annual variation in the nocturnal nekton assemblage of a tropical estuary nj quinn bl kojis

8/7/2019 Annual Variation in the Nocturnal Nekton Assemblage of a Tropical Estuary NJ Quinn BL Kojis

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Estuarine, Coastal and Shelf Science (1985) 2lr 5ll-537

I1

Ii

Annual Variation in the Nocturnal NektonAssemblage of a Tropical Estuary

NormanJ. Quinno and Barbara L. KoiisDFisheries Departmento and Department of Chemical Technologgb, Papua NewGuinea Unioersity of Technology, Lae, Papua New GuineaReceiaed 23 October 1983 and in revisedform 4 March 1985

Keywords: Oceanography; Fourier analysis; time-series; salinity; fish; watertemperature; regression analysis; Papua New GuineaA nocturnal demersal nekton assemblage was sampled fortnightly for two yearsat five sites in the Labu estuary using a 3 m beam trawl with a3.2 cm mesh net.Forty-eight species were caught, totalling 31 458 individuals with the five mostabundant species comprising over 950,1 of the catch. Using multiple regressiontechniques with Fourier transformations, the mean number of species, S, themean abundance, N, and mean weight, W, wete found to conform to a regularannual cycle with maxima in April and May. Seven of the 11 most abundantspicies demonstrated regular annual cycles of abundance. S, N and W weregreatest in the wider, middle sites and lowest in a shallow, stagnant side branchof the estuary. Catch weights and abundances were significantly correlated withphysical data.Salinity and temperature values in the estuary exhibited an annual cycle withmaxima occurring in February/March. The annual thermal variation of surfacewater outside the estuary followed a similar cycle. The salinity at the mouth ofthe Markham River is lowest during January/February, which correspondswith the rainy season in the Markham River catchment. Significant annual vari-ation existed between years in estuarine bottom salinity and salinity values inLabu Bay.

Several species exhibited a greater variation in abundance and mass betweenyears than within years. This supports the hypothesis that in the tropicsbetween-year variation in coastal marine biotic communities is greater thanwithin-vear variation.Introduction

Knowledge of the fish inhabiting Papua New Guinea estuaries is largely confined to listsof species (Munro, 1967; Liem & Haines, 1977; Haines, 1979; Berta et al., 1975;Collette, 1983), taxonomic descriptions (Collette, 1982) and studies of the biology ofbarramundi, Lates calcarifer (Moore, 1982; Moore & Reynolds, 1982; Reynolds &Moore, 1982). Studies of fish of the Huon Gulf and seasonality of Papua New Guineaestuarine fish are non-existent. There are only a few published accounts of the fishfaunas of the tropical estuaries of this region, e.g. Singapore (Thia-Eng,1973) and NorthQueensland (Blaber, 1980).The importance of estuaries as feeding and nursery grounds for fish and the need toassess the effects of existing or potential alterations by man have resulted in increased027 2-77 14185 I 1005r l + 27 $03.00/0

5ll@ 1985 Academic Press Inc. (London) Limited


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512 N. J. Quinn {s B. L. Kojis

attention to these areas throughout the world. Recently interest in mangrove communi-ties in Papua New Guinea has been stimulated by the prospects of three major develop-ment schemes - the Purari hydroelectric power scheme, proposals by Japanesecompanies to develop the large unexploited mangrove resources of the Papuan Gulf andthe Lae port expansion.Mangrove and coastal ecosystems in Papua New Guinea are relatively undisturbed.Local villagers use mangroves as a source of building material and firewood, butthe population density is low and the effect is small. Industrial use of mangroves isalso limited; only 19400 tons of mangrove bark were exported from I89l to 1970(unpublished report of the Office of Forestry, undated, entitled Mangroae Stands:Papua New Guinea). There has been no recent increase in mangrove exploitation.The only full-time commercial fishery is in the Gulf of Papua where increases incatches are recent (1981:. 32.8 tonnes fis}e, 4-7 tonnes crabs; 1982: 68'7 tonnes fish,3'0 tonnes crab) (Anon., 1983). As utilization of these virtually untouched coastalecosystems is inevitable, a baseline of information is necessary from which comparisonscan be made.This study describes the trawlable demersal fish and crustacean communities of theLabu estuary adjacent to the proposed expansion of the Lae wharf and discusses spatialand temporal changes in abundance and seasonality in relation to variations in abioticparameters.Additionally, the fauna from the estuary is compared with that of a subtropical estuary(Serpentine Creek, Brisbane, Queensland, Australia) (Figure l).

lVorkhom

t40 "E

PopuoNewGuineo Loe

t

I

QueenslondAuslro lio

Bri s bo ne140"8

expo ns ionVrl qqe

HuonGui fA

INorthltlkm

Figure l. (a) Regional map showing Lae, Papua New Guinea and Brisbane, Australia.(b) Labu estuary trawling sites. Trawl sites are numbered. Sites where hydrologicaldata were collected are indicated with X.

Porl


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N octurnal nekton assemblage aariation 513

Materials andMethodsPhysical data sampling

Sampling was carried out fortnightly from June 1980 to May 1982 from 17.00 to 23.00hat seven sites. Dissolved oxygen, temperature and salinity were measured in situ using a'Kahlisco' conductivity meter with thermistor and a dissolved oxygen meter at each site.Measurements were taken on the surface and near the bottom at the completion of eachtrawl. S7ater trursparency was measured using a 20 cm diameter Secchi disc. Rainfalldata for the years 1973 to 1982 were obtained from the Civil Engineering Department atthe Papua New Guinea University of Technology.

Biological samplingOn the basis of a pilot survey from March to June 1980 five sites were sampled on afortnightly basis from June 1980 to May 1982. A 3 m beam trawl with a stretched meshof 3'2cm, identical to that used by Quinn (1980), was trawled heading upstream forabout 300m at each site for 15 min at approximately one knot. The beam trawl waschosen because it is an active fishing gear that yields quantitative results which can becompared with work done at lower latitudes in Queensland, Australia.All sampling methods are biased because any one type of equipment is more suitablefor catching some species than others. For example, in this study the beam trawl caughtmostly bottom fish while surface feeding (e.g. gar) and schooling (e.C. mullet) fish werenot caught at all, although they were present in the estuary.Sampling was carried out on 4l out of a possible 48 dates. Inclement weather andother difficulties account for the missing sampling sets. $Tithin each sampling date not all

sites were trawled owing to snags, the presence of too many jellyfish (Catostylus sp.) andrequests by villagers to forego trawling a site when numerous gill nets had been set.Approximately 97o/, of sites were trawled within the sampling dates.To reduce collecting variability, trawling began at Site I about l-2 h after sunset.Replicate trawls were not taken owing to time limitations imposed by a suspected dielvariation in the fauna. This is discussed in greater detail in Quinn & Koiis (1983). Lunarphase was considered a controlled variable since sites were trawled each fortnight duringnew and full moons (Quinn & Kojis, 1984).Captured fish were counted, standard length (S.L.) measured to the nearest centi-metre and returned to the water. Samples of 12 species comprising the most abundanttaxa were collected and brought back to the laboratory for length/weight measurements.From these data a power curve equation for the length/weight relationship was derivedusing a Texas Instruments power curve programme. Veight estimates were made bytaking the median value for a species' size class and using the length/weight equation forthat species.Unfamiliar fish were preserved for subsequent identification. The genus Upeneas hadtwo morphologically similar 'species' that were difficult to separate in the field; one isprobably a new species (Johnson, personal communication). Authorities used in theidentification of fish were Munro (L967) and Carcasson (1977). Specimens were lodgedwith the Queensland Museum, Brisbane, Australia.

