estimating the potential fisheries production of three ......the results of the study underscore the...

Hazel O. Arceo1*, Joey P. Cabasan2, Rhea Mae A. Luciano2, Lovely Joy D. Heyres3, Samuel S. Mamauag4, and Porfirio M. Aliño2

Estimating the Potential Fisheries Production of Three Offshore Reefs in the West Philippine Sea, Philippines

*Corresponding Author: [email protected]

1Department of Biology and Environmental Science, College of ScienceUniversity of the Philippines Cebu, Lahug, Cebu City 6000 Philippines

2The Marine Science Institute, University of the PhilippinesDiliman, Quezon City 1101 Philippines

3College of Fisheries and Ocean Sciences, University of the Philippines Visayas Miag-ao, Iloilo 5023 Philippines

4Marine Environment Resources Foundation, Inc.Velasquez St., Diliman, Quezon City 1101 Philippines

Evaluating reef fisheries potential is crucial in understanding the benefits derived from coral reefs. In this study, fisheries production of three offshore reefs in the West Philippine Sea was characterized using both fishery-dependent and fishery-independent approaches. Experimental fishing was done using speargun and multiple hook-and-line in Pagasa Island and Sabina Shoal, Kalayaan Island Group (KIG) while interviews to assess fisheries production for the Scarborough Shoal were conducted in Masinloc, Zambales. Catch composition, total catch, and catch rates were obtained. Catch composition differed among gears although it was commonly dominated by Acanthuridae, Balistidae, Lethrinidae, and Scombridae. The catch rate was lowest for hook-and-line across all sites. Using varying levels of fishing days per year, mean catch rates ranged from 0.25–1.53 mt/fisher/yr for hook-and-line and 1.26–3.80 mt/fisher/yr for spearfishing. Estimated yields ranged from 2–31 mt/km2/yr. The potential annual yield for the three reefs was 1,053–2,733 mt/yr. When extrapolated, the KIG reefs can potentially produce around 61,557–90,850 mt/yr, or 3–5% of the total marine capture fisheries output. Interview results further revealed that the dominant gear type in Scarborough changed from speargun in the past to gillnets at present. This could be attributed to an observed shift in fishing grounds when access to the reefs became more restricted. The study shows that fisheries production in the three offshore reefs is still high compared with other areas in the country. However, these reefs have remained exposed to various anthropogenic threats, which could lead to significant fisheries losses if they remain unmanaged. Especially in offshore reefs where benchmarks are lacking, information on fisheries productivity should be compiled if it were to be sustained.

Keywords: coral reef, fisheries, Kalayaan Island Group, offshore, Scarborough, West Philippine Sea

Philippine Journal of Science149 (3): 647-658, September 2020ISSN 0031 - 7683Date Received: 16 Mar 2020

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INTRODUCTIONCoral reef fisheries play a significant role in the global society and the economy. It provides food and livelihood to millions of people in tropical and subtropical areas (Sadovy 2005; Teh et al. 2013), and also influences socio-cultural practices and identities (Leenhardt et al. 2016). The contribution of reef-associated fisheries to overall global marine fisheries is understated due to it being often lumped under small-scale fisheries. It has been estimated to comprise about 10% of the total global marine fishery landings (Sadovy 2005) and 11% for Southeast Asia (Teh et al. 2013). An estimated six million reef fishers live around the world (Teh et al. 2013), which makes up 2% of the 275 million people living within 30 km from coral reefs (Burke et al. 201 2). Half (3.35 million) of the estimated global reef fishers come from Southeast Asia (Teh et al. 2013).

In the Philippines where nearly 60% of the population lives along the coast, coral reef fisheries is an important sub-sector of the marine capture fisheries. With an estimated total area of 22,484 km2 and around 26% of the total reef area in Southeast Asia (Burke et al. 2012), Philippine coral reefs are one of the richest in the world both in diversity and ecosystem goods and services. Reefs with good live coral cover (> 50%) could potentially produce an annual yield of about 15–20 mt/km2 (Alcala and Russ 2002; Maypa et al. 2002). Using estimates of reef fisheries production and the aggregate area of coral reefs in the country, Campos (2000) reported that the apparent yield from the country’s reefs is about 5–10 mt/km2, depending on the reef area used. In the 1990s, reef fisheries contribute about 20–25% to total marine capture fisheries production in the country (Alcala and Russ 2002). Teh and co-authors (2013) estimated that there are around 912,000 reef fishers in the Philippines, which – together with Indonesia (1.7 million) and India (959,000) – make up about 58% of the world’s total reef fishers. This underlines the high dependency of small-scale fishers and coastal communities on coral reefs in these three developing countries.

Despite its perceived value, coral reefs remain one of the most vulnerable marine ecosystems. About 94% of the reefs in Southeast Asia are threatened (Burke et al. 2012). Because of their strong association with their habitats, reef fishes are impacted by similar threats that face coral communities – particularly degradation from destructive fishing practices, coastal development, and pollution. The continued deterioration of coral reefs in the Philippines is expected to largely affect reef fisheries and, consequently, the well-being of coastal communities. Presently, there is a paucity of data on the productivity of reef fisheries in the Philippines, especially its offshore reefs and islands. Previous studies have been done in nearshore reefs (e.g.

