White marlin are often mistaken for roundscale spearfish (Tetrapturus georgii), leading to a miscount in population size until their genetic differences were established in 2001. To differentiate between the two species, a close external examination is necessary. White marlin scales have a rigid and rounded posterior region, while roundscale spearfish scales possess a broadband, round anterior end. Additionally, the distance between the anal opening and the anal fin provides another clue for species identification, as it is greater in roundscale spearfish compared to white marlin.
Initially classified as Tetrapturus albidus by Felipe Poey in 1860, white marlin shares its genus with other billfish species such as shortbill spearfish, Mediterranean spearfish, roundscale spearfish, and longbill spearfish. Fossil records indicate the existence of the Tetrapturus genus dating back 15 million years, while ancestral species like Palaeorhynchus can be traced as far back as 56 million years. However, genetic testing conducted in 2006 by Collette and colleagues suggested that white marlin and Indo-Pacific striped marlin should be reclassified under the genus Kajikia, differentiating them from Tetrapturus species.
White marlin, characterized by their round cross-section bill and forked caudal fin, possess a streamlined body structure designed for rapid swimming. Females of the species are typically larger than males. Their dorsal fin, consisting of 28 to 46 rays, extends along the majority of the dorsal portion of the body. White marlin exhibit sexual dimorphism and display a distinctive coloring pattern—dark blue dorsal side and dirty white ventral side—that aids in countershading. The species also features prominent pectoral fins, pelvic fins, anal fins, and a noticeable lateral line.
White marlin inhabit the tropical and subtropical Atlantic Ocean between the latitudes of 45° N and 45° S. They are commonly found in the Gulf of Mexico, Caribbean Sea, and Mediterranean Sea, with occasional vagrants reported in regions like Brittany, France. The species prefers waters deeper than 100 m, although it tends to stay near the surface despite this preference. White marlin can be encountered near banks, shoals, and canyons, showcasing their adaptability to various locations within their range.
As apex predators, white marlin occupy a prominent position in the oceanic food chain. They exhibit a diverse diet and consume prey that is manageable in size, including schooling flyingfish, small tuna, mahi-mahi (dolphinfish or dorado), and squid. White marlin are known to forage individually or in association with other predators, enhancing their foraging efficiency. They employ a unique diving technique, descending in a V- or U-shaped parabola to depths of about 200 m in search of submerged prey. This strategy allows them to exploit food sources beyond the surface.
The lifecycle of white marlin begins with large-scale spawning in warm tropical waters near the equator. Females can lay an impressive number of eggs, ranging from 190,000 to 586,000. Prime spawning grounds for white marlin include the Gulf of Mexico, Mona Passage, Southwest Bermuda, and northwest Grand Bahama Island. After spawning, the adults migrate back to the warm, shallow, equatorial waters each year. White marlin exhibit rapid growth, with males reaching sexual maturity at a length of only 153.2 cm LJFL and females maturing at 189.9 cm LJFL. The species boasts a lifespan of 15 years or more.
White marlin fishing is a significant industry in many well-developed countries, generating substantial revenue. However, due to the detrimental impact of angling on fish health, regulations are in place to limit the size of fish that can be taken. To maximize the chances of survival after release, federal regulations in the U.S. Atlantic, Gulf of Mexico, and Caribbean waters require white marlin to be kept in the water, boatside, during the handling process. Circle hooks, which facilitate quicker dehooking, are recommended for fishing billfish.
It is important to note that approximately 90% of the annual white marlin catch worldwide is considered accidental bycatch. These billfish often fall victim to gillnets or longline hooks intended for other fish species, resulting in increased predation by sharks, pilot whales, and killer whales. Recognizing the decline in white marlin populations, marine life agencies have implemented acts and plans to protect vulnerable species, including the Atlantic Tunas Conservation Act and the Magnuson-Stevens Fishery Conservation and Management Act. In the United States, billfishing is reserved for recreational purposes only.
Ocean City, Maryland, proudly holds the title of the "White Marlin Capital of the World." The city hosts the annual White Marlin Open, a renowned big-game tournament that attracts anglers from around the globe. This highly anticipated event often awards prizes exceeding a million dollars to the winning team. While the tournament encourages tag-and-release practices, winning marlins are occasionally brought back to the marina for size and weight verification. The 2016 White Marlin Open experienced controversy when the only qualifying fish was disqualified due to a polygraph test failure by the crew, leading to the denial of the $2.8 million prize.