AnalysisD escriptia e statisticsThe mean total number of individuals per trawl is designated by N, the mean total


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514 N. J. Quinn {x B. L. Kojis

weight by lV and total number of species by S and are termed sample parameters. Theabundance and weights of individual species are identified by n and z{, respectively. Intemporal analyses the means were determined across sites, while for spatial analysesmeans were calculated through time. The amplitude of the coefficient of variation (C.V.)was used as an index of the degree of heterogeneity of the estuarine water and biota.

H armonic r egr e s sion p erio di ci tyIn ecological studies two types of non-random time-series patterns can occur. The firstmay involve a series of observations which show repetition although no apparent regu-larity. These are difficult to characterize and often reflect randomly fluctuating orirregular hydrological conditions. The second, and the one considered here, involves aseries of observations with regular repetition through time. Biotic cycles of this form arebelieved to be caused by regular variation in abiotic and/or biotic factors and usuallypersist for extended periods.\Ve fitted our data to a Fourier transform model using sine and cosine terms, becausethey provide a powerful tool for describing periodic phenomena. Bliss (1958) has pro-vided a comprehensive description of harmonic regression analysis with examples fromagriculture. A similar type of analysis was used by Maddock & Swann (1977) to investi.-gate trends in sea temperature and climate, by Hamon & Kerr (1968) to investigatethe time variation in the EaSt Australian current and by Quinn (1980) for the hydrologyof a sub-tropical estuary. Only regressions over the 95o/o confidence level were acceptedand plotted.

Studies of periodicity using mathematical models are uncommon and relatively recentin marine ecology. Platt & Denman (1975) in their review of spectral analysis in ecologycited only I I studies, of which seven dealt with marine organisms. Bulmer (197 4) used amixed model, which included periodic terms, to analyse a l0-year cycle in Atlanticsalmon angling records. Recently these techniques have been applied to the Australianmarine fauna (Stephenson, 1978, 1980a, 1981; Stephenson & Burgess, 1980; Stephensonet al.,l982a,b; Gilmour & Stephenson, 1983).

Multiple regressionsStudies analysing the effect of several abiotic parameters on fish (Risk, 1972; Oviatt &Nixon, 1973; Quinn, 1980) and prawn (Stephenson, 1980b; Stephenson & \Tilliams,1981) populations have only recently been analysed using statistical methods.As the composition of the nekton may be the result of physical conditions during theprevious several months, regressions were also performed on lagged physical data. Inthis analysis only temperature and salinity are used to estimatey values, the abundanceor weight of nekton populations. The lagging interval used ranged from one to fivefortnights. As the lag increases, the number of valid observations declines. Given thelimitations of the existing data set, five fortnights (2.5 months) was the longest lagexamined. If more biological knowledge about the populations had been available,further analyses with increased lags might have indicated which stages of the life cycleare most affected by certain abiotic factors (Stephenson & \Tilliams, 1981).

V ariations betw een y ear sUsing a paired r-test, variations in physical and biological data between years wereinvestigated. Similar lunar phases from June 1980 to May 1981 were compared withJune 1981 to May 1982. Owing to missed sampling dates in either of the years, a subsetof 15 lunar pairs were available for comparison.


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Nocturnal nekton assemblage aariation 515

ResultsPhgsical dataEstuarine sitesThe mean salinity and coefficient of variation for the five trawl sites per sample time are

plotted in Figure 2. The highest recorded bottom salinity was 30'5%o in February 1981,while the lowest was 3'9%o in October 1981 (range 28'6%o; annual mean over all times :18.2%o; C.V.:28'60/.; N:38). Surface and bottom salinities followed annual cycleswhich peaked in February (Table l). Mean surface salinity varied from 0'6%o to 26'6%o(range 26'0%'; r : 8'0%; C.V. : 75'7o/"; N : 39). The salinity range between sites wasgreatest in August/September.Bottom temperatures averaged over sites for each date were lowest in August 1980(26'5 "C) and highest in November 1980 (32'3 "C), a range of 5'8 "C (Figure 3)' Both thesurface and bottom temperatures followed an annual cycle that peaked in February. Thesurface temperatures ranged from a maximum of 32'l 'C in November 1980 to aminimum of 24'4 'C in August 1980 (range 7'7 "C; x : 29'2 'C; C.V. : 7'0'/.; N : 40).Bottom water temperature was slightly warmer (x : 29'6 'C; C.V. : 4'9'A;N : 39).Dissolved oxygen values followed no annual cycle (Figure 4). Mean surface valuesranged from 2'6mgl-1 to saturated at about 6'2mgl-1 at 30'C (range 3'6mgl-1;i:3'7 mgl-1; C.V.: 23'5'/,; N:24). Bottom readings varied from 0'2mgl I to3'8mgl-1 (range 3'6mgl-1; x :2'lmgl-1; C.V. :45'7'/Lt N:24.). r$fater trans-parency varied from 0'9 to l'7m G: l'2m; C.V.: l3'l%) with no annual cycle(P>0.05) (Figure 5). Hydrological differences between sites were calculated from the

oo\=:oU)

c.9,oooc9.9oO

ASONt980 J JAI 98r JFMA1982Figure 2. Times series of surface and bottom salinity mean values for five sites in theLabu estuary. -, predicted salinity values; -, observed values; -----,

coeffrcientof variation.


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516 N. J . Quinn Cx B. L. Kojis

TABLE 1. Regression coeffcients for hydrological observations from Labu estuary - hvesite mean

P2iAoMonth ofmaximumN value

Surface temperature, oCBottom temperature,'CSurface salinity, %oBottom salinity, %oSurface dissolved O, mg I tBottom dissolved O, mg l-lTransparency, m

-1.67 0.01 29.061.26 -0 0l 29.97- 6.98 -0.12 11.67-5.76 -0'22 t:u- 1.13-0 6l-2.38-0.47

0.53


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c.oa'aoo.o.9oU

i oEco00Eooi5

JJ A SOND J FMAMJ J ASONDJ FMA1980 r98t t982Figure 4. Time series of surface and bottom dissolved oxygen mean values for five sitesin the Labu estuary. -, observed valuesl - - - -, coefficient of variation.

J J A S O N D J F M A M J J A S O N D J F MAt980 l98r t9 82Figure 5. Time series of water transparency mean values for five sites in the Labuestuary.

-,observed valuesl - - - -, coefficient of variation.

