Reef Sharks:Why Their Decline and What Can be done to Stop It(Final)

This topic submitted by Chris Nicolaou ( at 2:41 PM on 6/5/08.

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Reef Sharks:
Why Their Decline and What Can be done to Stop It
Chris Nicolaou

With coral reefs declining all over the world, so are the species that inhabit those areas. Several factors are responsible for the decline of these areas such as increased sedimentation and nutrients in the water, blast fishing, destruction of mangrove forests, and over fishing. Out of all these problems, the one that affects reef sharks most directly is over fishing. What is being done to help these creatures and is it working? So many factors are responsible for their decline so is it even possible to slow or even reverse the trends that seems to be occurring? In the Great Barrier Reef in Australia, many people are making an attempt to save reef sharks. To see if their efforts are working, the two most abundant reef shark species were studied, the white tip reef shark and the grey reef shark in the Great Barrier Reed. The Caribbean reef shark is also being studied a great deal in the Caribbean to see how they affect the reed habitat and to see if protected areas in the southwestern Atlantic Ocean are working.

Reefs are in a delicate balance and taking anything out of a thriving reef could mean its slow destruction. From just a reef perspective, the coral, reef fish, mangroves, and sea grass all work together to keep the reef alive and healthy. Mangroves and sea grass protect the coral from the waves. Take either one away and the reef will decline. From a larger perspective, the temperature of the water, the atmosphere, and the health of other reefs sometimes thousands of miles away depend on a specific reefs survival. If the water becomes too hot or cold the coral cannot survive. If a reef down current starts to fail, the reef up current will not receive the eggs and sperm to have greater diversity in the coral. So many things are involved in keeping a reef healthy such as the conditions of the rainforest, amount of sedimentation, herbivorous fish keeping algae in check, amount of nutrients in the water, amount of sunlight, over fishing, and blast fishing (Davidson). However, reefs are resilient and can recover if conditions improve if one knows what is causing the decline. With reef sharks, knowing what to do and doing it may be two different things but are working hard to reverse the decline of these important predators.

The Caribbean reef shark is the most common top predators associated with tropical reef ecosystems of the western Atlantic Ocean. Endemic to this area, this shark’s habitat ranges from North Carolina, Bermuda, and the east coast of Florida to southern Brazil. It operates at depths ranging from 5 meters to 30 meters according to a study about juvenile Caribbean reef sharks. It is fished mainly for its meat and fins and is the main species of shark feeding ecotourism activities in the Bahamas and Caribbean (Amorim, p. 236). Recent studies have shown that a decline in large predators such as the Caribbean reef shark may have extensive effects on the ecological functioning of coral reef systems (Amorim, p. 237). Knowing where these sharks live is an important step for effective conservation and fisheries management. Also, enhancing the survival of juvenile sharks is an important step in recovering and sustaining exploited shark populations. It is important to know the time of parturition, seasonal patterns of juvenile abundance, and the spatial distribution of juveniles (Amorim, p. 237). Knowing these things is the key to the recovery and sustainability of the shark population. The study by A. F. Amorim shows that the nursery areas for the Caribbean reef shark is very important to conserve and have restrictions on because if the female sharks have no where safe to have their offspring and the offspring does not have a safe place to grow then there is no hope for the species.
Reef sharks diet consists mainly of reef fish as well as eel and squid. Due to the increasing fishing pressures of many fisheries, much of the shark diet is becoming scarce (Choat, p. 2314). Although limits have been placed on fishing, reef shark catches are rarely subject to these fishing limitations. So, many areas are now being put into certain zones, 4 to be exact. No entry zones are off limits to all boats, are strictly enforced by plane, and make up 1% of total reef area on the Great Barrier Reef (Choat, p. 2314). No take zones allow boats to anchor but do not allow fish to be taken and make up 30% of total reef area on the GBR (Choat, p. 2314). Limited fishing zones have tight restrictions on the type of fish being caught as well as the amount of fishing gear permitted. This zone makes up 4% of total reef area. Open fishing zones make up 60% of the total area and have fewer equipment restrictions than limited fishing zones (Choat, p. 2314). Substantially lower numbers of reef sharks were found outside of the no entry zone (Choat, p. 2315). The question is whether 1% of the total reef area set aside for no entry zones is enough to ensure the long term maintenance of viable shark populations (Dulvy, p. 991). The no takes zones make up almost a third of the zones but are ineffective because of the great deal of illegal fishing that goes on. If these zone laws were more strictly enforced, the shark population might be closer to that of the no entry zones (Dulvy, p. 990).

