04schiemer_063-080 (2)

CHAPTER 4

CATCHMENT CHARACTERISTICS, HYDROLOGY, LIMNOLOGY AND

SOCIO-ECONOMIC FEATURES OF LAKE TAAL, PHILIPPINES

1 Teresita Perez, 1 Evangeline E. Enriquez, 2 Rafael D. Guerrero III, 3 David Simon & 4* Fritz Schiemer

1 Ateneo de Manila University, Katipunan Road, Loyola Heights, Quezon City 1108, Philippines and previously Institute of Biology, College of Science, University of the

Philippines, Diliman, Quezon City, Philippines.2 Philippine Council for Aquatic and Marine Research and Development, Los Baos,

Laguna, Philippines. 3 Centre for Developing Areas Research, Dept. of Geography, Royal Holloway,

University of London, EGHAM, Surrey TW20 0EX, UK.4 Department of Freshwater Ecology, Faculty of Life Sciences, University of Vienna,

Althanstrasse 14, A-1090 Vienna, Austria.(* Author for Correspondence: Tel.: +43-1-4277-54340;

Fax: +43-1-4277-9572; E-mail: [email protected])

Key Words: Lake Taal, trophic state, biotic community, socio-economy of fi sheries

Abstract

The chapter provides a synthetic overview of Lake Taal and its catchment in southern Luzon Island, the Philippines, as context to the detailed comparative research undertaken by the international FISHSTRAT project. The material presented complements a survey of existing secondary sources with selected summary fi ndings from this project which have fi lled gaps in our knowledge. The holistic and multidisciplinary approach adopted by the project necessitates an integration of limnological, ecological and socio-economic perspectives. Accordingly, the principal foci here are the lakes catchment characteristics, hydrology, limnology and the demographic features and socio-economic conditions of the littoral population.

64

Introduction

Lake Taal, the third largest lake in the Philippines, is economically signifi cant as a source of livelihood for the littoral population through open water fi shery and fi sh cage culture. The lake is a multi-use resource where the dominant activity is fi sheries but it is also used for navigation and tourism centred on the central volcano island.

Maintaining the integrity of the lake is important in respect of its various uses and the numerous activities in its catchment area. Several issues and problems threaten the lakes integrity and ecological balance. The FISHSTRAT project analysed the structure, ecosystem processes and dynamics of Lake Taal in deriving a management tool for capture fi shery and aquaculture practices. The project studied the fi sherys potential as a resource base and the socio-economics of fi shermen living around the lake as the basis on which proposals for sound sustainable management strategies are made (Chapter 23). Drawing on the projects results on limnology, fi sheries and the socio-economics of the fi sherfolk and aquaculturists, combined with complementary data gathered from various sources, this chapter surveys the key characteristics of Lake Taal and its littoral environs.

Location and morphology of the lake

Taal Lake is the third largest lake in the Philippines (after Laguna de Bay and Lake Lanao). It is of volcanic origin, located in the southern part of Luzon Island, about 60 km south of Manila, situated only a few km from the South China Sea at an elevation of 2.5 m above sea level (Fig. 4.1). The lake lies within a caldera with walls that are 150-304 m high. The entire lake comprises the crater of a prehistoric volcano with the surrounding

T. Perez, E.E. Enriquez, R.D. Guerrero III, D. Simon & F. Schiemer

Figure 4.1: Catchment area of Lake Taal

65Chapter 4 Lake Taal, Philippines

mountains and the Tagaytay ridge as its caldera walls (Hargrove, 1991), and was once part of the sea (Plate 4.1).

The lake has an aggregate area (including islands) of 268 km2 and an aquatic surface area of 236.9 km2, with a maximum depth of 198 m (Castillo et al., 1974; Castillo & Gonzales, 1976). It is more than 27 km long and about 20 km wide, with a total shoreline of 120 km. It should be noted that other sources including the Integrated Master Plan (Presidential Commission on Tagaytay-Taal, 1997) cite different fi gures, including an

Plate 4.1: View of Lake Taal with Taal Island. In the foreground are fi shcages (Photo: R. Guerrero III).

Figure 4.2: Bathymetric map of Lake Taal. Indicated are the limnological sampling stations 1,2 and 4.

66 T. Perez, E.E. Enriquez, R.D. Guerrero III, D. Simon & F. Schiemer

aquatic surface area of 240 260 km2. In the centre of the lake lies a volcanic island (2.38 km2), the central feature of which is Taal Volcano, one of the smallest active volcanoes in the world. It reportedly erupted 42 times from 1572 to 1977 (Hargrove, 1991) and threatened to erupt during 1999. The main active crater contains a small crater lake as a lake within Lake Taal (see Hutchinson, 1975), surrounded by numerous craters and cones from previous eruptions. Thermal vents are found on the bed of both the crater lake and the main lake. In contrast to the fresh water in the latter, the crater lakes water is very acidic (pH 2.0).

