Basking Shark, Cetorhinus maximus (Gunnerus 1765)

Worldwide in cool temperate coastal seas and oceanic waters, occasionally venturing into subtropical waters.

Basking sharks are rare in Australian waters, being only known from scattered localities, mostly along the south coast - from north of Port Stephens (New South Wales) to Busselton (Western Australia), including Bass Strait and around Tasmania.

Although often seen at the surface, basking sharks undertake extensive vertical migrations to deep water. They may spend much of their time at mesopelagic depths, feeding on small fishes, invertebrates and zooplankton. One individual was recorded to a depth of over 1200 metres. Basking sharks usually occur near or at the surface in temperate waters, and at depths below the thermocline, in tropical waters.

Their habit of 'basking' at the surface may be a way of warming their bodies after long times feeding in cold waters below 200 metres.

Basking Sharks follow summer plankton blooms and are seasonally abundant in some parts of the world. 

Vertebrae: 107-110 (precaudal 50-53)

Body stout, streamlined, head large, snout pointed, eye small; 5 extremely long gill slits extend from the top to the underside of the head; mouth huge, extending well beyond the eye, with rows of minute curved teeth in jaws; first dorsal, pectoral and pelvic fins large, second dorsal and anal fins small, caudal fin crescent-shaped, lower lobe somewhat smaller than upper lobe.

Although basking sharks can grow to a length of more than 12 metres, and a weight of about 7 tonnes, most individuals are smaller. The smallest known Basking Shark measured about 1.7 metres, and very few young sharks have been encountered.

Basking sharks are ram filter feeders, and use thousands of bristle-like gill rakers to strain huge quantities of zooplankton from the water column. They are known to feed on crustacean larvae, copepods, euphasids, fish eggs, small fishes, chaetognaths and other zooplankton.

Despite being the second largest fish in the world and having been fished for centuries, much is yet to be learned about this huge filter-feeding shark. 

Basking sharks are aplacental viviparous (ovoviviparous). This means that the embryos develop within the uterus without a placenta to provide nourishment. Females produce a very large number of eggs, indicating that embryonic oophagy (egg-eating) may occur as it does with other lamniform sharks (the developing embryos feed on unfertilised eggs within the uterus). Females give birth to litters of up to 6 pups after a gestation period of more than one year. At birth the pups measure about 1.5-2 metres in length, and juveniles less than 3 metres in length are rarely encountered.

Male basking sharks mature between 5-7 metres in length, and females mature between 8-10 metres. 

Basking sharks were historically hunted for the oil in their livers which provided lighting (including for street lamps) and was used in early industries. The skin was also tanned for leather, and the flesh used for food or fishmeal.

The species has been fished for meat, liver oil and cartilage (Compagno 2001; Hoelzel 2001). Their large fins are also in high demand for sale in the Asian shark fin trade. Basking sharks are also taken as by-catch in a number of fisheries around the world.

Basking sharks are especially vulnerable to over-exploitation because they mature slowly, taking about 12–20 years, and females have long gestation periods (approx. 1-3 years) after which they give birth to few offspring (Compagno 2001).

In November 1883, a Basking Shark was captured off Portland Victoria and transported to Melbourne via the railway. In his Prodromus of the Zoology of Victoria, Frederick McCoy describes this specimen, and tells the tale of it being hauled up Swanston Street, Melbourne to be put on display during race week (in the heat)!

"The extraordinary circumstances of the individual I have here figured and described having come so far south gives special interest to this specimen, which was caught in November, 1883, at Portland, on the Western coast of Victoria. It, as often happens in the northern hemisphere, to which, until this occurrence, it was supposed to be confined, was found entangled in the nets of the fisherman, and having wrapped the nets round itself by rolling and struggling, it became exhausted and was killed. In other countries where fisherman have recorded their meetings with this monster, the accounts agree in showing it to be a quiet, sluggish creature quite destitute of the ferocity of the other Sharks, swimming along showing its back and dorsal fin above the water, and with its mouth open to catch its small, floating food, like a Whale, and when basking quietly on the surface being so indifferent to the approaching of a boat that the man may feel it without any alarm or movement or anger on the part of the Shark, unless harpooned, when it darts to the bottom with great force and velocity, and unlike a Whale, which must come up to breathe, it stays below, making it a dangerous captive for any ordinary fishing vessel.

I have here noted, the red pulpy mass filling the intestines of our example being altogether composed of body and shells of a species of the Cuvieria or Triptera, rather less than a line long, fusiform, pointed, and slightly arched at the posterior end, mouth contracted, oblique (which might be named Cuvieria minor), the mass being tinted of a "boiled-shrimp" red from the remains of the soft parts, colored like the much larger Triptera rosea of Quoy and Gaimard. I owe the knowledge of this food to my vigilant friend, Mr. M. Dusting, of Portland, who sent me a sample he had taken from the intestines when giving me notice of the capture of this Shark, the species of which he correctly recognised.

This is the largest species of the whole class of Fishes, and as, like many Whales, and unlike other Sharks, it migrates in shoals of one to two hundred individuals, each of which is worth from 30 pounds to 50 pounds, it is of great value where any peculiarity in the ocean induces it to come regularly within reach of the fishermen. The liver only is taken. The liver weighs about two tons, and yields 10 or 12 barrels (eight to the ton) of the finest oil, like spermaceti. The specimen figured, after its liver was taken out, was brought by railway to Melbourne, and attracted crowds in the streets as it came up Swanston-street on two of the largest lorries fastened together, drawn by a long train of horses to a stable-yard, where it was exhibited during the race week; the hot weather rendering it useless as a specimen for the Museum afterwards. The teeth and portion of skin were preserved, and all the measurements and drawings completed before it defied approach."

Some teeth and a small piece of skin, all that remains of this mighty specimen, are registered in the Fish Collection at Museum Victoria, in Melbourne, Australia.

Squalus maximus Gunnerus 1765, Det Trondhiemske Selskabs Skrifter: 33, Pl. 2 Type locality: Nordland County, northern Norway

Bray, D.J. 2023

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