Effects of Some Destructive Fishing Methods on Coral ... - Springer Link

Effects of Some Destructive Fishing Methods on Coral Cover and Potential Rates of Recovery JOHN W. MCMANUS* RODOLFO B. REYES, JR. International Center for Living Aquatic Resources Management MCPO Box 2631 0718 Makati, Philippines ˜ OLA, JR. CLETO L. NAN Marine Science Institute University of the Philippines Diliman, Q.C. 1101 Philippines ABSTRACT / Effects of fishing with explosives (blastfishing) and sodium cyanide and of anchor damage on live coral were investigated on a heavily exploited fringing reef in Boli-

Destructive fishing is common in coral reef areas where population and economic pressures lead to a state of intense competitiveness among coastal villagers (Galvez and others 1989, McManus 1988, McManus and others 1988, 1992, Men ˜ ez and others 1991). This situation has been termed ‘‘Malthusian overfishing’’ (Pauly and others 1989, 1990, see also Russ 1991, McManus and others 1992), and it is a problem that is growing rapidly as human populations grow in coastal developing countries. Two common forms of destructive fishing involve the use of explosives (blastfishing) and poison. Blastfishing is used worldwide on coral reefs in at least 40 countries or island dependencies (UNEP/IUCN 1988). Blastfishing and siltation are believed to be the two most important causes of reef destruction in Southeast Asia (Yap and Gomez 1985). Poisoning is used to capture fish in at least 15 countries or dependencies (UNEP/IUCN 1988). Damage due to anchors is prevalent in most countries with coral reefs and is associated with a variety of reef fishing methods. This paper is concerned with attempts to gain a perspective on the nature and relative importance of blasting, poisoning with sodium cyanide, and anchor damage on the forereef slope of a fringing reef subject to Malthusian overfishing. There have been several models of

KEY WORDS: Destructive fishing; Blastfishing; Cyanide; Coral; Coral reef; Coastal management *Author to whom correspondence should be addressed.

Environmental Management Vol. 21, No. 1, pp. 69–78

nao, Philippines from 1987 to 1990. A simple balance-sheet model indicated that approximately 1.4%/yr of the hermatypic coral cover may have been lost to blasting, 0.4%/yr to cyanide, and 0.03%/yr to coral-grabbing anchors, the potential coral recovery rate reduced by about one third from 3.8%/yr in the absence of disturbances to 2.4%/yr. These figures are subject to considerable uncertainty due to compounding of errors during computation. Reefs with patchy coral cover are more susceptible to damage from blastfishing because of targeting by fishers. Reefs with smaller corals may have greater resilience, because each unit of radial colony growth contributes a greater per cent increase in areal cover. Blastfishing in particular may reduce resilience to natural perturbations, leading to assemblages of small, sparse corals and reduced patchiness.

coral growth in assemblages, most of which have been interannual, dynamic, and stochastic (e.g., Maguire and Porter 1977, Hughes 1984, Reichelt and others 1985, Done 1988). In this study, simple calculations were used to compare expected rates of damage and regrowth within a one-year time frame. It was intended to provide preliminary information on the rates of damage and recovery and to highlight areas for further research in preparation for more predictive, dynamic modeling efforts in the future.

Study Site Santiago Island lies on the western tip of the Lingayen Gulf of Luzon, facing the South China Sea (Figure 1). The reef has been described in detail in McManus and others (1992), and some relevant aspects are summarized here. The reef includes a reef flat dominated by seagrass beds intersected by channels and lagoons. A swimming survey was conducted in 1986 involving four transects at 1- to 2-km intervals bisecting the reef flat north to south and totaling over 6 km. Examination of all coral patches encountered revealed that approximately 60% of all recognizable scleractinian coral (excluding rubble, distinguished by the absence of sharp surface features) was dead, and many patches showed obvious signs of blasting (e.g., fractured branching corals in radiating patterns). Participants in several informal surveys in 1978–1980 and examination of photographs from that era confirmed that the live coral had been highly dominant in nonsandy areas and

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J. W. McManus and others

Figure 1. Map of visual transect sites (T) from which blasts were recorded.

that dead coral (as defined above) was barely noticeable. Thus, it has been inferred that most of this damage had occurred within the previous six years (see McManus and others 1992). The reduction of coral and associated fish populations has led to intensified fishing on the reef slope, the subject of this study. The reef slope is separated from the reef flat by an irregular, wave-breaking reef crest. A narrow section of the slope extends at least 20 km to the northeast as a subsurface barrier reef. However, only the semicircular portion within 2 km of the reef crest is considered in this study. The bottom ranges from smooth to highly irregular because of ridges, rifts, and dense karst depressions. In many areas at 15–20 m, the slope rounds off into a wall extending to 20–30 m, into a sand and rubble talus slope of 10–20° broken by coral mounds. A jackknife estimation procedure indicated that at least 900 species of fish are to be found on the reef slope (Jaranilla and McManus 1992). The fish form indistinct and temporally variable aggregations influenced by depth (possibly including temperature), salinity, and surface roughness, especially at scales of less than 1 m (Nan ˜ ola et al. 1990). Scleractinian corals generally cover 10–30% of the bottom amid diverse benthic plant and animal assemblages, although dense coral patches covering hundreds of square meters occur sporadically. Visible coral destruction ranges from very little to 50% of hard corals, often with apparent blast patterns or standing dead coral. The corals of the reef slope include many newly settled colonies of several species growing on or amid damaged corals.

