ICES 1990 POSTER C.M.1990/L:41Sass. Q

•

PRELIMINARY TROPHIC MODEL OF THE COASTAL FISHERYRESOURCES OF SRUNEI DARUSSALAM, SOUTH CHINA SEA *

by

G. Silvestre

Intemational Centertor LivingAquaticResources Management (ICLARM)

M.e. PO Box 1501, Makati, Metro ManilaPhilippines

S. Selvanathan and A.H.M. Salleh

Firheries Department, Ministry ofIndustryand Primary Resources

P.O. Box 2161, B.S.B. 1921Brunei Darussalam

ABSTRACf

A steady-state trophic model of the coastal fisheries ecosystem of Brunei Darussalam isderivcd via ECOPATII II using selected parameters from studies conducted in the area andthe available literature. Biomass estimates of various groups so derived are consistent withindependent estimatcs from demersal trawl and pelagic acoustic surveys conducted inBrunei waters. These estimates of biomass combined with fishery catches give exploitationrates (E) between 0.011 and 0.191, confirming independent assessments which indicate thecoastal fishery resources to be lightly fished. Selected summary statistics relevant toeffidency of the system are given together with recommendations for research towardsrefinement of the preliminary model presented.

• ICLARM Contribution No. 650.

•

INTRODUCTION. .

, Brunei Darussalam (Fig. 1) has a langtradition.of fishing and one of the higbestper eapita eonsumption (40 kldperson/year)of seafood in Southeast Asia. Between 1985and 1988, roughly 5,300 t/year was eaught inthe eountry's eoastal watersz 40% of whichwas sold tlirough the fresh flSh markets ~mdtbe rest went to subsistenee eonsumption.About 1,900 tlyear of fishery produets wasimported dunng the same perlod. Tbeartisanal fishenes seetor eomprise 560full-time and 1,700 part-time fishermen,while the semi-industrial fleet eomprise 7trawlers and 2. purse seine vessels. Eventhough tbe. eapture fisheries is small byregional standards, its sustainability ISdeemed significant by local planners. This isin view of (i) its importanee to loeal freshfood supply and security, (H) efforts todiversny the eeonomy from the dominant oiland natural gas industry, and (iii) thenation's lang fishing tradItion and currentfood. preferences... Local authorities,therefore

ihave taken vigoraus interest in

sustainab e development and improvedmanagement of the fishery.

In . !ine .with such. interest,improvement of the biological input in thefisfleries .development . and, managementprocess has .been identified as a majorconstraint. In. this regard, demersal trawland pelagic acoustic surveys were initiatedin mid-1989 .to complement previousassessment studies in Brunei Därussalamwaters (see Chua et al. 1987 fOf a profile ofavailable assessments.) Initial results fromthe ,demersal " survey. indicate ,lowexploitation rates of .. available resOlirces(VIZ., (i) mean yield to biomass ~Y/B=F)ratio o( O.•08 for the fishe!'Y, and ii) meanexploitation ratio (E7'" FIZ). of.0.1 for. themore abundant demersal sp'ecles based. onELEFAN analyses Gayarnlo et a1. 1989).The present. contribution, part of demersalinvestigationS currently. in progress,attempts to verify estimates of biomass andexplOItation rates obtained thus far using anecosystem box model (ECOPATII II,Christensen and PaiIly 1990) and availableinformation on the various resource groups.Moreover,., it. atte~pts to illustrate thenature of avatlable nlformation on Bruneicoastal fishery resources and research areasrequiring attention.

