Status report on the abundance of condricthyian and pelagic teleost top predators at Tubbataha Reef National Marine Park, Philippines

Status report on the abundance of
             condricthyian and pelagic teleost top predators at
             Tubbataha Reef National Marine Park, Philippines
                                                 1                                        2
                         Stefan P. W. Walker and Nadia E. Palomar-Abesamis

1
  School of Marine biology and aquaculture, James Cook University. OLD, Australia. 4812.
Email: stefan.walker@jcu.edu.au
2
 Conservation International – Philippines, 20 South Lawin Ave, Philam Homes QC 1104 Philippines
Email: npalomar@conservation.org

Introduction

         Coral reef ecosystems play a major role in global biophysical processes and are
a primary source of resources and income for tropical communities and nations.
However the culmination of increased anthropogenic disturbances (global warming,
pollution and sediment loading, over fishing and destructive fishing methods) has lead to
20% of the world’s coral reefs being effectively destroyed, and a further 26% under long-
term threat of collapse (Wilkinson 2004). The coral reefs of the Philippines are among
the most heavily exploited, with 70% significantly damaged and more than 30% in a
critical state of degradation (Wilkinson 2004, Alcala & Russ 2002). This has severe
ramifications for the nation’s food security and its ability to benefit from sustainable
economic activities such as tourism (Barut et al. 1997). Furthermore, the islands of the
Philippines reside within a region of high biological significance. More than 60% of all
coral and tropical reef fish species know world wide can be found throughout the
Philippine archipelago, albeit many species at dangerously low levels of abundance.
Conservation of Philippine coral reefs is not only imperative to the livelihood and
sustainability of the Philippine people, but also to the functionality of the global tropical
marine ecosystem.
         Marine protected areas (MPAs) and fishing closures are among a suit of tools
available for managing the marine environment. The premise behind MPAs is that
undisturbed populations will produce a surplus of progeny due to enhanced numbers,
growth and reproductive output, and this surplus ‘spills over’ to neighboring reefs
through larval dispersal and post-larval migration. Also, because populations are free to
grow and reproduce without anthropogenic disturbance, MPAs often support high
population densities and diversity, and are therefore of significant aesthetic value and
tourism potential. The effectiveness of MPAs depends on their spatial and temporal
boundaries, the species assemblage within these boundaries, and the integrity of
enforcement, the latter being of greatest importance (Fisher et al. 2002).
       Tubbataha Reef Marine National Park is one of approximately 600 MPAs in the
Philippine archipelago, consisting of two coral reef atolls with a cumulative area of
33,200 ha situated 92 nm southeast of Palawan in the Sulu Sea. While the Philippines
support a large number of MPAs, Tubbataha is one of a very few with adequate and
sustained enforcement (< 20%), and one of even fewer that protects critical habitat and
fisheries species (< 2.5%) (Wilkinson 2004). As a cause and consequence of the
region’s protection program, Tubbataha reefs support a complex and diverse
assemblage of marine flora and fauna.
         This report documents a base line survey conducted on the abundance of
condrichthyian and pelagic teleost top predators within the reefs of Tubbataha National
Marine Park. This assemblage of fish are heavily targeted throughout the Philippine
archipelago by subsistence and commercial fishermen, however, these are also of high

value to the dive-tourism industry. These fish are usually the first to show rapid depletion
due to relatively small population sizes and long generation times, and are in critical
states of decline in many areas of the Philippines and coral reefs worldwide (Russ &
Alcala 2004, Wilkinson 2004)

Materials & Methods

        The abundances of pelagic chondrichthyian and teleost top predators were
measured at seven fixed sites within the Tubbataha reefs (8° 43.555’ - 8° 56.642’ N,
119° 47.854’ - 120° 02.174’ E). Five replicate belt transects at 100m in length were
carried out at each site. The width of the transect was standardized to visibility (20 m 5%
CV). Differences in species abundances between sites were analyzed with one-way
analysis of variance (α = 0.05), and results are presented graphically. Assumptions for
the linear model were tested with residual analysis. Data from the present report should
be perused in conjunction with data obtained in a separate report on the abundance and
distribution of benthic and reef-attached teleosts.