Fisheries The fisheries of the island have been described in several recent papers (e.g., del Norte and others 1989;

McManus 1989a,b; McManus and Men ˜ ez 1989; del Norte and Pauly 1990; McManus and Rivera 1990; McManus and others 1992). The large fringing reef provides the principal means of support through fishing and gathering. Approximately 350 species of fish, invertebrates, and seaweeds are sold in local markets. Fishing craft include small, single-person bamboo rafts and double outrigger canoes (bankas) ranging from 3 to 12 m. The larger bankas carry 15- to 20-hp gasoline engines. The most common fishing gears on the reef slope are hand lines, spears, drive-in surface nets, octopus lures, squid jigs, sodium cyanide, and various blasting devices. The primary fishing area (and study area) of the reef slope covers approximately 40 km2, representing 95% of fishing effort (McManus and others 1992). Most of the anchors are grappling hooks designed to catch on corals. They are usually constructed from iron reinforcing rods, with a span of 0.3–1 m. A variety of explosive devices are used in local fishing operations, including most of those described in studies of fisheries of soft-bottom areas (Galvez and Sadorra 1988; Galvez 1989; Galvez and others 1989). The most common bomb is constructed by filling a beer, gin, or soda bottle with layers of powdered potassium nitrate and pebbles. A commercial fuse or blasting cap is used so as to permit delayed, subsurface ignition. A small amount of gasoline is added immediately prior to use. Potassium nitrate is readily available, as it is sold commercially for spraying on mango trees to induce flowering. A single bomb can cost 1–2 US dollars (US$) to construct. Some fishers claim that a good catch can be 10–20 kg, with a market value of US$ 15–40. Bombs are often constructed at home by men, women, and children (Tungpalan and others 1991), and stored under the bamboo houses. Many people lose limbs or lives in premature explosions, but the return on investment is considered to be high enough to warrant the risk (Galvez and others 1989). Local fishers use poisons from a variety of leaves, roots, and berries. Bleach and insecticides have reportedly been used in tide pools. Sodium cyanide is believed to be the most commonly used poison, and accounts for approximately 70% of the fish captured for the aquarium industry (Hingco and Rivera 1991) and is also used in fishing for consumption (McManus and others 1992). The cyanide is sold as a tablet for mining operations. The tablet is broken up (sometimes by biting it) and mixed with seawater immediately before use in small squeeze bottles. A skin or hookah diver applies the poison by squirting the fluid at the desired fish or its abode among the corals (Galvez and others 1989). Alternatively, the tablet may be secured whole to a stick and held in the vicinity of the fish. The fish becomes

Destructive Fishing vs Coral Cover

stunned for easy capture, and often emerges from protective cover as it experiences respiratory stress. The fishes experience a high mortality after transit to international locations, and the Philippine aquarium industry suffers great losses because of its reputation for use of this technique (Albaladejo and Corpuz 1981, Rubec 1986, 1988). A single tablet costs approximately US$0.25–0.50 and suffices for two squeeze bottles. Cyanide and spearfishers using crude hookah equipment commonly suffer from decompression sickness, embolisms, hearing loss, and other diving-related maladies. A cyanide fisher’s net return is believed to greatly exceed that of the average fisher, whose income is generally about US$1/day (An ˜ onuevo 1989). Both poison fishing and blastfishing were banned in 1979, but continue to be used extensively.

Materials and Methods Fieldwork Field observations of the fishery and reef and interviews with fishers were conducted over a 14-year period, but principally during a period of monitoring from June 1986 to June 1992. The study involved over 800 h in underwater observations and 50 h of aerial observation at the study site. The ongoing program of fish community monitoring required teams of divers to survey 18 transects on the reef slope visually on alternate months. The methods and results of this survey are reported elsewhere (Nan ˜ ola and others 1990, McManus and others 1992), and it is sufficient to note here that frequencies of blasting were determined by the divers as they performed underwater fish counts along 100-m transects. During the period from November 1987 to September 1989, selected divers recorded time in the water and the number of blasts heard during the dive. Listening periods of less than 6 min were eliminated to reduce recording biases, leaving 87 sampling times totaling 30 h. All boats involved in fishing on the forereef slope were mapped at midday from 23 May 1989 to 16 December 1990 on a random day each week selected from a random-number table. Project personnel hired from local villages judged whether or not each boat was likely to have been engaged in blast fishing. The Model Rates of potential coral destruction from blasting were assessed against rates of potential coral regrowth using a balance sheet model. The model consisted of deterministic calculations performed on spreadsheet software, with separate calculations for worst, moderate,