Mean surface temperatures were approximately uniform (29.5'C) for all sites (Table2). Mean bottom temperature for site 4 was about I 'C higher than the other sites. Thissite was furthest upstream and in an isolated section of the estuary with no tributaries.The coefficient of variation was less for bottom than surface temperatures.Mean surface dissolved oxygen readings were uniform around 34mgl-r (Table 2).Sites I and 2 had similar mean dissolved oxygen readings of about 3 mg I - 1, while sites 3and 5 were slightly lower. Site 4 had the lowest dissolved oxygen readings and occasion-ally hydrogen sulphide odours were present. Bottom reading were more variable thansurface readings.Mean transparency ranged from l'1 to l'3 m (Table 2). Turbidity was slightly greaterat site I than at the other sites, probably owing to the increased effect of tidal mixing.There was greater variability in the hydrological observations through time thanthrough space (Table 2). The bottom temperature C.V. was l'3o1" between sites and

c,940 _eo200c.9ni; ooO

E 2coolocoFo

J


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518 N. J. Quinn s B. L. Kojis

T tstn 2. Summary of hydrological data for five sites in Labu estuaryPhysical data Mean C.V. N

Site 1Surface temperature,'CBottom temperature, oCSurface salinity, %oBottom salinity, %oSurface dissolved oxygen, mg I 1Bottom dissolved oxygen, mg I 1Transparency, mSite 2Surface temperature,'CBottom temperature, oC

Surface salinity, %oBottom salinity, %oSurface dissolved oxygen, mg I - 1Bottom dissolved oxygen, mg I - ITransparency, mSite 3Surface temperature,'CBottom temperature, oC

Surface salinity, %oBottom salinity, %oSurface dissolved oxygen, mg I 1Bottom dissolved oxygen, mg l- 1Transparency, mSite 4Surface temperature, oCBottom temperature,'CSurface salinity, %oBottom salinity, %oSurface dissolved oxygen, mg I IBottom dissolved oxygen, mg l- 1Transparency, mSite 5Surface temperature, "CBottom temperature,'CSurface salinity, %oBottom salinity, %oSurface dissolved oxygen, mg I - 1Bottom dissolved oxygen, mg I 1Transparency, m

29.329.5

9.519.84.13.41.1

29.429.58.3182372.91.2

29.42958.318.23.72.9r.2

30.030.46.61873.80.97.3

28729.46.717.2))t.4

7.3

6.45.39t.724.9229738t7.47.85.587933.726.561.8

15.5

40383835232337

4l393936)72338

5555555

7.9 4l5.6 3964.3 4025.7 3727.6 2049.8 2026.0 3766 415.5 397t.5 4032.4 37222 2357.1 2375.5 376.6 4t5.5 3971.5 4032.4 3722.3 23571 2315.6 37

Mean ztalues through sitesSurface temperature,'C 29.2 1.4Bottom temperature, 'C 29.6 1.3Surface salinity, %o 7.9 l3'9Bottom salinity, %o 18.4 4.6Surface dissolved oxygen, mg 1- 1 3.7 4.6Bottom dissolved oxygen, mg I - 1 2.3 42.1Transparency,m 1.2 62


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TABLE 3. Comparison between years of hydrological observations in Labu estuaryusing a paired l-testYear One Year Two

Physical data Mean Standardertor Standard Degrees ofMean error freedomSurface temperature,'CBottom temPerature, oCSurface salinity, %oBottom salinity, %oDissolved O, surface, mg l-tDissolved O, bottom, mg 1- 1Transparency, m

29.229.66.215.84.2241.2

0.400.230.980'840.590.320.05

29.029.98.820.93.62'0t-3

0.670.512.08r.330.300.470.04

t4t3t3t255t3

N.S. 0.50N.S. -0.74


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520

Tesrr 4. Analysis of variance of mean weekly rainfallSource ofvariance Degrees of Mean sumfreedom ofsquares

1.2r4

r.773

localities such as the Siassi Islands (120 km north-east of Lae) and stations up theMarkham Valley reported drought conditions during these latter months.There was a significant difference in mean weekly rainfall between years (P0.05) between weeks(Table 4). Rainfall was variable and could be considerable during any week of the year!(Figure 6).

Biological ob serzt ationsD es uiptizt e statisticsIn 4l trawling sets from June 1980 to May 1982 (24 months) 3L 458 individuals,weighing over L77 kg, from 38 fish species, nine crustacean species and a scyphozoanwere caught. Over 95o/o of the individuals belonged to five species (Table 5) while 25bony fish species were represented by more than l0 individuals. Most of the fish caughtwere juveniles. These were typically brackish water forms capable of tolerating a widerange of salinity by secreting a thick mucous layer over the skin (Equula), by possessinglarge scales (Gerres, Lactarius) or by having other modifications to minimize osmotic

changes (Thia-Eng, L973). Laryer fish were relatively few.No truly freshwater fish were caught. Scatophagus argus, Toxotes jaculator andAnodontostoma chacunda, which could tolerate fresh and estuarine conditions, were col-lected occasionally. The common marine fish that entered the estuary were the anchovy(Stolephorus), the snapper (Lutjanus), the grunter (Pomadasys) and the carangid(Caranx). Only large individuals of some of the less common species were caught, suchas Arothron reticularis.The length/weight equations for 12 fish species were very highly significant (Table 6)and were used to estimate catch weight. Eleven species of fish and prawns, each with aweight greater than lo/o of the total, account for about 97t/o of the total mass caught(Table 7).The overall mean number of individuals caught per night (1.25h total trawling time)was 796 individuals weighing 4'3kg with a mean of 14.0 species and a catch rate of3'4 kg h- 1 trawling.From interviews with the natives it was found that 31 of the 38 fish species and fivecrustacean species caught in the beam trawl were eaten. The Appendix contains thescientific names of the catch and an indication of those locallv eaten.

By yearYearResidualTotalBy weekrVeekResidualTotal

8458466

5l335386

12855.5854000.1 I I4152 1364927.2974t99.8704279.189


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Nocturnal nekton assemblage aariation 521

TABLE 5. Rank order and per cent abundance for species trawled in the Labu estuary.Authors of species are given in Appendix along with an indication of which specieswere eatenRankorder Number ofindividuals %oftotal CumulativeSpecies1 Equulaequula2 Metapenaeus demani3 Secutor ruconius4 Gazza achlamys5 Ambassis interruptus6 Polydactylusmicrostomus7 Pseudosciaena weberi8 Apogon amboinensis9 Lactarius lactariusl0 Caranx sexfasciatus

I I Gerres filamentosus12 Apogon hyalosoma13 PalaemonidaeL4 Lutjanusjohnil5 Pomadasys argyreus16 Upeneus sp.17 Anodontostomachacundal8 Stolephorusbataoiensisl9 Upeneus oittatus20 Setipinna papuensis2l Lutjanus ehrenbergi20 L. maxweberi23 Eleotris c.f. macrolepis24 Archamiaburoensis25 Arothronreticularis26 Lutjanusargentimaculatusfor each of the remaining species, fewer than tenindividuals were caught

Total 31458

H armoni c p erio di city analy si sAs with the abiotic data, multiple regression incorporating the Fourier transformationwas performed on each of the 1l most abundant and massive species to ascertain theirconformity to an annual cycle and to determine the period of peak abundance or mass.Seven species had annual cycles of abundance (Table 8). Five of these species were mostcommon in the five months ]une to October. Pseudosciaena ueberi had no cycle, but sig-nificantly increased in abundance through time. The most abundantfish, Equula equula)is most abundant in July (Figure 7). Secutor ruconius, rank order 2,was most abundant inFebruary/March while Metapenaeus demani peaked in November/December.Five species had changes in the weight of the catch that corresponded to annualchanges (Table 8). Three of these species also had maximum peaks from June to August.The most massive population, Equula equula, has its greatest catch of individuals andmass in July/August. Similarly, the largest catches of prawns are in November/December. Catches of Arothron reticularis, weight rank order 2,were too infrequent andirregular to fit the model.

