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Fast, predatory, warm-water fish of the family Istiophoridae characterized by having a long bill on the upper jaw that they use to stun their prey. The largest is the blue marlin (Maikaira nigricans), which in 25 years grows to a length of 4.5 metres (14.7 ft), and weighs up to 1,300 kilograms (2,866 lb). A relative, the sailfish (Istiphorus platypterus), holds the oceanic speed record, taking out 91 metres (300 ft) of line in 3 seconds—a speed of 109 kilometres per hour (68 mph).

Marlin generate such fast speeds by having red muscles, which are very rich in mitochondria that generate the muscle's energy. Heat is conserved in the muscle by the blood supply flowing through a counter-flow system keeping the muscle 10 °C (50 °F) warmer than the surrounding sea water. When they sprint, their main bulk of white muscle comes into action providing the additional power, but as in all sprinters, an oxygen debt quickly builds up and the white muscles become exhausted.

Marlin are prime sporting fish. In the USA alone there are 200,000 deep-water anglers, whose ambition is to catch a record-sized marlin. When long-lining was introduced in the 1960s, a quarter of a million marlin weighing 5,000 tonnes were caught annually in the Atlantic, but despite the conservation efforts of the International Commission for the Conservation of Atlantic Tunas (ICCAT), catches have fallen by 80%. ICCAT manages all the stocks of fishes that migrate transoceanically and are caught by long-lines and in purse seine nets in the open ocean. So serious is the problem that sea-anglers now use unbarbed hooks so any marlin they bring alongside can be released.

M. V. Angel

Subjects: Maritime History.

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