55

Philippine Journal of Science142 (1): 55-67, June 2013ISSN 0031 - 7683Date Received: ?? Feb 20??

Key Words: diversity, fish assemblages, native and introduced fish species

*Corresponding author: mark.corpuz@seafdec.org.ph marknellcorpus.@yahoo.com

1 Animal Biology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, College, Laguna

2 UPLB Limnological Research Station, College of Arts and Sciences, University of the Philippines Los Baños, College, Laguna

3 Southeast Asian Fisheries Development Center, Aquaculture Department, Binangonan Freshwater Station, Binangonan, Rizal

Three stream sections (upstream, midstream, and downstream) of Tayabas River, Philippines were surveyed during the wet and dry seasons of 2010 to evaluate the poorly known status of freshwater fish assemblages. The study collected a total of 1,070 individuals comprising 15 species, 13 genera, and 8 families. The three most abundant groups were poeciliids (61.85%), gobiids (26.16%), and cichlid (5.51%). Shannon-Weiner’s diversity indices ranged from 1.270 to 2.171. Relatively high Shannon evenness indices (0.653–0.846) and low Simpson’s dominance values (0.142–0.322) were calculated implying a fairly equitable distribution of niche space for dominant and non-dominant fishes. Significant change on fish assemblage in longitudinal gradient was observed (p<0.05), being the most diverse fish assemblage registered in the upstream. Species richness is mostly composed of native fish species (10 species) and mainly represented by stream gobiids (six species). The downstream, however, had the highest cumulative abundance, in which the larger proportion was from introduced species. Also, wet season had considerably more fish species and individuals relative to dry season (p<0.05). This significant spatio-temporal differences in fish assemblage data were evaluated by multivariate analyses (p<0.05). Canonical correspondence analysis identified the depth (seasonal water level fluctuations), vegetation growth, and dissolved oxygen concentrations (in order of importance) as the most influential environmental parameters affecting fish assemblage structure. Also, climatic stress (prolonged drought) and anthropogenically-induced habitat alteration could negatively affect the integrity of freshwater fishes within the river. The study suggests extensive management programs of the river for the protection of native fish species.

Diversity and Distribution of Freshwater Fish Assemblages in Tayabas River, Quezon (Philippines)

Vachel Gay V. Paller1, Mark Nell C. Corpuz2,3*, and Pablo P. Ocampo1, 2

INTRODUCTIONThe Mount Banahaw-San Cristobal Protected Landscape (MBSCPL) that covers an area of about 109 km2 is one of the few protected areas in Southern Luzon, Philippines. One of the main aquatic ecosystems of MBSCPL is

the Tayabas River, which harbors diverse biota, but its ichthyofauna remains poorly evaluated (LABB Inc. 2008).

The Philippine law (National Integrated Protected Area Law Systems Act of 1992) ensures the protection and conservation of these areas, particularly the forests and the diverse flora and faunathey host (PSDN 2012). In spite of the conservation efforts for MBSCPL, particularly the forest component, the watersheds and river systems

of Mt. Banahaw are said to be under constant threat due to human activities including illegal logging, “slash and burn” (kaingin system), and improper disposal of garbage and effluents to the river systems. Beyond these factors are the lack of community-based education and participatory protection of key aquatic habitats (Diesmos et al. 2004).

Diversity and distribution of riverine fish assemblages are generally influenced by biotic and abiotic factors (Paul & Meyer, 2001). These factors include, among others, stream water levels and flow variability (Bradford & Heinonen 2008), geo-hydrological feature of the river (Angermeier & Winston 1999; Angermeier & Davideanu 2004.), microhabitat heterogeneity (Shervette et al. 2007), and to a certain degree, aggravated by urbanization, habitat alteration, anthropogenically-induced climate change (Welcomme 1995; Zampella & Bunnell 1998; Vescovi et al. 2009; Paller et al. 2011) and presence of invasive alien fish species (Guerrero 2002).

Riverine ecosystems and its ichthyofauna support a wide array of indispensable resources (Shinde et al. 2009).The fish assemblages represent integrative biological indicators of the stability of fisheries, impacts of habitat deterioration and climate change, and ecosystem productivity (Zampella & Bunnell 1998; Cagauan 2006; Uy 2008).Thus, the use of fish assemblage data could reflect the environmental and ecological conditions within the longitudinal gradient of Tayabas River system. The understanding of the ichthyofaunal population structure is an important approach for potential sustainable use and conservation management of both the species and aquatic habitats (Paller et al. 2011). Moreover, the evaluation of the poorly known conservation status of native freshwater fish species will contribute to the development of future sustainable fisheries and instigate protection from invasive introduced faunas and beleaguered habitat conditions (Guerrero 2002; Ong et al. 2002).

