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New scientific study shows shark numbers in the Mediterranean have crashed by 99%

11/06/2008 10:34:10 whales/Mediterranenan_shark_catch

June 2008. A new scientific study funded in part by the Lenfest Ocean Program has concluded that all shark species assessed in the Mediterranean Sea declined by more than 97 percent in abundance and "catch weight" over the last 200 years.

The findings of the study, Shark Declines in the Mediterranean Sea: A Summary of New Scientific Analysis, published in the journal Conservation Biology, suggest several Mediterranean shark species are at risk of extinction, especially if current levels of fishing pressure continue.

Lead author Francesco Ferretti and his co-authors are concerned that the declines in sharks may have implications for the broader Mediterranean marine ecosystem.

Ferretti said: "The loss of top predators such as sharks in other sectors of the Atlantic has resulted in changes to the ecosystem. These changes are unpredictable and poorly understood but given the decline in Mediterranean shark numbers, there is cause to be seriously concerned about the effects this could have."

47 species of shark in the Mediterranean
Forty-seven species of sharks live in the Mediterranean Sea, of which 20 are considered top predators. The study authors only had enough information to assess the status of five of the twenty large predatory shark species in the Mediterranean.

Of those analyzed, almost all of the large sharks have decreased in abundance because of unintended capture in open ocean fisheries, targeted shark fishing, and human population pressure in coastal areas. Sharks are especially vulnerable to over fishing and slow to recover from depletion because they generally grow slowly, mature late and produce few young.

Smallest sharks in the world
The mean size of sharks caught in the Mediterranean is among the lowest in the world. The study reveals that size and weight declines over time indicate that more young and immature sharks are being caught.

Margaret Bowman, director of the Lenfest Ocean Program said: "This study makes an important contribution to our understanding of how multiple pressures are threatening sharks. We understand too little about the consequences of losing top predators to take shark declines so lightly."

No catch limits
There are currently no catch limits for commercially-fished shark species in the Mediterranean Sea. A comprehensive monitoring program for fisheries has been difficult to implement in the Mediterranean because of the artisanal (small and localized) nature of its fisheries and the large number of countries bordering the sea.

Shark decline facts

- Forty-seven species of sharks live in the Mediterranean Sea, of which 20 are considered top predators in coastal and open ocean (pelagic) ecosystems.
- Only 5 of the 20 large predatory sharks were detected at levels of abundance sufficient for analysis. They include 2 mackerel sharks, the blue shark, 1 hammerhead shark, and 1 thresher shark.
- All assessed Mediterranean shark species declined by more than 97 percent in abundance and biomass, or catch weight, over the last 150-200 years across the considered portion of the Mediterranean Sea.
- The rates of shark decline in the Mediterranean are higher than those for comparable species in the Gulf of Mexico and similar trends in the Northwest Atlantic Ocean.
- The mean size of sharks caught in the Mediterranean is among the lowest in the world.
- The study reveals a relative faster decline of biomass than abundance over time. This would imply a declining presence of mature specimens with detrimental effect on the reproductive potential of these species.
- Historically, large sharks occurred throughout the Mediterranean Sea. In recent decades, however, large sharks seemed to be restricted to the eastern and southern Mediterranean coast or to offshore open waters.
- The Mediterranean Sea has a long history of marine resource use. Its fisheries have traditionally targeted many high-value species, including tuna and swordfish.
- In the 19th and early 20th Century, sharks were considered a pest for many fisheries.
- In the early 20th Century many coastal fisheries targeted sharks or landed them as bycatch.
- There are currently no catch limits for commercially-fished shark species in the Mediterranean Sea.

Only five species of sharks offered sufficient information for analysis, including the blue shark, one thresher shark species, two mackerel shark species, and one hammerhead shark species. The authors combined the two mackerel shark species for the analysis because of ambiguity in some of the data sets regarding species identification.

The blue, smooth hammerhead and thresher sharks were classified as "Vulnerable" according to the latest IUCN-World conservation Union Red List Criteria for extinction risk. Two mackerel sharks, porbeagle and shortfin mako, were classified as "critically endangered". Many other large sharks are classified as "Data Deficient".

For more information about the program, please visit www.lenfestocean.org

Shark Species

Hammerhead Sharks
- Of the 5 species analysed, hammerhead sharks have declined the fastest.
- After 1995 no records of hammerhead sharks could be found.
- The records show an estimated 99.99% decline for the hammerhead shark.

Blue Sharks
- In the North Ionian Sea, landings of the blue shark declined by 73.76% in abundance and 83.01% in biomass, whereas in Spanish waters it declined by 99.78% in biomass.
- Over the past 56 years, the blue shark has declined by 96.53% in abundance.
- Over the past 49 years, the blue shark has declined by 99.83% in biomass.

Mackerel Sharks
- The mackerel shark has declined by more than 99.99% in both abundance and biomass in the last over the last 100 years.

Thresher Sharks
- The thresher shark is the only species detected in coastal waters in recent times.
- Overall though, the species by declined by more than 99.99% over the last 100 years.

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