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and best cases. The moderate estimates are those based on what are believed to be the most reasonable estimates for inputs. The worst and best case estimates are based on combinations of inputs (some based on 95% confidence limits from data sources), which result in higher or lower estimated damage rates, respectively. Because they involve combinations of all best and all worst inputs, they represent scenarios that are possible, but unlikely, to represent the real case. Sensitivity analyses were conducted by varying input values singly and graphing the net or gross coral loss for situations where total coral cover was 5%, 10%, and 15%. A description of the logic behind the inputs in the model is given here by line number (in brackets; see Table 1). [1] Underwater blast counts yielded 10 blasts per hour (63, 95% CI, N 5 87) in clear weather. ‘‘Good’’ hours (5–7 h with sufficient light to effectively target the corals, allowing for time at the end of the day to land catch for sale to late afternoon markets) were based on the results of the boat mappings described above. [4] Blasting is not common during periods of rain, wind, or siltiness after storms. Estimates (15–25%) are based on informal interviews with fishers. [7] The radius of coral kill from a blast (0.5–1.5 m) was estimated roughly based on our observations of blast patterns among corals, which confirmed those of Mathias and Langham (1978) and Maclean (1988). Variations could arise from sizes of bombs and from the frequency with which slightly damaged corals die from other factors, e.g., disease (Antonius 1981, Peters 1984). However, we are not aware of any evidence linking disease susceptibility to blasting effects. [9] The bottom cover in the patches that were targeted by fishers (40–60%) was based on field observations of coral patch densities in blasted areas. [12] The effective listening radius (2–3 km) was based on observations made jointly by boatmen and divers during blasting. This probably varies considerably with topography, as it is possible to escape unpleasant effects of nearby blasts in shallow water by dropping down along a wall, down-slope and perpendicular to the sound path. [15] The coral cover across the fished portions of the reef slope was estimated from towed-diver observations. [18] The average size of a coral in the area was estimated from data on corals on reef slopes at Puerto Galera, Mindoro, as 14 cm (61.3, 95% CI, N 5 801), each coral having been measured in a random direction through the center (unpublished data of Dr. Porfirio A. Alin ˜ o, University of the Philippines Marine Science Institute). The area is believed to be subject to levels and types of disturbance similar to Bolinao. The model assumes that corals of similar sizes inhabit the Bolinao reef slope. [20] Growth rates for 33 common Philippine species


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Table 1.

Balance sheet for coral recovery following blast fishinga Cases Worst

How many blasts? 1 Number of blasts per good hour 2 Number of good hours per day 3 Number of blasts on a good day 4 Bad weather days per year (%) 5 Number of good days per year 6 Number of blasts per year How much damage? 7 Radius of coral kill per blast (m) 8 Area affected per blast (m2) 9 Coral cover in target patch (%) 10 Coral affected per blast (m2) 11 Coral damage/yr in listen.area (km2) 12 Listening radius (km) 13 Listening area (km2) 14 Coral loss per km2 (km2) 15 Coral cover on reef slope (%) 16 Coral lost per year (%) How much recovery possible? 17 Average radius growing coral (m) 18 Starting area/coral (m2) 19 Radial growth/yr (m) 20 Ending area/coral (m2) 21 Area gained/coral/yr (m2) 22 Number corals per km2 23 Number of corals killed/km2 24 Remaining corals each year 25 Area coral growth/km2/yr (km2) 26 Corals replaced/yr (%) 27 Number new corals/yr 28 Max. new coral area after 1 y (km2) 29 Total coral growth/sq. km (km2) 30 Total coral growth per yr (%) 31 Net gain of coral/yr (%) aInput

Moderate

13 7 91 15 310 28,233

10 6 60 20 292 17,520

1.5 7.1 60 4.24 0.12 2.00 12.6 0.01 5 19 0.15 0.07 0.020 0.09 0.020 707,355 134,801 572,554 0.012 1 1348 2E-06 0.012 1.2 218

1.0 3.1 50 1.57 0.028 2.50 19.6 0.0014 10 1.40 0.14 0.06 0.025 0.09 0.024 1,624,030 22,762 1,601,268 0.038 10 2276 4E-06 0.038 3.8 2.4

Best 7 5 35 25 274 9,581 0.5 0.8 40 0.31 0.003 3.00 28.3 0.00011 15 0.07 0.13 0.05 0.030 0.08 0.027 2,825,236 2,005 2,823,231 0.077 50 1003 3E-06 0.077 8 8

