The negative effects of blast fishing on coral reefs in Indonesia: Can they recover?

Shannon England, Undergraduate Student, Dalhousie University

Abstract Blast fishing, the destructive and illegal fishing method that involves using dynamite, is the cause of extensive damage to many coral reefs throughout Southeast Asia. Using explosives not only kills the vast majority of organisms within the blast radius, but also shatters coral skeletons leaving large rubble fields that prevent the recovery of damaged coral. Methods of rehabilitation have been implemented in order to determine how effective rehabilitation is in aiding the regrowth and recovery of damaged reefs near Indonesia. Economically friendly methods such as using rock piles, plastic mesh and cement slabs as treatments were examined and compared. The results of the studies showed that rock piles increased biodiversity and favoured the recovery of hard coral cover more than the other two treatment methods. Although rehabilitation is necessary for reef recovery, the elimination of blast fishing is equally as important to ensure healthy reefs and newly recovered reefs are not harmed.

1. Introduction

Blast fishing, also known as dynamite fishing, is defined as the illegal practice of using explosives to stun or to kill schools of fish for easy collection. It is one of the most destructive and immediate threats to coral reefs all over the world (Fox and Caldwell 2006). There are many negative impacts on the productivity of coral reefs and there is a large amount of evidence showing that the destruction of coral habitats leads to immediate declines in fish species richness (Raymundo et al. 2007). Dynamite fishing destroys the coral reef habitat and kills all organisms within a 20-meter radius of each blast. This fishing method is extremely wasteful as only roughly 3% of the organisms involved are recovered from the blast and are able to be collected and sold (Lauridsen 2013).

This fishing method is particularly prominent in Southeast Asia, and this area will be the primary focus of this review. The Philippines and Indonesia are home to coral reefs with the highest diversity of coral species and other reef-dependent organisms in the world. The rapidly growing population and economy in Southeast Asia are posing a large threat to the coral reef ecosystems in the area. Out of all the coral reefs on earth, an estimated 18% of them are located in Indonesia, and over 85% of these reefs are threatened by human impacts (Fox et al. 2004). During World War II, blast fishing was introduced in Indonesia as a way to catch schooling fish. Fishermen more recently believe that this fishing method is the only way to catch enough fish to support their families due to the decline in other fisheries sectors

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(Pet-Soede et al. 1999). Although blast fishing was banned in Indonesia in 1985, this practice continues to occur. It is estimated as of 2006 that blast fishing has damaged over half of all the reefs in Southeastern Asia (Fox and Caldwell 2006).

Different methods of reef rehabilitation and restoration have been implemented in several different blast affected reef areas in order to determine whether the reefs are able to recover from the damage (Fox et al. 2004). Rehabilitation consists of using substrate stabilization as a way of enhancing natural reef recovery, whereas restoration involves re-establishing the biological structural and geological aspects of the reef. Many of these techniques are expensive and require excessive labor, which unfortunately may be too costly for developing countries to afford. However, there are less expensive “low-tech” techniques that can be useful in reef rehabilitation (Fox et al. 2004). This review will focus on analyzing various techniques for rehabilitating reefs damaged by blast fishing to prove that the most effective technique is the addition of loose rock. The benefits of rehabilitating these reefs and cost of leaving them untreated will also be discussed.

2. Review Body 2.1 Blast Fishing Effects on Ecosystem

Holding around one third of all described species in the ocean, coral reefs are the most biodiverse ecosystems in the world. There are millions of people on earth that are dependent on coral reef ecosystems for sources of protein and other services such as tourism. The extinction of a large portion of the biodiversity on earth could be a consequence of not resolving coral reef destruction (Veron et al. 2009). Blast fishing is particularly damaging due to the fact that it destroys the reef by removing the resource itself (Fox et al. 2004). Dynamite fishing alters the reef structure physically by creating expanses of unstable coral rubble and by shattering the coral skeletons. This harmful practice also lowers the survival of coral recruits, the first coral larvae to settle in a particular location (Fox and Caldwell 2006). The fragmented coral resulting from destructive fishing methods does not survive and the reef function and fish habitats are significantly reduced in the blasted areas (Raymundo et al. 2007). With blast damaged reefs reduced to rubble fields, it’s highly unlikely that these reefs would be able to sustain an active ecosystem (Pet- Soede et al. 1999). An example of this is that once a reef is blasted, all organisms on the reef fall victim to the explosion. The reef is no longer able to provide food and shelter to marine organisms and thus the once thriving ecosystem is destroyed. (Pet-Soede et al.1999).