2210632592860I 199584190186169t2tt02l0l8375646137373t3t28)')2ll8l7l5ll

70.310.39.13.81.90.6060.5o.40.30.30-30.20.20-20.10.10.10.10.199'4


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522 N. J. Quinn U B. L. Kojis

Tenrr 6. Length/weight relationships for Labu estuarine fishSpecies N

Ambassis interruptusAno dont o s toma chacundaApogon hyalosomaEquula equulaGazza achlamysGerres filamentosusLactarius lactariusP o ly d a c ty lus mi cr o s t omusPomadasys argyreusPseudosciaena weberiSecutor ruconiusS tolephorus bataztiensis

l'50 x 10-s1.03 x l0-s6.82 x l0 65'75 x 10 s6'13 x 10 s3.48 x l0-s3 01 x lO-s3.48 x 10 s1.74 x l0-s1 96 x l0-s4.53 x 70-s5.57 x l}-s

3.193.223.382-892.792.952952'923133012.30).61

o.9920.995o.9540.9770.9650.9940.9920.974a 9960.9700'7800.986


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N o cturnal nekton as s embl ag e a ari ati on 523

Tenrr 8. Regression coefficients for annual cycles in Labu estuary nekton

Species Peakmonth B M ll2Ai PCatch weightEquula equulaArothron reticularisMetapenaeus demaniGazza achlamysSecutor ruconiusP o ly da c ty lu s mi cr o s t omu sAmbassis interruptusLutjanus johniL, maxwebeiLactarius lactariusPomadasys argyreusNumber of individualsEquula equulaMetapenaeus demaniSecutor ruconiusGazza achlamysAmbassis interruptusPolydacty lus microstomusPseudosciaena weberiApogon amboinensisLactarius lactariusCarnax sexJasciatusGerres fi,lamentosusSummary parametersll/sN

Jul/Aug 275'0Nov/Dec 17'1f"t7tr{",ry:'Y-Jul/Aug 56.6Nov/Dec -7 1Feb/Mar

Iun 0'8Jr'rr/errgJuVAug 0'4Aug/Sep

Jul 123 5Jul 15Iun 25'8

2u4 y-r, rj' r43.4 r.311.9

0.5 -0.1040.3

t33 0t.7

269.7 < 0.001 0.68N.S. 0.20t5.7


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524 N. J. Quinn c B. L. Kojis

Tesrp 9. Regression coefficient for catch weight of ,Equula equula and transformed data

TransformationMonth ofmaximumoccurrence iAo

Square root4th rootlog (N+ 1)NoneJulJul/AugJulJu1/Aug

t5.43 0 738


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Nocturnal nekton assemblage oariation

TABLE 10. Catch summary values regressed against physical dataSurfacetemperaturecoefficient

Bottom Surface Bottomtemperature salinity salinity Linearcoefficient coefficient coefficient coefficient Constant rNumber of speciesNumber of individualsTotal weight -81 89 -169.5

The weight of each species was related to hydrological values (Table l2). Equulaequula weight, rank order l, was negatively correlated with surface salinity whileLutjanus johni, rank order 8, was positively correlated. Surface temperature was a weakindicator of Metapenaeus demani (rank order 3) and Lactarius lactarius (rank order l0)weight, with only 11076 and 20o/o of the variance explained respectively. The mean rvalue was 0'47, explaining 22"1; of the variance, about 15 f,u less than that explained withregressions on species abundances. Both the catch weight and number of individuals ofL. lactarius were correlated with the same hydrological observation. The only otherspecies with correlations for both weight and abundance was E. equula, but it wascorrelated with different variables.There are three types of complications to be expected in effecting regressions betweena given time set of hydrological data and a given time set of catch data:(1) The relationship may not be linear, and if not, exponential, logarithmic or powercurve fitting may be required.(2) The data may not be normally distributed and may require transformations whichmay in turn convert a non-linear to a linear relationship.(3) The catches may be influenced by several climatic conditions at an earlier time, andthis is referred to as the lag effect.

Hydrological observations lagged at fortnightly intervals were regressed against thenumber of individuals of commonly caught species (Table I l). Bottom and surface watertemperatures were the most common significantly correlated hydrological variables - l0and nine times respectively. Then followed surface (seven times) and bottom (twice)salinity. It is curious to note that the variable with the greatest temporal homogeneity(C.V., 4'9o/o), bottom temperature, was the most common significantly correlatedhydrological variable. In other words, the 'best' hydrological parameter from whichabundances can be predicted is the parameter that varies least throughout time andwhich probably reflects the small range in abundance. The model lag was threefortnights with eight significant correlations. A single fortnight lag had six correlations,two fortnights had three, four and five fortnights, five correlations. There is no apparentconsistency in hydrological variables ofprevious fortnights affecting abundances.The transformed catch weights of Equula equula and Metapenaeus demani wereregressed on lagged hydrological variables (Table 13). Correlations with bottom salinity(lagged five fortnights) and surface salinity (lagged three) and bottom temperaturerecurred in each regression for E, equula. Two regressions were significant with trans-formed catch weights of M. demani and both included surface temperature. As suspected

-0.19 r6.33137.55580.5


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TenrE I I . Regression coefficients between numbers of individuals and hydrological variables

Species Physical Surface Bottomdata lag' temperature temperature Bottom Linearsalinity coefficient ConstantSurfacesalinity PEguula equulaSecutor ruconius

Metapenaeus demani

Gazza achlamys

Ambassis interruptus

P o ly d a c tjt lu s mi cr o s tomu sApogon ambionensis

Gerres filamentosusLactarius IactariusCaranx sexfasciatusPseudosciaena ueberi

013452345)3453450I2345130I0I3

- 17.02-rt:o

- 0.98-t.42-o'28027-0 39-0.31-o.26- 0.38*0 23

8.58r0.5410.26

-2.61-412-4.80-3.83

_ ru

-5',-o.21yu

0.910.85r.200.380.19

-0 050. l50.29

- 0.10-0.24-0.18

-0'04

-0.06

601 3465.3-237.7-295.9-287-596.6138.5159.9t28.5-l.t- 0.1,3.2

1.816.743.r40.610.I8612.l10.59.98.47.00.97.2l.l1.04.O-4.5

0.55 < 0.01o.35


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TABLB 12. Regression coefficients between catch weight and hydrological variables

Species Physical Surface Bottom Surfacedata lag temperature temperature salinity Bottom Linearsalinity coefrcient Constant PEquula equulaArothron recticalnris

