You are here:
BBC >
Science & Nature >
Animals >
Conservation >
Sharks
 |
|
|
|
Sharks |
|
 |
|
Species at risk
Find out more about life on the edge.
|
|
 |
|
 |
|
What can you do?
Get involved in conservation efforts and tell your friends!
|
|
|
Saving Planet Earth |
|
 | | You can make a positive change to the planet we live on... |
|
|
| Introduction - What are the threats? |
|
|
|
 | Bycatch
Sharks are frequently caught in trawler nets or on longline hooks that are set for tuna or swordfish. Sharks are highly migratory and they often swim in groups that are the same size and age. This can mean that a key part of the population (mature females for example) can be wiped out in one fell swoop. Estimates vary, but bycatch (unwanted catch) accounts for a significant proportion of shark fatalities.
|
|
| | Shark fin soup
Around 100 shark species are deliberately targeted by the fishing industry. Shark fins are highly prized for use in shark fin soup, a high status dish that can sell for £65 a bowl, especially in Asian countries where growing wealth has increased demand. As demand is met, sharks become overfished, fins are harder to come by and the soup is therefore even more of a status symbol.
Conservationists estimate that about 100 million sharks are caught each year, many of them purely for use in shark fin soup. Hong Kong alone imported the fins of more than 28 million sharks in 1999. The sharks are caught, their fins are cut off and they are then thrown back into the sea where they either bleed to death or drown. Using DNA, it is now possible to identify shark species from their fins, a development which may be significant in monitoring the impact of this trade.
|
| | Shark meat
Demand for shark meat is booming. It is now possible to buy it in supermarkets in Europe, South America and the USA. The shortfin mako which is said to provide the best shark meat is classified as lower risk, but vulnerable species such as the porbeagle shark, are also taken. This trend may be indicative of the fact that so many other fish species are declining and that people have been encouraged to eat fish as a healthy alternative to meat. The Food Standards Agency, however, has advised against giving children shark meat to eat because of high levels of methylmercury that can damage the nervous system.
|
| | Shark skin and oil
Shark skins can be tanned and used as an alternative to leather (for belts, boots, bags, etc). In theory and on a small scale, this could be a useful by-product of a sustainable and managed fishery. In practice, the impact on shark populations has yet to be assessed or monitored.
Sharks have traditionally been fished for oil. Squalene is extracted from shark livers and used as a lubricant and in cosmetic and pharmaceutical products. It can take up to 3,000 shark livers to produce one tonne of squalene.
|
| | Shark cartilage
Sharks are cartilaginous - they have cartilage instead of bone. The cartilage is used in traditional medicines and is sold in powder or capsule form as a cancer treatment. There is no scientific evidence to suggest that it is in any way effective against the disease and the 'medicine' can be very expensive. There may, however, be other benefits in maintaining shark biodiversity, for example, shark cartilage has also been used in the development of a synthetic skin for burn victims.
|
| | Breeding age
Sharks have evolved over 450 million years to be among the ocean's top predators. They can take many years to reach sexual maturity, almost 30 years in the case of the sand bank shark. Larger sharks may only produce two young in a breeding cycle and only one of those is likely to survive. Shark species often only breed every other year and some have a long gestation period (up to two years). This low reproductive rate means that depleted shark populations can take a very long time to recover, if they recover at all.
|
| | Pollution
The health of the ocean environment is important for all marine species. Pollution from human activity often ends up in the sea. Sharks are at the top of the food chain so they are likely to have a higher concentration of the toxins that build up in the body fat of their prey. Because human development and subsequent pollution often occurs in coastal areas, important shark nursery areas are also at risk.
|
| | Hunting
Although most sharks are indifferent to humans and pose no threat, shark hunting is still a widespread trophy sport.
|
|
|
|