The bathymetry of Lake Taal (Fig. 4.2) reveals the existence of two basins separated by the volcanic island. The northern basin is smaller and less deep (maximum depth 90 metres, the southern basin is larger and deeper (maximum depth 198 m) (Castillo et al., 1974). Ramos (1986) prepared a bathymetric map using a marine echo-sounder. Fig. 4.2 shows a simplifi ed version based on his original isopleths.

Catchment characteristics

A mountainous terrain surrounds the lake, particularly in the northwestern portion where Tagaytay Ridge is found. The total area of the catchment is 683.73 km (Fig. 4.1; Castillo & Gonzales, 1976) extending through the greater part of the province of Batangas, and portions of Cavite and Laguna provinces (Tab. 4.1). The western and eastern lakeshore areas comprise rugged terrain dissected by deep, steep-sloped V-shaped gullies, while the northeast and southern shores have relatively fl at plains. The slopes range from 10 to more than 40 percent with short and steep creeks draining into the watershed (UPLBF, 1996). The catchment is basically composed of volcanic ash and tuff covers. It is characterized by an elevation range from 10-957 m above mean sea level, with Mt. Macolod as the highest peak, followed by the Tagaytay ridge. Lower elevations are found in the non-littoral municipalities of Taal, Ibaan and Sibul. The steep slopes cover about 30% of the catchment.

Table 4.1: Location and general characteristics of Lake Taal.

type volcanic lake

location 1355-1405N; 12055-121105E

altitude (m-amsl) 2.5

area (km) 236.9 mean depth (zmean, m) 90.4

max. depth (zmax, m) 198

volume (x 106m

3) 21,426

catchment area (km) 682.8 shoreline (km) 120+ (inc. main crater island)

fetch (km) ca. 10 km

retention (years) 45

geology volcanic ash and tuffs

inflows 37 small (and in part seasonal) rivers

mean outflow (ms-1) 15


Tabl

e 4.

2: C

limat

olog

ical

Dat

a fo

r L

ake

Taal

Sour

ce: P

AG

ASA

, Sta

tion:

432

A

mbu

long

; Lat

itude

: 140

05

N; L

ongi

tude

: 121

0 03

E

; Ele

vatio

n: 1

0.0

m.

Pa

ram

eter

Yea

rJ

an

F

eb

M

ar

Ap

r M

ay

J

un

J

ul

Au

g

Sep

O

ct

No

v

Dec

nu

mb

er o

f ra

iny

day

s 1

99

91

3

13

1

2

10

8

2

2

22

2

1

14

1

2

16

1

5

2

00

01

0

9

1

0

5

1

7

22

2

2

20

2

4

20

2

3

15

rain

(m

m)

19

99

4

2.4

8.5

1

69

1

59

.7

9

6.4

3

19

.6

12

2.7

4

52

.9

17

0.8

9

6.5

1

59

.2

16

1.9

2

00

0 4

4.3

7

9.4

73

.6 3

5.8

2

20

.6

15

6.8

4

29

.3

2

78

.7 3

95

.5

39

9.1

2

10

.4

13

3.5

tem

p (

C)

19

99

2

6.6

2

6

27

.6 2

8.3

2

8.6

2

7.8

2

7.8

27

.4 2

7.5

2

7.6

2

7.2

2

6.6

2

00

0 2

6.4

2

6.3

27

.5 2

8.1

27

.9

2

8.2

2

6.6

27

.12

7

2

7.1

2

6.9

2

6.4

rela

tiv

e h

um

idit

y (

%)

19

99

83

7

6

84

8

2

83

8

6

87

8

7

86

8

6

85

8

5

2

00

08

2

84

8

0

79

8

6

86

8

9

87

8

8

87

8

7

86

Tabl

e 4.

3: S

easo

nal c

hang

e in

phy

siog

raph

ic c

ondi

tions

of

Lak

e Ta

al (

Nor

ther

n ba

sin)

dur

ing

the

FISH

STR

AT

stu

dy p

erio

d. +

mea

ns s

trat

ifi ca

tion,

ope

n ci

rcle

arr

ow m

eans

wat

er c

olum

n m

ixin

g.L

ake

Taal

with

Taa

l Isl

and.

In

the

fore

fron

t fi s

hcag

es (

Phot

o: R

. Gue

rrer

o II

I).

1

99

9

20

00

Pa

ram

eter

Ma

r A

pr

Ma

y

Ju

n

Au

g

Oct

N

ov

J

an

F

eb

Ma

r A

pr

Ma

y

Ju

n

Ju

l

stra

tifi

cat

ion

~

+

+

+

+

+

+

+

+

+

te

mp

. (a

t su

rfac

e C

) 2

6.5

2

9.0

3

2.7

2

9.5

2

8.1

2

8.0

2

8.0

2

5.5

2

6.9

2

7.3

3

1.6

3

0.3

2

9.7

2

9.0

tem

p. (8

0m

dep

th

C)

