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Blue shark fishing: the shark that travels the Atlantic clockwise

A blue shark that researchers had tagged off New Zealand was recaptured west of Chile after 624 days — according to the German Wikipedia, at least some 8,575 km away. FishBase calls it probably the most widely distributed cartilaginous fish of all, and in the North Atlantic, according to the English and German Wikipedia, tagging shows a regular clockwise migration that follows the great currents: with the Gulf Stream to Europe, south along the coasts of Europe and Africa, and back to the Caribbean with the North Equatorial Current. This article is about the blue shark, *Prionace glauca* — in German Blauhai, in Spanish tintorera or tiburón azul, in Italian verdesca, in French requin bleu, in Portuguese tubarão-azul, in Dutch blauwe haai, in Danish and Swedish blåhaj, in Norwegian blåhai, in Finnish sinihai, in Russian синяя акула, in Turkish pamuk balığı, in Greek γλαυκοκαρχαρίας, in Croatian modrulj, in Japanese ヨシキリザメ (yoshikirizame), in Arabic القرش الأزرق, and according to GBIF in Slovenian sinji morski pes and in Albanian peshkaqen jeshil. According to the German Wikipedia it is one of the most popular quarry of offshore anglers — and that is exactly why this is about recognising it and releasing it.

A shark with a long back story

According to the German Wikipedia, it was scientifically described by Carl Linnaeus in 1758, as *Squalus glaucus*. By then it had long been known: Guillaume Rondelet described it as early as 1554 as *Galeus glaucus*, and Peter Artedi already gave an English name in 1738: “The Blew Shark”. The current genus name *Prionace* was introduced in 1849 by the zoologist Theodore Cantor; because it was disputed for a long time, the International Commission on Zoological Nomenclature fixed it in 1965 with Opinion 723. According to the English Wikipedia, the blue shark is the only living species in its genus and belongs to the requiem sharks (Carcharhinidae); a 2023 study even proposed placing it in the genus *Carcharhinus*. The names describe it: according to FishBase, *Prionace* means something like “saw point”, after the serrated teeth in the upper jaw, and *glauca* is Latin for bluish-green or grey — the colour of the sea.

How to recognise it

According to FishBase, a slender, graceful shark with a long, conical snout, large eyes and curved, triangular upper teeth with serrated edges; the pectoral fins are long and narrow, and there is no skin ridge between the two dorsal fins. The back is dark blue, the flanks bright blue, the belly white; the tips of the pectoral fins and the anal fin are dusky. According to the German Wikipedia it is often seen gliding slowly beneath the surface, first dorsal fin and tail tip above the water, its large pectoral fins spread out.

The fish you are most likely to confuse it with is the shortfin mako, to which this series devotes a group of its own. According to FishBase, the mako has smooth, hook-shaped teeth instead of serrated triangles and a crescent-shaped tail fin; its pectoral fins are — as the name says — short, while the blue shark’s are long and narrow. A difference between the sexes is recorded by FishBase and the English Wikipedia: females have skin up to three times as thick as males — a protection against the bites with which males hold on to them during mating. Many females carry the marks as semicircles of small cuts on their dorsal fins.

  • Size: FishBase gives 400 cm total length as the maximum, 335 cm as the common length and 205.9 kg as the heaviest published weight; it matures at around 199 cm (170 to 221 cm). According to the English Wikipedia, males usually weigh 27 to 55 kg, large females 93 to 182 kg.
  • Young: It is viviparous; the young develop via a yolk-sac placenta. After a gestation of 9 to 12 months, according to FishBase, 4 to 135 pups are born, usually 15 to 30, each 35 to 44 cm long. According to the German Wikipedia, a large female off South Africa had 55 scars in her uterus — the traces of a birth that had just taken place.
  • Age: FishBase gives 20 years as the highest reported age; according to the English Wikipedia the maximum lifespan is still unknown. There, females are said to mature at five to six and males at four to five years.

What it eats — and what eats it

According to FishBase it eats fish — in the northwest Atlantic, for example, herring, hakes, cod, haddock, mackerel and flatfish —, plus small sharks, squid, pelagic crabs, whale carcasses, occasionally seabirds and garbage. The English Wikipedia names squid as its most important prey. The German one describes how blue sharks swim through the spawning shoals of squid like grazing herbivores, swinging head and tail in wide arcs; the English one, how they herd prey fish together as a pack — and how tuna take advantage of this to catch the fish that escape the sharks.

It is hunted itself, too: according to the English Wikipedia, young and small blue sharks are eaten by great white sharks and tiger sharks, orcas hunt them, and even California sea lions, northern elephant seals and Cape fur seals have been observed eating blue sharks.

Where it lives — the Mediterranean included

FishBase: worldwide in temperate and tropical seas between 70° North and 55° South — in the western Atlantic from Newfoundland to Argentina, in the eastern Atlantic from Norway to South Africa, including the Mediterranean, in the Indo-Pacific from East Africa to New Zealand, in the eastern Pacific from the Gulf of Alaska to Chile. It is an oceanic fish, but comes close to the coast where the continental shelf is narrow. According to the German Wikipedia it is very common in the North Atlantic from the south coast of Great Britain to Senegal and around the Azores, the Canaries, Cape Verde and Madeira; it comes to the North Sea, the Skagerrak and the waters off Norway as a summer visitor. In the tropics, according to the English Wikipedia, it stays at greater depths, where the water is cooler.