2.2 Recovery and Rehabilitation: Small Scale Studies

In a study conducted by Fox and Caldwell (2006) in Pulau Tiga, Indonesia, areas affected by a single blast were examined over a period of several years of natural recovery. It was determined that the bombs detonated on the underlying reef layer when the blasts occurred in water that was approximately 5-10m deep. The explosion from the blast crushed the immediate coral into small pieces of rubble.

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The surrounding areas about 2-4m away from the center of the blast had been broken into larger pieces of rubble about five to ten times larger. The porosity of the rubble, the hard coral cover, as well as the taxon, size and location of each coral recruit was measured initially and then again several times over the next two years. The results of this study found that after one year, large remains of broken coral surrounded the affected rubble zone. The blast had killed over 70% of the coral initially and even more during the 12 months following the blast, however after 5 years there had been impressive recovery. The number of coral recruits increased after this time, filling in the rubble zone with the coral larvae and other surviving coral (Fox and Caldwell 2006).

Figure 1: The percent cover of hard coral on unblasted and adjacent blasted reef over five years (Fox and Caldwell 2006).

As seen in Fig. 1, the condition of the hard coral cover was determined to be almost the same as it had been before the blast, suggesting considerable recovery over the treatment period.

An additional study on coral rehabilitation conducted by Fox et al. (2004) was located around the Komodo National Park in eastern Indonesia. The analysis involved using three substrate stabilization treatments in a 1x1 m area in an attempt to stabilize the loose rubble. The first method of stabilization was the attachment of 5cm of wide mesh fishing net to the rubble using steel rebar-pins. The second method used cement slabs and attached them to the rubble and the final treatment involved covering the rubble by stacking 40cm high piles of rocks on top. Four replications of each treatment were applied to damaged areas of 1x1 m; in addition four untreated equally damaged areas were studied, to establish a baseline for the treatment. The results of this study showed that after three years, the rock piles were the most effective rehabilitation method, followed by the other two methods. The untreated rubble had the least effective recovery (Fox et al. 2004).

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Raymundo et al. (2007) used a similar method of rehabilitation as Fox et al. (2004) on reefs located in central Philippines. Treatment was applied to five 17.5 m2 areas of rubble field in the Calagalag Marine Protected Area. This method involved using plastic mesh screens and laying them directly on the rubble and anchoring them in place and then constructing rock piles and placing them on top of the mesh. Improvements in the hard coral cover were observed, as well as less rubble covered area than on the untreated area (Raymundo et al. 2007).

2.3 Recovery and Rehabilitation: Large Scale Studies

Fox and Caldwell (2006) investigated the natural recovery of nine different larger rubble fields off the coast of Indonesia. The rubble fields were in 5-10m of water and greater than 300 square meters in area. The researchers then divided the sites into three groups and according to the speed of the current in that location. The sites were classified as low, medium or high current. The coral recruitment was evaluated every year for six years in each rubble site by measuring the location, number and size of hard coral recruits. The results determined that after six years in the large rubble fields, there was no significant increase in coral recruit and therefore a lack of recovery in these heavily damaged areas. The rubble sites classified as high current areas had much more rubble movement, and this increased movement was found to correspond to a much smaller survival rate of the corals relocated into the rubble sites (Fox and Caldwell 2006).

As determined in the small-scale study done by Fox et al. (2004), the rock pile method was the most successful rehabilitation method studied. For the large-scale analysis of stabilizing substrate in areas greater than 1000 m2, different rock pile designs were evaluated. The same volume of rock (140m3) was used for each design to determine which design would offer the best recovery and restoration for the same cost. The study found that the rock pile treatments were successful in transforming the rubble sites into habitats with improved structure, as well as a larger diversity of fish on the rock pile than the rubble site (Fox et al. 2004).

2.4 Effects of Rehabilitation on Fish Communities

Raymundo et al. (2007) used the plastic mesh and rock piles and measured the amount of individuals from each different fish species and the amount of coral recruitment in the area four times annually for the next four years. The groupings for the fish community were based off of the abundance and family of the reef fish. The data collected was analyzed to determine whether the rehabilitation method had a positive impact on the fish communities.

In Fig. 2, it is seen that the total fish biomass significantly increased in the rehabilitated area indicating that the fish community had reacted positively to the treatment. Herbivores and planktivores, plankton-eating species, both showed the largest increase in biomass and variability (Raymundo et al. 2007).

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Figure 2. The changes in fish biomass per trophic group over time, in (a) rubble field (RU), (b) rehabilitated area (RHB), and (c) healthy reef (HR) (Raymundo et al. 2007).