Alcala and Luchavez 1981; Campos et al. 1994; Maypa et al. 2002). This is a large gap considering that offshore reefs make up a large portion of Philippine reefs. In fact, the KIG in the West Philippine Sea is estimated to cover about 30% of the total reefs in the Philippines (Ong et al. 2002). Other offshore reefs, such as the Scarborough Shoal off the coast of northwestern Luzon, serve as important traditional fishing grounds for Filipino fishers. Offshore reefs are not immune to rising threats and may even be more vulnerable due to their remote location and distance from any management program. In fact, recent political developments have made access to some offshore reef areas more difficult. It is thus crucial to determine the degree of dependence of Filipino fishing communities on these reefs, as well as the potential socio-economic losses that may be incurred because of access constraints.

The main objective of this study was to determine the fisheries productivity of three offshore reefs in the West Philippine Sea using both fishery-dependent (one-on-one interviews with fishers) and fishery-independent (experimental fishing) approaches. In particular, focus was given on the catch composition, catch rates, and potential yield from two commonly used fishing gears in reef fisheries: speargun and hook-and-line. Changes in the local fisheries of an offshore reef where access has become more restricted over time are also presented to highlight potential losses from reduced access in these fishing grounds. The results of the study underscore the importance of coral reefs for developing countries like the Philippines through the contribution of reef fisheries to total marine capture fisheries production. With a potential net value of Php 2.0–2.5 billion in 2006 (Padilla 2009), this has often been unreported and underestimated.

MATERIALS AND METHODS

Study AreaThe West Philippine Sea encompasses the maritime areas on the western side of the Philippines and includes the Luzon Sea, all the waters around, within, and adjacent to the KIG and Bajo de Masinloc (also known as the Scarborough Shoal), and is located within the larger South China Sea. It is one of the highly important fishing grounds in the Philippines, contributing to about 20% of the country’s annual commercial fisheries production (Aliño and Quibilan 2003). The KIG is a group of over 50 features and their surrounding waters and is estimated to cover a reef area of about 3,257.70 km2 (Ong et al. 2002). It has been identified as one of the marine key biodiversity areas in the Philippines and is considered as a priority conservation area (Ong et al. 2002). The three offshore reefs included in the study were Pagasa Island

Arceo et al.: Estimating Fisheries Production in Offshore Reefs

Philippine Journal of ScienceVol. 149 No. 3, September 2020

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and Sabina Shoal, which are part of the KIG and under the jurisdiction of the Municipality of Kalayaan in the province of Palawan, and the Scarborough Shoal (Figure 1A). The Scarborough Shoal, also known as Panatag Shoal or Bajo de Masinloc, is a submerged coral reef area that encloses a 150-km2 lagoon and lies off the Zambales coast in northwestern Luzon. The total coral reef area for each site was determined from GoogleEarth® satellite images.

Fisheries AssessmentIn February 2017, one-on-one interviews with fishers were conducted in Masinloc, Zambales to obtain pertinent fisheries information for the Scarborough Shoal. This municipality was found to have the highest number of fishers known to be dependent on the shoal based on initial scoping visits in different coastal towns along the Zambales coast. A key informant interview is a survey

Figure 1. Location of the three offshore study reefs in the West Philippine Sea. (A) Inset maps showing sampling stations for experimental fishing conducted in Pagasa Island (left, top) and Sabina Shoal (left, bottom). Green circles denote spearfishing stations while yellow circles denote hook-and-line fishing stations. (B) Area of fishing in Scarborough Shoal as identified by past and present fishers during the interviews. Darker yellow color denotes a higher frequency (or intensity) of fishing. Source map: Google Earth.



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tool where the interviewer directly asks the fishers using a standard questionnaire to document fishing practices, catch composition, mean catch per fishing trip for major gears, catch rates, fishing gears used, and market flow. Snowball sampling was employed wherein respondents referred the interviewers to nearby candidates for another interview. A total of 89 fishers participated in the interviews in Masinloc. Twenty-nine (29) respondents confirmed that they fish or used to fish in the Scarborough Shoal. The majority of these fishers come from one village, Barangay Inhobol. Of the 29 who confirmed, 19 fishers were still going to the shoal as of the time of the surveys while the remaining 10 respondents have stopped going (hereinafter referred to as “past fishers”). For the interviews, each respondent was considered as a replicate.

Experimental FishingExperimental fishing was done at two sites in the KIG, particularly Pagasa Island and Sabina Shoal (Figure 1A), during a ship-based research expedition in May 2017. Two fishing stations in each reef site were randomly selected from maps overlain with 100 m x 100 m grids. Using a handheld digital depth sounder, actual depth was recorded while substrate type and physical conditions of the designated fishing area were noted. The stations were located over similar reef bottom characteristics near the reef crest at depths of 6–8 m. Two types of fishing gears were used: (1) multiple hook-and-line, which consisted of hooks, sinker, and mainline cords made up of nylon monofilament (line #40 with three hooks of #23); and (2) manual speargun.