No take and no entry zones are often the same size and are interspersed among open fishing and limited fish zones. No entry reefs may be found 1-2 kilometer away from open fishing reefs, yet shark populations are much more abundant in the no entry zones. The movements of reef sharks are normally limited to 0-3 kilometers, suggesting a high level of site fidelity (Choat, p. 2315). This evidence leans toward the theory that illegal fishing in no take zones is the difference between a healthy shark population and one that unhealthy. Also, if has been found that the density of sharks in no entry zones is similar to the densities found in remote reefs of Keeling Island which has no record of commercial shark fishing which indicates that the no entry zones are effective in the recovery of shark populations and that the populations are being sustained.

From the two examples above, the main trend seems to be a mix of fisheries management and protected areas to deal with the recovery and sustainability of shark populations. However, another important part of the equation is reproduction. In areas where there is such low population densities of sharks, increases the difficulty of finding suitable mates which may make the population collapse increasingly difficult to reverse as time progresses (Choat, p. 2315).

Studies of husbandry and reproduction of white tip reef sharks at Steinhart Aquarium show signs of aggression toward other young pups. The sharks at the aquarium were caught in the wild and competed for food. Sharks would attack the pregnant mom as well as the newly born pups. The lack of food due to over fishing may be the cause of this aggression toward the young pups (Schaller, p. 232). The shark pups that were born in the tank with the other sharks all had bit wounds and died within days. The sharks that were put in a holding tank during birth and then put back into the main tank did not suffer the same fate (Schaller, p. 239).

In conclusion, there is a great deal to be done if the decline of reef sharks is to stop. Obviously the best thing to do would be to stop fishing all together but that is not a plausible solution. The important reef areas need to be protected and better measures need to be taken to stop illegal fishing in specified zones. Over fishing in general needs to stop to allow not only shark populations to grow but the species of fish that are used commercially as well. Sharks are very important to the reef ecosystem as well as ecotourism in many countries. Future research should compare reproduction in over fished areas compared to healthy reefs to see if aggression toward shark pups by other sharks is increased due to the scarcity of food. This will aid in conservation efforts to help increase the density of shark populations in protected areas. The reef shark population will continue to decline as long as fisheries are put under large amounts of pressure to catch fish that they must break the law and fish in no take zones. The success on no entry zones can be duplicated in no take zones if people would not break the laws. If not the reef shark population will continue to decline and it will be too late to save them.

Works Cited
Amorim, A.F., Garla, R.C., Chapman, D.D., Shivij, M.S. “Habitat of juvenile Caribbean reef shark.” Fisheries Research 81 (2006): 236-241.

Armstrong, Christina "Wrestling Sharks for Better Management." Australian Geographic 51 (1998): 92-93.

Choat, Howard J., Robbins, William D., Hisano, Mizue, Connolly, Sean R.“Ongoing Collapse of Coral Reef Shark Populations.” Current Biology 16 (2006): 2314-1319.

Davidson, Osha G. The Enchanted Braid: Coming to terms with nature on the coral reef. New York: John Wiley & Sons Inc, 1998.

Dulvy, Nicholas K. “Conservation Biology: Strict Marine Protected Areas Prevent Reef Shark Declines.” Current Biology 16:23 (2006):989-991.

Schaller, P “Husbandry and Reproduction of Whitetip reef sharks at Steinhart Aquarium, San Francisco.” The Developing Zoo World 40 (2006): 232- 240.

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