In the Mediterranean it breeds, according to the German Wikipedia, with its centre in the Adriatic. The Italian Wikipedia writes that it used to be fairly common in the Mediterranean, especially in the Adriatic, but always far offshore — and that its numbers are declining today. The Croatian Wikipedia counts it among the 29 shark species of the Adriatic: it lives throughout the Adriatic, but not densely, most of all in the open sea of the southern Adriatic; in winter it moves to greater depths, in summer it is at the surface — and then also in bays and channels. Genetically, according to a 2023 study (German Wikipedia), the blue sharks of the Mediterranean differ weakly from those of the North Atlantic.

Endangered — and what that means on the line

According to the German Wikipedia, the blue shark is one of the seven largest species for which the International Game Fish Association (IGFA) keeps record lists; on the hook it is capable of fast sprints and can partly leap out of the water. According to the English Wikipedia it rarely bites humans: from 1580 to 2013 it was linked to 13 bite incidents, four of them fatal. FishBase lists it as potentially dangerous.

The reverse view matters more. According to the English Wikipedia, blue sharks make up 85 to 90 % of all sharks and rays caught as bycatch in high-seas fisheries; according to the German Wikipedia, in 2023 it accounted for around 64 % of the shark catches reported by EU vessels. The IUCN lists it worldwide as Near Threatened (assessed on 6 November 2018, FishBase); in the Mediterranean, according to the Spanish Wikipedia, it is considered Critically Endangered, and in the Adriatic, according to the Croatian Wikipedia, threatened. Since November 2023 it has been listed in Appendix II of the CITES convention (German Wikipedia). And release alone does not always save it: according to the German Wikipedia, studies found a post-release mortality of about 10 to 35 %. Which rules apply on your water today is something you check yourself before the trip — with the harbour office, the fisheries authority, the guide. Anyone who hooks a blue shark releases it as gently and as quickly as possible in the water.

Eight contradictions, left standing

  • How big does it get? FishBase: at most 400 cm, commonly 335 cm. The English Wikipedia: large individuals up to 3.8 m, on average around 3.1 m — and the often-printed figure of 6.1 m has never been scientifically confirmed.
  • How heavy? FishBase: 205.9 kg as the heaviest published weight. The English Wikipedia: 391 kg as the heaviest reported — plus unconfirmed stories of 800 to 900 kg.
  • How many young? FishBase gives, on the same page, 4 to 63 and 4 to 135 (usually 15 to 30). The English Wikipedia: 4 to 135 — and in its introduction “25 to over 100”.
  • How deep? FishBase: 0 to 1,082 m, usually 1 to 220 m — and elsewhere: usually down to at least 150 m. The English Wikipedia: from the surface to about 350 m. The German: dives to 1,160 m documented.
  • How cold does it like it? FishBase: 7 to 21 °C. The English Wikipedia: prefers 12 to 20 °C, seen at 3.9 to 31 °C — and further down in the same article: prefers 14 to 16 °C, found at 8.5 to 17.5 °C. The German: at the surface 7 to 16 °C, more rarely up to 21 °C and above.
  • How threatened in the Mediterranean? Worldwide: Near Threatened (IUCN according to FishBase). The Spanish Wikipedia: Critically Endangered in the Mediterranean. The Croatian: threatened in the Adriatic. The Italian: once fairly common, today declining — without a classification.
  • Bonn Convention (CMS) — which appendix? FishBase and the German Wikipedia: Appendix II (according to the German Wikipedia since 2017). The Spanish Wikipedia: Appendix III.
  • Pack or not? The German Wikipedia: often in large aggregations, but not in tightly organised schools. The English: blue sharks have been observed cooperating as a pack to herd prey together.

Four names that lead to the wrong fish

  • “Tintorera”. According to the Spanish Wikipedia, in Spain this is the name of the blue shark — but in the Spanish-speaking countries on the Gulf of Mexico it means the tiger shark (*Galeocerdo cuvier*). The Mexican film “Tintorera” from 1977 also means the tiger shark.
  • “Aozame” — Japan’s “blue shark”. In Japanese the blue shark is called ヨシキリザメ (yoshikirizame). アオザメ (aozame) does literally mean “blue shark” according to the Japanese Wikipedia, after the colour — but it refers to the shortfin mako.
  • “Blauhai” and “blue shark” — not always this one. GBIF also lists both names for the shortfin mako. If you read “blue shark” or “Blauhai”, it is best to check the scientific name.
  • “Tintureira”. According to the Portuguese Wikipedia, a common name of the blue shark — but also of the sea hares (sea snails of the genus *Aplysia*), of pokeweed and of several grape varieties with dark flesh.

That leaves the question every article in this series starts with: when. Habitat, prey and habits are set out above, and they are fixed. Everything else changes every day — and that is exactly where it is decided whether a day on the water is worth it. That is what StrikeAhead works out: it takes the conditions on your water and tells you when the trip is worth it. And because you cannot read current edges, baitfish schools and the blue of the open sea from day one — and because a blue shark that is to be released needs experienced hands —, StrikeAhead Pathfinder tells you who to go out with: curated guides and skippers, personally vetted before listing — licence and insurance —, with verified catches instead of promo photos, no paid ranking and, for you as an angler, no booking fee. The app tells you when, Pathfinder tells you who with.

Fish the right moment →