A Place For Sharks
By now, it’s no secret that shark populations world-wide are getting ‘hammered’.
Over the past 50 years, global commercial landings of sharks have roughly quadrupled. Fishery catches typically follow an all-too-familiar pattern of “boom and bust” — high initial success followed by a sudden economic ‘crash’, as shark populations collapse under the weight of sustained fishing pressure. Of 26 countries considered “major” harvesters of sharks by the United Nation’s Food and Agriculture Organization, only 3 (12%) — the United States, New Zealand, and Australia — have shark management plans in effect. Far offshore, in international waters away from prying eyes, open ocean sharks are slaughtered without restraint and in unprecedented numbers.
Sportmen, using state-of-the-art equipment, also take their toll on shark populations, targeting prized species with ruthless efficiency. The fearsome-looking but inoffensive Grey Nurse Shark (Carcharias taurus) was nearly extirpated off southeastern Australia by throngs of macho idiots armed with explosive powerheads. In 2001, the species was declared "critically endangered" by the Australian government. In the wake of JAWS, catching and killing White Sharks (Carcharodon carcharias) for sport became a popular fad, reducing these spectacular animals to faded Kodak memories and dried jaws gathering dust on pub walls. World-wide, shark species singled out by sportsmen are nowhere near as abundant as they were historically and their populations show little — if any — signs of recovery.
And yet the killing continues, almost unabated. As a consequence, some shark populations in the western North Atlantic — including the once-abundant Sandbar Shark (Carcharhinus plumbeus) — have been reduced by as much as 80% during the 20th Century. Collectively, on a world-wide basis, more than 100 million sharks were killed last year for human food and sport in such directed fisheries — that’s nearly 300,000 per day or 12,500 per hour. Tens of thousands more sharks die in various “shark control” efforts, such as the beach meshing programs conducted off eastern Australia and the Natal coast of South Africa. Even ‘harmless’ species are not immune, should they become ‘inconvenient’. In the 1950’s, off British Columbia, Canada, the then-abundant Basking Sharks (Cetorhinus maximus) kept running afoul of fishing gear. In response, more than a hundred Baskers were sliced in two by a fishery patrol boat outfitted with a knife-like blade attached to the bow. Basking Sharks have been rare in BC waters ever since.
Even more worrisome than the sheer bulk of sharks taken by directed fisheries is that captured incidentally to other fisheries as “bycatch”, which — unlike commercial landings — often go unreported and are thus difficult to quantify, let alone quash. The relatively recent rise in Asian affluence spawned a highly lucrative fishery for shark fins. In China and neighboring countries, some 6.6 million pounds (3 million kilograms) of shark fins are sold each year. Often the sharks are “finned” alive, the remainder of their bodies dumped overboard to be set upon by other sharks or condemned to a slow death by starvation. No matter how one feels about sharks, this cruel practice is a disgusting waste of wildlife.
Even more recently, world-wide interest in ‘alternative’ therapies has stimulated a lucrative market for shark cartilage, hailed by medical quacks as a cure for everything from arthritis to cancer. Based on the best available scientific evidence, these ‘cures’ don’t seem to work inside the human body. This adds to the ecological injury of shark harvesting the human injury of medical fraud and the cruelest kind of predation on the false hopes of the desperate.
The situation is dire, but not yet hopeless.
A small but growing cadre of people is discovering the joys of encountering sharks in the wild. Boatloads of shark watchers happily pay for the opportunity to watch Basking Sharks off the Island of Man, England, and White Sharks off the Farallon Islands, California. Each year, thousands of snorkellers and divers flock to observe — for example — Whale Sharks (Rhincodon typus) off Ningaloo Reef, Western Australia, Grey Reef Sharks (Carcharhinus amblyrhynchos) off Blue Corner, Palau, White Sharks off South Africa and South Australia, schooling Scalloped Hammerheads (Sphyrna lewini) off Cocos Island, Costa Rica, and the Galapagos Islands, or Caribbean Reef Sharks (Carcharhinus perezi) in the Bahamas. Such eco-tourists do more than take boat rides and diving trips. They also hire cars and hotel rooms, eat in restaurants, and buy souvenirs. It has been estimated that each individual Caribbean Reef Shark in the Bahamas is worth about US$150,000 to the Bahamian economy each and every year. On a per shark basis, such non-consumptive shark exploitation generates — in perpetuity — thousands of times more revenue than could ever be earned by selling a carcass once for however many cents per pound.