Fishing was done by two research technicians, who were also experienced fishers, using each of the gear types. Baits used for hook-and-line fishing were either natural (i.e. shrimp, sardines) or artificial lures. For manual spearfishing, speargun was used by freediving. Spearguns are very simple catapults propelling towards the target by stretching a piece of rubber. The two fishers concurrently operated at the same station but maintained some distance to avoid any overlap. Each spearfishing trial ran for 1–3 h, while each hook-and-line trial ran for 1–1.5 h. After each trial, the catch was collected, photographed, and identified up to the species level whenever possible. The length and weight of each fish were measured. A total of six spearfishing trials (four in Pagasa and two in Sabina) and 12 hook-and-line fishing trials (six in Pagasa and six in Sabina) were completed. Each trial was considered as a replicate. Experimental fishing ran for two days in Pagasa (03 May and 05 May 2017) and only one day in Sabina (13 May 2017). The short duration was due to constraints during the expedition – particularly limited time spent in each reef site, availability of small boats that can go near the reefs, and unfavorable sea conditions.

Data AnalysesData from the interviews were summarized according to gear types, fishing grounds, catch composition, and catch volume. Descriptive comparisons were also made from information between the present and past fishers to determine temporal trends. Interview data for hook-and-line fishing and spearfishing are presented with experimental fishing data, where applicable, to compare patterns across sites. Experimental fishing data were also summarized to catch composition and catch volume. For both data sets, catch rate or catch-per-unit-effort (CPUE; in kg/man-h and converted to mt/fisher/yr) was computed. Only actual fishing hours were included in the fishing effort, and travel time was not included.

Yield per unit area (in mt/km2/yr-) was calculated by dividing the catch rate with the effective fishing area set at 0.1225 km2 (350 m x 350 m) for both gear types. This dimension was based on direct observations of the estimated distance covered by the spear-fisher in this study while fishing and was also applied as a proxy for hook-and-line fishing in the absence of empirical data on bait attraction area. The term “effective fishing area,” as defined in this study, refers to the actual area fished (following the definition of Miller and Hunte 1987). Specifically, it covers the estimated search area during spearfishing or the estimated attraction area by the bait used for hook-and-line fishing. Catch rate per hour was converted to annual estimates by assuming that a fisher spends six hours a day and a set number of fishing days a year using the values reported by Muallil and co-workers (2014) for various towns in the West Philippine Sea: 166 days, 245 days, and 214 days for low, high, and mean (of 12 towns) number of fishing days per year, respectively. The total annual yield for each reef site (in mt/yr) was computed by multiplying yield per unit area with the estimated total reef area for that site. A two-sample t-test assuming unequal variances was used to test for significant differences in total catch and catch rates between gears using the experimental fishing data.

Statistical tests to compare fisheries production across sites were not carried out due to the inherent differences between the sampling methods, which were not done together in all sites for several reasons. Interviews were not conducted in Pagasa Island because of limited land-based activities and personnel while Sabina Shoal is an uninhabited atoll. Meanwhile, experimental fishing was not done in Scarborough Shoal due to security issues since the area was already being occupied by foreign armed forces. Given these limitations, across-site analyses were limited to descriptive comparisons.



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RESULTS

Fishing GearsThe fishing gears used in the Scarborough Shoal mainly comprised of variations of gillnets (bottom-set, drift, and ring nets) and hook-and-line (drift, multiple, and simple handlines), as well as speargun and jig. Past fishers (n = 10) used bottom-set gillnet (2), drift longline (1), multiple hook-and-line (1), simple handline (2), jig (1), and speargun (4). Speargun was the most common gear used in the past. Meanwhile, about 48% of the fishers who were still fishing in the Scarborough used gillnets (specifically, bottom-set gillnet = 3, drift gillnet = 7, and encircling/ring net = 3) while the rest used hook-and-line (multiple = 1 and simple handline = 10) and speargun (3). The total number of gears does not match with the total number of fishers, as some fishers used multiple gears during a fishing trip.

Catch CompositionFishes belonging to nine and seven families were caught using hook-and-line and spearfishing, respectively. Catch composition differed between gears but was similar for spearfishing across reef sites. Catch from hook-and-line was dominated by Balistidae in Pagasa (38% of total catch), Lethrinidae in Sabina (52% of total catch), and Scombridae in Scarborough (identified by 50% of respondents). Catch from spearfishing in Pagasa and Sabina was mainly dominated by Acanthuridae (76% and 72% of the total catch, respectively) (Figure 2). In Scarborough, differences in catch composition were observed between the present and past fishers using both gears. For hook-and-line, Lethrinidae and Mullidae were the most common fish presently caught while Carangidae has become less dominant in the catch than in the past (Figure 2). For spearfishing, Scarinae (Family Labridae) and Lethrinidae were no longer caught at present while

Figure 2. Percentage contribution of the different fish families to total catch using hook-and-line (top) and speargun (bottom) in the three offshore reefs in the West Philippine Sea. Data for Pagasa Island and Sabina Shoal (to the left of dashed line) reflect relative abundance in total catch obtained from experimental fishing, while data for Scarborough Shoal (to the right of dashed line) reflect frequency from fishers’ responses obtained from interviews.