Equation A1 A2 A3 A4 A5 A6

Input Input 5 A1 3 A 2 Input 5 365 3 (1 2 A4) 5 A3 3 A 5

A7 Input A8 5 p 3 A27 A9 Input A10 5 A8 3 A 9 A11 5 A6 3 A 10 3 1026 A12 Input A13 5 p 3 A212 A14 5 A11/A 13 A15 Input A16 5 A14/A 15 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 A31

Input 5 p 3 A217 Input 5 (A17 1 A 19)2 3 p 5 A20 2 A 18 5 A15/(A 18 3 1026) 5 A16 3 A 22 5 A22 2 A 23 5 A21 3 A 24 3 1026 Input 5 A23 3 A 26 5 p 3 A219 3 10 26 3 A27 5 A25 1 A 28 5 A29 5 A30 2 A 16

variables and calculations are indicated in the right-most column.

reported (Gomez and others 1985) averaged 2.5 cm (60.6, 95% CI). These values are based on field measurements and so account for growth reductions upon reaching maximal sizes for some species and feeding by fish and invertebrates (e.g., Neudecker 1979, Moyer and others 1982). The model assumes, for simplicity, that the reef slope supports the average species from this selection, growing with no particular directional bias (hence, circularly on average). In reality, the slope supports a wide variety of species but is dominated by poritids and faviids for which 2.5 cm is a reasonable estimate. The slope is large, gradual, and irregular in direction, so growth directional bias is not expected to be substantial. [24] Estimations of numbers of corals assumed no significant overlap of corals and circular morphologies on average. [28] The percent of corals that would be replaced each year was a rough estimation based on field observations. Alin ˜ o and oth-

ers (1985) cleared all corals away in a 24-m2 area of backreef (in a reef adjacent to the present study site) and found that the combined soft and hard coral cover after one year had reached only 1% of initial cover. As shown [30], the new corals have a negligible effect on annual growth calculations. The model is based only on one year of losses and gains, and thus does not allow the new corals to grow to sizes of significance. At the beginning of a year, corals settling from previous years are accounted for in the cover and mean size estimates. A more dynamic model would require accounting for changes in size structure over multiple years. Potential effects of sodium cyanide fishing and anchor damage were similarly modeled (Table 2). [34] Ferrer and others (1988) reported that the aquarium fish industry in Binabalian, Santiago Island, involved approximately six managers with ten divers each, and four managers with three divers each. Hingco and


Table 2.

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Balance sheet for coral damage from cyanide and anchor usea Cases

How important is damage from cyanide? 32 Total number of users 33 Area of use (km2) 34 Users/km2 35 Bottles/hour good hours 36 Corals dosed per bottle 37 Dosed corals that die (%) 38 Corals killed per bottle 39 Corals killed/h/user good hours 40 Good hours per day 41 Good days per year 42 Corals killed/yr/km2 43 Corals killed each yr (%) How important is anchor damage? 44 Total number of boats/day 45 Boats/km2/day 46 Number of anchor drops/day/boat 47 Number of anchor drops/day 48 Total area of fishing (km2) 49 Drops per km2/day 50 Number corals killed per drop 51 Good days per year 52 Corals killed/yr/km2 53 Corals killed each yr (%) aCalculations

Worst

Moderate

Best

50 35 1.4 3 60 10 6.0 18.0 7 310 55,845 8

40 40 1.0 2 40 5 2.0 4.0 6 292 7,008 0.4

30 45 0.7 1 20 1 0.2 0.2 5 274 183 0.01

A32 A33 A34 A35 A36 A37 A38 A39 A40 A41 A42 A43

Input Input 5 A32/A 33 Input Input Input 5 A36 3 A 37 5 A35 3 A 38

21 0.47 2 42 45 1 0.5 274 128 0.005

A44 A45 A46 A47 A48 A49 A50 A51 A52 A53

Input 5 A44/A 48 Input 5 A44 3 A 46 Input 5 A47/A 48 Input 5 A5 5 A49 3 A 50 3 A51 5 A52/A 22

25 0.71 4 100 35 3 2.0 310 1,773 0.25

23 0.58 3 69 40 2 1.0 292 504 0.03

Equation

5 A5 5 A34 3 A 39 3 A40 3 A41 5 A42/A 22

are continued from Table 1.