Synthetic diversity indices are now commonly applied to the study of fish composition and distribution, primarily to assess the health condition of rivers (Begonet al. 1996; Kwak & Peterson 2007). Likewise, appropriate multivariate gradient techniques are being employed to correlate the patterns of fish assemblage structure to different habitat variables at spatial and temporal levels (May & Brown 2000; Shervette et al. 2007).

There is no known information on the current status of freshwater fish assemblages in Tayabas River and how environmental factors influence the spatial and seasonal conditions related to these assemblage structures. Hence, the aim of this study was to characterize the freshwater fish assemblage within the longitudinal gradient of Tayabas River, comparing fish assemblage between the selected stream reaches and between the two seasons (wet and dry). Specifically, we described the spatio-temporal variations

in diversity, abundance, and distribution of the native and introduced fish assemblages, and their associations to environmental variables.

MATERIALS AND METHODS

Study siteThe study site is relatively dry from November to April and wet during the rest of the year (PAGASA 2010). Fishes were collected in Tayabas River in Quezon, Philippines (14o02’N, 121o31’E) (Figure 1). The river is water-fed by the springs of Mt. Banahaw and run-offs from highlands and nearby tributaries. It runs approximately 8.5–9.0 km traversing areas within the cities of Tayabas and Lucena before draining to Tayabas Bay.It is located in the southeastern portion of the mountain, approximately 8 km heading about 120o towards the city of Tayabas. The whole stretch presents typical mountain stream characteristics. Upstream and midstream sites are surrounded by primary and secondary forests. The river banks in either side are primarily lined by mosses, bryophytes, and other riparian vegetation, with some steep areas surrounded with coconut plantations and perennial weeds. Downstream sites are within the city proper of Tayabas. A large proportion of inhabitants is engaged in fisheries, farming, and livestock raising.

Sampling DesignThree stretch sections of the river (upstream, midstream, and downstream) were used in this study. Three sampling stations were selected along each stream reach (a total of nine sampling stations). Each station had approximately 600–700m stream reach with three 200–250m sampling run/site, which were considered replicates within each station. Unit area sampled was equal to the maximum length of seine net (8 m) multiplied to the distance seined (m). Individual sampling run lasted 40–50 min and were done during day time. A three-day sampling period was carried out in February and September 2010 to represent wet and dry season, respectively. A total of 18 samples were made (nine sampling sites x two seasons).

Fish specimens were collected using a seine net (1.2 x 1.2-mm mesh), hand nets, fish trap, angling, and 12-v electro-fishing equipment. Captured fish were immediately counted and identified at lowest possible taxon. Specimens were either housed in laboratory as live samples or preserved in 10% buffered formaldehyde for further documentation and identification. Some voucher specimens were deposited in the fish collection at University of the Philippines Los Baños Museum of Natural History, Philippines.

Paller et al.: Fish Assemblages in Tayabas River, PhilippinesPhilippine Journal of ScienceVol. 142 No. 1, June 2013

56

Before collection, dissolved oxygen (mgl-1, Hanna HI 3810), water temperature (oC), pH (Oakton pH tester 30), and salinity (ppt, Atago hand refractometer) were recorded for each site. Geographic position and elevation were also recorded for each sampling station using a GPS

device (CarNAVi Pro 400). Depth (cm) was measured using an improvised 100-cm wooden ruler at two or three points for each site. Water current or stream flow (m s-1) was measured using a simple float. Dominant bottom type was recorded and categorized as organic detritus,

Figure 1. Map outline of study areas of Tayabas River in Quezon, Philippines. Upstream (□), midstream (▲), and downstream (+). Sites (numbers) within each reach are also included.

120'50"E

14'24"N

14'09"N

13'50"N

14°02'N

121°31'E

121'17"E 121'40"E

Paller et al.: Fish Assemblages in Tayabas River, PhilippinesPhilippine Journal of ScienceVol. 142 No. 1, June 2013

57

silt, mud, sand (0.02–2 mm), gravel (2–64 mm), cobble (64–256 mm), boulder (˃256 mm) (May &Brown 2000). Vegetation cover (%) was estimated visually as determined by the relative amount of submerged and floating aquatic plants to sampling path as well as those occupying both sides of the riverbanks.

