BASKING SHARKS NEW ZEALAND'S LARGEST FISH

Forest and Bird, Issue 265, 1 August 1992, Page 38

BASKING SHARKS NEW ZEALAND'S LARGEST FISH

Alan Tennyson

At twelve metres long, the basking shark is one of the most extraordinary of marine creatures. Its size and its filter-feeding habits are more like those of a whale than a fish. Little is known about them yet they are still hunted for their fins and livers. ALAN TENNYSON examines these gentle giants and looks at moves to give them greater protection. HE PUBLIC IMAGE of the basking shark, Cetorhinus maximus, is pretty lousy. Few people have heard of them and when "shark"’ is mentioned, most people are likely to conjure up an image of a great white shark in attack mode. People fear sharks because they are one of the few animals, apart from the large cats, that can hunt and kill humans. Being a shark, particularly a big one, has meant that the basking shark has received more than its fair share of fear and loathing. Many stories of "monsters" or "sea serpents" were sparked by sightings of this much-maligned animal. And despite some maturing in our view of sea creatures, inflated and fanciful stories about basking sharks have continued into the 20th century. An article in The Dominion of 16 May 1932, headlined "‘17-foot monster shot at Makara’’, continues: Shortly before 9 am it was seen cruising quietly round the bay enjoying the sun on top of the water... Mr Charles Smith . . . went out in a dinghy ... Mr Smith had a .303 rifle with him, and put a bullet through the back of the head, following this up with further shots which were effective in disabling the monster. One bullet hit the jaw and split its nose . . . Later in the morning Mr WJ. Phillips, the museum specialist on fish, . . . identified the monster as a basking shark. References in newspaper files describe

basking sharks in terms such as "ugly monster’, "an unwelcome visitor’, ‘"‘an enormous, ugly looking thing". They are commonly described as dangerous. To this day large sharks near swimming areas are hunted and shot by authorities such as police without any attempt being made to separate harmless from dangerous species. Yet basking sharks are quite unlike the ferocious great whites. They are plankton feeders with only tiny teeth, and are as harmless as the plankton-feeding whales.

N ADDITION to their huge size, basking sharks look strange. They have five huge gill slits (as do most sharks) which almost completely encircle the head, a bulbous nose with tiny eyes at its base, and a vast, cavernous mouth. In young basking sharks the nose is more elongated and can resemble a short trunk. Each gill slit is lined with thousands of filters called gill rakers, similar to the baleen screens of large whales. Feeding and breathing are combined.

Copepods, barnacles, decapod larvae and fish eggs are their main food and their enormous mouths allow them to filter more than 2,000 tonnes of water an hour. Sharks are one of the most ancient vertebrate groups roaming the planet. Along with skates and rays they are mainly distinguished from other fish in having a cartilaginous rather than a bony skeleton. The earliest known sharks date from rocks about 400 million years old. Fossil basking sharks have been found in

Cretaceous rocks 70-100 million years old. The basking shark was first formally described by scientists in 1765 from a specimen taken near Norway. The species 1s found worldwide, particularly in higher latitudes. It is widespread around New Zealand, including the subantarctic, but it is most commonly seen around Cook Strait and down the east coast of the South Island as far as Timaru. Most New Zealand sightings are between September and January.

Sightings at sea in the spring or summer are often of large schools. These can be a spectacular sight. One evening in January this year, the LPG carrier Tarahiko reported sighting a large school south of Banks Peninsula. The skipper of the ship reported "fins as far as we could see" and it took him an hour to steam through the school at a speed of 11 knots. A dense school off Britain was described as being "‘like a herd of submerged elephants’. Worldwide, little is known about the seasonal movements of basking sharks. Sightings are mainly on the continental shelf, both coastal and well offshore. In most areas they are seen at the surface in the warmer months. Off California, however, basking sharks are more common in the cooler months when the water is rich with plankton. Around New Zealand and Britain sightings are much less common in autumn and winter and it is assumed most of the sharks go into deeper water. Their biology during this time is virtually unknown. It has been speculated that some hibernate when food supplies are scarce because, on rare occasions, basking sharks without gill rakers have been taken. It is argued that since they could not feed without this apparatus, they may periodically fast, perhaps hibernating or becoming inactive, while the gill rakers are replaced. Migration may account for appearances and disappearances of basking sharks at some localities. Off the Atlantic coast of North America, they appear in the south in spring (March-May) and apparently shift north in summer (June-August), disappearing for the rest of the year. Off the Pacific coast of North America, basking sharks appear in their greatest num-