Metapenaeus demani

Secutor ruconius

Gazza achlamysP o ly d acty lus mi cr o s t or/tusLutjanusjohni

Pomadasys argyreusAmbassis intenuptusLactarius lactariusLutjanus maxuteberi

0235045,345400I2335450I

-rs.n3.6

--9 5-1.4-7.4-2.5-2.6

-57.4- 91.9-t.t- 10.316.820-918.7

2-4-2.2-9.5:

-3t.4

l'-4-2

1.6

17.9

0.6- l.lJt.o

716.6t799'2t275.82521.8-7t.5299'l344'56'6466.5- 585.5-520.r5.536.935.1-22.6-23.7270.270.8

45.6238.3303.r82.O85.4

2.22.L

0.65


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Tesrr 13. Regression coefficents between carch weights and lagged hydrological variablesSpecies a'aE Transformation Variable Constant P

Equula equula

Metapenaeus demani

square rootsquare rootsquare root4th root4th root4th rootlog(n + 1)log(n + 1)log(rz+ 1)4th root4th rootlog(zf 1)

bottom salinitybottom salinitybottom temperaturesurface salinitybottom salinitybottom temperaturesurface salinitybottom salinitysurface salinitybottom temperature

surface temperaturesurface salinitysurface temperature

o.57 < 0.05

0.84 < 0.00105235235340I3I

37.16t.2t-3.71-0.620.14-0 41-0.070.06-0.03-0.16

0. 150.030.09

- 13r.83116.50

15.13

6'66

-183- l.l8

0.89

0910.360.700.54


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Nocturnal nekton assemblage z;ariation 529

the relationship is clearly complex. It is postulated that hydrological parameters alongwith interactions of other species, such as the presence of predators, need to be con-sidered in the models. This analysis was not attempted owing to small catches of knownpredators of the dominants.

V ariation betw een y ear sThe data from similar lunar phases for two years (June 1980 to May 1981 and June 1981to May 1982) were compared using a \Tilcoxon matched pairs non-parametric test todetermine if there was a significant difference between years in the total catchabundance, mass) or number of species caught (Table l4). No significant difference waspresent for N and IZ although both means were higher during the second year. The

TABLE 14. Comparisons between years of catch summary statistics from Labu estuaryusing a paired r-testYear one Year two

StandardMean error StandardMean errorDegreesoffreedom P

Mean total number of individualsper site per timeMean total weight (g) per siteper timeNur,'rber of fish species per time

77.5442.1t2.4

7.458.60.5

92.0479.9r4.3

t0.260.9o.7

15 N.S. t-2315 N.S. 0.s415


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530 N. J. Quinn s B. L. Kojis

Tesrn 16. Comparisons between years of catch weight of selected species from theLabu estuary using a paired l-testYear one Year two

StandardMean error Standardetror

Degreesoffreedom

Equula equulaArothron recticularisMetapenaeus demaniSecutor ruconiusGazza achlamysP o ly d a c ty lu s mi cr o s t omu sLurianus.iohniPomadasgs argyreusAmbassis interruptusLactarius lactariusApogon amboinensisGerres filamentosus

404.3t68.429.432.427823'628.915'92267929.77.1

79'073.86'718.08.97.78.410.0b.92.42.12.4

624.152.544.327.346'820.03.53.920.5

11.15.3

95.628.68.78.4

13.94.61.82.15.2331.6t.7

t5l515l58

15t5l515l5l5t5


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N o cturnal nekton as s emb lag e a ari ati on

resulted in the annual variation of hydrological parameters in the Labu estuary. $7hilecycles in salinity have been recognized in tropical estuaries, it has been commonlythought that the temperature remains nearly constant all year (Rodriguez, 1975).Although tropical estuarine temperature variation is less than that observed in subtropi-cal waters (Quinn, 1980), there is still a regular annual cycle to which fish could respond.There is no apparent cycle in dissolved oxygen or turbidity.Temperature/salinity cycles are probably related as lower temperatures occur duringperiods of lowest salinity in the estuary. The months of July/August in Lae are charac-terized by cloudy days with prolonged periods of rain. This agrees with the observationby Egborge (1972) in a study of the hydrology of the Oshun River, Nigeria, that lowertemperatures in flood periods occur because of increased cloud cover.The Labu estuary is stratified with significant differences between surface and sub-surface hydrological values. The differences between near substrate and mid-river sur-face temperatures are similar to results from other studies; for example, 3'0'C in aGhanaian river (Thomas, 1966) and 1.0'C in a Malayan stream (Bishop, 1973). This isexpected in sheltered coastal waters where there is little wind-generated water move-ment to mix the less dense freshwater on the surface with higher salinity water below.Additionally, the small tidal range (maximum range l'1 m) does not encourage mixing.

Despite its limited extent, the estuary was occupied by at least 38 species of bottomfish from 26 different families. Thirty one of these species were eaten by local villagers.Some small demersal fish species were probably missed owing to the mesh size and othersampling considerations. Schooling fish (e.g. mullet) and surface feeders (e.g. gar) werepresent in the estuary, but not caught.The fish recorded are generally typical of those recorded from similar locations in theIndo-west Pacific tropics, except for the absence of members of several families such asPlatycephalidae, Cynoglossidae, Sillaginidae and Soleidae. The assemblage is appar-ently much less diverse that that of Trinity Inlet, Queensland (16'55'S), with 54 species(Blaber, 1980), and Ponggal estuary, Singapore (1'N), with 80 species (Thia-Eng, 1973).The use of fine mesh seines in these studies undoubtedly increased the number of speciescaught. Only six species (11%) were common with the Trinity Inlet and five species(6?i,) with Ponggol estuary.The assemblage was dominated by Equula equula, representing 70'3oio of all individ-uals caught and 59.19i, of the mass. It was the most ubiquitous teleost occurring in all 41trawl dates. No published studies of E. equula are available, but in a detailed study arelated species, Leigonathus breairostris, was found to spawn throughout the year in theGulf of Mannar (8"N, 79'E) with individual fish possibly spawning more than once ayear (James & Badrudeen, 1975). The presence of juvenile E. equula (S.L.


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532 N . J . Quinn {s B. L. Kojis

The main feature of the life cycles of some coastal fish is the division into a juvenilephase which is largely estuarine and an adult phase which is primarily marine. It is com-monly thought that most species breed on the continental shelf, because only a few smallspecialized forms have adapted their entire life cycles to the variable conditions oftemperature, salinity and turbidity characteristic of estuaries (Vallace & van der Elst,1975). Generally, there is a seasonal movement of adult populations into the inshorespawning grounds. Fish in pre-spawning and partially spawned condition tend to movein and out of the lower reaches of estuaries with the tides, while post-spawners generallyleave the system.Lowe-McConnell (1977) outlined four zones from inshore muddy water to clear, deepwater with characteristic fish populations and suggested that broad shelf communitiesare highly diverse, while shelf communities near large rivers with seasonal outflowsgenerally were less diverse and contained dominants. As the continental shelf of theHuon Gulf was extremely narrow (


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Nocturnal nekton assemblage zsariation

between-year variarion in estuarine biota. In this study hydrological variation wasgreater between years than within years and a few species experienced significantchanges between years.The hydrological and biological consequences of exceptionally wet or dry years arelargely unknown. It is obvious that periods of high rainfall will have a tremendous effecton the hydrodynamics and sedimentation of the estuary. The biological effects of lowsalinity will also be considerable. On the other hand, drought conditions are also likely tohave an ellect as evaporation would increase the salinity. A severely reduced runoffmight also allow sediment to block the mouth as occurs in South Africa (Blaber, 1973)and effect the assemblage composition.During the second year of this study, drought conditions were experienced in theMarkham River valley and higher salinities were experienced in the estuary. The signifi-cant population variation between years could be related to the hydrological variation.llowever, it is possible that some species have a 'supra'-annual cycle and these cyclescould have accounted for the community changes. Stephenson (1980c) noted manymacrobenthic species had cycles of three to six years. The testing of this hypothesis usingtwo-year data should only be considered as preliminary.