Rivera (1991) reported that 70% of the divers used cyanide. We assumed that 80% of the fish come from the reef slope and that the remaining 20% came from the reef flat. Thus of 72 divers, approximately 40 divers fished with cyanide on the reef slope. Uncertainty arises from the proportion fishing the slope versus the flat, and from the possibility of fishers from other villages using cyanide. Cyanide fishing for food was believed to be primarily a problem on the reef flat and was not included here. [35] The fishing area that included 95% of the activity was determined from the weekly mappings of fishing boats (McManus and others 1992). [37] The number of bottles used each hour and [38] the number of corals dosed per bottle were determined from a few informal interviews and were highly variable. [39] The mortality of dosed corals was difficult to estimate, because of a paucity of published information on the subject (Rubec 1986). Experience with the use of cyanide for scientific fish collection indicates that the percentage of exposed corals that die may not be high, but further studies are needed. For the exploratory purposes of the model, values were chosen ranging from 1% to 10% mortality of corals directly exposed to cyanide by fish collectors. The likelihood that 5% was the most reasonable value was confirmed through informal discussions with fishers familiar with cyanide fishing.

[46] The boat mapping yielded a mean of 23 6 2.4 (95% CI) boats per day. [48] The number of times a boat drops its anchor in a day was based on interviews and familiarity with fishing activity patterns. [52] The local boats usually drift until the anchor becomes hooked on a solid coral or overhang. The anchor often dislodges several corals before catching hold, and one or more corals are often broken while retrieving the anchor. The wave and current action are such that a broken coral has little chance of regaining a secure hold later.

Results Blastfishing during the period November 1987 to August 1989 occurred with a frequency of 10.1 blasts/h (62.8, 95% CI, N 5 87 dives). The number of boats on the reef slope during the period July 1988 to December 1990 was 23.0 boats/day (62.4, 95% CI, N 5 101 days), of which those believed to be engaged in blastfishing were 0.53 boats/day (60.34, 95% CI), or 2.3%. The number of fishers during the same period was 34.6 fishers/day (64.0, 95% CI, N 5 101 days), of which 0.76 (60.44, 95% CI) or 2.2% may have been involved in blastfishing. Moderate case estimates place the loss of coral cover on the reef slope to blastfishing at approximately

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Figure 2. Effect of varying the estimated effective listening radius on net annual coral growth under the blastfishing model in Table 1 with moderate inputs. The dotted line assumes 5% coral cover, solid line 10% and dashed line 15%. Vertical lines indicate range of values used in Table 1. The range of values considered here extends beyond this range to illustrate the expected variations under other conditions.

Figure 3. Effect of varying the amount of coral cover within clumps on net annual coral growth (symbols and assumptions as in Figure 2).

1.4%/yr, reducing the recovery capacity of the coral from 3.8% to 2.4% per year. Note that in this model, the distribution of sizes of corals lost is assumed to equal the distribution of sizes of corals present. Thus, a percent loss in numbers would equal the same percent loss in area (for large numbers). Coral mortality from fishing with sodium cyanide may have also been about 2%/yr. The loss to anchor damage may have been about 0.3%/yr. Compounding of errors of estimation during calculations resulted in considerable levels of uncertainty, such that in each case, the difference in estimated rates of damage differed between best- and worst-case models by two orders of magnitude. The moderate estimate of net coral growth (accounting for blasting) varies by less than 1.3% if one assumes that the effective listening radius was 2 km vs 3 km (Figure 2, variation on the vertical axis associated with a shift in radius). The uncertainty associated with the coral cover has a greater effect, resulting in a variation in estimated net growth of approximately 5% for the

otherwise moderate model scenario. In four of five sensitivity analyses (Figures 2, 3, 5, and 6), lower bottom covers led to greater uncertainty effects. A variation in the estimated density of coral in clumps from 40% to 60% resulted in a variation of net coral growth of only 0.6% (Figure 3). Diminishing degrees of clumping strongly reduce the sensitivity of the reef to blasting, especially when overall cover is low, because less of the total coral area is reduced per blast. The smaller the mean size of the corals making up a particular percent bottom cover, the greater the percent annual growth of coral (Figure 4). However, the net coral growth from average corals of 13–15 cm varied only by 0.6%. In this analysis, less coral cover resulted in less of an effect on net coral growth. This is because lower coral covers would indicate that there are less corals to grow in a given year, and thus less of an effect of variability in the size on the total regrowth. There is considerable uncertainty about the mortality effect of sodium cyanide exposure on corals (Figure 5). This uncertainty would be especially problematic in


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Figure 4. Effect of varying the mean radius of coral colonies on net annual coral growth (symbols and assumptions as in Figure 2).

Figure 5. Effect of varying the percent of dosed corals that die on net annual coral growth based on the moderate coral poisoning scenario of Table 2 (symbols as in Figure 2).

analyses of effects on reefs with very low coral covers. The relationship between coral mortality because of anchor damage and the concentration of boats over a reef (Figure 6) indicates that reefs with low coral covers would be particularly susceptible to anchor damage. This is because the anchors tend to drag until one or more corals are encountered, and the number of corals damaged would not be strongly affected by a reduction in the total number of corals.