2.5 Other Explanations of Reef Damage

It is evident that dynamite fishing has had a large negative impact on the coral reefs affected but it is important to understand that it is not only blast fishing that contributes to coral reef deterioration, as there are also other anthropogenic causes as well as several natural contributors. Common natural sources include wave

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action, fluctuations in the temperature, movement of tectonic plates, large storms, increased number of predators and diseases developing on the reefs. Other human contributions include pollution and other forms of overfishing (Pet-Soede et al. 1999).

3. Conclusion

The most effective method of low technology and low-cost rehabilitation was found to be the rock pile procedure (Fox et al. 2004; Raymundo et al. 2007). This technique favoured the recovery of hard coral cover and the biodiversity and abundance of fish in the treated rubble fields (Fox et al. 2004; Raymundo et al. 2007). Coral recruitment was also increased, which indicates healthy recovery of coral communities by promoting regrowth of coral (Fox et al. 2004). Fox and Caldwell (2006) found that large rubble fields left untreated do not recover from blasts after several years, and it is not yet known if they would ever make a significant improvement. This shows that human intervention is necessary for large- scale blast affected areas if recovery is desired.

From the point of view of many blast fishers, this technique is believed to be the last resort to make enough money for their families. This is especially the case with unspoiled reefs. The amount of fish caught by a blast fisherman in two days would take three weeks to catch using traditional fishing methods (Pet-Soede et al. 1999). This would explain why fishermen break the law in order to use this destructive method. Although it takes much less time to use blast fishing as opposed to traditional fishing, it is so wasteful and far less sustainable that it only seems logical to harvest coral reef fish in a way that would recover the majority of the resource as opposed to a mere 3%.

In order to fully succeed in the pursuit of healthy and sustainable coral reefs, it is essential that both prevention of the main cause of damage, blast fishing, is terminated completely and also successful rehabilitation is achieved on all affected reefs. From the studies done regarding rehabilitation, it can be concluded that using rock piles is a cost effective form of rehabilitation that can be afforded by developing countries and is successful in achieving hard coral cover recovery, increased coral recruitment and restoration in fish communities. The studies examined support the hypothesis that damaged a coral reef is capable of recovery given time, protection and proper rehabilitation.

In the future, research involving the progress of the rehabilitation of treated reefs should be re-assessed. This is to see if, after 10 or more years, the treated areas are continuing to improve. This affordable form of rock pile rehabilitation should be implemented on all small-scale blast-affected reefs all over the world to ensure that new life is able to succeed on reefs that had once been destroyed. Fox and Caldwell (2006) determined that applying the rock piles helped significantly improve the reef condition in large rubble fields, but it does not seem completely viable for human intervention on such large areas. This is because of the human labor required to

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apply this treatment. Future research consisting of a better treatment alternative for large spatial scales, or a lower-effort method of applying the rock piles is encouraged.

More action is required to monitor and enforce the cessation of blast fishing where it is still occurring perhaps by having more law enforcement patrolling popular blast areas in hopes of catching any illegal explosive fishing activity. In the future, this stabilization method could be to park reef-management programs in hopes of restoring ecological as well as economic value to coral reef ecosystems. There is still support is needed from organizations and the public to encourage better management when it comes to rehabilitation of damaged reefs.

References Fox HE, Caldwell RL. 2006. Recovery from blast fishing on coral reefs: a tale of two scales. Ecol Appl. 16 (5):1631-1635.

Fox HE, Mous PJ, Pet JS, Muljadi AH, Caldwell RL. 2004. Experimental assessment of coral reef rehabilitation following blast fishing. Conserv Biol. 19: 98-107.

Lauridsen M. 2013. Dynamite Fishing- A lethal threat to tourists and marine life. Mar Pollut Bull. 66(2):2-3.

Pet-Soede C, Cesar HS, Pet JS. 1999. An economic analysis of blast fishing on Indonesian coral reefs. Environ Conserv. 26(2) 83-93.

Raymundo LJ, Maypa AP, Gomez ED, Cadiz P. 2007. Can dynamite-blasted reefs recover? A novel, low-tech approach to stimulating natural recovery in fish and coral population. Mar Pollut Bull. 54(7):1009-1019.

Veron JE, Hoegh-Guldberg O, Lenton TM, Lough JM, Obura DO, Pearce-Kelly P, Sheppard CR, Spalding M, Stafford-Smith MG, Rogers AD. 2009. The coral reef crisis: The critical importance of <350ppm CO2. Mar Pollut Bull. 58(10):1428-1436.

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