Results & Discussion

        A total of 12 pelagic top predator species were sighted throughout the monitoring
program; 2 requiem sharks from the family Carcharinidae, 4 jacks from the family
Carangidae, 2 barracuda from the family Sphyraenidae, 1 jobfish from the family
Lutjanidae, and 1 tuna from the family Scombridae (Tab. 1). There was little variability in
species abundances between sites, with only Triaenodon obesus displaying significant
differences (Tab. 1). Tukey’s HSD post hoc comparison test revealed this difference to
be between site 3 and 4, with site 3 having the highest mean abundance at 2.6 ± 0.51
individuals per 2000m2, and site 4 having the lowest mean abundance at 0.2 ±
individuals per 2000m2. Furthermore, no significant difference in abundance was found
between sites when species were pooled into family (Carcharhinidae: F6, 28 = 2.2, p =
0.065; Carangidae: F6,28 = 0.53, p = 0.53; Other: F6,28 = 1.87, p = 0.12).

Table 1. Descriptive statistics of pelagic top predator species at Tubbataha Reef National Marine Park.
(between site comparisons: α = 0.05)

  Common                                                              Pooled    Pooled    Between site
  name      Family           Species             Common name        frequency   mean       comparison
                                                                                          F          P
                             Carcharhinus
  Sharks    Carcharhinidae                       Grey reef shark       3         0.08     NA       NA
                             melanopterus
                                                                                                  *0.036
                             Triaenodon obesus   Whitetip shark        39        1.1     2.660
                                                                                                   (3*4)
  Jacks     Carangidae       Gnathodon speciosus Golden trevally       2         0.06     NA       NA
                             Caranx ignobilis    Giant trevally        44        1.26    2.303    0.062
                             C.sexfaciatus       Bigeye trevally      160        4.6     0.625    0.709
                             C. melampygus       Bluefin trevally     366       10.45    0.883    0.520
                             Unidentified         ----                 89        2.5     0.595    0.732
  Barracuda Sphyraenidae     Sphyraena jello     Giant seapike         1         0.03     NA       NA
                             S. barracuda        Great barracuda       25        0.71    0.683    0.665
  Jobfish   Lutjanidae       Aprion virescens    Green jobfish         16        0.46     NA       NA

Tuna           Scombridae              Gymnosarda unicolor Dogtooth tuna   17   0.49   1.247   0.313

        Carangidae was the most abundant family among the predator species counted,
with Caranx sexfaciatus and C. melampygus being the numerically dominant species
(Table 1, Figure 1). The Carangids were followed by the carcharhinid Triaenodon
obesus with a pooled mean abundance of 1.1 ± 0.23 individuals per 2000m2 (Table 1).
Remaining species from the families Sphyraenidae, Lutjanidae and Scombridae all
displayed low abundances (Table 1). The same holds for the carcharhinid Carcharhinus
melanopterus, however this species is typically found in greatest numbers within leeward
reef and lagoon waters (Robbins pers. com., personal observation), which lay outside
the current sampling regime.

Figure 1. Mean abundance of pelagic top predator fish pooled for family across the surveyed sites at
Tubbataha Reef National Marine Park. Black bars = Carcharhinidae, hatched bars = Carangidae, white bars
= all other (see table 1). Asterix = within family between site significant differences (α = 0.05)

                                60
                                                                              *
                                50
           abundance / 2000m2

                                40

                                30

                                20

                                10                                      *

                                0
                                     1           2          3           4     5     6       7
                                                                      Site