Discussion The results of the simulation suggest that blastfishing in Bolinao may reduce the growth capacity of scleractinian coral on the reef slope by approximately one third (Table 1, lines 30 and 31, moderate scenario). This would be expected to considerably reduce the resilience of the ecosystem to damage from natural perturbations such as storms and outbreaks of coral predators. The former may be of particular concern, as the area is

in the path of several typhoons each year. At best, the blastfishing would have no substantial effect, and at worst, it could result in a net loss of coral cover of 14% per year. The variability is a result of compounding errors in calculations (see Rastetter and others 1992), and the primary uncertainty to which the model is sensitive appears to be the estimation of bottom cover (Figures 2–6). The model indicates that reefs with smaller corals would exhibit a higher resilience in terms of annual percent regrowth of coral cover (Figure 4) because a given amount of radial growth in a colony contributes a greater proportion of colony increase in smaller corals. The density of corals in patches affects the degree of damage inflicted by blasting, as patches with higher density would exhibit higher rates of mortality per blast (Figure 3). The effect on overall cover would be greatest when the corals are very patchy and overall coral cover is low. Combining these two effects, one would infer that, as blasting continues over time, the effect of

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Figure 6. Effect of varying boat densities on the coral mortality from anchor damage estimated in Table 2 (symbols as in Figure 2).

blasting on the percent coral cover would diminish somewhat, because the average coral size would lessen, increasing resilience, and the amount of coral in patches would decline, reducing the percent of coral area damaged per blast. Additionally, one would expect that blasting would become less cost-effective as coral densities in target patches declines. Thus, blastfishing should lead to reef slopes of low patchiness, but have reduced effects as coral cover becomes sparse. Widespread population reduction, however, could lead to diminishing recruitment of new corals and thus decreasing resilience. Coral species that are rare throughout most of their range could be threatened with extinction, especially when the range is encompassed by countries subject to substantial reef damage. Furthermore, recent evidence indicates that the reduction of habitat in patchy ecosystems may threaten dominant species at least as much as rare ones, depending on factors including the degree to which the dominant species are dependent on high abundances for survival (Tilman and others 1994). Fishing with cyanide appeared to have much less effect on coral cover than blasting, at the rates of usage estimated for Bolinao. The estimated mortality from cyanide ranged from 0.01% to 8% of corals per year (Table 2, line 43). The upper value in particular helps to emphasize the need for studies to determine the actual rates of mortality of corals in the field exposed to cyanide during fishing operations. Anchor damage had surprisingly little effect on overall coral cover in the simulation. The model would indicate (very tentatively) that anchor damage would only become a major factor (1% mortality/yr) as coral cover diminished to about 5% or less and boat densities increased to 10 boats/km2/day. One would also expect anchor damage to alter the coral community composition over time, favoring encrusting forms over branch-

ing and fragile platelike forms. The boats in this study were on average smaller, and used smaller anchors, than the dive boats in many tourist areas. Concentrations of 10 or more dive boats daily are common on popular diving sites. Damage in such sites would tend to be highly concentrated at particular coral patches. Thus, the results of the model do not apply to anchoring in the context of tourism. The simulation model presented is a very preliminary attempt to answer questions such as: how does the rate of damage from destructive fishing compare to the rate of growth of the corals? The approach used involved basing simple calculations on estimates of coral size, patch densities, and other inputs for which ‘‘reasonableness’’ was based on experience and literature values. The model highlights some potential areas of concern for reef management, as well as research areas which should be prioritized, such as studies of effects of cyanide on corals. It also highlights the need for caution in even simple calculations from the compounding of uncertainties from estimation. The model is particularly limited in its concentration on annual balances, while omitting factors of importance interannually such as coral recruitment and selection. It is hoped the work here will encourage the development of more useful, dynamic models of anthropogenic coral reef perturbation and recovery in the future.

Acknowledgments The authors wish to thank all those who have been involved in the monitoring effort, especially K. Kesner, J. A. Cabansag, E. Dumeran, J. Castrense, W. Campos, A. Campos, J. Cabansag and J. Pasamonte. Helpful information was provided by P. Alin ˜ o, L. McManus, N. de Perio, B. Elefante, G. Ragos, C. Consaga, C. Diolazo, and F. de Guzman. Suggestions from G. Russ, C. Wilkinson, T.


Hughes, T. Done and were greatly appreciated. This research was funded by USAID Biodiversity Program grant DAN-4024-G-SS-9113-00 and the USAID Fisheries Stock Assessment Collaborative Research Support Program grant DAN-4146-G-SS-5071-00, while the senior author was connected with the University of Rhode Island and the University of the Philippines, and by European Commission contract 87-5040/93/32 while at the International Center for Living Aquatic Resources Management (ICLARM). This is contribution number 260 of the Marine Science Institute, University of the Philippines and ICLARM contribution number 1259.