Data analysesSpecies richness was determined by the number of species present in a community. The relative abundance for each species was calculated as:

= (ai / A) 100%

where: ai is the number of individuals caught in the ith species and A is the total number of species collected in one sampling area during a sampling period. Diversity index was computed following the Shannon-Weiner diversity index (H’) (Shannon & Weaver 1949):

H’ = - ∑ pi ln pii = 1

S

where: s is the number of species; p is the proportion of individuals found in the ith species and ln is the natural logarithm. Evenness (J’) was computed following the Shannon’s diversity index:

J’ = H’ / ln S

where: S is the total number of species. Species dominance was computed using the Simpson’s index formula (λ) (Simpson 1949):

λ = ∑ni(ni1)N(N1)i = 1

S

where: s is the number of species, ni is the number of individuals in the ith species and N is the total number of individuals.

Homoscedasticity (Levene’s test) and normality (Shapiro-Wilk test) of variances were tested for species richness, log10 (x+1) transformed abundance data, and water parameters. Number of taxa and values of Shannon’s evenness, and Simpson’s dominance for each site in two seasons were compared to one another. Bootstrapping method using 1,000 random pairing was used to test the significance (p<0.05). Comparison of Shannon-Weiner diversity indices between the two seasons and among the stream sites were examined using diversity t-test described by Magurran (1998). Similarity among reaches at two collection seasons was measured using Morisita-Horn

Index (Wolda 1981) and the unweight pair group average method (UPGMA) was used to cluster similar group (sites) according to their composition and log-transformed abundance data. Pool of log-transformed abundance of native and introduced fish assemblages between seasons were compared using Hotelling’s T2 test (a multivariate analogue to the t-test) (p<0.05). Descriptive statistics were also computed for each stream reach in two sampling periods. Pairwise comparison of the mean of each parameter was tested using Tukey’s honestly significant differences (p<0.05).

Correspondence analysis (CA) was used to examine and visualize temporal variation among and between native and introduced fish assemblages using the pool of abundance data. Canonical correspondence analysis (CCA) was used to investigate the association of sampling sites with environmental and habitat variables Monte Carlo test with 1,000 random permutations was applied to test the significance (p<0.05) of the fish assemblage structure and sites to environmental variables (Ter Braak & Verdonschot 1995; Legendre & Legendre 1998). All statistical analyses were performed using Statistica version 7.0.

RESULTS

Composition and Abundance of Fish Assemblages Our ichthyofaunal survey recorded 431 (dry season) and 639 (wet season) specimens belonging to 15 species, 13 genera, and eight families (Table 1). Fish species composition in the river system is largely composed of indigenous species (10 species) and predominated by gobiids (six species). Although exotic species comprised a small portion of fish composition (five species), two of the most dominant fish species were from this group. The two most abundant species, which consisted at least half of the total fish specimens were Poecilia sphenops (wet= 32.55%; dry= 41.30%) and P. reticulata (wet= 26.29%; dry= 26.91%). This is followed by a native species, Glossogobius celebius (wet= 24.57%; dry= 22.74%). These three most frequent species, jointly with Orechromis niloticus, Channa striata, and Clarias batrachus were common residents along the three stream reaches in either seasons.

Variation in Ichthyofaunal DiversitySpecies richness ranging from 6–13 was found to be significantly different between seasons (U= 60, p<0.05), with upper stream areas of wet season having the most numerous taxa (13 species) (Table 2). Furthermore, overall number of fish caught in the wet season (639) was more

Paller et al.: Fish Assemblages in Tayabas River, PhilippinesPhilippine Journal of ScienceVol. 142 No. 1, June 2013

58

Tabl

e 1.

Rel

ativ

e ab

unda

nces

and

den

sitie

s (in

par

enth

esis

, fis

h 10

m-1

) of f

resh

wat

er fi

shes

from

Tay

abas

Riv

er, P

hilip

pine

s. U

s= u

pstre

am, M

s= m

idst

ream

, Ds=

dow

nstre

am.

Fish

spec

ies

Cod

eW

et S

easo

nD

ry S

easo

nSe

ason

s Com

bine

d

Us

Ms

Ds

Us

Ms

Ds

Us

Ms

Ls

Cyp

rinid

ae (C

arps

and

Min

now

s)*

P

untiu

s bin

otat

usPb

in1.

56 (0

.34)

0.47

(0.1

)0

(0)

0 (0

)0

(0)

0 (0

)0.

930.

280

Eleo

trida

e (S

leep

ers a

nd G

udge

ons)

*

B

utis

but

isB

but

0 (0

)0

(0)

0.47

(0.1

)0

(0)

0 (0

)0

(0)

00

0.28

E

leot

ris f

usca

Efus

0.31

(0.0

6)0.

47 (0

.1)

0 (0

)0

(0)

0 (0

)0

(0)

0.19

0.28

0

Gob

iidae

(Tru

e go

bies

)*

G

loss

ogob

ius c

eleb

ius

Gce

l3.