bers in autumn and winter (SeptemberFebruary) in the south, shifting further north in spring and summer. Satellite tracking using transmitters attached to the sharks is already underway in the north-east Atlantic. This should help unravel some of the mysteries surrounding the movements of this giant fish. The sharks are no doubt capable of making very long journeys, travelling hundreds or even thousands of kilometres through coastal and international waters. Basking sharks can reach 12 metres in length, and can weigh up to six to eight tonnes. Most are less than ten metres long. As in most shark species, the females grow larger than males. Out of about 400 species of shark worldwide, the basking

shark is the second largest after the whale shark. It is also the only filter-feeding shark known to occur in New Zealand waters. HE BREEDING HABITS of basking sharks are largely a mystery but, like other sharks, they probably have a very low reproductive rate. Most sharks are long-lived (12-70 years), grow slowly, and produce small numbers of young (2-50) each year. By comparison, most bony fish produce thousands of eggs each year. The way young sharks develop varies considerably. Some are hatched from eggs enclosed in horny capsules laid on the sea

bed, some hatch inside the mother fully developed and feed on other eggs or developing young before birth, and others are nurtured by the mother through a placenta before birth. Basking sharks are thought to fall into the second category (where embryos cannibalise their siblings), but there are two cases, where captured females gave birth to five and six young, suggesting the possibility of placental development. Juveniles smaller than three metres and pregnant females are virtually unknown, which suggests that they rarely come to the surface. Gestation for basking sharks may take as long as three and a half years. The smallest basking shark captured was 165 cm long, which is thought to be near to the size of a new-born pup. Growth rings on vertebrae indicate that males mature at six or seven years when four to six metres long. Commercial basking shark fisheries off Scotland and Ireland have taken 18-25 female sharks for each male. Most of the females caught around Britain are subadult, while most of the small number of basking sharks caught in winter are males. This indicates that at least in some parts of the world, the sexes have markedly different habits. Off Scotland and Ireland, males may be more solitary, tend to occur at greater water depth or further offshore, or occupy a different geographic area to females. It has been suggested that dominant males may have harems which they defend from other males. Unfortunately the history of most shark fisheries is one of boom and bust. Sharks are easily over-exploited because

of their low breeding rates. Basking sharks have long been targeted by fishers, yet because of their especially low reproductive rate, they may be more vulnerable to over-fishing than most commercially sought sharks.

OR CENTURIES basking sharks have been the object of small-scale, sporadic harpoon fisheries from small boats off the coasts of Norway, Ireland, Scotland, Iceland, California, Peru and Ecuador. In the 1940s, spotter planes were used to locate the sharks off California. The Norwegians in 1960 caught an incredible 4,266 sharks, but by 1987 their entire quota was 400 tonnes of liver (about 800 sharks). In recent years the number of basking sharks off Ireland has declined so much that biologists are worried about the future of the species. Currently basking sharks are being heavily fished around China and Japan by harpoon. Fishing for basking sharks has primarily been for their huge and valuable oil-rich livers. Unlike many other fish, sharks do not have air-filled swim bladders to give them buoyancy. They compensate for this by having a large, buoyant, oil-filled liver. The livers are about 20 percent of their total body weight, sometimes weigh more than a tonne, and yield up to 2,000 litres of oil. In New Zealand, there has been sporadic commercial interest in the oil from shark livers for the last 50 years. At one time basking sharks were hunted by harpoon off Kaikoura. Today, basking shark

and other shark livers are still regularly boiled down at Kaikoura by a local company for the Japanese market. The company receives sharks, which have been caught mainly as a by-catch in gill nets set for ling and groper, sent in from fishers around the South Island. The main lipid or fat in the rich oil of shark livers is a vitamin rich substance called squalene. Squalene has been used extensively in the manufacture of skin moisturisers, sunscreen lotions, lubricants, pharmaceuticals, aromatics, steroid hormones and some health foods. The liver oil was formerly used for tanning leather and for lamp oil. These days the oil is not so valuable because substitutes can be produced synthetically. However, more recently there has been a growing market for natural skin care products. Basking shark fins are used for shark fin soup, and sometimes the meat is used for human consumption or fishmeal, and the skins for leather. Basking sharks are regularly caught in New Zealand waters as by-catch in gill nets or by large deep-water trawlers. The gill net problem seems to have been greatest at Kaikoura. A local fisherman was quoted by the Kaikoura Star in 1974 as saying that "these sharks can be a great nuisance when they become entangled in the nets, not only for the time involved in untangling, but also the damage caused, and sometimes the loss of a net." This seems to be a common problem wherever gill nets are used within the range of basking sharks. Salmon gill netters off the North American Pacific and Atlantic coasts, for example, regularly catch these sharks, and Irish fishers used to hunt basking sharks because they damaged their salmon nets. However, not all incidental basking shark captures may be regarded as a nuisance. Sometimes when one basking shark is caught by a large trawler, targeted fishing for more basking sharks may occur. The bellies of the sharks are slit open to remove the large livers and the bodies discarded.