Literature Cited

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Philippines, Diliman, Quezon City, Philippines, 204 pp. (unpublished). Galvez, R. E. 1989. Blast fishing and government response in Lingayen Gulf. Pages 2286–2299 in O. T. Magoon and others (eds.), Proceedings of the sixth symposium on coastal and ocean management. American Society of Civil Engineers, New York, New York. Galvez, R. E., and M. S. M. Sadorra. 1988. Blast fishing: A Philippine case study. Tropical Coastal Area Management 3(1):9–10. Galvez, R. E., T. G. Hingco, C. Bautista, M. T. Tungpalan. 1989. Sociocultural dynamics of blast fishing in two fishing villages in the Lingayen Gulf area. ICLARM Conference Proceedings 17:43–62. Gomez, E. D., A. C. Alcala, H. T. Yap, L. C. Alcala, and P. M. Alin ˜ o. 1985. Growth studies of commercially important scleractinians. Pages 199–204 in Proceedings of the fifth international coral reef congress, Vol. 6. Antenne MuseumEphe, Moorea, French Polynesia.

Albaladejo, V. D., and V. T. Corpuz. 1981. A market study of the aquarium fish industry of the Philippines: An assessment of the growth and the mechanics of the trade. Pages 75–81 in E. D. Gomez and others (eds.), The reef and man: Proceedings of the fourth international coral reef symposium, Vol. 1. Marine Sciences Center, University of the Philippines, Quezon City, Philippines.

Hughes, T. 1984. Population dynamics based on individual size rather than on age: A general model with a coral reef example. American Naturalist 123(6):778–795.

Alin ˜ o, P. M., P. V. Banzon, H. T. Yap, E. D. Gomez, J. T. Morales, and R. P. Bayoneto. 1985. Recovery and recolonization on a damaged backreef area at Cangaluyan Is. (Northern Philippines). Pages 279–284 in Proceedings of the fifth international coral reef congress, Vol. 4. Antenne Museum-Ephe, Moorea, French Polynesia.

Jaranilla, M. H. S., and J. W. McManus. 1992. Applications of jackknife estimations of species richness and diversity to a coral reef fish community in Bolinao, Philippines. Pages 223–225 in Proceedings of the first national symposium in marine science. Marine Science Institute, University of the Philippines, Quezon City, Philippines.

An ˜ onuevo, C. 1989. The economics of municipal fisheries: the case of the Lingayen Gulf. ICLARM Conference Proceedings 17:141–155.

Maclean, J. L. 1988. Blast fishing and poisoning threaten the Philippines’ last undersea wilderness area. Naga, ICLARM Quarterly 9(1):14–16.

Antonius, A. 1981. Coral pathology: A review. Pages 3–6 in E. D. Gomez and others (eds.), The reef and man: Proceedings of the fourth international coral reef symposium, Vol. 2. Marine Sciences Center, University of the Philippines, Quezon City, Philippines.

Maguire, L. A., and J. W. Porter. 1977. A spatial model of growth and competition strategies in coral communities. Ecological Modelling 3:249–271.

del Norte, A. G. C., and D. Pauly. 1990. Virtual population estimates of monthly recruitment and biomass of rabbitfish, Siganus fuscescens off Bolinao, northern Philippines. Pages 851–854 in R. Hirano, and I. Hanyu, (eds.), The second Asian fisheries forum. Asian Fisheries Society, Manila, Philippines. del Norte, A. G. C., C. L. Nan ˜ ola, J. W. McManus, R. B. Reyes, W. L. Campos, and J. B. P. Cabansag. 1989. Overfishing on a Philippine coral reef: A glimpse into the future. Pages 3087–3097 in O. T. Magoon and others (eds.), Proceedings of the sixth symposium on coastal and ocean management. American Society of Civil Engineers, New York, New York. Done, T. J. 1988. Simulation of recovery of pre-disturbance size structure in populations of Porites spp. damaged by the crown of thorns starfish Acanthaster planci. Marine Biology 100:51–61. Ferrer, E. M., C. An ˜ onuevo, G. Castillo, R. Catelo, H. Chan, R. Rivera, and S. Rodriguez. 1988. Marketing studies of selected commodities in Lingayen Gulf. ASEAN Coastal Resources Management Program report. College of Social Work and Community Development, University of the

Hingco, T. G., and R. Rivera. 1991. Aquarium fish industry in the Philippines: Toward development or destruction? ICLARM Conference Proceedings 22:249–253.