91 (0

.84)

11.2

7 (2

,4)

9.39

(2.0

)4.

18 (0

.6)

6.96

(1.0

)11

.6 (1

.66)

4.02

9.53

10.2

8

G

obio

pter

us c

huno

Gch

u0.

78 (0

.16)

0 (0

)0

(0)

0 (0

)0

(0)

0 (0

)0.

470

0

R

edig

obiu

s bik

olan

usR

bik

0.94

(0.2

0)0.

78 (0

.16)

0 (0

)0

(0)

0 (0

)0

(0)

0.56

0.47

0

S

tipho

don

eleg

ans

Sele

0.63

(0.1

4)0.

16 (0

.04)

0 (0

)0

(0)

0 (0

)0

(0)

0.37

0.09

0

S

tipho

don

sem

oni

Ssem

0.47

(0.1

0)0

(0)

0 (0

)0

(0)

0 (0

)0

(0)

0.28

00

S

ycop

us sp

.Sy

co0

(0)

0 (0

)0

(0)

0.23

(0.0

4)0

(0)

0 (0

)0.

090

0

Syng

nath

idae

(Pip

efis

hes)

*

D

oric

hthy

s mar

tens

iiD

mar

1.72

(0.3

2)1.

56 (0

.34)

0 (0

)0

(0)

0 (0

)0

(0)

1.03

0.93

0

Cha

nnid

ae (M

urre

ls)

C

hann

a st

riat

aC

str

0.16

(0.0

4)0.

16 (0

.04)

0.16

(0.0

4)0.

46 (0

.66)

0.46

(0.6

6)0.

70 (0

.10)

0.28

0.28

0.37

Cla

riida

e (F

resh

wat

er C

atfis

hes)

C

lari

as b

atra

chus

Cba

t0.

16 (0

.04)

0.31

(0.0

6)0.

47 (0

.10)

1.03

(0.5

0)0.

70 (0

.10)

0.23

(0.0

4)0.

090.

470.

47

Cic

hlid

ae (T

ilapi

as)

O

reoc

hrom

is n

ilotic

usO

nil

0.78

(0.1

6)3.

13 (0

.66)

1.10

(0.2

4)1.

86 (0

.26)

1.39

(0.2

0)3.

02 (0

.44)

1.21

2.43

1.87

Poec

ilida

e (L

iveb

eare

rs)

P

oeci

lia re

ticul

ata

Pret

3.13

(0.6

6)9.

34 (2

.00)

13.7

7 (3

.0)

5.57

(0.8

)8.

58 (1

.24)

12.7

6 (1

.82)

4.11

9.06

13.3

6

P

oeci

lia sp

heno

psPs

ph3.

76 (0

.8)

10.6

4 (2

.26)

18.1

5 (3

.8)

8.12

(1.1

6)9.

98 (1

.44)

23.2

(3.3

4)5.

4210

.09

19.8

1

Tota

l num

ber o

f spe

cies

from

eac

h si

te13

117

76

614

117

*nat

ive

fish

fam

ily

Paller et al.: Fish Assemblages in Tayabas River, PhilippinesPhilippine Journal of ScienceVol. 142 No. 1, June 2013

59

Table 2. Abundance, number of taxa, and diversity indices recorded from the three stream reaches of Tayabas River, Philippines in two sampling seasons. Us= upstream, Ms= midstream, Ds= downstream. H’= Shannon-Weiner diversity index; J’= Shannon Evenness Index; λ= Simpson’s species dominance index.

Wet Season Dry Season

Us Ms Ds Us Ms Ds

Individuals 117c 245b 278a 92b 121a 222 a

Taxa 13a 11ab 7b 7b 6b 6b

H’ 2.171a 1.667b 1.270c 1.518b 1.384c 1.289c

J’ 0.846ab 0.695c 0.653d 0.780b 0.772bc 0.720c

λ 0.142c 0.232b 0.322a 0.261b 0.285ab 0.319a

For each biological index, means with same superscript letter are not significantly different (p>0.05)

than 32% of that in the dry season (431).

Shannon-Weiner’s diversity indices calculated for the three reachesin both sampling periods varied from 1.270–2.171 (Table 2). Spatially, the upstream reach showed significantly highest diversity among the sampling areas (p<0.05), while downstream sites were the least diverse (p<0.05). Significant temporal variation in the mean diversity index was also measured with wet season (1.69) being more diverse than the dry season (1.35) (Diversity t= 6.47, p<0.05).