26

.5

27

.5

27

.8

27

.8

27

.4

27

.1

- 2

5.4

2

6.9

2

7.0

-

27

.4

26

.6

27

.9

O2

(80

m d

epth

mg

l-1

) 8

.5

5.8

3

.2

3.5

2

.2

2.8

4

.4

8.5

8

.5

8.1

2

.8

2.3

1

.6

1.6

con

du

ctiv

ity

(S

cm

-1)

16

50

1

67

3

16

71

1

64

6

16

80

1

64

0

16

45

1

61

2

16

67

1

69

8

17

05

1

70

5

17

29

1

68

9

z SD (

cm)

42

0

37

5

37

0

22

0

31

0

41

0

47

5

41

0

52

1

63

3

27

2

19

9

38

3

35

2

chl-

a (g

l-1

) 4

.0

- -

- 5

.8

8.0

1

0.0

6

.0

8.0

1

8.0

5

0.0

2

5.0

2

0.0

2

0.0

pH

7

.2

7.5

7

.5

7.4

7

.3

7.2

7

.4

7.1

7

.1

7.3

7

.4

8.9

8

.7

7.4


Climate and weather

The entire Lake Taal watershed has a climate characterized by a pronounced dry and wet season. The dry season from November to March represents the north-east monsoon, and the wet season from July to September the south-west monsoon. October to November and April-June are intermonsoonal periods.

During the principal fi eld research period (1999-2000), the lowest rainfall was recorded in January and February 1999 and in January 2000. Rainfall peaked during August 1999 and July 2000 (Tab. 4.2). Mean monthly temperatures ranged from 26.0C in February to 28.6C in May 1999 and from 26.3C (February) to 28.2C (June) in 2000. Wind is strong during the dry season and because of the large wind fetch leads to high waves and strong mixing. Thermal stratifi cation of the water column builds up during the rainy period from May onwards (Tab. 4.3).

Hydrology

Thirty-seven tributaries drain into the lake, most of them only seasonally. No long-term records of their infl ows exist. In the course of her work on external nutrient loading, Hilario (2000) recorded the fl ow of three main infl ows, with average values for the period August 1999 to February 2000 of 0.07 m3s-1 for the Laurel River, 1.0 for the Balete River and 0.74 for the Wawa River. The only outlet from the lake is the 8.2-km long Pansipit River, located between the municipalities of Agoncillo and San Nicolas on the south-western shore, which opens into the Balayan Bay of the South China Sea (Fig. 4.1). According to the Philippine National Water Resources Board (NWRB; see NWRC, 1983) the average outfl ow rate of the Pansipit River is 15 m3s-1 based on a time series of 12 years. The monthly means range from lows of 7.0-7.5 m3s-1 in April and May to highs of 20-23 m3s-1 during September to November. Based on the outfl ow data and the huge volume of Lake Taal basin (21,426 106 m3), the theoretical retention time is 45 years. The annual seasonal water level fl uctuation for the period 1987-1994 was about 0.75 m as reported by the Philippine Institute of Volcanology and Seismology (PHIVOLCS, unpubl.).

Figure 4.3: Hypsographic curve of Lake Taal


Limnological conditionsTemperature, stratifi cation, transparency Temperature and oxygen profi les were measured in the northern basin (station 1 see Fig. 4.2) at monthly intervals from February 1999 to August 2000 (Tab. 4.3). Temperature in the surface layers of the open water column ranged from 25.5-32.7 C and in deep water (80m) from 25.5-27.5 C. Lowest values, both at the surface and at 80m depth, occurred in January to March and highest values in April to June. Water temperature is higher (by 2.5-4.5 C) during the early part of the rainy season than in the dry season. Higher temperatures were also observed in the areas with intensifi ed fi sh cage culturing.

Based on temperature and oxygen gradients, it is apparent that the water column was stratifi ed during the period May to November 1999 and from April 2000 onwards. Complete mixing occurs under conditions of lower water temperature in the period of the north-east monsoon from January to March. The consequence of complete water column mixing, locally known as duong, for the oxygen distribution in the water column is shown in Fig. 4.4: The whole column becomes unsaturated and represents a heterotrophic state (see Chapter 22 for further discussion). Chl-a levels and trophic status change seasonally from mesotrophic to eutrophic conditions depending on temperature stratifi cation and mixing. Under conditions of deep mixing and low values of z

eu/z

mix, we fi nd lower chl-a

levels. Seasonal variability is high: chl-a peaks under conditions pertaining at the onset of thermal stratifi cation. Our measurements revealed a mean Secchi disk reading of 3.2m for the area with cages and 4.4m in the area without cages over a 13-month period (Oct. 1998 Nov. 2000).

Figure 4.4. Temperature (a) and oxygen (b) stratifi cation in the northern basin of Lake Taal (max. depth 90m) in February (full line) and August (broken line) 1999. Graph (c) compares Secchi depth (z

SD), the depth of the euphotic zone (z

eu) and the mixing depth (z

mix) at the two seasons (from

Schiemer et al., 2001).