2

MATERIALS ANO METHODS

The approach used here to. derive asteady-state trophie model ~f the. eoastalfishery resources of .. Brunel DarussalamreHes primarily on the ECOPATH model(Polovma and Ow 1983, 1985) as mödifiedby Christensen and Pauly (1990). In theabsence of site-specific food studies, thetrophiC groupin~s and food compositiondata given by Llew and Chan (1987) andChanand Liew (1986) for a similar tropicaleCOsystem (off Trengganu, Malaysia) wereutilized. Table 1 gives a summary of inputparameters to ECOPATII II used in thepresent, study. . BiomaSs estimates asobtainei:l from demersal (Silvestre et a1., inpress) . rind pelagic surveys (DOF 1989)conducted

2in Bninei Darussalam waters

(7,396 km from .the shoreline to 100 indepth) were partitioned into the. varioustrophlC: groups as shown. in Appendix 1.However, glVen .. th.e ., confid~nce, limitsassociated with the bIOmass estImates fromsuch surveys and the variation in catchabilityand escaiJement ratios characteristic of eachgroup, only .thc hiomass estimates fordemersal zoobenthos feeders (aSsumed tobe thc best sampled) was utilized.

Production to biomass ratios (PIB = zor iristantaneous total mortality) f(Jr groups6-9 were obtaincd from length-basedass.essm.erits .(via ELEF.AN) using demersalsurvey data (see Appendix 2). Apart fromthese, thc rest of the entries in Table 1 weretaken from literature values, as follows: (i)phytoplankton and detritus biomass andphytoplankton PIß from Linden et a1.(1989) and Pauly et a1. (1987); (ii)PIB aridQIB ratios from Liew and Chan (1987) andPoloVina and Ow (1983); (Hi) catches fromstatistics .. of . the Fisheries Department,Brunei Darussalam (Silvestre el a1., in

. press) adjusted for subsistence consumptionand discrirdin~ practices; ... ,and, , (iv)ecotrophicefficlency (EE) assumed to be0.95 for groups (1) to (8) (see Polovina1984)..Table 2. ~lves .a summaI"Y, of .foodcomposition . ratlOS used, .aslnput toECOPATH II in the present study. Allentries are from Liew and Chan (1987) withminoe modifications to reflect relative preyabundance/availability in Brunei waters.

3

RESULTS AND DISCUSSION

The steady-state trophic model. far t.he ,Brunei Damssalam coastal flshenesecosystem as derived using ECOPATI-I 11 isiIIustrated in Fig. 2. A summary of seIectedoutput statistics is given iil Table 3. Note,that the system is primarily driven by theIarge detritus biomass similar to the findingsof Liew and Chan (1987) for the coastalwaters oi Trengganu, Malaysia. The biomassestimates (B) obtained VIa ECOPATI-I 1Iare consistent with those (Le., B') obtainedfrom demersal trawl and peIagie acoustiesurveys conducted in Bninei waters duringthe 1989-1990 period. The B' estimates forIarge crustaeeans, heterotrophie benthos,small pelagics and Iarge zoobent~lOs feedersare believed to be underestlmates forreasons of low catchability and 'above-average escnpemerit from the trawlused for the demersal surveys, and the factthat the peIngic acoustic sUIyey datnnvnilnbIe were only for a penod w~en

pelagic, biomnss wns beIow average (I.e.,Jurie 1989 or mid-southwest monsoonperiod). The B estimates for the, other~roiJps (Le., demersal zoopInnkton feeders,mtermediate predators and Iargezoobenthos feeders) are consistent withthose obtained via the surveys, nIbeit nt the 'lower end oi the 95% confidenee limits ofH'. Overall, the biomnss outputs fromECOPATI! IJ for the varimis groups areconsistent with those available in theliterature for similar ecosysterris.

, The B vaIues obtained via ECOPATHII together with estimates of. fi.she.ry catch I

given in TahJe 1 impJy Jow explOItatIOn rales .(E). These vary from E=O.Oll for demersal :zoobenthos feeders to E = 0.191 for largepredators. The range oi vall;les. areconsistent with those observed m otherfisheries wherein the larger and morevaluable target species are mo~e heavilyexploited amI me, in fact, the first to heovercxploitcd. Moreov~r, the .E valu~s

herein obtained confirrn independentassessments cited above that Brunei'Darussalam coastal fishery resources arerelatively lightly fished.