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Haemulidae, which was not reportedly caught in the past, was reported in the present catch (Figure 2).

Species-level catch composition was only obtained from the experimental fishing. A total of 397 individuals from 39 species belonging to nine families and one sub-family were identified (Appendix Table I). Some families were only caught using a particular fishing method. Specifically, Acanthuridae, Holocentridae, Pinguipedidae, and Scarinae were only caught using spearfishing while Balistidae and Labridae were only caught using hook-and-line (Table 1). Total abundance and weight of fish caught using hook-and-line were higher than spearfishing (Table 1). This was mainly attributed to Gnathodentex aureolineatus (Lethrinidae) and Melichthys vidua (Balistidae), which were observed to be present in schools at the stations during the time of the fishing trials. Except for Lethrinidae which dominated the catch in Sabina Shoal, the major fish families caught in both reef sites in terms of abundance and weight were Acanthuridae, Balistidae, and Serranidae.

Catch RateCatch and effort for speargun, hook-and-line, and other fishing gears reportedly used in the Scarborough Shoal are shown in Table 2. Fishing duration in Pagasa and Sabina was set at 1–3 h during the experimental fishing trials. Total catch for spearfishing and hook-and-line are shown for all trials and was higher for spearfishing although not statistically significant. Mean catch for spearfishing was generally higher than hook-and-line for the two reef sites but the difference was not statistically significant.

Fishers still going to Scarborough reported the total number of hours spent fishing for each trip, which ranged from 36–73 h across the different gears (Table 2). Bottom-set and drift gillnets required longer fishing hours. The majority of

the fishers were part of the crew of large fishing vessels, which have a total of 10–30 crew members. The total catch reported by the respondents was mostly for the whole crew but some only reported their individual catch for the whole trip. The highest catch from spearfishing and hook-and-line was 730 kg and 1000 kg, respectively, while catch from gillnets reached several tons (Table 2).

The catch rate was observed to be highly variable among gear types but lowest for hook-and-line across all sites (Table 2). In general, higher catch rates were observed for the different variations of gillnets being used in Scarborough. When converted to annual catch rates, estimates for hook-and-line ranged from 0.67–0.99 mt/fisher/yr in Pagasa, 1.04–1.53 mt/fisher/yr in Sabina, and 0.25–0.37 mt/fisher/yr in Scarborough, depending on the annual fishing days (Table 3). The annual catch rate for spearfishing was higher across sites, ranging from 1.26–1.87 mt/fisher/yr in Pagasa, 1.66–2.45 mt/fisher/yr in Sabina, and 2.57–3.80 mt/fisher/yr in Scarborough across varying fishing days per year (Table 3).

YieldAnnual yield per unit area in Pagasa ranged from 10.32–15.22 mt/km2/yr for spearfishing and 5.45–8.05 mt/km2/yr for hook-and-line (Table 3). In Sabina, the estimated annual yields for spearfishing and hook-and-line were 13.53–19.97 mt/km2/yr and 8.49–12.53 mt/km2/yr, respectively. Scarborough had the highest estimated annual yield per unit area for spearfishing but the lowest for hook-and-line across reef sites. Meanwhile, the total annual yield was highest in Sabina for hook-and-line but was highest in Scarborough for spearfishing (Table 3). However, if the yield for both gears were combined, the total annual yield was highest in Sabina among the three

Table 1. Summary of catch per fish family after 25 h of experimental fishing in Pagasa Island and Sabina Shoal, KIG, West Philippine Sea.

Family/sub-familySpeargun Hook-and-line

Number caught Total weight (g) Number caught Total weight (g)

Acanthuridae 92.00 13,747.00 – –

Balistidae – – 66.00 13,245.00

Holocentridae 4.00 660.00 – –

Labridae – – 39.00 2,900.00

Lethrinidae 7.00 910.00 93.00 7,556.00

Mullidae 4.00 520.00 3.00 140.00

Lutjanidae – – 2.00 200.00

Pinguipedidae 2.00 50.00 – –

Labridae: Scarinae 9.00 2,100.00 – –

Serranidae 10.00 1,125.00 66.00 4,340.00

Total 128.00 19,112.00 269.00 28,381.00



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sites. If scaled up to the whole KIG, the total annual yield for the two gears ranged from 61,556.64–90,850.19 mt/yr (Table 3).