Pseudosciaena weberi (S.L. 3-10 cm) was caught only during the second year ofsampling. This catch variation differs with pseudosciaenid populations in India whichare prolonged breeders and resident in the estuary throughout the year (Nair, 1977).llowever, it has been suggested that within the tropics fish populations vary greatly fromyear to year owing to changes in abiotic and biotic factors (Lowe-McConnell, 1979). Thesalinity in the estuary was higher during the second year and the populationdemonstrated a correlation with salinity values of the previous several fortnights. Thedifference between years may be related to other unmeasured abiotic factors such as theinjection of nutrients into the system) or by biotic pressures such as the alteration of apreferred habitat for predators and subsequent decrease in their populations. Suchinfluences may impose a between-year variation in the relatively aseasonal estuarineenvironment that restricts efforts to determine stable annual patterns in suchenvironments.It is evident from the foregoing that the distribution of juvenile fish in Labu estuarycannot be satisfactorily explained solely with regard to physical factors. It is likely thatthe community structure depends on small environmental changes interacting with pre-dation and other biotic pressures. In this study, large piscivorous fish such as sharks,carangids and sciaenids were not caught in any of the sites. The absence of such pred-ators from the shallow sampling sites may increase the attraction of these areas as sanctu-aries for juvenile fish, as was suggested for a north Queensland estuary (Blaber' 1980).Predation by birds on juvenile fish in African estuaries has been shown to be high(Blaber, 1973). However, few birds were observed in the Labu estuary, possibly becausetheir plumage is commonly sought by local villagers for decoration. Intense humanpredation probably results in small bird populations and consequently bird predation offish was probably not important.This work uses the same sampling device, a 3 m beam trawl, as previous work (Quinn,1980; Quinn & Kojis, 1981) carried out in a similar estuary at approximately the samelongitude (150'E), but with a 20' latitudinal difference. It is commonly thought thatspecies diversity increases as latitude decreases (Pianka, 1966). However, along the EastAustralian/Papua New Guinea coast, this does not appear to be true. Vhile 45 speciesof fish were caught in the subtropical Serpentine Creek, only 39 were caught in this

533


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534 N. J. Quinn Cx B. L. Kojis

study. This was in spite of a longer sampling programme for the latter study. Thesubtropical estuary was characterized by three species, Spheroides pleurostictus, Gerresor.)atus, and Sillago maculata, each representing about 20, 17 and l7o/o of the totalabundances respectively (Quinn, 1980). The tropical estuary was dominated by a singlespecies, Equula equula, representing 70'3% of the catch. The sub-dominant fish Secutorruconius occurred in 9'loft of the catch with Metapenaeus demani representing l03%.Thus, the low latitude, tropical Labu estuary is less diverse than the subtropicalSerpentine Creek.MacArthur (1965) suggested that the number of species within a habitat can be expec-ted to increase with productivity, with structural complexity and lack of seasonality ofresources. As there are no studies of the productivity of the Labu estuary, no com-parisons can be made. Less seasonal variation of resources in the Labu estuary has notresulted in increased diversity. It is possible that the Serpentine Creek estuary is a morecomplex habitat than the Labu estuary and thus alters the latitudinal effects.It is further postulated that the diversity of the estuarine assemblage is also related todiversity of the shallow-water fauna of the Huon Gulf. Moreton Bay is a large shallowbay with a variety of habitats and physico-chemical environments which support a largenekton community which has been described by Bradbury (1980) and Stephenson andBurgess (1980). As there is no study of the demersal fish of the Huon Gulf, it is imposs-ible to compare the open water stocks available to both studies and relate it to estuarinenekton diversity. Ifowever, the area of shallow water is known to be small in the HuonGulf and a narrower range of habitats and physicochemical environments is likely. It issuggested that future studies investigate the community structure of the demersalnekton in the waters < 180 m of the Huon Gulf. Populations studies should focus on thesuspected dominant family, Leiognathidae.Alternatively, according to present theory, high diversity can be maintained only in anon-equilibrium or sub-climax state (Patrick,1967; Odum, 1969; Slobodkin & Sanders,1969; Louchs, 1970). According to this 'intermediate disturbance hypothesis' (Connell,1978), diversity declines during long stable interludes due to competitive elimination,resulting in resource monopolized climax assemblages composed of few species. Distur-bances such as cyclones and wide ranges of temperature and salinity interrupt and setback this process of competitive exclusion. Organisms are killed, populations decimatedat various scales of frequency and intensity. If the intensity and frequency of disturbanceis sufficient to affect all, or most species, then the assemblage will return to pioneeringstages and diversity will be low. If, however, intensity and frequency of disturbance areof a magnitude which affects only certain species, thus acting in a selective manner as a'pruning device' to prevent resource monopolization, diversity will attain a maximumrelative to the extremes of no disturbance or severe disturbance.The Labu estuary is a relatively disturbance-free habitat for euryhaline species anddiversity is low. As the estuary is not directly connected to the Markham River, annualvariation in salinity is not affected by heavy rains far up the valley and hence the annualvariation in salinity is small. Only locally intense rains are likely to greatly reduce thesalinity and serve as a disruptive influence. As less than average rain fell during most ofthe sampling period, it is impossible to assess how much the bottom salinity would dropand to what extent the freshwater intrusion would affect euryhaline populations. Furthersampling during and after a year of heavy rain is necessary to determine the extent thecommunity is altered after an unusually large lowering of salinities.


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Nocturnal nekton assemblage uariation 535

Acknowledgernents\We are indebted to the people of Labu Butu village for their assistance and cooperation.$7e would like to gratefully acknowledge the Papua New Guinea University of Tech-nology for financial assistance for this study. Additional financial support was providedby the Papua New Guinea Harbours Board and the South Pacific Commission.

Messers R. Adams, K. Bakoma, M. Blowers, R. Hancock, K. Kapi, M. Matmillo, M.Sappu, H. Silver, D. Stewart, C. $flright and T. Yamelo assisted with the fieldwork. MrJ. Johnson of the Queensland Museum kindly assisted with fish identification. Mr S.Frusher, Department of Primary Industry, Dr A.J. Bruce, Northern Territory Museumof Arts and Sciences, Mr P. Davie, Queensland Museum and Dr P. Rothlisberg, CSIROhelped identify the Crustacea. Prof. W. Stephenson kindly assisted with computeranalysis performed at the lJniversity of Queensland. Both he and Prof. J.M. Thomsonconstructively criticized portions of the manuscript. Dr G.R. Huntsman and ananonymous reviewer offered useful suggestions.