The economic message is clear: in terms of cold, hard cash, a live shark can be worth a great deal more than a dead one. But increasing world demand for alternate sources of marine protein make it unlikely that sharks will not continue to be killed for human and animal food. Therefore, if we want a world that includes wild, free-swimming sharks, we must strive to find ways to utilize and manage them intelligently.
More than any other species — and, arguably, more than any species should — we humans are capable of imposing rapid, large-scale alterations on the environment. In a mere two decades, protective meshing of potentially dangerous sharks off the Natal coast of South Africa has radically altered the structure of the local marine ecosystem. Among the most striking of these changes is the proliferation of juvenile Dusky Sharks (Carcharhinus obscurus) and the reduction in small coastal teleost fishes. In response to the selective removal of large sharks from Natal coastal waters, the population of juvenile Duskies on which they fed has increased enormously. In turn, the small teleosts on which juvenile Dusky Sharks feed have been decimated by these efficient little predators. The result is a veritable ‘monoculture’ of small Dusky Sharks where once there was a diverse marine ecosystem — flowing with a wide variety of organisms, including large sharks and teleosts. Such an artificially simplified ecosystem may be more unstable and vulnerable to collapse than the original one.
But it doesn’t have to be that way. Concerned for both human safety and environmental integrity, the Natal Sharks Board is presently experimenting with alternatives to meshing that are effective yet non-lethal to sharks. Among the most promising of these is a system of electrical barriers that afford ocean-using humans protection from large, potentially dangerous sharks without killing them or noticeably altering the structure of the local marine environment.
A spin-off of this technology, called the “Shark POD”, surrounds a diver with an electric field which many sharks will not broach. But, rather than scaring off sharks, many divers would rather get close to them. This desire creates problems of its own. The truth is many sharks are very wary of divers and must be enticed within close range by baiting. Although most scientists regard organized shark dives as reasonably safe opportunities for tourists to observe sharks and learn a bit about their ecological role and intrinsic value as wildlife, a few argue that feeding sharks may not be healthy for them and teaches these toothy animals to associate humans with food. I and others are more concerned, however, that in attacking and competing for bait, sharks may injure themselves or each other — requiring them to divert energy stores toward wound healing that might have gone toward predator evasion, reproduction, or other activities vital to their survival.
More important than the survival of individual sharks is the continued existence of entire species. Species which enjoy wide distributions are generally less prone to extinction than those that occupy restricted ranges. But relatively few sharks — mostly exceptionally large species — are generally regarded as having a truly global distribution. Although — as we have seen — many shark species are highly adaptable to a range of habitat types, most small- to medium-sized sharks have rather restricted ranges. A shark’s range may be constrained by environmental tolerances (to such factors as temperature, salinity, dissolved oxygen content, and vulnerability to predators), various isolating mechanisms (such as current systems, continental landmasses, oceanic drop-offs, or geologic upheavals), and the practical limits of their inherent dispersive ability (in general, small sharks cannot store sufficient energy for long-distance travel). From tagging studies, we know that some shark species are migratory, while others don’t appear to be. But, in the vast majority of cases, we really don’t understand which specific conditions various shark species need to survive.
We do know that, for many shark species, access to suitable nursery areas is one of the most important factors in their survival. Shark nurseries typically occur in shallow coastal waters, where they provide relative safety from predators during the young sharks’ most vulnerable stage of their lives as well as plenty of food, enabling them to grow large enough so that few would-be predators are able to tackle them. Bulls Bay, in South Carolina, is a traditional nursery area for no fewer than nine species of sharks. Cleveland Bay, in northeastern Australia, is used as a nursery by at least eight species of sharks. If anything were to render either of these bays unsuitable as nursery areas, the long-term survival of all shark species that rely on them would be significantly reduced. Yet humans tend to settle near the coast, often favoring the same ‘pretty’, sheltered bays that many shark species rely on for use as nursery areas.