Other Fishery Trends in the Scarborough ShoalA shift in the fishing grounds in Scarborough Shoal was observed based on the responses of fishers during the interviews. From 1995–2010, fishing was concentrated within or near the shoal but has moved farther from the shoal towards more offshore areas at present (Figure 1B). When asked about observed changes in their fishing conditions (e.g. fish catch and composition, location of their fishing ground), most respondents noted decreasing catch and a change in species composition. They attributed these changes to the destruction of coral reefs, illegal fishing practices, and increased number of fishers. They also reported that the giant clam population in the shoal, which was once abundant inside the lagoon, has decreased due to heavy extraction by foreign fishers. Because of foreign security threats, some Filipino fishers have chosen not to go near the shoal and have opted to fish farther offshore or near the Zambales coast instead.

For past fishers, strong weather conditions and the presence of foreign vessels were cited by the respondents as the major reasons for ceasing their fishing activities in the shoal. For safety reasons, fishers have stopped fishing within or near the shoal because, when weather conditions

became severe, they could no longer seek refuge inside the lagoon since it was now being heavily guarded by foreign military forces. If the fishers experience heavy rains and strong waves while at sea, they just continue to sail offshore until they find calmer areas in the open ocean.

DISCUSSIONThis study assessed the fisheries production of three offshore reefs in the Philippines, particularly for spearfishing and hook-and-line fishing. These fishing gears are the most common gears being used in reef fisheries in the Indo-Pacific region (Dalzell 1996; Maypa et al. 2002; Frisch et al. 2008; Muallil et al. 2014; Humphries et al. 2019). They are popular in developing countries because their operations require minimal cost (Dalzell 1996). Results of the interviews also revealed that these gears were being utilized by the fishers in Scarborough Shoal; thus, their use in the experimental fishing trials was appropriate.

Estimated fishery yields per unit area for the three offshore reefs ranged from 2.0–31.0 mt/km2/yr. The yields estimated from Scarborough were based on fishers’ perceptions and may have been under- or overestimated because it depended on the accuracy of their memory recall. Estimated annual yields of the present study relative to those reported

Table 2. Catch, effort, and catch rates for the different fishing gears used in the three offshore reefs in the West Philippine Sea obtained from experimental fishing and interviews. Numbers in parentheses are the mean values.

Site Gear type Replicate Fishing duration (h) No. of fishers Total catch(kg)

Mean catch ratea

(kg/man-h)

Pagasab Speargun 4 trials 1–2 1 0.95–4.3 (2.2)

1.27 ± 0.61

Hook-and-line 6 trials 1–1.5 1 0.3–1.3 (0.7)

0.67 ± 0.41

Sabinab Speargun 2 trials 3 1 4.7–5.3 (3.3)

1.66 ± 0.13

Hook-and-line 6 trials 1 1 0.9–1.2 (1.0)

1.04 ± 0.12

Scarboroughc Speargun 3 respondents 15–70 (36.3) 4–10 (11.3) 3–1000 (667.7)

2.58 ± 2.25

Hook-and-line 10 respondents 4–70 (42.6)

1–30 (22.7) 1–720 (115.1)

0.25 ± 0.45

Bottom-set gillnet 3 respondents 30–105 (73.0) 20–27 (24.7) 50–21,020 (10.698.3)

4.12 ± 3.72

Drift gillnet 7 respondents 16–112 (60.9) 24–30 (27.4) 2,000–10,000 (4,485.7)

3.33 ± 2.55

Ring net 3 respondents 24–32 (42.6) 24–27 (25.3) 32–7,010(3,347.3)

5.61 ± 6.12

aValues showing mean with standard deviationbData obtained from experimental fishingcData derived from fisher interviews



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from other reefs in the Philippines are presented in the Appendix. Yields from the experimental fishing in Pagasa and Sabina are comparable to those of nearshore reefs with management histories, such as along Apo and Sumilon Islands in the central Philippines where yields have been maintained at 15–20 mt/km2/yr over two decades (Maypa et al. 2002). They are significantly lower than the estimates of Aliño and co-workers (1998) for the KIG, which was 78–105 mt/km2/yr, although their estimate was based on catch data from pa-aling, which is a type of drive-in gillnet similar to muro-ami and is much more efficient than spearfishing or hook-and-line fishing. However, the current estimates were higher than the reef fishery yield for the whole country reported by Campos (2000), which was

5–10 mt/km2. They are also higher than yields estimated by Alcala and Gomez (1985) for reef areas with less than 50% live coral which was 4 mt/km2/yr. Mean hard coral cover in five reefs in the KIG, including Pagasa Island and Sabina Shoal, was 14.5% (Cabasan et al., unpublished data). Recent studies are postulating that coral conditions may not be reflective of reef fishery production, especially for target food fishes. Structural complexity may be a more important driver that influences reef fish community structure and fishery productivity (Rogers et al. 2014; Darling et al. 2017). The use of multiple parameters describing benthic conditions [e.g. indices in (Mantachitra 1994)] may also be more informative than a single parameter, such as live coral cover alone.

Table 3. Estimated annual catch rate, yield per unit area, and total yield at varying levels of annual fishing days for the different gears used in the three offshore reefs in the West Philippine Sea obtained from experimental fishing and interviews. Values for Pagasa and Sabina were averaged (*) and extrapolated for the whole KIG.