The other statistics given in Table 3for the vaI-ious ~roups cO,nsidered ~ere a~econsistent with slmilar esttmates avmlable Inthe literature (see Christensen and Pauly,this vol. and Jorgensen 1979)..Ecotrophlcefficiericy (E~) nnd ~ros~ efficlency (G~)are low for groups high In the food cham(e.g., large {Jredators), an? vice:v,ersa (e.g.,zooplankton). Tbe ommvory mdex IS ameasure of the variance in troJ?hic level ofthe prey of a given ~rou:p (qtnstensen a!1dPauly, this vol.) whlch In thls study vanesfrom 0.007 for demersal" zooplanktonfeeders (which fceds almost solelyonzooJ?lankton) to 0.427 for large crustaeeans(whl~hfe.~d ~m a wide v~riety ofprey groupsin fauly slmtlar proportIOn). Further,~a~le4 and Fig. 3 give seIected summary st~.tlstICSfor the ßrunei Darussalam coastal flsheryecosystem used by Christensen and Pnuly(this vol.) in comparison .with " otherecosystems. Thc "thinness" of the Li?demanpyramid (Fig. 3) comb~ne~, ~vI~h thesummary statlstics in Table 4, l~dlcate .thatthe Brunei coastal ecosystern IS reIatIvelyefficient in its transferslflows.

Tbe presentcontribution, iIlustr~testhc extent of insights that, can be denve~from ecosystem, apprc)3ches (albeltstcady-state) on fishery systems such ~those in the coastal waters of DrunciDarussnlam. Tt also shows, however, tl~e

amount of progress that is still needed. Inunderstanding such systems. The extenSIverecourse to the literature andapproximations used herein emph~ize theneed for increased research efforts mto thefood consumption and compqsiti~n of th~various species/rcsource grollps m Umnelwaters. Improvement of the. fishery c~tchstatistics also appears to be In. order glVenthat only riIark.et~d fish a~e bemg presentlymonitored. TblS mformatlOn should lead toa refim:ment of the prelirilinary modelpresented hefe (incorporating morehoxcs/groups heUer suitctl for managcm~nt

purposes ullimately leading on to simulatIonmodels) towards better managem~nt a!1dsustainable development of the fIshenesresources.

.<•

•

•

•

.'ACKNOWlEDGEMENTS

This study was conducted,under theauspices of the ASEAN." US CoastalResources "Management Project (Task220-B, Bniriei Darussalarn) funded jointlyby the US Agency for InternationalDevelopment (UNAID) and theGovernment of Brunei Darussalam.

REFERENCES

Chan, ER. and H.c. Liew. i986. Charaet6ristics of anexploited tropica1 sballow-water demersal fisbcommunity m Malaysia, p. 349-352." In 1.Maclean, L. Dizon and L. Hosillos (eds.) Tberust Asian Fisheries Forum. Asian FisheriesSociety, Manila.

C1U1stensen, V. and D. Pailly. 1990. Adraft gwde tothe ,ECOPATH 11 program (ver. 1.0).ICLARM Software 6, 22 p.

Chua, ,T.-E., L.-M. Chou aitd MiM. Sadorra,editors. 1987. Tbc coastal environmentalprofJJc of Brunei Oarussalam: resourceasscssment and management issues. ICLARMTech. Rep. 18, 193 p.

DOF. 1989. Pelagic resource survey (intenm report).Department of FlSheries, Ministry of Industryand Primary. Resources, Brunei Darussalam.26 p. and 4 appendices.

Gayanito, F.C• .Tr.r M. Soriano, and D. Pauly. 1989. Adraft gWac to the Compleat ELEFAN.ICLARM Software 2, 67 p.

4

1~rgensen. S.E. 1979. Handbook of environmeniaidata and ecological parameters. InternationalSociety Ecologica1 Modelling.

Linden, 0.; B., Ganning and L. Lindestlöm. 1989.Preliminary .' studics . on .' plankton, Pr.Unaryproduction and [lSh m thc Inner Brunel Bay.Malayan Nature Joum. 43:33-52.

Liew, H.C. and E.H. Chan. 1987. ECOPATH modelof a tropical shallow-water community inMalaysia. MS, 32 p.