In some cases, legislation can be erected to protect important shark nursery areas. For example, the Dry Tortugas — a remote part of the Florida Keys — are an important mating and pupping site for Nurse Sharks (Ginglymostoma cirratum). Breeding is absolutely vital to this species continued survival in these waters, yet can be easily disrupted by the activities of waders, divers, strobe-using underwater photographers, and pleasure boaters. In response, a pair of researchers recently submitted a proposal to the U.S. National Park Service proposing that a section be declared a marine protected area, restricting public access during the Nurse Sharks’ breeding season (May through July). The proposal was approved in October 1995.
One of the greatest challenges to shark conservation efforts is lack of biological data. For many years, the International Union for the Conservation of Nature (IUCN) Shark Specialist Group has lobbied to award limited protection for the Whale Shark, Basking Shark, and White Shark under Appendix II of the Convention on International Trade in Endangered Species (CITES). In April 2000, the motion for all three species failed to receive the two-thirds majority vote required to pass. In large part, the vote failed to pass due to lack of data on each of these species population size, dynamics, and status. Undaunted, the IUCN Shark Specialist Group is presently lobbying to get the same three shark species listed under CITES Appendix III. But the problem of lack of supporting data remains.
Perhaps the most insidious threat to shark survival is aquatic pollution. We humans are a highly wasteful species, and much of what we throw away — in one form or another — ends up in the ocean. Lost or abandoned fishing gear continues to ensnare all manner of marine creatures, including sharks. Plastic wrapping straps often get caught around the gill region of young sharks, cutting deeply into their flesh as the animal grows until infection or strangulation eventually kills them. This is a particularly serious problem for Dusky and Tiger (Galeocerdo cuvier) Sharks off Western Australia and Florida, respectively. There is even a bizarre case of a large Tiger Shark caught near Havana, Cuba, in 1937, with an automobile tire encircling its gills.
Less dramatic, but every bit as detrimental for sharks, are the chemicals we introduce into the marine environment. Many heavy metal pollutants are known to have adverse effects on shark health. Cadmium constricts blood vessels, increases heart rate, and kills sperm. Mercury interferes with salt secretion via the rectal gland and also with sperm production. Zinc interferes with gill function. And copper increases blood pressure and changes blood parameters, often resulting in death. The effects of these chemicals increase with concentration. Since sheltered bays — such as those used as nursery and mating areas — and, especially, freshwater habitats have limited water exchange, chemical pollutants can accumulate to dangerous levels, posing very serious problems for sharks and every other inhabitant of these aquatic environments.
History has demonstrated over and over that we urgently need to modify our thinking with regards to shark conservation. Given the boom-and-bust nature of most commercial shark fisheries, I think we need to outgrow the economically-driven concept of “maximum sustainable yield” in favor of more cautious, ecologically responsible exploitation. Given the serious lack of biological data on most shark species that renders virtually any formal conservation effort impotent in the eyes of organizational opposition, we need to invest the time, money, and effort to scientifically assess the size, dynamics, and status of as many shark species as we can. Given the unwarranted fear and loathing with which many people regard sharks, we need to educate the general public about the ecological importance and intrinsic value of sharks as wildlife. Given the complexly interconnected nature of aquatic ecosystems, single-species conservation efforts — such as those that have been attempted to ‘save’ the spectacular and celebrated Great White Shark — are short-sighted and seem doomed to failure.
Given all these things, we need to adopt a habitat-wide approach to shark conservation. After all, even the most elegant fishery management model, the most complete life history studies, the most effective pro-shark PR campaign, and the best-intentioned conservation laws mean absolutely nothing if sharks don’t have a place to live.