Fishing gear Fishing days/yra Pag-asab Sabinab KIG Scarboroughc

Estimated reef area (km2) 66.79 84.08 3,257.70 56.60

Mean catch rate (mt/fisher/yr)

Hook-and-line Low 0.67 1.04 1.19* 0.25

Mean 0.86 1.34 1.10* 0.32

High 0.99 1.53 1.26* 0.37

Speargun Low 1.26 1.66 2.09* 2.57

Mean 1.63 2.14 1.88* 3.32

High 1.87 2.45 2.16* 3.80

Yield per reef area (mt/km2/yr)

Hook-and-line Low 5.45 8.49 6.97* 2.03

Mean 7.03 10.94 8.98* 2.62

High 8.05 12.53 10.29* 3.00

Speargun Low 10.32 13.53 11.92* 21.00

Mean 13.30 17.45 15.37* 27.07

High 15.22 19.97 17.60* 30.99

Total yield (mt/yr)

Hook-and-line Low 364.14 713.82 22,709.01 114.91

Mean 469.43 920.22 29,275.47 148.13

High 537.44 1,053.52 33,516.30 169.59

Speargun Low 688.99 1,137.89 38,846.64 1,188.54

Mean 888.21 1,466.92 50,079.40 1,532.21

High 1,016.88 1,679.41 57,333.89 1,754.17

All gears Low 1,053.03 1,851.71 61,555.64 1,303.44

Mean 1,357.65 2,387.14 79,354.86 1,680.34

High 1,554.31 2,732.94 90,850.19 1,923.76aBased on fishing days per year reported for towns in the West Philippine Sea by Muallil et al. (2014)bData obtained from experimental fishingcData derived from fisher interviews



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Different studies have estimated varying yields across reef sites. The differences may be due to reef habitat structure and degree of exploitation (Campos et al. 1994), manner of fishing, and variability of catch which can be influenced by productivity in the area and fish community structure. Alcala and Russ (2002) noted that high yields may be expected from reefs where herbivores and planktivores predominate, as seen in Sumilon Island where yields of up to 36.9 mt/km2/yr were observed in 1983–1984 and may have been caused by the high proportion of planktivorous fusiliers (Caesionidae) in the catch. The estimated yield will also depend on the actual area fished, termed “effective fishing area” in this study following Miller and Hunte (1987). Although easier to estimate for spearfishing since the actual search area covered could be derived, additional experiments would have been ideally made to obtain the attraction area for hook-and-line fishing in the present study. There is a paucity of studies that estimate effective fishing areas of hook-and-line although there are some for traps, which ranged from 25–348 m2/trap (Miller and Hunte 1987) and 577 m2/trap to 9,348 m2/trap (Aedo and Arancibia 2003), depending on the type of trap used and species being targeted, such as fish or crabs. The estimates for traps are much smaller than those used in this study; however, hook-and-line baits may have a larger attraction area since they are not confined and are thus more exposed in the water column, unlike the traps which are set at the bottom.

In 2016, the total output of the country’s marine capture fisheries was 1.87 million tons (FAO 2018). Using this figure, the potential fishery yield for the whole KIG, which was extrapolated at 61,556–90,850 mt/yr in the present study, comprises 3–5% of the total annual output. If the KIG reefs make up 30% of the total reefs in the country, reef fisheries can thus potentially contribute about 11–16% to the total annual Philippine marine capture fisheries. Alcala and Russ (2002) reported that reef fisheries make up 20–25% of total marine fisheries production in the late 1990s using the average sustainable yield for good reefs. However, if the actual condition of Philippine reefs wherein the majority have a live coral cover of 50% or less were taken into account, they stated that the total annual fishery production from coral reefs would only be about 11% of the total marine production. Meanwhile, Padilla (2009) used reef fishery yield estimates based on varying live coral cover and estimated the total annual yield from Philippine reefs at 169,000 mt, which was about 8% of the total marine fisheries production in 2006. As previously discussed, the relationship between live coral conditions and reef fishery production needs to be revisited.

Catch rate data for both spearfishing and hook-and-line fishing were generally comparable with previous studies in other areas in the country, which ranged from 1.1–1.33

kg/man-h for spearfishing (Campos et al. 1994; Amar et al. 1996) and 0.70–2.0 kg/man-h for hook-and-line (Maypa et al. 2002). However, most of these values were obtained more than two decades ago and mainly from nearshore reefs. A more recent study done from 2015–2017 using data from 55 coastal municipalities in the country showed that 80% of the sites have mean catch rates for spearfishing of less than 1.0 kg man/h (Arceo et al., unpublished data). This trend suggests that the catch rates in the three offshore reefs of the West Philippine Sea are still generally higher compared with other areas in the Philippines. These initial estimates still need to be validated since travel time was not included in effort computation, which could substantially decrease catch rates. However, most offshore fishers often bring multiple gears during extended fishing trips to optimize time and resources; hence, total catch rates that include other fishing gears could still be high. Meanwhile, catch rates were variable across gears but were highest in gillnets. Net fishing has also been reported to have the highest catch rate compared with spear- and line-fishing in the Hawaiian Islands (McCoy et al. 2018). Gear efficiency does not necessarily translate to higher monetary value, especially for highly selective gears that target species that command higher prices. Based on the interviews, the Scarborough fishers perceived that spearfishing was more efficient compared with gillnet; however, it will require them to fish near the shoal, which is no longer feasible for them due to access restrictions.

