Over the past 20 years human exploitation of sharks has substantially increased worldwide, with the result that some populations are now believed to be endangered in several areas. It is far from easy to estimate the impact of the fishing pressure and of worldwide population trends from the available figures. Hard data are scarce, but biologists think that of the 100 exploited species, 20 or so are in most trouble and are considered vulnerable, endangered or critically endangered. There are signs that governments, too, are beginning to take the problem seriously.
Many shark species are particularly vulnerable to over-exploitation due to their biological characteristic of low reproductive potential and therefore limited capacity to recover from overfishing. Historically, there are documented decreases in shark stocks due to intensive catches, such as the California tope shark in the 1940s, the Australian schoolfin shark in the 1940s, 1950s and 1970s, the picked dogfish fishery of British Columbia (1940s) and in the North Sea (1960s), the porbeagle shark fishery in the Northwest Atlantic in the 1960s and the basking shark in the 1950-60s.
Limited knowledge of shark biology, of the size and status of their stocks, of the real volume of their captures and of their population dynamics presents serious difficulties for fishery management. Few nations sponsor shark research, monitor shark trade or conduct other sustainable management programs for sharks. No international treaties and management strategies exist for shark fished on the high seas, and only Australia, Canada, New Zealand, and the USA (Atlantic coast only) have begun to manage sharks within their coastal waters. Management plans are in development by Mexico and South Africa. Shark fishing restrictions are currently set up in South Africa, Australia, New Zealand, European Union, Canada, USA, Brazil, Philippines, and Israel.
A growing international concern over the possible effects of continued exploitation on marine food chains is emerging together with the need for improved control of fishing for shark species. CITES resolution on the biological and trade status of sharks (Conf. 9.17) and Decision 10.73 and respective related decisions by COFI XXI, XXII and the Kyoto Conference in 1995 resulted in an FAO work programme of which this book is one of the outputs and which led to the adoption of the IPOA (national plan of action for conservation and management of shark stocks) on sharks (full text in Appendix I).
Castro, Woodley and Brudeck have evaluated the status of all valid species of sharks listed by Compagno with a few additions or changes. The species have been divided into two groups: Not-exploited species (species that are not currently targeted by fisheries, and that are not normally found in the bycatch of any fisheries) and Exploited species (species that are directly exploited by fisheries or taken as bycatch). In turn, the exploited species have been divided into the following categories:
Category 1: Exploited species that can not be placed on any of the subsequent categories, because of lack of data.
Category 2: Species pursued in directed fisheries, and/or regularly found in bycatch, whose catches have not decreased historically, probably due to their higher reproductive potential.
Category 3: Species that are exploited by directed fisheries or bycatch, and have a limited reproductive potential, and/or other life history characteristics that make them especially vulnerable to overfishing, and/or that are being fished in their nursery areas.
Category 4: Species in this category show substantial historical declines in catches and/or have become locally extinct.
Category 5: Species that have become rare throughout the ranges where they were formerly abundant, based on historical records, catch statistics, or experts reports.
The following species are classified as category 3:
Bluntnose sixgill shark (Hexanchus griseus), Kitefin shark (Dalatias licha), Greenland shark (Somniosus microcephalus), Pacific angel shark (Squatina californica), Pelagic thresher (Alopias pelagicus), Bigeye thresher (Alopias superciliosus), Basking shark (Cetorhinus maximus), Great white shark (Carcharodon carcharias), Longfin mako (Isurus paucus), Gummy shark (Mustelus antarcticus), Blacknose shark (Carcharhinus acronotus), Copper shark (Carcharhinus brachyurus), Silky shark (Carcharhinus falcifomis), Finetooth shark (Carcharhinus isodon), Bull shark (Carcharhinus leucas), Blacktip shark (Carcharhinus limbatus), Oceanic whitetip shark (Carcharhinus longimanus), Spot-tail shark (Carcharhinus sorrah), Blue shark (Prionace glauca), Scalloped hammerhead (Sphyrna lewini), Great hammerhead (Sphyrna mokarran), Smalleye hammerhead (Sphyrna tudes).
The species listed below are considered as category 4:
Bramble shark (Echinorhinus brucus), Picked dogfish (Squalus acanthias), Sand tiger shark (Carcharias taurus), Thresher shark (Alopias vulpinus), Shortfin mako (Isurus oxyrinchus), Porbeagle (Lamna nasus), Whiskery shark (Furgaleus macki), Tope shark (Galeorhinus galeus), Leopard shark (Triakis semisfasciata), Dusky shark (Carcharhinus obscurus), Sandbar shark (Carcharhinus plumbeus), Night shark (Carcharhinus signatus) and the Blacktip shark (Carcharhinus limbatus) when found in shallow coastal waters.
No species have been classified in the category 5.
According to the Ocean Wildlife Campaign, a coalition of six conservation groups, some Atlantic species may have declined as much as 80%, partly because of overfishing. They claim that there is a decline of large coastal sharks such as sandbar, bull (Carcharhinus leucas), tiger, dusky, lemon (Negaprion acutidens) and nurse sharks.