Water chemistry, nutrients, trophic stateSeveral academic and governmental agencies have monitored the lake for varying periods. The geochemical features of the lake are characterised by high electrical conductivity (i.e. high ionic content), moderately hard water with a high chloride content (Zafaralla, 1993; Zafaralla et al., 1992). In terms of nutrient chemistry, the lake is characterised by low levels of nitrogen but high levels of phosphorus (Castillo & Gonzales, 1974; Zafaralla, 1993; Zafaralla et al. 1992).

During the FISHSTRAT research phase from February 1999 to July 2000, a hydrochemical sampling programme was carried out at station 1 (open waters in the northern part of the lake) and station 2 (located in the fi sh sanctuary where there had been a proliferation of fi sh cages). At station 1, parameters were measured at depths of 2.5 m, 20 m, 40 m, 60 m and 80 m, while in the fi sh sanctuary (station 2) sampling depths were 2.5 m and 20 m. Data summarised in Table 4.4 characterise the hydrochemical nature of the lake and some of its tributaries. These values support the earlier fi ndings.

Conductivity ranged from 1600 to 1700 S.cm-1 (Tab. 4.3) during the study period. The infl ows (Laurel and Balete) are characterised by much lower conductivities due to distinctly lower NaCl concentrations. Ionic composition differs from the standard composition and is characterised by the prominence of sodium chloride (NaCl), resulting from the vicinity of the sea. In terms of m-equivalent cations, the range is Na+ - Mg2+

- Ca2+ - K+ , and in anions Cl1- , SO42- - HCO3-. The pH values of the euphotic zone of the

lake lie in the neutral to slightly alkaline range (annual mean pH of 7.4). Higher values > 9 are an expression of high phytoplankton production. In the Laurel River, Hilario (2000) reported large quantities of particulate and dissolved materials from the watershed as a result of agricultural activities and widening of the river.

Lake Taal was initially described as oligotrophic, deep and generally clear with limited biological activity (Zafaralla, 1993). Over time, refl ecting anthropogenic activities in the catchment and excessive feeding in the fi sh cages (Castillo & Gonzales, 1976; Chapter 18), the lake has been transformed into mesotrophic conditions and might be in the early stage of eutrophication in some areas.

With the onset of the wet season, a pronounced increase in the nutrient concentration (NO

3 N and NH

4 N, total phosphate and soluble phosphate) occurs. This is sustained

during its entire hydrological regime (Tab. 4.4). Zafaralla (1993) and Alcanises (1997) also observed an increase in nutrient concentration during the entire wet season.

Hilario (2000) analysed the nutrient inputs from three major tributaries in detail. Nutrient loading from the Balete and Wawa rivers, which combine high loadings of phosphorus, nitrates and ammonia with comparatively high fl ow, has a substantial impact. Sediments and silt, including municipal waste, are also discharged in substantial volumes. Agricultural activities have also contributed signifi cant nutrient loadings into the lake water.

In the areas of high fi sh cage concentrations, reduced dissolved oxygen was observed at 10 or 15 metre depths due to the accumulation of unconsumed feeds as a result of the excessive feeding practice. Our comparison of the dissolved oxygen levels and Secchi disk readings in areas with and without cages showed distinct effects of cage culture on the limnological conditions. Total phosphorus, soluble phosphorus and NO

3 N levels in

the fi sh cage areas were statistically higher compared to the open water (Enriquez, 2001) (Plates 4.2 & 3).


Tabl

e 4.

4: H

ydro

chem

ical

cha

ract

eris

tics

of L

ake

Taal

and

som

e infl o

ws

(Lau

rel a

nd B

alet

e R

iver

). c

ond.

= e

lect

rica

l con

duct

ivity

Sta

tio

n

Da

te

Dep

th

con

d.

