Swordfish vs blue marlin: how to tell them apart

Swordfishup to 455 cm · 650.0 kg

blue marlinup to 500 cm · 636.0 kg · 20 years

SwordfishWorldwide in tropical, temperate and sometimes cold seas, including the Mediterranean, Sea of Marmara, Black Sea and Sea of Azov; from the surface to 2878 m, usually 0 to 550 m, at 5 to 27 °C, preferring 18 to 22 °C (FishBase). Oceanic, sometimes near the coast; moves to temperate or cold waters to feed in summer and back to warm water in autumn (FishBase). Mostly deep by day, at the surface at night (Wikipedia).

blue marlinTropical and temperate Atlantic, oceanic, from the surface down to 1000 m, at 22 to 31 °C (FishBase). Roughly 45° N to 35° S; scarcer in the eastern Atlantic, where it lives mostly off Africa between 25° N and 25° S (Wikipedia). Spends most of its time between the surface and 100 m, mostly near the surface at night; in summer its range expands north with warm currents such as the Gulf Stream (Wikipedia). In the northern Gulf of Mexico it prefers blue water (FishBase). FishBase lists the Indo-Pacific blue marlin (Makaira mazara) as a separate species, while many scientists and German Wikipedia treat it as one worldwide species, so Hawaiian fish count as the same species or not depending on the source.

SwordfishIn the Atlantic it spawns all year, mainly April to September in the Caribbean, the Gulf of Mexico, off Florida and in the southern Sargasso Sea (German Wikipedia); FishBase gives spring in the southern Sargasso Sea, at 0 to 75 m and about 23 °C. Off southern Brazil from November to February (Wikipedia). A 168 kg female carried 1 to 16 million eggs, a 272 kg female 29 million (FishBase).

blue marlinIn the North Atlantic from July to October (German Wikipedia); English Wikipedia says late summer and autumn. A female may spawn up to four times a season, often releasing over seven million eggs of about 1 mm (Wikipedia). Mature at two to four years; larvae off the southern United States, Jamaica, the Bahamas, the Dominican Republic, Puerto Rico and Brazil (Wikipedia).

SwordfishDeep dropping by day: baits with 2.5 kg or more of weight down to about 460 m, boat drifting (Wikipedia), Night drifting with baits fished shallower, usually under 90 m (Wikipedia), Marking baits with glow sticks or waterproof lights (Wikipedia), Heavy rods and reels, long fights (Wikipedia)

blue marlinOffshore trolling with large lures, Trolling rigged dead baitfish, Slow-trolling live bait along edges and floating debris (rule of thumb), Trolling teasers, then switching to a bait (bait and switch, rule of thumb)

SwordfishWhole squid, Whole mackerel, Mullet, Bonito, Squid imitation with a light

blue marlinLarge skirted trolling lure, Rigged ballyhoo, Live small tuna or bonito, Mackerel, Squid

SwordfishA good food fish, but large ones accumulate a lot of mercury; the FDA advises children and pregnant women against it.

blue marlinRich flesh, but Texas has issued a mercury consumption warning; usually released.

SwordfishIUCN: Near Threatened (assessed 1 May 2021; FishBase). USA, Atlantic and Gulf: HMS Angling permit or HMS Charter/Headboat permit for the vessel (NOAA Fisheries, retrieved 21 Oct 2026). Minimum size 47 inches lower-jaw fork length or 25 inches cleithrum to caudal keel (NOAA Fisheries). With an HMS Angling permit one fish per person, up to four per vessel per trip; charter boats one per paying passenger, up to six; headboats up to 15; none may be kept if a hammerhead or oceanic whitetip shark is on board (NOAA Fisheries). Pacific off California, Oregon and Washington: charter vessels need a Pacific HMS permit (NOAA Fisheries). A state saltwater licence is also required (NOAA Fisheries).

blue marlinIUCN: Vulnerable (assessed 10 May 2021; FishBase). USA, Atlantic and Gulf: a vessel fishing for marlin needs an HMS Angling permit or HMS Charter/Headboat permit; it covers everyone on board, costs 24 dollars and must be renewed every year (NOAA Fisheries, retrieved 21 Oct 2026). Minimum size 99 inches lower-jaw fork length; no per-angler bag limit, but combined US landings of blue marlin, white marlin and roundscale spearfish are capped at 250 fish a year; no billfish may be kept if a hammerhead or oceanic whitetip shark is on board (NOAA Fisheries, page updated 4 Aug 2025). Every angler also needs a state saltwater licence or registration, except in Hawaii, Puerto Rico and the US Virgin Islands (NOAA Fisheries). Pacific and other countries: separate rules, check with your operator and the authority before the trip.