The IUCN Red List assessments for Elasmobranchii (updated from the 1996 Red List of threatened animals) considered the following species as:
Ganges shark (Glyphis gangeticus), freshwater sawfish (Pristis microdon) in South East Asia, smalltooth sawfish (Pristis pectinata) in Northeast and Southwest Atlantic, largetooth sawfish (Pristis perotteti), Brazilian guitarfish (Rhinobatos horkelii), giant freshwater stingray (Himantura chaophraya) in Thailand.
Sandtiger shark (Carcharias taurus) in Southwest Atlantic and Eastern Australia, freshwater sawfish, smalltooth sawfish, common sawfish (Pristis pristis), common skate (Raja batis).
Sandtiger shark, great white shark, porbeagle in Northeast Atlantic, basking shark, dusky shark in the Northwest Atlantic, giant freshwater stingray.
lower risk, near threatened:
Bluntnose sixgill shark (Hexanchus griseus), porbeagle, blacktip shark, dusky shark, sandbar shark, kitefin shark (Dalatias licha), blue shark.
data considered deficient for:
Whale shark, deepsea skate (Bathyraja abyssicola).
In general the following species are considered to be at risk: blue, thresher, mako, porbeagle, salmon (Lamna ditropis), silky, oceanic whitetip shark (Carcharhinus longimanus) and hammerheads. These species are relatively abundant but there is concern about the great number of these sharks caught incidentally. Other species such as great white shark, whale shark, cookiecutter sharks (Isistius brasiliensis and labialis), largetooth cookiecutter (Isistius plutodus), pygmy shark (Squaliolus aliae and Euprotomicrus bispinatus), spined pygmy shark (Squaliolus laticaudus), and longnose pygmy shark (Heteroscymnoides marleyi) are landed in relatively low amounts but, being rather scarce, they are potentially at risk.
Among the species considered endangered are the great white, basking shark, the whale shark and picked dogfish.
The white shark is rather rare and ranges all the worlds oceans. It has a low reproductive potential. The greatest threat to this species, irrespective of region, is indirect commercial fisheries. Although not universally so, white shark flesh often has a high market value and is readily marketed for human consumption, often lumped for sale with the flesh from other more common Lamnidae. Furthermore, it has a role as a hunted trophy. In April 1991, South Africa became the first country to ban the killing of great white sharks. This species is actually protected from directed fishing in Namibia (1994), the Maldives, Gulf of Mexico, Atlantic Coast of the USA, California. Since December 1997 the great white shark is protected in all commonwealth waters of Australia, replacing earlier legislation enacted on a unilateral state-to-state basis by Tasmania, Western Australia, Queensland, and New South Wales. On 28 February 1998, the white shark achieved the status of endangered species in the area of São Paulo State in Brazil. Future additional effort will probably include the Mediterranean, after ratification of the Barcelona Conventions appendix II (which cites white sharks, alongside basking sharks and devil rays, as endangered Mediterranean fish).
Basking sharks were protected off the Isle of Man and, since 9 March 1998, throughout UK national waters. There is concern about the status of its stocks as basking sharks are considered one of the species most vulnerable to overfishing. In the 1950s the population of basking sharks was depleted off the coast of the west Ireland and there is still no sign of recovery.
On March 25, 1998, faced with sharply decreasing numbers of whale sharks and manta rays, the Philippine government has banned killing or selling them. The whale sharks are fully protected in Western Australia under the Wildlife Conservation Act and CALM (Department of Conservation and Land Management) Act. Fisheries targeting whale sharks are very small and exist mainly in India, the Philippines, and Taiwan Province of China. Whale shark has scarce commercial importance elsewhere. It was mainly fished for its meat but nowadays the fins and oil are also used.
Picked dogfish are considered to be seriously overfished in the Atlantic. The average size of mature females is reduced and, according to Castro, Woodley and Brudeck, their conservation status is highly vulnerable. Catches of this species have considerably increased in the last decade. There has been a substantial decline in the Northeast Atlantic and a huge growth in the Northwest Atlantic. There is a major problem due to the fact that this species lives mainly in schools of fish of uniform sex or size and fisheries for picked dogfish target mainly mature females, which are larger than males, as the European market especially appreciates larger specimens. The decline in female dogfish numbers affects the reproduction of this species particularly as female picked dogfish do not begin to reproduce until they are at least 13 years old. The gestation period is two years long.
[23 ]In Israeli waters there
is a generalized protected status for all Elasmobranchii.|
[24 ]CASTRO J.I, , WOODLEY C.M and BRUDEK R.L., idem.
[25 ]CAMHI M., FOWLER S., MUSICK J., BRÄUTIGAM A., FORDHAM S., "Sharks and their relatives. Ecology and conservation", IUCN, 1998.
[26 ]CASTRO J.I, , WOODLEY C.M and BRUDEK R.L., idem.