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Maryland’s Big Game Billfish - August 9, 2015

Billfish are among the most prized of big game fish in North America, as demonstrated by tournaments such the White Marlin Open. They belong to the taxonomical family Istiophoridae, which is distinguished by a long, spear-like rostrum that is used to stun and kill prey and they have prominent dorsal fins that run along a large portion of their body to help with swimming stability and control. The billfish family includes species such as Sailfish, Spearfish, Swordfish and Marlin. These apex predators are highly migratory and can be found throughout the world’s oceans, primarily in tropical and sub-tropical waters. The species found off Maryland’s coast include Swordfish, Sailfish, Roundscale Spearfish, Blue Marlin, and the famed White Marlin. 

Swordfish have the widest range of billfish due to their ability to tolerate a wide range of temperatures as they search for food. Warm water habitats are preferred but Swordfish have been found in waters where the temperature was near freezing. Unlike other billfish, Swordfish actually belong to the taxonomical family Xiphiidae. The bill of a Swordfish is much longer proportionally to its body than that of other billfish species, hence their common name. Their diets typically consist of cephalopods such as squid and other small fishes. 

Sailfish are some of the fastest fish in the ocean and can reach speeds of more than 68 miles per hour which is about the same speed as a cheetah. There are two subspecies of sailfish, the Indo-Pacific Sailfish and the Atlantic Sailfish. Sailfish are distinguished by their large and colorful dorsal fins, which give them their common name. They tend to eat small fish such as sardines and anchovies, and cephalopods like squid and octopus. A unique characteristic of Sailfish is that they have the ability to change their coloration based on their level of excitement. Their coloration can change from dark blue and white to light blue with yellowish stripes to confuse prey and help make it easier to capture and eat. 

The Roundscale Spearfish is a recently discovered species of billfish. Prior to this discovery, this species was often mistaken as either White Marlin or Hatchet Marlin due to their similar appearances.  The primary differences in appearance between a White Marlin and a Roundscale Spearfish are truncated anal fins and distinct round scales on the Spearfish. White Marlins have rounded anal fins but occasionally they can appear to be truncated similar to the Spearfish. Genetic testing on White Marlin caught at tournaments shows that about 18% of all White Marlin weighed in are actually Roundscale Spearfish. 

Blue Marlin are one of the largest billfish species and are easily recognized by their cobalt blue and silvery coloration.  They can reach lengths of over sixteen feet and weigh over 2,000 pounds. Females tend to be significantly larger than male Blue Marlins. Similar to Sailfish, Blue Marlin are divided into two subspecies, the Indo-Pacific Blue Marlin and the Atlantic Blue Marlin. The Indo-Pacific subspecies tend to be larger than our Atlantic subspecies. Their diet consists of squid and fish such as mackerel and tuna. They will use their bills to slash through schools of fish and will return to eat their wounded prey. 

White Marlin are only found in the tropical and warm temperate waters of the Atlantic Ocean. They are among the smaller species of billfish with lengths up to nine feet and weighing up to 200 pounds. Similar to Sailfish, the White Marlin can change their coloration based on their level of excitement. The primary predators of White Marlin are sharks such as the Great White Shark and Shortfin Mako. Due to the recent discovery of the Roundscale Spearfish, population estimates for the White Marlin may be overestimated as the two populations were counted as one. Females tend to live longer and be larger than male White Marlin.  

Marlin populations are in decline due to increased pressure from the commercial fishing industry. In the United States, only the recreational fishery is allowed to fish for billfish. Commercial fishing vessels are required to release all billfish however, 25-30% of all marlin caught on commercial longlines are dead prior to arrival of commercial vessels. Commercial fishing methods such as longlines, gillnets, and purse seines are responsible for about 99% of reported Atlantic marlin kills. Recreational fishing is only responsible for less than 1% of marlin kills due to their catch and release methods to help conserve the population. Circle hooks are being used by the recreational fishery as they have been shown to reduce release mortality and are more likely to hook in the jaw reducing injury. 

Billfish are apex predators in the food chain and help maintain healthy marine ecosystems. They are touted as prized game fish and bring in millions to the local economy by way of billfish tournaments. It is important to preserve these fish so events such as the White Marlin Open may continue in the future. 

 

Katherine Phillips is the Science Intern for the Maryland Coastal Bays Program. 



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