pH

C

a

Mg

N

a

K

A

Cl

P

-PO

4

P-s

P

-t

N-N

O3

N-s

Kj

N

-tK

j

Si-

SiO

4

m

S

m

val

m

val

m

val

m

val

m

val

m

val

g/l

g/l

g/l

g/l

g/l

g/l

m

g/l

Taa

l 1

1

.3.9

9

0.5

1

64

0

7.1

1

.88

2

.70

1

2.8

3

0.7

7

- 1

0.8

9

20

8

21

2

24

0

19

7

11

8

19

5

-

Taa

l 1

1

.3.9

9

40

.0

16

60

7

.0

1.1

3

3.4

2

12

.18

0

.72

-

10

.69

2

02

2

04

2

15

2

60

-

- -

Taa

l 1

1

.3.9

9

85

.0

16

40

-

1.8

8

2.9

5

11

.74

0

.72

-

10

.89

2

02

2

13

2

15

2

30

1

30

-

-

Taa

l 2

1

.3.9

9

2.5

1

64

0

7.1

1

.88

2

.70

1

2.8

3

0.7

4

- 1

1.0

6

19

1

21

8

22

0

13

6

19

2

23

5

-

Taa

l 2

1

.3.9

9

20

.0

16

40

7

.1

1.8

8

2.6

7

12

.18

0

.72

-

10

.92

1

90

2

30

2

34

1

46

1

30

-

-

Taa

l 4

5

.3.9

9

0.5

1

64

9

- 2

.50

1

.90

1

1.7

4

0.6

9

- 1

0.8

6

- 1

83

1

90

9

2

11

3

17

1

-

Lau

rel

1

.3.9

9

0.2

4

50

7

.2

2.1

3

1.1

5

1.7

0

0.3

1

- 0

.51

-

19

9

20

2

- -

10

6

-

Taa

l 1

2

6.8

.99

0

.5

16

80

8

.5

2.0

8

2.8

0

12

.00

0

.82

3

.40

1

0.6

6

20

8

23

4

24

0

36

3

69

7

63

8

.3

Taa

l 1

2

6.8

.99

8

5.0

1

68

0

- -

- -

- 3

.42

-

21

6

23

4

23

9

- -

- 1

2.9

Lau

rel

2

6.8

.99

0

.2

4

60

7

.9

- -

- -

3.4

6

- 2

40

2

68

4

42

-

- -

-

Taa

l 1

2

9.7

.00

0

.5

16

90

8

.8

1.8

8

2.6

2

11

.96

0

.66

3

.36

1

0.7

5

19

6

20

6

22

1

72

2

29

2

89

3

.2

Taa

l 2

2

9.7

.00

0

.5

16

85

8

.6

1.8

8

3.0

0

11

.96

0

.69

3

.40

1

0.5

8

17

8

18

8

21

0

67

1

92

3

10

3

.0

Lau

rel

2

9.7

.00

0

.2

4

50

8

.0

2.1

3

1.1

2

2.2

2

0.3

6

3.6

4

0.6

8

19

3

19

9

29

7

68

3

15

1

39

1

44

.9

Bale

te

29

.7.0

0

0.2

4

70

8

.0

1.7

5

1.3

8

2.0

4

0.3

3

4.3

0

0.2

0

33

3

33

4

35

5

17

23

-

- 4

5.5


Plate 4.2: Fish cage area (Photo: R. D. Guerrero III).

Plate 4.3: Fish cage operation (Photo: R. D. Guerrero III).

Biotic communities

The lake has a very interesting fauna and fl ora which represent a combination of fresh water elements, short term migrants from the sea and species of marine origin adapted to freshwater. The best example of the latter is the endemic fresh water sardine, Sardinella tawilis, which forms the basis of an important commercial fi shery. A further interesting species is the endemic sea snake, Hydrolophis semperi (Garman, 1881).

The species list of phytoplankton identifi ed during the FISHSTRAT research period by Rott et al. (Chapter 5) comprises 44 species: Cyanophyceae (9 spp., all rare), Diatomophyceae (5 spp., 2 rare, 3 frequent: Actinocyclus normani, Cyclotella cf. comensis, Thalassiosira visurgis), Cryptophyceae (3 spp., 2 rare, 1 frequent: Rhodomonas minuta), Dinophyceae (2 spp., 1 rare, 1 frequent: Ceratium furcoides), Chlorophyceae (20 spp., all


rare), Zygnemaceae (5 spp., all rare). Taxa richness in Lake Taal is lower than in the other 4 water bodies studied during the FISHSTRAT project; however, the specifi city is higher (35% of the species are found only in Lake Taal). Rott et al. (Chapter 5) characterise the phytoplankton community as being dominated by large dinofl agellates (Ceratium furcoides) during the rainy period and thermal stratifi cation and by small centric diatoms during the dry period with strong winds (Jorge & Pacamara, 2000). Several small centric diatom taxa e.g. Thalassiosira visurgis, are endemic to Lake Taal (Rott et al., 2001).

Signifi cant seasonal variability is encountered due to the seasonal changes in mixing pattern and nutrient supply as observed also for Lake Lanao (Lewis, 1978). Lake Taal is strongly infl uenced by monsoon winds, especially the NE monsoon, which lasts over 2 months and provides a prolonged period of wind mixing of the water column. The phytoplankton pattern therefore follows the change from the dry and windy deep mixing situation (February to March) to an almost stagnant situation in the inter-monsoonal period, with the fi rst strong rainfalls in May. Zafaralla (1993) reported the phytoplankton to be composed primarily of non-heterocystous blue-green algae (see also Zafaralla & Orozco, 1989). A later study in 1996 still mentioned the predominance of Cyanophyta or blue-green algae (42-71%), followed by the Chlorophyta or green algae (20-52%). Chrysophyta and Euglenophyta were also collected.

A detailed study of phytoplankton seasonality was executed by Enriquez between 1999 and 2000. The most abundant phytoplankton throughout this period in all months and at various depths was Ceratium, except for January 2000 when centric diatoms prevailed. High cell counts were observed during the wet season, particularly in open waters. This observation coincided with the high chlorophyll-a values concentrated at depths of 2.5 and 5 m during the wet season. The consistency of Ceratium, even at greater depth, may be due to its characteristic motility and ability to perform vertical migration patterns in the water column (Reynolds, 1984). Merismopedia and Aulacoseira showed increased cell counts particularly during May 2000 (Enriquez, 2001).