Only two to three families dominated the catch for any type of gear in the study sites. Maypa and colleagues (2002) observed a similar trend in Apo Island from long-term data with only five families accounting for about 50–90% of the total catch. Catch composition also differed among the fishing gears, and some species were only caught using particular gears. These patterns could have been influenced by inherent site differences (e.g. community structure, level of exploitation, reef characteristics, etc.). They could also reflect the selectivity of gears to target certain species. For instance, spearfishing is known to be highly selective in terms of species and size, such that larger and more commercially prized species can be caught (Frisch et al. 2008). Variants of line fishing also tend to target specific fishes although they are generally less selective than spearfishing. Lloret and co-workers (2008) observed that hook-and-line fishing has more incidental impacts due to larger by-catch and damage from hooks that get stuck to the substrate. However, the bias of spearfishing to catch larger-sized fishes increases the intrinsic vulnerability of these species to fishing (Lloret et al. 2008). A low overlap in catch composition has also been observed in Indonesia (Humphries et al. 2019) but was contrary to what was observed by Frisch and colleagues (2008), wherein catch composition between the



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two gears greatly overlapped. Such overlaps would further increase the vulnerability of target species. Because of non-overlap, reef fishers tend to bring multiple gears on the same fishing trip to maximize catch. This highlights the complexity of the multi-species and multi-gear nature of reef fisheries, as well as the significance of reef structure and complexity.

Fishery trends in a traditionally important fishing ground where access became limited over time were apparent. Before 2010, the Scarborough Shoal was a major fishing area for reef fishers in northwestern Luzon. In 2012, disputes between Chinese and Filipino fishers escalated resulting in stand-offs and eventual displacement of the Filipino fishers who were prohibited from entering the lagoon which was now heavily guarded, or from going very near the shoal. The results of the interviews with Scarborough fishers showed the impacts of the increased restriction on their fishing grounds. One major change was in the type of fishing gear used, i.e. from speargun to gillnets. As access to the reefs became restricted, fishers moved towards more offshore areas where gillnets were more appropriate for fishing. The effects of the shift in gear usage were also reflected in the catch composition for spearfishing. Parrotfishes (Scarinae) and emperors (Lethrinidae) were no longer reported by present fishers in their catch. The most extreme impact of reduced access was the termination of fishing operations in the shoal altogether, even if it meant transferring to farther or less productive areas.

Access restrictions also affect potential scientific research in the area, such as in the present study. Actual in situ estimation of fisheries production would have made the results for Scarborough be more accurate and more comparable with that of the two other study sites. Instead, interviews were done which – although fishers’ perceptions provided much-needed information from an otherwise data-poor reef site – may hold some degrees of error as they depend on the accuracy of memory, participation, and comprehension of the respondents (McCluskey and Lewison 2008). Depending on the age range of the respondents, there may also be inaccuracies in documenting historical trends due to shifting baselines since different age groups would differ in their memories of fishery- and environmental-related changes (Bunce et al. 2008). Because of this constraint, only descriptive comparisons were done, and the findings should still be validated further.

Time and logistic constraints during data collection also limited the study, resulting in low sample replication for both the experimental fishing trials and interview respondents. This necessitates further substantiation of results and expansion to more reef sites. Additional experiments to determine effective area fished, as well

as possible changes in fishing exploration strategies as a response to access constraints (i.e. stochastic vs. Cartesian fishing, Cabral et al. 2010), should also be pursued. Despite these limitations, the catch and yield estimates obtained from the study provide a useful basis to evaluate the potential contribution of coral reef fisheries to both local livelihood and overall fisheries production, which has been under-reported and undervalued. The value of reef fisheries, which is usually considered as subsistence fishing, is not often included in resource valuation studies (Sadovy 2005) although the sub-sector has been increasingly included in recent global, regional, and national status reports (FAO 2018) albeit using statistical assumptions and extrapolations. There are still few studies on production and CPUE estimates for reef fisheries (McCoy et al. 2018).

CONCLUSIONThe present study, which was one of the first attempts to empirically estimate fisheries production of offshore reefs in the West Philippine Sea, confirms the high fisheries potential in the area as has been previously reported by Aliño and colleagues (1998). It also highlights the possible losses from continued habitat loss and overfishing. Alcala and Russ (2002) projected a 48% reduction (valued at US$167,500 based on 1997 market rates) in total potential reef fisheries yield due to reef degradation. Coral reefs are being heavily threatened by different stressors, both anthropogenic and natural in origin, and their continued deterioration is expected to largely affect reef fisheries due to the habitat loss of reef-associated fishes.

