Whale shark

Rhincodon typus is the only species in the family Rhincodontidae, order Orectolobiformes ^[1]. It is by far the largest fish alive: adults reach 7 m or more, and yet it feeds by filtering water ^[2]. The Peruvian regulation that protects it calls it «tiburón ballena», and since July 2017 catching, landing and selling it have been banned in Peruvian waters ^[3].

Andrew Smith described it in 1828 as Rhiniodon typus, in a Cape Town newspaper, from a specimen stranded in Table Bay, South Africa ^[2]. Smith himself and later authors spelled the genus in many different ways, such as Rhinodon, Rhineodon or Rhincodon, until in 1984 the International Commission on Zoological Nomenclature, in its Opinion 1278, fixed the spelling Rhincodon and the family name Rhincodontidae ^[2]. The holotype is a stuffed male of 4.6 m kept at the National Museum of Natural History in Paris ^[2].

It cannot be mistaken for anything else. The head is very broad and flattened, the snout is squared off and the mouth is huge, transverse and almost at the tip of the head, in front of the eyes ^[2]. Its teeth are tiny and extremely numerous, in adults and subadults they form more than 300 rows in each jaw, and inside the gill slits it carries filtering screens found in no other shark ^[2]. Strong ridges run along the flanks; the lowest one widens into a keel on each side of the tail stalk ^[2].

The back, grey, bluish or a reddish or greenish brown, is covered by a checkerboard of white or yellowish spots and pale horizontal and vertical lines; the belly is white or yellowish ^[2]. The first dorsal fin is large, while the second dorsal and the anal fin are small ^[2].

Its maximum size is not known with certainty. Lengths of 17 to 18 m and even 21.4 m have been reported, but individuals over 12 m are uncommon; 13.7 m is the figure usually given as the largest measured, and most published records fall between 3 and 12 m ^[2]. A pregnant female caught off Taiwan was about 10.6 m long and weighed 16 t ^[2].

Similar species

• Cetorhinus maximus: The basking shark is also a giant filter feeder, but it has a very large scoop-shaped mouth and relies on swimming forward to push water through it; the whale shark stands out for its checkerboard of spots and pale lines and for a mouth set at the front of the head ^[2].

It lives in every tropical and warm temperate sea, both in the open ocean and near the coast; in the eastern Pacific it has been recorded from southern California to Ecuador, Peru and northern Chile ^[2]. It is often seen far offshore but regularly comes close to beaches and reefs, and is usually seen at the surface of warm water; even so, satellite tagging off Belize shows that it can dive to 700 m and cross water of 7.8 °C ^[2].

It appears in the updated list of 115 chondrichthyans from Peruvian waters ^[4]. A compilation of 27 records along the Peruvian coast pointed to the north of the country as the area where it turns up most ^[5]. Between 2009 and 2018, leaving out 2011, 347 whale sharks were georeferenced off the northern coast, between 3° S and 4° 30′ S; depth was the variable that best explained their presence, followed by chlorophyll a, and the model placed them mainly in shallow coastal water in the northernmost part of the area ^[6].

It is ovoviviparous: the eggs develop inside the mother. This was confirmed by an adult female caught off Taiwan that carried about 300 young in her uteri, in three size classes, from embryos still in their egg cases to term foetuses of 58 to 64 cm ^[2]. At birth it measures between 55 and 64 cm ^[2].

Males of 299 cm or less are immature, those of 390 to 540 cm are maturing, and adult males of 705 to 1026 cm have been recorded; females of up to 760 cm that were examined were immature ^[2]. Its age and growth rate are still debated: one tentative estimate gave it a lifespan of about 100 years, while other authors proposed that it grows very fast when young ^[2]. The IMARPE report on which Peru's protective regulation is based describes it as a long-lived species with slow growth, late maturity and low fecundity ^[3].

