Chondrichthyes (cartilaginous fish, including sharks, rays and chaemeras) >

Conservation and management of cartilaginous fish

Do cartilaginous fishes need protection? We think so, but in southern Africa most people might think otherwise. There seem to be plenty of sharks, rays, and chimaeras about, and to many people these `inedibles' are trash fish, `man-eaters' and objects of hatred, that could stand for culling or even extermination. However, cartilaginous fishes, because of their essentially mammalian life-history style, are endangered by ever-increasing human exploitation. The threefold increase in fisheries for cartilaginous fishes since World War II highlights the biological, environmental and management difficulties with these fishes that need careful consideration to insure their long-range survival. Cartilaginous fishes are typically slow-growing, long-lived, mature late in life, and have a low reproductive rate. In addition the females of most species grow to a larger size than males. These life-history characteristics make cartilaginous fishes easy to overexploit, and make sustained fisheries for them nearly impossible with the nonselective practices of most fisheries operations. Numerous case histories for such fisheries indicate that initial exploitation usually results in rapid declines in catch rates and in some instances a complete collapse of the fishery.

Cartilaginous fishes are limited by their mode of reproduction, which produces low numbers of offspring and allows them little flexibility in compensating for increased exploitation. This is very different from bony fishes that sustain massive fisheries, such as cod and hake, which produce millions of eggs per female fish and have enormous reproductive potential to replenish the next generation despite heavy exploitation of adults. Exploitation of cartilaginous fish populations diminishes the replenishment of young by direct predation on the young and adults; fewer young are available to become adults, fewer young are produced by the diminished adults, and numbers rapidly decline. Some species such as the bluntnose spiny dogfish (Squalus megalops) seem a vast, inexhaustible resource, but this is deceptive because, with heavy exploitation, their low reproductive rates cannot sustain their numbers as individuals are removed, and fisheries accordingly will crash.

It is currently not known how to `fine-tune' a fishery for cartilaginous fishes, to produce sustainable yields over an indefinite period. Methods of doing so might be based on those used to regulate mammal populations with low fecundity rather than bony fishes, including selective fishing of individuals that might be surplus to the reproductive population, as well as strict seasonal, geographic, and catch limits on the fishery. The difficulties with management of cartilaginous fishes arise from severe limits to our knowledge of the biology of these fishes, the unselective nature of most fisheries for cartilaginous fishes, and the fact that fisheries for cartilaginous fishes worldwide are largely unnoticed, unstudied, unregulated, and are essentially out of control. Many fisheries take cartilaginous fishes as a bycatch, and are driven by primary catches of more fecund bony fishes; thus declining catch rates for cartilaginous fishes need not regulate or even effect a given fishery as bony fishes can still be caught in commercially viable quantities.

It is instructive to estimate the numbers of individual sharks, rays, and chimaeras taken in the world cartilaginous fish catch. Using the 627,000 tonne catch of 1986, and assuming that each individual weighed as much as a human being (68 kg), some 9.2 million cartilaginous fishes were killed in 1986, compared to an estimated 30 humans killed annually by sharks. The yearly `human attack' fatality rate on cartilaginous fishes was thus some 322,000 times higher than the shark attack fatality rate. However, the actual numbers of cartilaginous fishes taken are probably much higher, because the average size of cartilaginous fishes is smaller than for human beings. Using an average weight of, say, 10 kg, the number of cartilaginous fishes caught worldwide in 1986 would be approximately 63 million, about twice the human population of southern Africa. This sets shark paranoia and hysteria into another perspective; from a shark's viewpoint, humanity is a deadly danger, while sharks pose a miniscule problem to the vast armed legions of humankind.

World catches of cartilaginous fishes are not keeping pace with those of more fecund bony fishes, and seem to be leveling off in the present decade. In the next few decades we suspect that world cartilaginous fish catches will begin to decline as increasing fisheries pressure, driven by ever-burgeoning humanity, exhausts most accessible populations.

A particularly worrisome, huge and shadowy fishery that affects shark populations worldwide is the oriental sharkfin trade. The value of shark fins have soared in recent years. The sharkfin fishery fits in nicely as a bycatch operation of fisheries for bony fishes; and sharks that otherwise had low value and might compete with more valuable bony fishes for hold space in a fishing vessel can be turned into a high-value, low-volume bonus for commercial fishermen. Thus the rigging of pelagic longline vessels are festooned with hundreds of drying sharkfins, and pelagic shark populations are being decimated. The sharkfin trade is powered by a tremendous market in the populaces of China and Taiwan and in Chinese communities worldwide. Virtually nobody seems to notice the effects of this trade or cares, although much hue and cry was given in the late 1960's to the plight of spinner dolphins, which were being killed by tuna purse-seiners in the eastern south Pacific.

