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Shark Info   (03-15-2000)



Aliwal Shoal

Shark Info

  Main article:

Aliwal Shoal - a paradise for sand tiger sharks

Andrew Cobb

  Article 1:

Viviparous Sharks

Prof. H. Greven

  Article 2:

Molecular biology helps protect sharks

Prof. M. S. Shivji

  Fact Sheet:

Sand Tiger Sharks

Dr. E. K. Ritter

Molecular biology helps protect sharks

By Prof. Mahmood S. Shivji

There is mounting and widespread concern over the health of shark populations worldwide. Driving this concern is the recognition that shark fisheries have increased rapidly since the early 1980s, with little or no concurrent implementation of management and conservation efforts by most nations participating in the fishery to protect and preserve natural shark populations. Although sharks have a long history of being utilized for their products (meat, skin or liver oil), this utilization generally remained at low levels until the 1980s. Since that time, however, sudden changing marketing conditions parallel to expanded commercial fishing as a whole have intensified tremendously so that the portion of sharks caught as bycatches literally exploded.

The sudden interest of the market in sharks was triggered by the alleged pharmaceutical effects of their cartilage (Editor's Note: An effect which to date has still not been scientifically proven) and the increased demand for shark fins in Asian markets for shark fin soup. Furthermore, the declining availability of bony fish has increased the demand for shark meat as a substitute for traditional fish products. The reason for the alarming increase in bycatches of sharks is due to the worldwide intensification of deep-sea fishing targeting pelagic fish such as tuna, billfish and the mahimahi or large gold mackerel (Coryphaena hippurus).

Many authorities on this subject are convinced that bycatches pose the greatest threat to current shark populations. A statistic prepared by the FAO (Food and Agricultural Organization) clearly illustrates the magnitude of shark bycatch: In 1991 alone, the tuna and billfish longline fishing fleets of Japan, Korea and Taiwan deployed approximately 750 million hooks which incidentally caught an estimated 8.3 million sharks!

Although sharks are not the target species in many fisheries, incidentally caught sharks, which used to be thrown back into the ocean, are today harvested for their fins. With their fins cut off, the mutilated bodies of the animals, many of which are still alive, are simply discarded at sea.

Scientists and animal welfarists agree that there is an urgent need to implement protective regulations and measures to ensure long-term management of shark populations which are so vital to the ecology of the sea. It is a fact that sharks can no longer compensate for the immense pressure which the fishing industry puts on their populations with their slow growth, late maturation and limited number of offspring. Currently as a rule, there are absolutely no controls on shark fishing, no plans for population management and no consideration for either closed seasons and size, as exist for bony fish (e.g. herrings). However, planning effective conservation measures and management measures requires profound scientific knowledge and understanding about the animals to be managed. Regrettably, little effort has traditionally been devoted to collecting scientific information on sharks and thus it is currently very difficult to establish any scientifically based management plans for shark populations.

A major problem is the lack of reliable statistical data on numbers of each different shark species being landed, incidentally caught and discarded in shark targeted and nontargeted fisheries. The absence of such data makes it practically impossible to quantify the impact of the fishing industry on individual shark species. Like other vertebrates, shark species differ from each other in their biological characteristics and behavior (e.g. number of offspring, movements, feeding habits, growth rates, physiology, etc.). Collecting catch data on a species-specific basis is therefore critical to prevent overexploitation of individual species that are more vulnerable to fishing pressure due to their particular biological characteristics.

Shark carcasses

Shark carcasses without heads, fins, tails and guts as they are sold portside. In most cases not even specialists can identify the individual species. (Source: J. Castro)

© Prof. M. S. Shivj

There are two main reasons for the almost complete lack of species-specific catch data. First, individual fishing nations have simply not made the effort to collect such data. And second, even nations which practice some form of shark fishery management still find it very difficult to collect reliable, species-specific catch data. The major reason is that frequently only a trained eye can accurately identify individual shark species from each other, which is especially true of many species in the commonly harvested shark genus Carcharhinus. Compounding this identification factor is that landed sharks are processed immediately on the fishing vessel, with the fins, head, tail and guts removed to prevent spoiling of the meat and to reduce the required storage space in the vessel's hold. Large carcasses are usually cut into smaller pieces and are delivered to portside buyers. Accurate identification is extremely difficult, even for experts such as port fishery observers or fish merchants who deal with sharks on a daily basis.