Although the lakes littoral zone is narrow, fourteen species of macrophytes distributed along the coastal areas were identifi ed, dominated by Valisneria gigantea (eel grass), Hydrilla verticillata, the emergent Paspalum sp. Potamogeton blognus, and the fl oating Eichhornia crassipes (Bleher, 1996). Eichhornia crassipes and Potamogeton malaianus were commonly observed in river mouths. These macrophytes provide a good sanctuary and feeding ground for juvenile fi nfi sh.

Zooplankton collected from the open waters consisted of rotifers, cladocerans and copepods. The copepods were dominant at all stations sampled, including those in the fi sh cage area. Rotifers and cladocerans ranked second and third, respectively (UPLBF, 1996). The density of these organism groups is signifi cant because of their grazing on the phytoplankton. Our results confi rm those of previous studies, which found that copepods were dominant at most stations sampled, including those in the fi sh cage areas. Rotifers and cladocerans ranked second and third, respectively (UPLBF, 1996). Zooplankton composition is specifi c when compared with the reservoirs in Sri Lanka and Thailand. According to Chapter 8, the most abundant species of copepods are Tropodiaptomus vicinus, Microcyclops varicans and Thermocyclops crassus and among the cladocerans, Osmina fatalis, Ceriodaphnia cornuta, Diaphanosoma sarsi and Moina micrura.

During the FISHSTRAT research period, zooplankton was found down to a depth of 80m. The seasonal variability in zooplankton densities was high and the secondary


production distinctly higher compared to the reservoirs studied in Sri Lanka and Thailand (6.00 vs 0.05-0.09 g dry wt m-2d-1). We found that, relative to its algal biomass, Lake Taal had not only a high zooplankton production per unit volume, but because of its large depth, also an extremely high production per unit area. In this lake the whole water column to a depth of at least 80 m is inhabited by zooplankton. A similar phenomenon was observed for copepods in Lake Tanganyika (Vuorinen et al., 1999). This high zooplankton productivity provides a high carrying capacity for zooplanktivorous fi sh.

The benthic community is dominated by chironomids, followed by amphipods. Other crustaceans, such as Macrobrachium spp., Caridina sp. and other molluscs, such as Ampullaria luzonica, Vivipara angularis and Corbicula manilensis, have been identifi ed. The wide distribution of bottom organisms, including molluscs and arthropods, indicates their signifi cant role in the food chain. Traditionally, crustaceans and molluscs constitute an important component of the fi shery resources of Lake Taal. A large quantity of atyid shrimps (family Atyidae) and grapsid crabs are being gathered and used extensively as human as well as animal food (UPLBF, 1996). Snails (family Melanidae) are collected for use as duck feed.

The fi rst detailed report on fi sh species of Lake Taal was produced by Herre (1927a, b). Bleher (1996) lists 32 species, including migratory diadromous fi shes entering Lake Taal via the Pansipit River (Tab. 4.5). Ten species have been reported as endemic, with seven species introduced. Among the migratory fi shes, Caranx ignobilis and Caranx sexfasciatus are of high value. Sardinella tawilis, a freshwater sardine, is considered to be endemic (Aypa et al., 1999). It is of high economic signifi cance (see Chapters 15 and 18). Villadolid (1937) provided the fi rst study of Lake Taals fi sheries. Oreochromis niloticus (tilapia) has been introduced into the lake and is now cultivated in fi sh cages in the fi sh sanctuary (Plate 4.4). Table 4.5 compares the most abundant fi sh caught during the seasonal study of FISHSTRAT with adult beach seines and gill nets set in the sublittoral region with the commercial catch. Apart from the species listed, it is worth mentioning the presence of small-sized species, e.g. a syngnathid caught in the offshore zone with ichthyoplankton nets, a small blenniid, and Toxotes jaculatrix in the littoral zone.

Fifteen fi sh species are caught by fi shermen in the lake using various types of fi shing gear. Based on commercial landings, the fi sh with signifi cant contributions were tawilis (Sardinella tawilis), silversides (Atherinomorus endrachtensis) and tilapia ( Oreochromis niloticus), followed by the cardinal fi sh (Apogon sp.), common carp (Cyprinus carpio) and silver perch (Therapon plumbeus). The active types of fi shing gear (i.e., motorized push net, ring net and beach seine) yielded the highest catch per day for the period 1994-1998 (Chapter 15). There has been a drastic decline in the number of migratory fi sh species in the Lake Taal Pansipit River system, with a drop of 84% from 31 in 1927 to only 5 in 1996, due to overfi shing and the obstruction posed by fi shing and fi sheries structures (i.e., corrals, cages, and pens) that impede the migration of diadromous fi sh.