ReferencesAnon. 1983 Frsheries Research Annual Report, 1982.Depanment of Primary Industry, Port Moresby. 68 pp.Berra, T.M. Moore, R. & Reynolds, L.F.1975 The freshwater fishes of the Laloki River system of NewGuinea. C op eia, 191 5, 316-326.Bishop, J.E. 1973 Limnology of a small Malayan river, Sungai Gombak. Biological Monographs,22,1485.Blaber, S.J.M. 1973 Population size and mortality of juveniles of the marine teleost Rhabdosargus holubi(Pisces, Sparidae) in a closed estuary. Marine Biology,2l,219-225.Blaber, S.J.M. 1980 Fish of the Trinity Inlet system of North Queensland with notes on the ecology of fishfaunaoftropicallndo-Pacificestuaries. AustralianJournalofMarineFreshwaterResearch,3lrl3T-746.Bliss, C.L 1958 Periodic regression in biology and climatology. Bulletin of the Connecticut AgricultureExperimental Station, I, l-61.Bliss, C.I. 1970 Statisrics in Biology, Statistical Methods for Research in Natural Sciences, Vol. 2.McGraw-Hill, New York. 215 pp.Box, G.E. & Cox, D.R. 1964 An analysis of transformations. Journal of the Royal Statistical Society,26,2tt-2,52.Bradbury, R.H. 1980 Complex systems in simple environrnents, a demersal fish community. MarineBiology,50, 17-28.Bulmer, M.G. 1974 A statistical analysis of the 10 year cycle in Canada. Journal of Animal Ecologg,43,701-71 8.Carcasson, R.H. 1977 A Field Guide to the Reef Fishes of Tropical Australia and the Indo-Pacific Region.Collins, Sydney. 320 pp.Collette, B.B. 1982 Two new species of freshwater halfbeaks (Pisces, Hemiramphidae) of the genusZenarchopterus from New Guinea. Copeia, 1982, 265-27 6.Collette, B.B. 1983 Mangrove fishes of New Guinea. ln Tasks for Vegetation Science, Vol. 8, (Teas, H.1.,ed.). pp. 9l-102.Connell, J. 1978 Diversity in tropical raintbrests and coral reefs. Science, 199, 1302-1310.Copeland, B.J. & Bechtel, T.l. 1974 Some environmental limits of six Gulf coast estuarine organisms.Contributions in Marine Science,18, 169-204.Dalzell, P.J. 1980 Baitfish research in New Ireland. Harvest, 6, 109-1 16.Dow, R.L. 1977 Effects of climatic cycles on the relative abundance and availability of commercial marineand estuarine species. Journal du conseil permanent international pour I'expLoration de la mer,37,27+-280.Egborge, A.B.M. 1972 Th'e physical hydrology of the river Oshun, Nigeria. Archix ftir Hydrobiologie, TO,72-80,Gilmour, R.J. & Stephenson, rJ7. 1983 Transformation in cyclical regressions. Proceeding of the Royal

S o ci etg of Queens l and, 9 4, 61-67 .llaines, A.K. 1979 The subsistence fishery of the Purari delta. Science in New Guinea,6, 80-95.Hamon, D. & Kerr, K.L. 1S68 Time and space variation in the East Australian current from merchant shipdata. Australian Journal of Marine and Freshwatei Research,19, I 0l-106.James, P.S.B.R. & Badrudeen, M. 1975 Biology and fishery of Leiognathus breairostris (Valenciennes) fromthe Palk Bay and the Gulf of Manoar. Indian Journal of Marine Science,4,50-59.


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Kailola, P.J. & rVilson, M.A. 1978 The trawl fishes of the Gulf of Papua. Research Bulletin No. 20, Dept.Primary Industry, Port Moresby. 85 pp.Konchina, Y.V. 1977 Some data on the biology of grunts (Family Pomadasyidae). Journal of lchthylogy, 17,548-558.Liem, D.S. & Haines, A.K. 1977 The ecological significance and economic importance of ttre mangrove andestuarine communities of the Gulf Province, Papua New Guinea. Purari River (Wabo) HydroelectricScheme Environmental Studies Vol. 3., Office of Environment and Conservation, IJ(/aigani, andDepartment of Minerals and Energy, Konedobu, Papua New Guinea. 35 pp.Livingston, R.J., Kobylinshi, G. J., Lewis, F.G. & Sheridan, P.F. 1976 Long-term fluctuations of epiben-thicfishandinvertebratepopulationsinApalachicolaBay,Florida. FisheryBulletin,T413ll-321.Louchs, O. 1970 Evolution of diversity, efficiency and community stability. American Zoologist,l0rlT-25.Lowe-McConnell, R.H. 1977 Ecology of Fishes in Tropical W'aters. Camelot, Southampton. 64 pp.Lowe-McConnell, R.H. 1979 Ecological aspects of seasonality in fishes of tropical waters. Syznposia of theZoological Societg of London, 44,219-241 .MacArthur, R.H. 1965 Patterns of species diversity. Biological Reaiews,40r 510-533.Maddock, L. & Swann, C.L. 1977 A statistical analysis of some trends in sea temperature and climate inPiymouth area in the last 10 years. Journal of Marine Biological Association of the United Kingdom, 57,3r7-338.Moore, R. 1982 Spawning and early life history of barramundi, Lates calcarifer (Bloch), in Papua NewGuinea. AustralianJournal of Marine of Marine and Freshwater Research,33r647-661.Moore, R. & Reynolds, L.F.1982 Migration patterns of barramundi, Lates calcarifer (Bloch), in Papua NewGuinea. Australian Journal of Marine of Marine and Freshwater Research,33r 67l-82.Munro, I.R.S. 1967 Fishes of New Guinea. Govt. Printer, Sydney. 778 pp.Nair, K.V.S. 1977 Maturity and spawning of Johnius (fohnieops) seza (Cuvier) at Calicut during 1969-72.Indian J ournal of Fi sherie s, 29, 241.Odum, E. 1969 The strategy ofecosystem development. Science,1641262-270.