The species identification problem is even more difficult when it comes to finning. Since only the fins remain, it is virtually impossible to reliably identify the species based only on fin form and texture. Most shark fishery experts are convinced that the largest impact on shark populations comes from the finning industry. Years ago, sharks caught as bycatches were simply tossed overboard - alive - at sea. Today they are mutilated by finning and die. Given the magnitude and constant growth of this industry, it is obvious why precise knowledge of catch numbers are imperative for the management and conservation of individual species.

Shark fins

Shark fins whose origin can only be determined using molecular biological methods.
© D. Perrine

To enable the collection of catch data on a species-specifc level, we investigated the application of molecular biological methods and DNA technology to see if they were suitable to solve these identification problems. Based on earlier research in my laboratory, we discovered that certain genetic regions in the shark's chromosomes were almost the same for one shark species, but that the same areas varied in other species. In other words, we found diverse DNA sequences typical for different shark species which can be considered equivalent to their individual fingerprints.

Applying this discovery together with already known and extremely efficient molecular- biological techniques, we were able to develop a series of DNA markers which could be used to clearly identify certain shark species. Tissue samples for this analysis can be very small, 10 mg of dried or fresh fin, skin, meat or blood are sufficient. These are checked for a specific genetic fingerprint of a species. So far we have developed DNA markers for nine commonly harvested or endangered shark species, in other words we can accurately identify even minute tissue samples stemming from the white shark (Carcharodon carcharias), blue shark (Prionace glauca), common thresher shark (Alopias vulpinus), porbeagle shark (Lamna nasus), shortfin and longfin mako (Isurus oxyrinchus, I. paucus), Caribbean reef shark (Carcharhinus perezi), dusky shark (Carcharhinus obscurus) or the sandbar shark (Carcharhinus plumbeus). And work continues to expand this list.

In order to enable the large-scale DNA testing required to evaluate catch data from commercial fisheries, we are experimenting with streamlining the identification process. For example, we have developed an exciting new system which strongly simplifies and speeds up the screening of tissue sample while maintaining its accuracy. By optimizing DNA markers and test conditions we can now simultaneously distinguish between nine different shark species in one single test. This reduces the amount of work involved by nearly 90% compared to screening for one species at a time. In this way we can analyze larger numbers of unknown samples in less time. Current research now aims at recording the DNA sample on a biochip to allow application of microarray technology which permits automation and large-scale sample screening.

As indicated earlier, an assessment of which sharks and how many of each species are being harvested is of fundamental importance for effective long-term management and conservation. The methods we have developed provide a practical solution to the longstanding problems of shark species identification. As soon as diagnostic markers for additional species have been established, there will be no logical reason why those industrial countries who wish to effectively manage and protect their shark populations cannot implement these methods in their data collection efforts. The only prerequisites are certain financial means and a laboratory equipped with very modest molecular biological testing equipment. Today such laboratories are found in practically every large city. Industrialized countries are responsible for the bulk of global shark fishing. Their participation in collecting species-specific catch data would thus be of invaluable help in scientific investigations on the impact of the fishing industry on global shark populations.

An extension of our research program is analyzing the origin of shark fins offered on the market by both wholesale and retail markets on a global basis in order to determine which shark species are mainly caught for their fins. Since markets in different countries favor different types of fins, we anticipate that targeted species may differ depending on the country involved. The objective of our research is to ascertain which shark species in which regions are preferred for finning purposes and are subjected to the most pressure through the fishing industry. In this way we can help national and international conservation organizations implement protective programs based on solid facts.

Another important advantage benefiting shark protection, afforded by the ability to identify shark species and body parts, is that it will allow enforceability of current and future CITES regulations for sharks. For the first time it will be possible to identify endangered shark species based on minute tissue probes, even when only parts of their bodies are available, so that violations against regulations can be punished accordingly.

We anticipate that when implemented globally, our new shark identification method will contribute significantly towards better shark protection and management worldwide.

DNA Editor's note: DNA stands for "deoxyribonucleic acid" which is found in the cell nucleus of allmost all life and contains the building instructions for all bodily proteins.

* Prof. Mahmood S. Shivji is Assistant Professor at the Oceanographic Center of Nova Southestern University in Dania Beach, Florida, USA.

May be published only by indicating the source: Shark Info / Prof. Mahmood S. Shivji



last change: 06-04-2016 11:48