It is a great migrant. In the Gulf of California, one satellite-tagged shark travelled 1723 km in about 3 months and another 3708 km in 5 months ^[2]. According to a 2012 review, photo-identification shows that it gathers each season to feed in groups dominated by certain sizes and one sex, and that many individuals return to those sites or stay nearby; satellite tracking, on the other hand, reveals that animals from these aggregations can migrate on the scale of a whole ocean basin ^[7]. The Peruvian records include newborns; together with presumably pregnant females tracked earlier by satellite, they suggest that northern Peruvian waters are used as a pupping ground ^[5].

It filters water by suction, so it does not need to swim forward to feed and can take both plankton and active prey: small crustaceans such as copepods, sardines, anchovies, mackerel, small tunas and squid ^[2]. It often feeds at the surface, sometimes hanging vertically with its mouth upwards ^[2]. It commonly travels with schools of pelagic fish, especially scombrids, and off Belize it gathers to eat the spawn released by snappers ^[2].

Its natural predators are poorly known: a newborn was found in the stomach of a blue shark, and for adults killer whales and white sharks are possible candidates; the main predator is humans ^[2]. Off northern Peru its presence becomes more likely as chlorophyll a and sea temperature rise, and spring offers the most favourable conditions in both La Niña and El Niño years; the authors read this as seasonal gathering there to exploit food-rich areas ^[6]. The management plan of the Reserva Nacional Mar Tropical de Grau highlights how often the species occurs in the Arrecifes de Punta Sal sector, which apparently is an important feeding area for it ^[8].

In Peru, Ministerial Resolution No. 331-2017-PRODUCE, published on 14 July 2017, bans taking it in Peruvian waters, as well as landing, transporting, keeping, processing and selling it ^[3]. If one is caught by accident it must be returned to the sea at once and unharmed, and the event reported to IMARPE; according to the IMARPE report cited in the regulation, Peru has no fishery aimed at the species and it shows up only sporadically in landings as bycatch ^[3].

Internationally, the Convention on Migratory Species has listed it in its Appendix II since 1999 and in its Appendix I since 2017 ^[9]. Worldwide, a 2012 review notes that in the preceding decades fisheries targeting the species to supply restaurants in Asia grew greatly, and that on top of them comes poorly quantified bycatch in tuna purse seines ^[7].

In the 27 Peruvian records compiled, every interaction was with net fisheries, and they were seen in 89 % of cases ^[5]. In the most suitable areas of northern Peru it is exposed to fishing, bycatch, collisions with vessels, unmanaged tourism and pollution ^[6]. The management plan of the Reserva Nacional Mar Tropical de Grau names it among the charismatic or flagship species whose presence makes the sea of northern Peru important ^[8].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

Despite its size it is regarded as harmless: many divers have approached large individuals, touched them and even ridden them without any aggressive reaction, although they may dive or move away when disturbed ^[2]. A few cases are known of one butting sport-fishing boats, perhaps drawn by bait or by hooked fish ^[2].

Its meat is eaten fresh, frozen, dried or salted, and its fins fetch a high value in the Asian trade because of their size; it has been harpooned in Pakistan, India, the Maldives, the Philippines and Taiwan ^[2]. At the same time its docility has made it the focus of dive tourism in several countries, and at places such as Ningaloo, in Australia, access to the animals is limited by a strict code of conduct ^[2].

In Peru, the organisation EcOceánica has studied the species since 2012 ^[8]. In the Arrecifes de Punta Sal sector it is carrying out a 24-month study of whether swimming with whale sharks could be offered ^[8].

According to the 2026 management plan of the Reserva Nacional Mar Tropical de Grau, the northern part of the Arrecifes de Punta Sal sector is the main seasonal whale shark sighting area in Peru, and the stretch between the Punta Sal resort and Punta Mero holds the largest number of records in the country; some individuals have been seen both there and in the Cabo Blanco – El Ñuro sector ^[8]. In the latter sector the species is rare ^[8]. The same document states that in the north it appears mostly near the surface in spring and summer ^[8].

In the compilation of 27 records published in 2018, reports were more frequent from January to March and from October to December ^[5]. The 347 whale sharks georeferenced between 2009 and 2018 were recorded mostly during La Niña events, in the southern-hemisphere summer and spring ^[6].