Land use in the catchment

Table 4.6 shows the various land uses in the catchment area, where 71% is used for crop production such as sugarcane, upland rice, vegetables and root crops. A signifi cant proportion of the watershed is planted with coconut, together with mangoes and other fruit trees. Non-cultivated areas, on the other hand, are covered with secondary growth


forest, bamboo, with patches of swamps at the lakeshore (PCTT, 1993). Residential areas have been developed on the steeper slopes within Talisay and Laurel towns.

Agriculture is the main use of the watershed (Tab. 4.6), followed by tourism focused on the Volcano Island and Tagaytay Ridge, and fi sheries in the lake. Anthropogenic activities, such as quarrying, the mushrooming real estate, such as the Tagaytay Highlands and golf areas, plantations of various crops such as coffee, coconut, mango, corn and cassava affect the quality of the water that drains into the lake through the river systems.

Plate 4.4: Oreochromis niloticus from fi sh cages (Photo: R. D. Guerrero III)

Table 4.5. Common fi sh species (19 out of a total of 38 recorded) in the experimental and com-mercial catch of Lake Taal. The percentage composition is based on a catch of 12,836 fi sh caught by adult seine nets and 14,115 fi sh caught by gill netting. The commercial catch is expressed in % of biomass.

Family Species Adult seine [%] Gill nets [%] comm. catch [%]

Anguillidae Anguilla bicolor McClelland - - -

Clupeidae Sardinella tawilis (Herre) 3.4 0.2 58.7

Chanidae Chanos chanos (Forsskl) - - -

Cyprinidae Carassius auratus auratus (L.)

Cyprinus carpio L.

1.2 - 3.3

Clariidae Clarias batrachus (L.) - - -

Hemirhamphidae spp. 1.6 - -

Atherinidae Atherinomorus endrachtensis Quoy & Gaimard 4.4 84.0 15.4

Teraponidae Leiopotherapon plumbeus (Kner) 28.6 2.4 2.1

Apogonidae Apogon thermalis Cuv.

Ambassis sp.

25.2 7.4 5.4

Carangidae Caranx ignobilis (Forsskl)

Caranx sexfasciatus Quoy & Gaimard

0.3 0.1 1.4

Cichlidae Oreochromis niloticus (L.) 33.4 1.3 12.0

Gobiidae Glossogobius celebius (Val.)

Glossogobius giuris (Hamilton)

Oligolepis acutipennis (Val.)

1.5 2.4 -

Channidae Channa striata (Bloch) - - -

Mugilidae Mugil sp. 0.04 - -


Socio-economics and demography

The socio-economic environment is one of the major determinants of the potential for sustainable use/management of fi sheries resources. Relevant information is only patchily available, and the following paragraphs summarise key contextual variables as a prelude to the primary fi eld research reported in Chapters 18-20.

Given the number and diversity of administrative units in the Taal catchment, precise determination of the de facto littoral population proved diffi cult. Accordingly, data from the 11 littoral municipalities, namely San Nicolas, Agoncillo, Cuenca, Santa Teresita, Alitagtag, Balete, Mataas na Kahoy, Lipa City, Talisay, Tanauan and Laurel, provide a reasonable approximation (Tab. 4.7). Based on the 2000 population survey, the large urban area of Lipa City had the highest total population (218,447); of the remaining municipalities, Tanauan had the highest population (117,539) and San Nicolas the smallest (16,278). These 11 municipalities accounted for approximately 535,000 (28%) of Batangas Provinces total population of 1,900,000, and 102,000 (27.34%) of the provinces 373,000 households. Since these municipalities constitute only 19.5% of the surface area of Batangas Province, they had higher population densities than non-littoral municipalities. Average household size was 5.25, while population densities ranged from 11.5 per ha in Talisay to a modest 4.05 in Laurel (Tab. 4.7).

Table 4.6: Land use of Lake Taal catchment (1995).

Land use type Area (km2) Percent (%)

sugarcane with corn patches 80 12.0

rice land with corn intercrop 60 9.0

coconut, mango and other fruit trees 170 25.0

forest 100 14.0

volcano island 20 4.0

lake water 250 36.0

swamp and marshes 2.8 0.4

This table also reveals the rapid recent growth rates since 1995, refl ecting a combination of natural increase and net migration over the period of this research project. Growth rates were faster during the 1990s than the 1980s. As with many poor countries, the age pyramid is steep, with 36.5% of the Batangas population aged under 15 in 1995; in all 5-year cohorts up to 44, men outnumber women but above that age the balance is reversed.

In April 1996, the Batangas labour force comprised 606,000 employed and 63,000 unemployed adults (out of a total population aged 15 and over of 1,063,000). However, there was a sharp gender difference, with 365,000 males and 242,000 females working and 42,000 males and 19,000 females unemployed. The summary statistics do not reveal the proportions of full- versus part-time employment. Agriculture was still the most important employment sector, accounting for 158,000 full- and part-time jobs, of which 140,000 were held by men and only 18,000 by women (i.e. 38.4% and 7.4% of those employed, respectively), refl ecting traditional local gender divisions of labour.

