Sharks and rays under pressure
Sharks have been swimming the planet's oceans for over 400 million years. They have survived mass extinction events that saw the end of the dinosaurs. However, in recent times sharks and rays around the world have come under increasing pressure from humans. Some species are now threatened with extinction, and some sharks and rays have disappeared from areas where they were once found in large numbers.
Sharks and rays are vulnerable
Over millions of years sharks and rays have evolved to become perfectly adapted to the ocean environment. However, some of the traits that have helped them become so successful have also made them vulnerable to human impacts.
Sharks and rays are top level predators. Once fully grown, they have very few natural enemies so most sharks and rays live for a long time. Sharks and rays also reproduce very slowly and only produce a small number of young. Furthermore, many species of sharks and rays only begin to reproduce at a late age. For example, the sandbar shark (Carcharhinus plumbeus) lives for up to 35 years, but only begins breeding at 13 years of age, and only breeds every two years. When they do breed, female sandbar sharks only give birth to about 13 pups at a time.
Unfortunately, these traits make sharks and rays vulnerable to human impacts. As each breeding female only produces a few pups, reducing the number of adult sharks will also reduce the number of pups being born. Since these pups may take a long time to reach maturity, removing a large number of adult sharks in a short period can quickly result in too few pups being born to replace these losses which causes the population to collapse. Once this occurs, it can take a very long time for numbers to recover because the remaining adults will only produce a few young every season, and these pups may take a long time to reach maturity and start reproducing themselves.
The status of sharks and rays around the world
Around the world, sharks and rays are taken in fisheries ranging from small subsistence fisheries in inshore waters, to large industrialised fisheries in the open ocean. Since the 1950s, the number of sharks and rays caught around the world has greatly increased as traditional fisheries have declined, and due to increased demand for shark meat and liver oil. Since the1980s, there have been further increases in shark catches due to the demand for shark fins to make the traditional Asian delicacy, shark fin soup. The United Nations Food and Agricultural Organisation estimates that the global catch is over 100 million sharks and rays every year.
Around the world many shark fisheries have declined or collapsed from fishing. Examples include:
- Tope or soupfin shark (Galeorhinus galeus), California. The fishery expanded in 1937 and collapsed in 1945. Over 50 years later, no recovery has been recorded. Click here to find out more about the tope shark
- Basking shark (Cetorhinus maximus), West Ireland. The fishery began in 1947, peaked during the early 1950s but catches steadily declined from 1955. The fishery ended in 1975 and basking sharks are rarely seen today.
Click here to find out more about the basking shark
- The common skate (Raja batis), Europe. In the late 1900's the common skate was considered to be one of the most common elasmobranchs caught in north-west Europe, and used to be the main fish in "Fish and Chips" served throughout the United Kingdom. In 1981 it was declared to be extinct in the Irish Sea, more recent reports suggest that it has also disappeared from the North Sea.
For more information about the disappearance of the common skate, download the publication Sharks and their relativesand refer to page 17.
- The school shark (Galeorhinus australis), South Australia. The fishery peaked in 1949, with catches declining since 1994. Recent estimates put the pup production rate at only 12-18% of the production rate prior to commercial fishing.
Click herefor more information about the school shark
- Probeagle shark (Lamna nasus), Norway. Catches reached over 8,000 tonnes per year in 1964, but declined to 200 tonnes per year by 1989. Fishers no longer target porbeagle sharks, even though market demand and prices for porbeagle are still high. There were simply to few porbeagle sharks left for fishers to make the effort to fish for them.
Click here for more information about the porbeagle shark
There are many shark fisheries still operating around the world. However, little is known about how many sharks and rays they catch, or whether they are sustainable. Another problem is that fishermen targeting species such as tuna may accidentally catch sharks and rays in their nets and lines. While these sharks and rays may not be kept, many of them may be dead or injured by the time they can be released. The booming market for shark fins has also prompted many fishermen around the world to cut the fins off any sharks taken as bycatch instead of releasing them.
While a few shark fisheries have not declined, these fisheries usually have a relatively low level of fishing pressure and high levels of research and management to make sure that catches are sustainable. Some of these fisheries also target faster growing sharks and rays that produce more pups. However even these fisheries may take slower growing and more vulnerable sharks and rays as bycatch (for example the bycatch of school sharks in the Australian Southern Shark Fishery).
The World Conservation Union produces a list called the Red List that describes the extinction risk facing the world's animal and plant species. In 2004, the Red List identified 66 species of sharks and rays threatened with extinction around the world, and a further 70 sharks and rays as near threatened. Rising shark catches, collapsing fisheries, and increasing concerns about sharks and rays have highlighted the need to increase efforts to study, manage and conserve sharks around the world.
The status of sharks and rays in the Great Barrier Reef
There are about 125 species of sharks and rays on the Great Barrier Reef, however little is known about the biology or ecology of most of these species. For most species, basic information about how long they live, how often they reproduce or how quickly they grow has not been studied. However, in their role as top predators, sharks and rays are thought to play an important part in maintaining the Reef's ecological balance. Sharks and rays are also important sources of food for Aboriginal and Torres Strait Islander communities, who also have strong cultural connections with sharks and rays through art, totems and Dreamtime stories. Sharks are also recognised as important natural tourism attractions at dive sites in the Great Barrier Reef and Coral Sea.
The main pressure on sharks and rays in the Great Barrier Reef is commercial fishing. Since 1994, commercial fisheries logbooks report a fourfold increase in the amount of sharks taken by fisheries, with the commercial net fishery taking over 90% of the catch. It is unknown whether current fishing levels are sustainable. Some species such as hammerhead sharks or tiger sharks are also known to travel great distances, meaning that these sharks may also be caught by fishers in other parts of Australia, and throughout the Indo Pacific.
Given the vulnerable nature of sharks and rays, and declines in shark fisheries overseas, the increasing catch of sharks and rays in the Great Barrier Reef is a significant concern.