Mathias, J. A., and N. P. E. Langham. 1978. Coral reefs. Pages 117–151 in T. E. Chua and J. A. Mathias, (eds.), Coastal resources of western Sabah. Penerbit Universiti, Sains, Malaysia. McManus, J. W. 1988. Coral reefs of the ASEAN region: Status and management. Ambio 17(3):189–193. McManus, J. W., E. M. Ferrer, and W. L. Campos. 1988. A village-level approach to coastal adaptive management and resource assessment (CAMRA). Pages 381–386 in Proceedings of the sixth international coral reef symposium, Vol. 4. The Sixth International Coral Reef Symposium Executive Committee, Townsville, Australia. McManus, J. W., C. L. Nan ˜ ola, R. B. Reyes, and K. N. Kesner. 1992. Resource Ecology of the Bolinao Coral Reef System. ICLARM Studies and Reviews 22, 117 pp. McManus, L. T. 1989a. Coralline resources of Lingayen Gulf, Philippines: A proposal for their management. Pages 3098– 3107 in O. T. Magoon and others (eds.), Proceedings of the sixth symposium on coastal and ocean management. American Society of Civil Engineers, New York, New York. McManus, L. T. 1989b. The gleaners of Northwest Lingayen Gulf, Philippines. Naga, ICLARM Quarterly 12(2):13.

78


McManus, L. T., and L. A. Men ˜ ez. 1989. Status of coralline resources in Lingayen Gulf. ICLARM Conference Proceedings 17:63–70. McManus, L. T., and R. A. Rivera. 1990. Population and socioeconomics. ICLARM Technical Report 22:38–43. Men ˜ ez, L. A. B., L. T. McManus, N. M. Metra, J. F. Jimenez, C. A. Rivera, J. M. Conception, and C. Z. Luna. 1991. Survey of the coral resources of western Lingayen Gulf, Philippines. ICLARM Conference Proceedings 22:77–82. Moyer, J. T., W. K. Emerson, and M. Ross. 1982. Massive destruction of scleractinian corals by the muricid gastropod, Drupella in Japan and the Philippines. Nautilus 96(2):69–82. Nan ˜ ola, C. L., J. W. McManus, W. L. Campos, A. G. C. del Norte, R. B. Reyes, J. B. P. Cabansag, and J. N. D. Pasamonte. 1990. Spatio-temporal variations in community structure in a heavily fished forereef slope in Bolinao, Philippines. Pages 377–380 in R. Hirano, and I. Hanyu (eds.), The second Asian fisheries forum. Asian Fisheries Society, Manila, Philippines. Neudecker, S. 1979. Effects of grazing and browsing fishes on the zonation of corals in Guam. Ecology 60(4):666–672. Pauly, D. 1990. On Malthusian overfishing. Naga, ICLARM Quarterly 13(1):3–4. Pauly, D., G. Silvestre, and I. R. Smith. 1989. On development, fisheries and dynamite: A brief review of tropical fisheries management. Natural Resources Modeling 3(3):307–329. Peters, E. C. 1984. A survey of the normal and pathological histology of scleractinian corals with emphasis on the effects of sedimentation stress. PhD dissertation. University of Rhode Island, Narragansett, Rhode Island. Rastetter, E. B., A. W. King, B. J. Cosby, G. M. Hornberger, R. V. O’Neill, and J. E. Hobbie. 1992. Aggregating fine-scale

ecological knowledge to model coarser-scale attributes of ecosystems. Ecological Applications 2(1):55–70. Reichelt, R. E., D. G. Green, and R. H. Bradbury. 1985. Discrete simulation of cyclone effects on the spatial pattern and community structure of a coral reef. Pages 337–342 in Proceedings of the fifth international coral reef congress, Vol. 3. Antenne Museum-Ephe, Moorea, French Polynesia. Rubec, P. J. 1986. The effects of sodium cyanide on coral reefs and marine fish in the Philippines. Pages 297–302 in J. L. Maclean, L. B. Dizon, and L. V. Hosillos, (eds.), The first Asian fisheries forum. Asian Fisheries Society, Manila, Philippines. Rubec, P. J. 1988. Cyanide fishing and the International Marinelife Alliance net-training program. Tropical Coastal Area Management 3(1):11–13. Russ, G. R. 1991. Coral reef fisheries: effects and yields. Pages 601–635 in P. F. Sale (ed.), The Ecology of Coral Reefs. Academic Press, New York, 754 pp. Tilman, D., R. M. May, C. L. Lehman, and M. A. Nowak. 1994. Habitat destruction and the extinction debt. Nature 371: 65–66. Tungpalan, M. T. V., M. F. Mangahas, and M. P. E. Palis. 1991. Women in fishing villages: Roles and potential for coastal resources management. ICLARM Conference Proceedings 22: 237–243. UNEP/IUCN. 1988. Coral reefs of the world, 3 vols. UNEP Regional Seas Directories and Bibliographies. IUCN, Gland, Switzerland and Cambridge, UK/UNEP, Nairobi, Kenya. Yap, H. T., and E. D. Gomez. 1985. Coral reef degradation and pollution in the East Asian Seas region. UNEP Regional Seas Report Studies 69:185–207.