Shannon’s evenness indices exhibited comparable spatial pattern to that of Shannon-Weiner’s diversity indices that ranged from 0.653–0.846 (Table 2). Highest measurement were calculated in upstream, which was significantly different from the middle and downstream reaches (p<0.05). Diversity t-test for evenness, however, showed no significant seasonal differences (wet= 0.644; dry= 0.695) (p>0.05).

Simpsons’ dominance values ranged from 0.142–0.322 and had a definite inverse relationship with diversity and evenness. Apparently, upstream and downstream had the significant lowest and highest dominance values, respectively (p<0.05). Temporally, mean dominance index were significantly different (wet= 0.24; dry= 0.299) (p<0.05).

SimilarityAnalysis on spatial and temporal similarity produced two conspicuous clusters. The first cluster was composed of sites from the upstream and midstream during wet season, and the second one was composed of all sites from dry season including the downstream of wet season. The first group registered a similarity of about 92%, which deviated from the second group with approximately 73% level of similarity. Interestingly, downstream in wet season was

Figure 2. A dendrogram of UPGMA showing the clustering of sites derived from species composition and log-transformed abundance data. Upstream at wet season (UW); midstream at wet season (MW); downstream at wet season (DW); upstream at dry season (UD); midstream at dry season (MD); downstream at dry season (DD).

clustered with the dry season sites at no less than 95% level of similarity (Fig. 2).

Native and Introduced Fish SpeciesAlthough there was more numerous native species, their cumulative relative abundance was lower than the introduced fish species at wet season (natives= 34.90%; introduced= 65.10%) and dry season (natives= 22.97%; introduced= 77.03%) (Fig.3). Likewise, dominance in numbers of introduced fishes was observed in dry season, having no less than 75% of the total relative abundance (Fig. 3). The only observation in which the relative abundance of native fish species was higher (56.41%) than introduced fish species (43.59%) was found in upstream at wet season. This, however, drastically reduced with

Paller et al.: Fish Assemblages in Tayabas River, PhilippinesPhilippine Journal of ScienceVol. 142 No. 1, June 2013

60

Figure 3. Stacked bar of percent representation in abundances of native (gray bars) and introduced (black bars) freshwater fishes from the three sampling sites in wet and dry seasons. Upstream at wet season (UW); midstream at wet season (MW); downstream at wet season (DW); upstream at dry season (UD); midstream at dry season (MD); downstream at dry season (DD).

decreasing altitude (midstream and downstream).

The Hotelling’s T2 test validated the significant variation on fish assemblage (composition and log-transformed abundance) between seasons (Hotelling T2= 43.02, F=

Figure 4. Plot and population centroids (5% concentration ellipse level) for CA scores of native and introduced fish assemblages between seasons. Native species of wet season (NatW, □); introduced species of wet season (IntroW, ∆); native species ofdry season (NatD, ■); introduced species of dry season (IntroD, ▼).

3.41, p<0.05). This was also visualized by CA plot (Fig. 4). The CA produced two axes that contributed to 58.62% of the differences in species relative abundance. Loads of variables and centroids of wet season groups were clearly separated to that of dry season in Axis 1 (eigenvalue= 0.16) and partially overlapped at Axis 2 (eigenvalue= 0.07) (Fig. 4). Furthermore, native species abundance also significantly changed across seasons, with higher abundances on the wet season (HotellingT2= 78.27, F= 4.83, p<0.05). On the contrary, quantities of introduced fishesdid not changed significantly (HotellingT2= 9.00, F= 0.56, p>0.05) across seasons.

Canonical Correspondence AnalysisFish assemblages were significantly different between the three reaches when using abundance data (p<0.05). The sites-environment relationships outlined by the CCA had eigenvalues of 0.22 and 0.07 on the first two axes, with 79.00% variability in fish assemblages explained (Table 3). Scores of upstream and midstream areas were partially separated from the downstream, and all sites of the dry season (Fig. 5A). CCA also recognized mean depth, vegetation, and DO (in order of importance) as the most weighted causative abiotic parameters structuring the fish assemblage pattern

Rel

ativ

e A

bund

ance

(%)

CA

(18.

51%

)

CA (40.11%)

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61

Figure 5. Canonical correspondence analysis plot scores on the first two axes derived from sampling sites (A) and species abundance data (B). Group enclosed by continuous curve line was formed by upstream sites. Group enclosed by dashed lines were formed by midstream sites.Group enclosed by oval were formed by downstream sites. upstream (□); midstream (▲); downstream (+). Abbreviations of species are given in Table 1.

CC

A 2(

19.5

6%)

CC

A 2(

19.5

6%)

CAA 1(59.44%)

CAA 1(59.44%)

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Table 3. Correlations of significant abiotic variables of the first two CCA ordination axes. Most significant weights on CCA 1 and CCA 2 are in bold.