Pauly, 0., M. Soriano and M.L. Palomares. 1987.Improved construction, p'arametrization andintc!p'retation of steaöy-state ecosystemmodels. Paper presented at thc Ninth Shrimpand Fm rlSberies Management Workshop, 7-9Dec. 1987, Kuwait.

Polovina, JJ. arid M.D. Ow. i983. ECOPATH: auser's manual and program listings. NationalMarine Fisheries Service, NOAA, Honolulu.Admin. Rep. #83-23, 46 p.

Poiovin~Jj. 19M. Modei of a coral reee ecOsystem I.Tbc ECOPATII model and its 'Y'pücation toFrench Frigate Shoals. Corat ReefS 3(1): 1-11.

Polovina, IJ. and MD. Ow. 1985. Ari approach toestimating an ecosystem box modeL FlSh. Bult.83(3): 457-460. .

SUvestre1 .G., S. Subramaniam anti D. Pauly. ResultsO( demersal resource investigations in. thecoastal waters of Brunei Oarussatam, rlSheriesDepartment, Bandar Sen Begawan,. BruneiDarussalam and Internation31 Center .. forLiving Aquatic. Resources Manasement,Makäti, Metro Manila, Philippines. ~unpubl.MS).

5

Table 1. Summary of Input Parameters used to derive (via ECOPATH 11) a preliminary steady-state trophiemodel of the coas18l fishery resourees of Brunei Darussalam.

f',

Catc~eGroupGroup name

Biom~sPBd asd EEno. (t/km ) (t/km )

, "

1 Zooplankton 67.00 280.00 0.000 0.952 SrnalJ molluses/worms 6.85 27.40 0.000 0.953 SmaJl crus18ceans 62.00 310.00 0.000 0.954 Large crus18ceans 4.00 21.90 0.174 0.955 Heterotrophie benthos 3.00 12.50 0.003 0.95

3.40',-"

6 Demersal zooplankton feeders 14.00 0.005 0.957 Demersal zoobenthos feeders 5.579a 2.15' 10.75 0.131 0.95

Srnall pelaglcS 2.37'"

8 7.90 0.283 0.95'-

9 Intermediate predators 1.74' 8.70 0.060 •10 Large zoobenthos feeders 0.40 6.10 0.12011 Large predators 0.60 9.50 0.05812 Phytoplankton 12.825b 71.15b 0.00013 Detritus 120.000c 0.000

a from de~rsaJ trawl survey (1989-1990) conduct8ct In thä ares (Siivestre et al., unpubJ. MS) coveringb 7,396 km the shoreline to 100 m.

based on Linden et al. (1989).C based on equatlon A5 of Pauly et al (1987). ' " ' ,d based on figures used by L1ew and Chan (1987) and Polovina and Ow (1983) unless otherwise[ indicated.• from catch statistlcs of Rsheries Department, Brunei Darussalam adjusted tor subsistence consumption, and discards., ,-_

trom length frequency da18 collected in the area analyzed using ELEFAN (Silvestre et 1lI., unpub. MS).

Table2. Summary of food composition ratios ot various trophic groups as used in ECOPATH 11 to derivea steady-state modelot the coas18l fishery resourees ofSrunei Darussalam. Da18 trom Uew andChan (1987) with minor modifications indicated by entries in parentheses. (See Table 1 for groupnames/definitions; desk entries imply zero occurence). •

Group ,-

no. 1 2 3 4 5 6 7 8 9 10 12 13

1 0.100 0.650 0.2502 0.300 0.050 0.050 0.100 0.5003 0.150 0.050 0.8004 0.005 0.250 0.180 0.190 (-) 0.010 (0.365)5 0.100 0.060 0.070 0.010 0.020 0.100 0.6406 0.883 0.062 0.0557 0.008 (0.260) 0.536 (0.006) 0.154 0.005 0.012 0.014 (0.005)8 (0.700) 0.050 (-) 0.050 (0.010) (0.190)9 0.043 (0.047) 0.006 (0.004) (0.815) (0.041) (0.044)10 (0.170) 0.664 (0.013) (0.153)11 0.050 (0.005) (0.340) (0.500) (0.100) (0.005)

6

Table3. Summary of select~ output statistlcs obtained via ECOPATH 11 forthe Brunei Darussalam coastaifisheries ecosystem.