`Popularity' may be destroying at least one species of shark. The `success' of the JAWS films touched an atavistic streak in the minds of humankind, and in the aftermath of these science-fictional films macho-men swarmed out to pit their virility against the great white shark. Here and elsewhere, off California, New York, and Australia, shark after shark was caught, by anglers, divers, and commercial fishermen, with the perpetrators congratulating themselves in conquering these horrible man-eating monsters and ridding humankind of a supposed scourge. Entrepreneurs sprang up, photographing live white sharks, leading expeditions of the nature-loving rich to huddle in shark cages off Dangerous Reef in South Australia, exhibiting the frozen or preserved carcasses of white sharks, and selling their mercury-laden meat, teeth, and jaws. Other sharks were not spared either, as shark fishing became extremely popular. Large public aquaria captured white sharks alive for display, which so far have uniformly died after a few days or weeks. The value of large white shark jaws soared to fantastic heights, and erratic and lucrative spot fisheries for jaws arose in southern Africa and elsewhere. Dangerous Reef, where most of the spectacular cinemagraphic and still-photography of white sharks occurred, was recently rid of most of the small group of white sharks that regularly attended boats as big-game anglers and commercial fishermen moved in after the cinema people, diver-photographers and shark-cage entrepreneurs.

All this pressure on the great white shark may be creating problems for its survival equivalent to those afforded elephants and rhinoceros by the persistent ivory and rhino horn trades. As white sharks feed on seals and other large marine organisms that in turn feed on commercially important bony fishes, the effects of removing white sharks may be detrimental. We suggest that proposals for the protection of the white shark and banning of the white shark jaw trade be considered and placed into operation both locally and internationally before this shark is exterminated. We note that, JAWS and much adverse publicity notwithstanding, many local anglers have sympathy for white sharks and oppose their capture, because of their predation on Cape fur seals.

The prospect for cartilaginous fishes in the next century is grim, as the human population soars and these fishes are increasingly hammered by fisheries. The difficulties in managing and conserving cartilaginous fishes are enormous, and exacerbated by the negative `man-eating' JAWS image afforded sharks, which hampers conservation and encourages anti-shark measures, unregulated exploitation, and wanton destruction of cartilaginous fishes. The ecological impact of the removal of cartilaginous fishes, top predators in the sea, is unclear, but we suspect that it will be far-reaching and ultimately detrimental to marine ecosystems and ultimately humankind.

We call for the public to acquaint itself with the local cartilaginous fishes, and to realize that they are of little harm and are integral to healthy marine environments. We hope that at least some people will take heed of their plight, and will acquire a mature, respectful, appreciative attitude towards a group of animals honed to predatory perfection by over 450 million years of evolution. Many land predators were quite recently considered vermin, to be shot on sight, but are now conserved and protected. Conservationists and the general public in the West have helped to conserve those species of whales that were threatened by the excesses of international whaling. Such conservation efforts towards sharks and other cartilaginous fishes will be extremely difficult but increasingly necessary in the immediate future. It is an act of blind self-indulgence to morbidly embrace shark-attack paranoia or actively exploit such fear while sharks and other cartilaginous fishes are quietly being overfished and destroyed.
We propose that cartilaginous fishes should be viewed as a necessary prerequisite to maintaining a sound marine ecosystem, rather than as unnecessary vermin that should be exterminated. It has become clear in recent years that in order to maintain many of the large game reserves the predators need to be protected rather that eliminated. Unfortunately, people have been slow to recognize that this same principle applies to the marine environment. Often we have heard that by killing a shark one would save a seal or sea otter, yet this is a very one-sided and narrow-minded approach. Not only are sharks a positive stabilizing factor in the maintenance of healthy marine ecosystems, but they are interesting and rewarding animals to observe. More detailed studies of cartilaginous fishes will reveal a better and hence more complete understanding of marine communities by examining the chief predators. If one is truly concerned about maintaining the marine ecosystem, then we need to consider the impact that is being imposed on it by the removal of these top predators.

We hope that much of what is written in this website gives YOU the reader some insight into the diversity of cartilaginous fishes and the intricate and delicate relationships between these fishes and their environment. For these are extremely complex animals whose biology we are only beginning to understand. Hopefully, the information we have presented will cause you, as an environmentally concerned individual, to stop and think of these creatures not as monsters or pests, but as an integral and essential part of the WHOLE MARINE ENVIRONMENT.

Text by Leonard J.V. Compagno, David A. Ebert and Malcolm J. Smale

  Iziko Museums of Cape Town, 2008

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