CCA 1 CCA 2Eigenvalues 0.22 0.07% Variation 59.44 19.56

DO 0.35 0.33pH 0.20 0.21

Temperature (-)0.33 (-)0.15Depth 0.67 0.27

Vegetation 0.51 (-)0.30Velocity (-)0.35 0.18

Table 4. Summary of habitat and water quality parameters: mean ± standard deviation collated from three stream sections of Tayabas River at two sampling periods.

Seasonal Variation Spatial Variation

Wet Dry t Upstream Midstream Downstream F

DO (mg l-1) 5.96 ± 0.19 5.01 ± 0.10 4.36* 5.13 ± 0.65a 5.8 ± 0.68a 5.51 ± 0.33a 1.67NS

pH 7.34 ± 0.12 7.29 ± 0.07 0.38NS 7.21 ± 0.29a 7.53 ± 0.31a 7.2 ±0.08a 2.94NS

Temperature (oC) 23.77 ± 0.80 24.68 ± 0.85 -0.78NS 21.23 ± 0.69a 26.17 ± 0.96b 25.27 ± 1.58b 31.92*

Depth (cm) 67.33 ± 9.13 41.56 ± 4.32 3.76* 58.5 ± 22.68a 62.33 ± 16.52a 42.5 ± 14.94a 1.97NS

Water velocity (m s-1) 1.10 ± 0.17 1.2 ± 0.30 -0.86NS 1.38 ± 0.28a 0.97 ± 0.08b 1.1 ± 0.11b 8.46*

Vegetation (%) 60.00 ± 9.13 60 .00 ± 9.41 1.06NS 86.83 ± 4.66a 67.00 ± 6.42b 29.17 ± 10.68c 87.23*

*significant at 5% level of confidence, NS not significant at 5% level of confidenceFor each abiotic variable, means with same superscript letter are not significantly different at 5% level of confidence

(Table 3). In this analysis, mean depth and vegetation percentage were highly correlated with the first axis, while DO and vegetation were the factors most correlating with the second axis (Table 3).

The first ordination axis (left and right reading) (59.44%) explained the fish assemblage variation caused by the difference in longitudinal gradient characteristics. The CCA diagram identified an aggregation of scores of several native fishes in Axis 1. The Puntius binotatus, Eleotris fusca, Gobiopterus chuno, Redigobious bikolanus, Stiphodon elegans, Stiphodon semoni, and Dorichthys martensii were most correlated to the upstream and midstream, while a single native species, Butis butis is correlated to the downstream (Fig. 5B). The most common riverine inhabitants, Poecilia reticulata, P. sphenops, Glossogobius celebius, Channa striata,Clarias batrachus intermediated within the plot. The second axis (up and down reading) (19.56%) also explained the gradient of fish assemblage with B. butis, and Sycopus sp., representing the upper and lower axes, respectively. The former was the typical species of the downstream, while the latter was the common species of the upstream (Figs 5B).

Water Parameters and Habitat VariablesTemporal and spatial comparison habitat and water quality parameters were presented in Table 4. Significant temporal differences were recorded in DO and mean depth (p<0.05), albeit with no significant spatial variation. Aeration brought by the water current could be the contributory factor in the increase of DO level. Means of water temperature, vegetation percentage, and water current were statistically varied among stream reaches (p<0.05). Water temperature was higher in the downstream and water velocity was faster in the upstream. Conditions of pH were fairly basic in all sites and in two sampling seasons. Upstream and midstream had considerably deeper water levels as compared to the lower stretch. Water depth drastically reduced during the dry season. Vegetation growth was significantly denser in upstream and remained unchanged after the rainy months. The whole stretch of the river is presented a substrate composed of sand, gravel, cobble, and boulder, a main typical feature of a mountain stream.

DISCUSSIONSThe main characteristic of Tayabas River system is its relatively diverse ichthyofauna (species= 15, H’= 1.55), mostly represented by native species. The richness and diversity are relatively higher compared tothe mountain streams of Mount Makiling Forest Reserve including Dampalit (species= 12, H’= 1.12) and Molawin (species= 12, H’= 1.19) (Paller et al. 2011), but lower than those have been calculated in Bulusan River in Sorsogon (species= 16, H’= 2.41) and Pansipit River in Batangas (species= 21, H’= 3.05) (Corpuz et al. 2010; 2011). Although the mountain rivers are not as diverse compared to estuarine-linked streams, they remain very important ecosystem for freshwater biota and for the communities that rely on their resources (Ong et al. 2002).