B'a EEbMean

Group Groupname B E GEc Trophie Omnivoryno. (t/km2) (t/km2) (=FIZ) Level index

1 Zooplankton 2.455 0.950 0.239 2.11 0.1112 Small molJuscs/worms 4.173 0.950 0.250 2.46 0.330

3 Small erustaceans 0.769 0.950 0.200 2.17 0.1574 large crustaceans 0.413 >0.087 0.105 0.950 0.183 2.83 0.427

5 Heterotrophie bethos 4.395 >0.064 0.950 0.240 2.33 0.310

6 Deminsal zooplankton feeders 0.114 0.112- 0.013 0.950 0.243 3.14 0.007·0.348

7 Demersal zoobenthos feeders 5.579 4.380- 0.011 0.950 0.200 3.30 0.049• 8 SmaJl pelagies 1.812 ~1.273 0.066 0.950 0.300 2.97 0.2939 IntimllEKliate predators 1.156 1.042- 0.030 0.489 0.200 4.25 0.112

3.22510 L.8.rge zoobenthos feeders 0.180 0.170- 0.167 0.500 0.066 3.25 0.018

0.43311 L.8.rge predators 0.505 >0.234 0.191 0.191 0.063 4.18 0.1n12 Phytoplankton 12.825 0.524 1.0013 Detritus 120.000

•

a from demersal trawi survey using "swept area" method and Initial results of pelagie acoustle survey(DOF 1989). .. ..

b eeotrophlc efficlency (proportion of fishing plus predatory mortality to total mortality).C gross effieieney = production/food consumption. .d net efficlency = produetion/(food eonsumption - egestion).e see Christensen and Pauly (1990)•

Table 4. Selected summary statlstics for Brunei Darussalam eoastal flsheries ecosYztem for comparisonwith other ecosystems (see Christensen and Pauly, thls vo!.). Units In t/km Iyear unless lndlcatedotherwise.

Sum of all production ~ncluding export)Sum of all ImportsSum of all respiratory flowsSum of äll f10ws Into detritusTotal system throughputTotal caPacityAseendency

Throughput eycledCycling Index (cycled to total throughput)

1,197

o912826

2,95311,887

15.933111.3

f10wbits

%

%

7

Appendix 1.Cheekllst of families/groups oeeurlng In demersal and pelaglc catehes In Brunel DarrusaJamdistributed among trophie groups usecl by Uew and Chan (1987).

Large Predators

Careharhinidae, Seombridae (exeluding Rastrelliger), Thunnidae

Large Zoobenthic Eeeders

Dasyatididae, Rhynehobatidae, Ephippidae, Rajidae, Gymnuridae

Intermediate Predators

Carangidae (exeluding Decapterus. Selar, Alepes, Selaroides, MegaJaspis),Seiaenidae, Synodontidae, Ariidae, Lutjanidae, Triehiuridae. Psettodidae,Raehyeentridae. Serranidae, Sphyraenidae. Fistularidae, Paraliehthyidae.Muraenesoeidae. Seorpaenidae, Chiroeentridae

Small Pelagics

Carangidae (e.g., Deeapterus. Selar, ete.). Clupeidae, Loliginidae. Rastrelliger,Engraulidae

Demersal Zoobenthos Eeeders

Lelognathidae, Mullidae, Nemipteridae, Haemulidae, Ariommatidae, Priaeanthidae,Theraponidae, Ballstidae. Tetraodontidae, Platyeephalidae. Laetaridae, Bothidae.Apogonidae, Triglidae. Daetylopteridae, Lethirinidae, Monoeanthidae. Sparidae.Stromateidae, Triacanthidae, Polynemidae. Siganidae, Ostraeiidae, Labridae,Cynoglossidae, SilJaginidae, Diodontidae, Gobiidae, ete.