        The outstanding feature of this survey is the ubiquitously high abundance of T.
obesus between sites. While there are no published accounts of abundance estimates
for this reef shark, work in progress by Robbins (unpublished data) suggests that
Tubbataha supports the highest population density of T. obesus known to date. Robbins
conducted surveys along undisturbed reefs of the Cocus Keeling islands and on the
Great Barrier Reef (GBR) at a sample area of 10,000m2 (1 ha), and found abundances
to be less than half of that found in the present survey. By converting the sample area,
the current survey suggests that Tubbataha supports a mean density of 5.5 individuals
per ha, with density reaching as high as 13 individuals per ha in some areas. Studies
conducted by Anderson and Ahmed (1993) and Millar (2004) illustrate the high potential
economic value of this, and other reef shark species, in terms of tourism revenue. Millar
surveyed recreational divers visiting the GBR, and found sharks, rays and turtles to be
the major attraction, and of highest aesthetic value. Anderson and Ahmed came to
complementary conclusions for divers visiting reefs of the Maldives, and furthermore
conducted an economic evaluation of the shark assemblage in relation to the Maldives’
recreational diving industry. The major findings were that local fisherman may receive a
one-off payment of US$ 32 per shark for human consumption however the average live
shark is worth approximately US$ 3,500 per annum to the tourism market, and worth up
to US$ 33,500 in dive areas with high shark abundance. Given the life span of reef

sharks (up to 18 years), this equates to an individual shark value ranging from US$
63,000-603,000 (1992 figures).
        Tubbataha Reef National Marine Park has vast potential for attracting and
sustaining environmentally sustainable economic activities such as diving, snorkeling,
turtle and cetacean watching, and eco-tours. Continued protection of the area will not
only ensure the maintenance of diverse and healthy habitat imperative to eco-economic
development, but will also contribute to the maintenance of healthy stocks of targeted
tropical fish and invertebrate species. While small-scale current regimes have not been
adequately mapped for the Sulu Sea, large-scale mapping suggests that a large body of
water is retained and circulated around the Tubbataha reefs, suggesting significant
retention of larvae and subsequently high levels of self-recruitment. However for much of
the year, prevailing currents shift water from Tubbataha to the mid- and north-eastern
coast of Palawan, the southwestern peninsula of Panay, and the western coast of
Negros (Naval Coast Ocean Model 2005). This is likely to equate to the export of larvae
to these regions, replenishing invertebrate and fish populations. In terms of the present
report, this is of particular interest in respect to the carangids, which were found in very
high abundance throughout the Tubbataha sites. As a heavily targeted fish family
throughout the Philippines, the export of carangid larvae and adults from Tubbataha to
neighboring reefs is likely to be of significance to commercial and subsistence
fishermen.

References

Alcala, A.C., Russ, G.R. (2002) Status of Philippine coral reef fisheries. Asian Fish. Sci. 15(2):
177-182

Anderson R.C. 1998. Sharks mean business. Scientific American Presents, 9(3): 72-73.

Anderson R.C. and Ahmed H. 1993. Shark fisheries of the Maldives. Ministry of Fisheries &
Agriculture,
Maldives & FAO, Rome, 73pp.

Barut, N.C., Santos, M.D. & L.R. Garces. 1997. Overview of Philippine Marine Fisheries, pp. 62-
71. In G. Silvestre & D. Pauly (Ed’s.) Status and Management of Tropical Coastal Fisheries in
Asia. ICLARM Conf. Proc. 53.

Fisher, J., Murphy, P., Craik, W. (2002) Marine protected areas and fishing closures as fisheries
management tools. In Beumer, J.P., Grant, A., Smith, D.C. (Eds). Aquatic Protected Areas: what
works best and how do we know? Proc. of the World Congress on Aquatic Protected Areas.
ASFB, WA, Australia.

Millar, D. (2004). Major attractions for divers on the Great Barrier Reef. In Wilkinson (Ed) Status
of coral reefs of the World. Australian Institute of Marine Science, Townsville, Australia.

Naval Coast Ocean Model (2005). Naval Research Laboratory.
http://www7320.nrlssc.navy.mil/global_ncom/sul.html

Robbins, W. School of marine biology and Aquaculture, James Cook University, QLD, Australia.
Email; will.robbins@jcu.edu.au

Russ, G. R., Alcala, A.C. (2004) Marine reserves: long-term protection is required for full recovery
of predatory fish populations. Oecologica 138: 622-627.

Wilkinson, C. (2004) Status of coral reefs of the World. Australian Institute of Marine Science,
Townsville, Australia.