Oviatt, C.A. & Nixon, S.W. 1973 The demersal fish of Narragansett Bayr an analysis of community struc-ture, distribution and abundance. Estuarine Coastal and Marine Science,l,36l-378.Patrick, R. 1967 The effect of invasion rate, species pool and size of area on the structure of the diatomcommunity. Proceedingsof theNationalAcademyof Sciencesof theU.S.A.,58r1335-1342.Pianka, E.R. 1966 Latitude gradients in species diversity, a review of concepts. American Naturalist, lO0,3H6.Platt, D. & Denman, R. 1975 Spectral analysis in ecology. Annual Reaiew of Ecology and Systematics,6,r89-210.Quinn, N.J. 1980 Analysis of temporal changes in fish assemblages of Serpentine Creek, Queensland,Australia. Entironrnental Biology of Fishes, 5, 717 -133.Quinn, N.J. & Kojis, B.L. 1981 The lack of changes between new and full moon phases in a nocturnal fishassemblage. Enoironmental Biology of Fishes, 6, 213-218.Quinn, N.J. & Kojis, B.L. 1983 Evaluation of day night differences in trawl catches in a tropical estuary.Science in New Guinea,lO, 172-186.Quinn, N,J, & Kojis, B.L. 1984 Lunar variations in trawled organisms from a tropical estuary. Papua NewGuinea Uniaersity of Technologg Fisheries Department Research Series,5,1-I7.Reynolds, L.R. & Moore, R. 1982 Growth rates of barramundi, Lates calcarifer (Bloch), in Papua NewGuinea. Australian Journal of Marine of Marine and Freshwater Research,33,663-70.Risk, M.J. 1972 Fish diversity of a coral reef in the Virgin Islands. Atoll Research Bulletin,l53,74.Rodriguez, G. 1975 Some aspects of the ecology of tropical estuaries. ln Some Aspects of the Ecology oJTropical Estuarres (Golby, F.B. & Medina,E'., eds.). Springer-Verlag, New York. pp.313-333.Slobodkin, L. and Sanders, H. 1969 On the contribution of environmental predictability to species diver-sity. In'Diversity and Stability in Ecological Ecosystems'. Brookhaoen Symp. Biol.,22r82-95.Sokal, R.R. & Rohlf, F.J. 1969 Biometry: The Principles and Practice of Statisticsin Biological Research.Freeman and Company, San Francisco. 498 pp.Sreekumari, A. 1977 Development and distribution of the larvae of the whitebait Stolephorus zollingeriBleeker (Engraulidae, Pisces) along the southwest coast of lndia. Proc. Symp. W'arm W'ater Zoo-plankton. Natl. Inst. of Oceanography. pp.44U449.Stephenson, W. 1978 Analyses of periodicity in macrobenthos using constructed and real data. Australian

Journal oJ Ecology, 3, 321-336.Stephenson, W. 1980a Time patterns of macrobenthos species in Moreton Bay. Australtan Journal ofEcology, 5,245-262.Stephenson, W. 19806 Relationships of the macrobenthos of Moreton Bay, to prawns and to abiotic factors.Australian Journal of Ecology, 5, 143-149.Stephenson, W. 1981 Long term cycles caused by patchy predation. Australian Journal of Ecology,6,357-364.Stephenson, W. & Burgess, D.A. 1980 Skewness of data in the analysis of species-in-sites-in-times. Proceed-ing of the Royal Society of Queensland,9l,37-52.


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N o cturnal ne kton as s embl ag e a ariation 537

Stephenson, \7. & 'i0illiams, M.J. 1981 Analysis of south Queensland prawn catches landed at Queenslandfish board depots. Proceeding of the Royal Society of Queensland,92,57-74.Stephenson, rW., Chant, D.C. & Cook, S.D. 1982a Trawled catches in northern Moreton Bay. I. Effects ofsampling variables. Memoirs of the Queensland Museum,20r375-386.Stephenson, I7., Chant, D.C. & Cook, S.D. 1982b Trawled catches in northern Moreton Bay. II. Changesover two years. M emoir s of the Que ens Iand Mus eum, 20, 387 -399 .Thia-Eng, C. 1971 An ecological study ofthe Ponggol estuary in Singapore. Hydrobiologia,43,505-33.Thomas, J.D. 1966 On the biology of the catfish Clarias senegalensrs, in a man-made lake in the Ghanaiansavanna with panicular reference to its feeding habits. Journal of Zoology,148r 476-574.Wallace, J.H. & van der Elst, R.P. 7975The estuarine fish of the East Coast of South Africa. Part 4. Oceano-gr ap hic Res ear ch Institute, 42, 3-18.Appendix: List of organisms caught in the beam trawl

Species Family LocallyeatenAmbassis interraprzs Bleeker 1956Anodonto stoma chacunda (H.-B.) 1822Antennarius hispfdzrs (Bloch & Schneider) l80lApogon amboinens,s Bleeker 1858A. hyalosoma Bleeker 1952Ar chamia buroensi s (Bleeker) I 956Arothron reticularis (Bloch & Schneider) 180 IAutaous grammepomus (Blecker, I 849)Callianassa c.f . karumbaCharybdis helleriCaranx sexfascicrzs Quoy & Gaimard 1824Eleotrisfuscus (Bloch & Schneider) 1801E. c.f. macroleprs (Bleeker) 1875Epinephelus tauztina (Forskhl) L7 7 5Equula equula (Forskil) I 775Gazza achlamgs Jordan & Starks 1917Gerres filamentoszs Cuvier 1829Glossogobius circumspectus (Macleay, 1884)Harpodon translucens Saville-Kent 1889Himantura granulata (Macleay) 1883Lactarius lactarius (Bloch & Schneider) l80lLutjanus argentimaculatus (Forsk6l) 1775L. ehrenbergi (Peters) 1869L. johni (Bloch) 7792L. maxweberi? Popta, 1921Metapeneaus demaniMonodactylus argenteus (L.) 1758Mur aene so x ciner eus (ForskAl) I 775Oratosquilla nepaOxyurichthys tentacularis? (C. & V., 1837)Palaemonid prawnsPenaeus semisulcatusPlatax orbicularui (Forskil) 1775P oly dacty lus micro stomus (Bleeker) I 85 IPomadasys argyrens (Valenciennes) 1833Portunus pelagicusP seudo sciaena we beri (Bleeker) 187 7Scatophagus argus (L.) 7766Secutor runconius (H.-8.) 1822Setipinna papuezsrs Munro 1964S tol ephorus bataoi ensis Hardenberg I 933Tetraroge barbara (Cuvier) 1829Thalamita sp.Toxotes jaculator (Pallas) 1766Triancanthus indicus Regan 1903Upeneus ait t atus (Forskil) 1 775Upeneus sp.V aruna litt er at a (Fabricius) I 798

ChandidaeDorosomidaeAntennariidaeApogonidaeApogonidaeApogonidaeTetrodontidaeGobiidaeCallianassaPortunidaeCarangidaeEleotridaeEleotridaeEpinephelidaeLeiognathidaeLeiognathidaeGerridaeGobiidaeHarpodontidaeDasyatidaeLactariidaeLutjanidaeLutianidaeLutjanidaeLutjanidaePenaeidaeMonodactylidaeMuraenesocidaeSquillidaeGobiidaePalaemonidaePenaeidaePlatacidaePolynemidaePomadasyidaePortunidaeSciaenidaeScatophagidaeLeiognathidaeEngraulidaeEngraulidaeTetrarogidaePortunidaeToxotidaeTriacanthidaeMullidaeMullidaeGrapsidae

YesYesNoYesYesYesNoNoNoNoYesYesYesYesYesYesYesNoYesYesYesYesYesYesYesYesYesYesYesNoYesYesYesYesYesYesYesYesYesYesYesNoNoYesNoYesYesNo

annual variation in the nocturnal nekton assemblage of a tropical estuary nj quinn bl kojis

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