. This physiological trait is especially important in swordfish, since the temperature in their deepwater habitat can reach near freezing.

The opah, also known as the moonfish, is the only true “warm blooded” fish

The opah is the only truly “warm-blooded” fish. According to National Geographic, opah generate their heat from metabolic activity, just like most other fish. But rather than losing heat to the colder ambient water, they conserve it and circulate the heat throughout their entire body, warming their muscles, heart, and brain.

June 29, 2017 – Billfish Breathing

Did you know that the cone shaped mouth on billfish is designed to do more than just maximize the fish’s hydrodynamic profile? Their large, smooth cone shaped mouths funnel massive amounts of water over their gills as they swim. Billfish and tuna-like species are ram-ventilators, meaning that they breathe by swimming with their mouth open, forcing water through their gills. In contrast, fish like groupers take in water by creating a vacuum in their mouths to “suck” it in, a method called buccal pumping. This allows them to breathe while stationary, which is why you may often find them motionlessly hiding out under a rock outcropping waiting for unaware prey.

Cone shaped mouths help billfish funnel massive amounts of water through their gills

The fact that billfish can only breathe while swimming means that they must constantly be moving at a decent pace to ensure that they receive enough water to their gills. This is why it’s crucial to keep them moving forwards in the water when reviving them. No movement… no oxygen!

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