The distribution of freshwater fish assemblages showed low dominance (0.142-0.322) and relatively high evenness

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(0.653 - 0.846), which means that the allocation of niche space is fairly distributed equitably for most dominant and non-dominant fish species thriving in the river (Begon et al.1996). The results indicate that abundance of dominant species (particularly poeciliids) rose significantly without measurably displacing harder and robust freshwater fish species. It is rather assumed that poeciliid populations are regulated by non-abundant highly effective piscivorous predators. This can be possible given the fact that poeciliids (P. sphenops and P. reticulata) are highly prolific, yet they are diminutive omnivores, and have pelagic swimming behavior (Burns et al 2009; UPLB-LRS 2011). This scenario follows the keystone species concept as characterized by few non-dominant predators controlling the distribution and abundance of large numbers of prey species (Mills et al. 1993). In this riverine system, channids, gobiids, and clariids are the potential keystone species. This could also be the possible explanation on fairly high equitability values (J’), in spite of very high relative abundance of few taxa (P. sphenops and P. reticulata). Nevertheless, our assumption remains inconclusive but requires a comprehensive study to further assess the overall fish fauna compositions of main watersheds in MBSCPL, and analyze the influence of introduced fishes towards the dwindling populations of indigenous fishes.

Higher diversity and equitability calculated in wet season (Table 1 & 2) serve as an indicator to water and habitat qualities. The results attribute this fish diversity to the wide range of riverine habitats formed with the rising water level (depth) brought by frequent precipitations (Table 2). During rainy months, it provides sufficient volume of aerated water (DO) to replenish and refill the watersheds and, thus facilitates the improvement of carrying capacity for the optimum sustenance of diverse aquatic biota (Vescovi et al. 2009). Similarly, pooled fish richness and relative abundances were apparently higher during the wet season. This supports the assumption that most of the fish populations are intrinsically increasing during rainy seasons (spawning season) in response to environmental stimuli triggered by seasonal changes (Griffin & Ojeda 1992). Environmental stimuli directly affect endocrine pathways and known to regulate metabolism and reproduction in ectothermic fishes (Redding & Patiño 1993). During the breeding season, fish prefers suitable locations (e.g. vegetative and rocky substrates) to deposit, nest their eggs, and/or shelter themselves. These fish breeding substrates including vegetation and remnants of dead plants, rock formations, banks, and shallow pools are usually found in the sampling stations. As expected, a number of gravid fish as well as juveniles were found in the seine sampling (data not shown), which suggests continuous and successful recruitments within the river.

Temporal and spatial variations of fish assemblage and the

underlying factors that contributed to these variations were detected by multivariate gradient analyses (Figs. 4, 5A, & 5B). In CCA, direct gradient analysis showed the most influential environmental variables causing fish assemblage variability (Figs. 5A & 5B). As reflected in the first ordination axis, fish assemblage structure was significantly influenced by mean depth and vegetation growth. These parameters were regarded as good predictors of gradient change in fish assemblage structure (Ross 1986; Shervette et al. 2007; Vorwerk et al. 2007). The second strongest gradient exhibited by the second ordination axis is best explained by the DO level (Fig. 5A; Table 3). The species scores of P. binotatus, E. fusca, G. chuno, R. bikolanus, S. elegans, S. semoni, and D. martensii that are correlated to the upstream in Axis 1 represent the pattern of fish species in the upstream. Central scores from P. reticulata, P. sphenops, G. celebius, C. striata, and C. batrachus revealed that such species are the most typical residents along the stream reaches. Furthermore, B. butis on extreme upper left represents the species of the downstream.As reflected in CA, the effect of seasonal and climatic change could also alter the fish composition and abundance, particularly the native one (Fig. 4).

Freshwater native fish assemblage is largely composed of stream gobies that are well-adapted in pristine, vegetated, fast-flowing, and cool headwater reaches. Unlike the populations of G. celebius that are distributed throughout the whole stream sections, all other native species (native cyprinid, pipefish, and gudgeons) were observed to be restricted in the upstream and midstream (Table 1). In ecological viewpoint, the occurrence (also preference) of these fish populations are generally dependent on the environmental components and habitat feature of their ecosystem including vegetation structure (Herre 1927; Vorwerk et al. 2007), water depth (Ross 1986), elevation (May & Brown 2000), water velocity (Herder & Freyhof 2006), and bottom substratum type (May & Brown 2000). Mainly, because of their reliance in habitats in which they live, these native fish species can be considered asone of the ecologically important bioindicators of riverine health status (Zampella &Bunnell 1998; Angermeier & Davideanu 2004; Cagauan 2007).