HE HISTORY of human attitudes to wild animals is generally one of increasing awareness and concern. In New Zealand nearly all the larger native land animals now have absolute protection. Yet we have always treated marine life differently from terrestrial life. Nearly every marine creature can be taken by amateur or commercial fishers. No thought is given to whether a fish caught is a rare or threatened species, and the wider effect of catching fish on the marine ecosystem is seldom considered. Yet many marine

ecosystems are being stripped of life and several species of fish are likely to be threatened. What is needed is a change in attitude towards marine life. Under current law only turtles, black coral, red coral, toheroas and one species of fish — the black spotted groper — have been given total or near-total protection under the Fisheries Act within New Zealand waters. Marine mammals, on the other hand, are protected under the Marine Mammals Protection Act, and seabirds, out to 12 nautical miles [22 km], under the Wildlife Act. Under 1991 Fisheries Regulations, it is already illegal to commercially target any fish, including basking sharks, not subject to a quota. However, plenty of

non-target fish still get caught. It is virtually impossible to police this law because no-one can prove that a non-target species was being targeted. Most species caught as by-catch are allowed to be sold commercially, so often there is financial incentive to fish non-target species. HY SHOULD basking sharks be given protection? Firstly, very little is known about their biology. It can be safely assumed that they have a very slow reproductive rate and, because of this, it is likely that they have already been overfished by direct hunting and incidental catches. In New Zealand there is evidence of local depletion — numbers at Kaikoura, for example, appear to have declined in the last 20 years. Large and visible schools of basking sharks belie the probable small size of populations worldwide. This species may be threatened, but the long-term effects of fishing on populations are unknown. Secondly, basking sharks are a potential tourist drawcard. While they may not have as much appeal to the public as whales and dolphins, they are spectacular creatures because of their size. In Scotland tour companies advertise basking sharks as an attraction around the Hebrides and the Isle of Mull. In future, if protection leads to an increase in basking shark numbers, tourist trips could be organised in New Zealand. The Kaikoura whale watching ventures would almost certainly benefit from increased numbers of these marine giants. Finally there is the moral issue. Worldwide there is a growing awareness that basking sharks are creatures to be cher-

ished. In New Zealand they are perhaps our most impressive fish. Should they be treated like spotties and anchovies or do they deserve protection similar to that we give native birds and marine mammals? Certainly there is some government support for the idea of extending more protection to fish. In 1991 the Department of Conservation, in a submission to the fisheries legislation review, singled out basking sharks and manta rays as species that it should be illegal to kill, injure, capture or otherwise harass. Overseas, campaigns for protection are mounting. The Marine Conservation Society of the United Kingdom has been running a campaign to promote conservation of the basking shark for the last five years. Last year the Joint Nature Conservancy Committee in the UK recommended that the species be given full protection, although this is being opposed by some government agencies. In other countries threatened shark species are already gaining legal protection. In Australia the grey nurse and smalltooth sand tiger shark are now totally protected off the New South Wales and Queensland coasts. The killing of great whites is now banned in South Africa, as is the trade in their jaws and other souvenirs. The killing of great white, tiger, hammerhead and lemon sharks is also to be banned in United States waters. Recent changes in legislation regarding shark finning should reduce the commercial incentive to catch basking sharks. "Finning" is the practice of removing shark fins and discarding the rest of the carcass at sea. It is to be banned in the United States and a code of practice has been introduced in Australia to curtail the custom there. In New Zealand, what have we got to lose by protecting basking sharks? A few commercial fishers would lose revenue from selling the fins or liver of the occasional one that gets caught in their trawl net or tangled in their gill net. No-one would lose their livelihood. Giving basking sharks absolute protection would assist international conservation efforts to preserve and enhance the populations of this giant and mysterious fish. Acknowledgements Thanks to Larry Paul, Diana Pipke, Clinton Duffy, Margaret Palmer and Barry Dunnett for providing information. "

is a re-

searcher with Forest and Bird specialising in marine conservation issues.

What should be done?

Basking sharks deserve full protection under the law, so that the capture, harassment and selling of any parts of this species is illegal, and all captures are reported. New Zealand should be pushing for an international treaty protecting this species. Shark "finning" should be banned. Gill netting should be phased out. This fishing method is indiscriminate and wasteful and catches many basking sharks. Attitudes to sharks need to change — very few sharks attack people. Officials sent out to shoot sharks for the safety of swimmers should be educated about the different types of sharks.