Blue marlin are one of the world’s largest bony fish and although adult males seldom exceed 150 kg (300 lb), females may reach far larger sizes well in excess of 1,000 lbs. A Pacific blue weighing 1,805 lb caught in 1970 by a party of anglers fishing out of Oahu, Hawaii aboard the charter boat Coreene C skippered by Capt. Cornelius Choy (this fish often referred to as ‘Choy’s Monster’) still stands as the largest marlin caught on rod and reel. This fish was found to have a yellowfin tuna of over 155 lbs in weight in its belly. In the Atlantic the heaviest sport fishing capture is Paulo Amorim’s 1,402 lb fish from Vitoria, Brazil. Commercial fishermen have boated far larger specimens, with the largest blue marlin brought into Tsukiji market in Tokyo supposedly weighing a massive 1,106 kg.
Large blue marlin have traditionally been the most highly prized angling captures, and a fish weighing 1,000 lb (450 kg), a “grander”, has historically been regarded by blue and black marlin anglers as the benchmark for a truly outstanding catch. Today, much effort is still directed towards targeting big blue marlin, but smaller blues are also sought by anglers fishing lighter conventional tackle and big game fly fishing gear.
Blue marlin occur widely in the tropical oceanic waters of the Atlantic and the Indo-Pacific, with many fish making seasonal migrations into the temperate waters of the northern and southern hemispheres to take advantage of feeding opportunities as those waters in spring and summer. Warm currents such as the Gulf Stream in the western Atlantic and the Agulhas Current in the western Indian Ocean serve as oceanic highways for blue marlin migration and have a major influence on their seasonal distribution. Blue marlin have a limited ability to thermoregulate, and the lower limit of their temperature tolerance is thought to be in the region of approximately 20 degrees Celsius (68 degrees Fahrenheit) although individual fish have been caught in cooler temperatures. Larger individuals have the greatest temperature tolerance, and blue marlin encountered at the limits of their range tend to be large fish. This wide distribution brings blue marlin in contact with anglers in many parts of the world.
Blue marlin are eclectic feeders preying on a wide range of prey species and sizes. Scientific examination of blue marlin stomach contents has yielded organisms as small as miniature filefish. Common food items include tuna-like fishes, particularly skipjack tuna and frigate mackerel (also known as frigate tuna), squid, mackerel, and scad. Of more interest to sport fishermen is the upper range of blue marlin prey size. A 72-inch white marlin has been recorded as being found in the stomach of a 448 lb blue marlin caught at Walker’s Cay in the Bahamas, and more recently, during the 2005 White Marlin Open, a white marlin in the 70 lb class was found in the stomach of one of the money-winning blues. Shortbill spearfish of 30 to 40 lb have been recorded as feed items by Kona blue marlin fishermen. Yellowfin and bigeye tuna of 100 lb or more have also been found in the stomachs of large blue marlin.