Many coastal communities depend on coral reefs for their economy, food, and livelihood. In the Philippines where more than half of the population lives along the coast, coral reef fisheries play a critical role in the communities. The high demand for fish imposes considerable pressure on an increasingly dwindling resource. Even offshore reefs are vulnerable in their remoteness because of their open access situation. In fact, the recent political developments in the Scarborough Shoal and other offshore reefs in the West Philippine Sea have brought attention to the reef destruction occurring in this region. Unless well-protected, Philippine reefs will continue to be exposed to unregulated threats and damage.

Because reef fisheries are under-reported or under-monitored, they are also typically under-managed and unregulated (Sadovy 2005). Estimating reef fisheries production is crucial in understanding the benefits being derived from coral reefs. There is an urgent need to implement protective management measures that will address continued habitat degradation and



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overexploitation if productivity were to be maintained and sustained. Current fisheries management should include reef fisheries despite its complexities. Special attention should also be given to remote areas such as offshore reefs, where open access predominate and management can be very challenging. These can be addressed by understanding the processes of connectedness of social and ecological systems that will require both national and international scientific cooperation and adaptive management approaches.

ACKNOWLEDGMENTSFinancial support was provided by the Department of Environment and Natural Resources Biodiversity Management Bureau through the Coastal Assessment for Rehabilitation Enhancement: Capability Development and Resiliency of EcoSystems (or CARE-CaDRES) Program. The authors would also like to thank the local government units of the Municipalities of Kalayaan, Palawan and Masinloc, Zambales; and the Palawan Council for Sustainable Development for their permission to conduct the study in their areas. The valuable contributions of D. Valino, F. Sabban, M.J. Cabiguin, V. Olivar, and R. de Guzman in data collection are appreciated.

NOTES ON APPENDICESThe complete appendices section of the study is accessible at http://philjournsci.dost. gov.ph.

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APPENDIX

Table I. Summary of catch per species after 25 h of experimental fishing in Pagasa Island and Sabina Shoal, Kalayaan Island Group, West Philippine Sea.

Family/subfamily

Species Speargun Hook and line

Number caught Total weight (g)

Number caught

Total weight (g)

Acanthuridae Acanthurus japonicus 1 140

Acanthurus lineatus 11 2810

Acanthurus nigrofuscus 5 770

Acanthurus olivaceus 2 370

Ctenochaetus binotatus 17 1,962

Ctenochaetus striatus 54 7,255

Naso lituratus 2 440

Balistidae Balistapus undulatus 16 2,710

Melichthys vidua 43 9,610

Odonus niger 1 140

Rhinecanthus rectangulus 2 285

Sufflamen chrysopterum 4 500

Holocentridae Myripristis hexagona 1 80

Myripristis kuntee 3 580

Labridae Cheilinus trilobatus 1 200

Gomphosus varius 2 135

Halichoeres hortulanus 9 995

Oxycheilinus digrammus 2 140

Oxycheilinus unifasciatus 5 820

Thalassoma lunare 1 55

Thalassoma quinquevittatum 19 555

Lethrinidae Gnathodentex aureolineatus 5 510 92 7,316

Monotaxis grandoculis 1 240

Lethrinus amboinensis 1 190

Lethrinus erythracanthus 1 210

Mullidae Mulloidichthys vanicolensis 2 250

Parupeneus crassilabris 1 100

Parupeneus cyclostomus 1 170

Parupeneus multifasciatus 3 140

Lutjanidae Lutjanus kasmira 2 200

Pinguipedidae Parapercis clathrata 2 50

Labridae: Scarinae Chlorurus bleekeri 1 120

Chlorurus sordidus 1 190

Scarus forsteni 5 1,250

Scarus oviceps 2 540

Serranidae Cephalopholis urodeta 6 570 63 4000

Epinephelus erythrurus 1 85

Epinephelus quoyanus 1 180 3 340

Epinephelus spilotoceps 2 290

Total 128 19,112 269 28,381



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Table II. Published fishery yields from coral reefs in the Philippines.

Site Area fished (km2) Yield(mt/km2/yr)

Source

Apo Is., Negros Oriental 1.5 15–20 Maypa et al. (2002)

Sumilon Island, Cebu 0.5 14.0–36.9 Dalzell (1996)

Pamilacan Is., Bohol 1.8 10.7 Dalzell (1996)

Hulao-Hulao Reef, Negros Occidental 0.5 5.2 Dalzell (1996)

Bolinao, Pangasinan 24 10.1–14.5 Campos et al. (1994)

Malalison Is., Antique 5.8 Amar et al. (1996)

Pagasa Island, KIG 0.1225 5.4–15.2 This study

Sabina Shoal, KIG 0.1225 8.5–20.0 This study

Scarborough Shoal 0.1225 2.0–31.0 This study



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Interview questionnaire adopted from the People and the Environment: Assessing Reef-fish Resiliency and associated Livelihood Project of the National Assessment of Coral Reef Environment Program (NACRE-PEARRL) funded by the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development of the Department of Science and Technology (DOST-PCAARRD).



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estimating the potential fisheries production of three ......the results of the study underscore the...

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