The invasion success of introduced fish species occupies the whole stretch of the study site, albeit the overall pattern of their abundance is greater in the downstream. The expansive nature of these fishes is accounted for their high reproductive capacity and for being habitat generalists (Guerrero 2005; Cagauan 2006). Their populations have also the tendency to occupy warmer, shallow low gradient streams and rivers. This occurrence of introduced species is often attributed to accidental and deliberate introduction by the fisherfolks and their escaping from nearby rice paddies cum ponds (Joji Roxas, personal communication). As suggested by Kennard et al. (2005) their presence may

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signify both a warning sign and a cause of decline in river health and the integrity of native fish assemblages.

Significant change on fish assemblage in the stream longitudinal gradient was observed. In our findings, there was a gradation in ichthyofaunal composition, with fish assemblages within the river traversing the downstream sites or within the cityproper being least diverse (Table 2). The observations can be associated to the repercussion of anthropogenic disturbances to the ichthyofaunal diversity. Species diversity seems to decrease in areas exposed to different stressors. Moreover, introduced fish species are more likely to occur in anthropogenically impacted environments (Kennard et al. 2005; Vescovi et al. 2009). Secondary forest cover and aquatic vegetation growth were minimal in the downstream considering most of its embankments and foreshores were landscaped and converted into residential areas. Domestic and agricultural run-offs may also contribute to the pollution that negatively affects the fish assemblage structure.

All sites exhibited apparent changes on fish assemblage over the seasonal transition (Fig. 4), which implies a functional instability of Tayabas aquatic ecosystems under seasonal stress. It is worth mentioning that Luzon areas had experienced a long period of drought correlated to El Niño on the first six months of the year 2010. The condition resulted to the evident decrease in the water depth along the stretches of the river and may lead to the reduction in habitat availability, food production, and water quality (lesser DO and higher stream temperature) (Bradford & Heinonen 2008) causing the decline of fish abundance and compisition during the dry season (Uy 2008). This incident caused a profound ichthyofaunal alteration, which is bias against the more vulnerable native fish species, following exposure to extreme climatic stress (Kennard et al. 2005; Xenopoulos et al. 2005). Conversely, introduced species mainly dominated the fish abundance during the 2010 El Niño phenomenon (Figs. 4 & 3). Threats like these may pose a level of ambiguity on the survival of the indigenous fish species. For example, cryptic genera such as herbivorous gobies (Stiphodon and Sycopus), diminutive gobies (Gobiopterus and Redigobius), cyprinid (Puntius), and pipefish (Dorichthys) and related congeners were once abundant in the river and adjacent tributaries in 1970s. The species, however, are now rarely encountered in the Tayabas River system (Joji Roxas, personal communication). A similar plight was also documented in the current conservation status of fishes in the watersheds of Mount Makiling Forest Reserve (Paller et al. 2011).

Headwaters support higher species richness (represented by native species) than the downstream. The latter, however, possessed a greater number of fish individuals, in which the larger proportion was from the introduced species. The

diversity and distribution of fish assemblage in Tayabas River system are affected by interacting environmental processes, seasonal changes, and anthropogenic pressures. Water levels, vegetation growth, and DO levels are the most prominent environmental factors structuring the ichthyofaunal diversity and distribution within the river. To some extent, anthropogenic disturbances and climate change could degrade the riverine habitats impacting ultimately on diversity loss of more susceptible group, the native fish species. Thus, proper management strategies (e.g., urban planning and reforestation) for downstream sites of MBSCPL are in the utmost importance to revive the declining populations of native species. This ichthyofaunal study updated the inventory of freshwater fishes in Tayabas River and provided essential dataset for future ichthyofaunal survey and conservation program by any concerned entities.

ACKNOWLEDGMENTThis paper is a study of FishArk Philippines: Direction for the Conservation of Native and Endemic Philippine Freshwater Fishes, which is funded by the Department of Science and Technology (DOST) through the Philippine Council for Aquatic and Marine Research and Development (PCAMRD). The authors would like to convey their sincerest gratitude to the DOST for funding the project; University of the Philippines Los Baños Museum of Natural History; City of Tayabas, Quezon; Luksong Alyansa para sa Bundok ng Banahaw Inc.; UPLB Limnological Research Station: BV Labatos,OE Matalog, RR Alvarez, RL Willy,N Salvador, B Lontoc, and G Oldan for the logistics during the survey; UPLB Institute of Biological Sciences: JC Gonzales, R de Chavez, GR Ugaddan, and MVC Camacho; SEAFDEC/AQD-Binangonan Freshwater Station: MRR Eguia, MLC Aralar, E Aralar, and FA Aya.

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