Demersal Zooplankton Eeeders

Gerrldae, Centriseidae

Heterotrophie Benthos

Seplidae, Octopodidae, Eehinoderms, Sponges, Large Mollusks

Large Crustaeeans

Seyllaridae, Portunidae, Penaeidae, Palinuridae, ete.

•

•

8

Appendix 2. Estlmates ot PIS ratios for selected trophic groups as derived tram /ength catch curve analysistor Z on selected trawl-caught species in Srune/ DarussaJam (Silvestre et a1. In press). Va/ues inparenthesis are est/mates based on /iterature values.

Group Representatlve % otgroup Zno Group/family/genera generaispecies blamass (= PIS)

9 IntermecHate predators a.u 1.B.

Carangidae Carangoides ma/abaricus 29.4 2.07Sclaenidae Johnius coitor, Pennahia 23.2 2.13

macrophtha/musSynodontldae Saurida tumbil 14.4 1.19Arildae kius thalassinus 11.1 1.04Psettodidae Psettodes erumei 3.6 0.85

• 8 Sma" pelagics .1OO.Q. 2.3Z

Carangidae Decapterus, Se/ar 50.3

rOßIClupeidae Sardinel/a 42.1 2.70Lol/gin/dae Loligo • 3.4 2.05Rastrelliger Rastrel/iger 2.7 3.04Engrau/idae Slo/ephorus 1.5 2.26

7 Demersal zoobeD1hos feeders az..a 2.J.5.

Lelognathldae Le/ognathus splendens, 43.4 2.32L. bindus, L. e/ongatus,L. equu/us, Seeutor/nsidiator, Gazza minuta,L. smithursti

Mullidae Upeneus su/phureus, 12.3 2.21U. tragula

Nemlpteridae Nemipterus japonicus, 11.7 1.74N. hexodon, N. nematophorus,

• N. virgatrusHaemullda Pomadasys argyreus, 10.5 2.02

P. maculatusPrlacanthldae Priacanthus tayenus, 3.4 1.62

P. macracanthusTheraponidae Therapon theraps 1.5 1.88

6 Small demersal zooplankton feedern ~

Gerrldae Pentaprion longimanus 3.40

15'

"5·N "

"10090m,

SOm

15'

45

,""

30

Rg. 1. Brunei Darussalam coastal area.

45

tN

•

•

-Q)

::­Q)-o.-. .c0­oL-

I-

5.00

4.00

3.00

2.00

1.00

130

Q:J 1.2e Int.predalors L

predalors

Ci 14.81g

<D N <D If) 0r:! aI ~ d d a 0

~dQ7Lzoob. ;;j ~ "i€ Dem.zoob. MDem. ZOOP·.I d Nfeedersfeeders leeders o...!!

Sm.

~.ILII pelagics1,60.01 11.61

.,02 d 0.3

r-!!- 06Lcruslaceans ... - N t'! N ~ ~ \d 1Z-3

Ili ~ \tiNoi ci d GI ci OJ

~d '" o ,.;~19.11 II ~

Cl! "': 0 " Si ~.,

ß. ß,., o C'l d ci 0

Het.

~Sm.

mollhvorms 1.6 r-ll- ~ Pbenthos Sm.Zooplanktoncrustaceans

(114.311~4.91

1238.411687.31

CllN '" Cll r~~ 0 "l

~ ': ~l" "" ri~ ~ If)Ci ... ., If)

- 'f ., ::: N

434.1 03

Phytoplankton Delritus

.1182631

Fig. 2. Steady-state trophic model of the coastal tishery resources of BruneiDarussalam as obtained uSlng ECOPATH 11 (Christensen and Pauly 1990). See Tables 1and 2 ~r input parameters and TablZs 3 and 4 tor summary output statistics. Units arein t/km Iyear tor an area ot 7,396 km .

•

Fig. 3. Undeman pyramid for the Brunei Darussalam coastal fishery ecosystem asobtained using ECOPATH 11. See Tables 1 and 2 tor input parameters, Tables 3 and 4tor related summary statistics and Christensen and Pauly (this vol.) tor comparison withother ecosystems.

•

•