In 1995 monthly household and per capita monetary incomes in Pesos (i.e. excluding subsistence production) in the 11 municipalities varied considerably, with Talisay the


lowest (P 1,849 and P 345, respectively), most between P 2150 and P 2900 (P 380-P 500 per capita), and Mataas na Kahoy (P 4131 and P 815 respectively) and Lipa City the highest (P 6247 and P 1211, respectively), again demonstrating the effect of larger cities.Poverty was substantial in Batangas, with 25.6% and 25.9% of the population classifi ed as living below the provincial annual per capita poverty threshold of P 13,313 in 1997 and P15,305 in 2000 respectively. However, this was below the Philippines national averages of 33.0% and 34%, respectively, despite lower monetary thresholds of P 9,843 and P 11,605, respectively. The provincial poverty level therefore rose more slowly than the national average. The Batangas annual per capita food thresholds (i.e. income required to meet basic food needs) were P 8,283 and P 9,484 in 1997 and 2000, compared to the national averages of P 6,801 and P 7,829, respectively.

The socio-economic characteristics of the capture fi shers and fi sh cage operators in our sample broadly mirrored those of the wider littoral populations (Chapter 19), especially those engaged in agriculture. Almost 32% had received no or only some primary education, 25% had completed primary school and 52% had post-primary education. The fi shers and cage operators were overwhelmingly male (90% and 92%, respectively), married (88% overall) and derived no incomes from secondary livelihood activities (75% of fi shers and 83% of cage operators). Most had incomes well above the offi cial poverty level. However, the lowest-earning 18% of fi shers needed a secondary income to stay above the offi cial poverty level for a family of fi ve (the Batangas average) or six (the average size in our survey). In the poorest households, even a low-waged second income earner would not have been adequate, with some households earning only 39% of the family poverty level without pensions or other welfare payments. Competitive pressures, both among capture fi shers and between fi shers and cage operators in terms of use of the lake surface, have been increasing substantially and many capture fi shers feel their livelihoods to be less secure nowadays.

Table 4.7: Lake Taal littoral population (Census 2000). Source: Offi ce of the Provincial Planning Development Coordinator, Batangas City, 1996 & 2001.

Municipality Land area (ha) Population (1995) Population (2000) Density.ha-1

(2000) Households (2000)

Laurel

Talisay

Tanauan

Balete

Mataas na Kahoy

Lipa City

Cuenca

Alitagtag

Santa Teresita

San Nicolas

Agoncillo

6,812

2,822

10,716

2,504

2,213

20,924

4,036

2,344

1,250

2,664

5,468

23,781

26,997

103,868

14,383

16,726

177,894

22,758

18,639

14,017

14,509

23,358

27,604

32,465

117,539

15,792

20,706

218,447

25,642

20,192

14,074

16,278

26,584

4.05

11.50

10.97

6.31

9.36

8.50

6.35

8.61

11.26

6.11

4.86

5,153

6,246

21,912

3,067

3,918

41,962

5,222

3,708

2,762

2,946

5,029

TOTAL 61,753 456,930 535,323 x = 7.99 101,925

Batangas 316,581 1,658,567 1,905,348 - 372,896


Conclusion

This picture of substantial and slowly increasing poverty levels with a rapidly growing population in littoral municipalities, against a background of national economic crisis and stagnation, presents substantial challenges to sustainable fi sheries management. Competition over access to Lake Taals resources has been intensifying, especially in relation to fi sheries and leisure usages, although water abstraction and wastewater infl ow from the growing urban and tourist developments within the steeply sloping caldera surrounding the lake, poses particular problems. Data in subsequent chapters highlight declining water quality, a substantial progressive increase in the level of fi sh cage culture (despite some efforts at control), and an annual average decrease in capture fi shery catches of 3.3%.

Two immediate implications are a decrease in the labour productivity and incomes of small/artisanal capture fi sherfolk, and the increasing confl ict between aquaculture and capture fi sheries through direct competition for space and the impact of mass fi shkills triggered by excessive concentrations of fi sh culture cages. An indirect implication but one of central importance to this study is the extent to which the lake can continue to exist as a sustainable protein source for the people.

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Biology, College of Science, University of the Philippines, Diliman, Quezon City.Aypa, S.M., Galicia, A.M. & Lapasaran, E.S. 1999. The reproduction biology and life cycle of the

freshwater pelagic sardine Harengula (Sardinella) tawilis (Clupeidae) in the volcanic Lake Taal, Philippines. in: van Densen, W.L.T. & Morris, M.J. (eds), Fish and Fisheries of Lakes and Reservoirs in Southeast Asia and Africa., Westbury Academic & Scientifi c Publishing, Otley, UK: 245-258.

Bleher, H. 1996. Bombon. Aqua Geographia 12(4): 6-34. Castillo, B., Castillo, A. & Gonzales, C. 1974. Tawilis fi shery resources investigation of Taal Lake.

Terminal report. Bureau of Fisheries and Aquatic Resources. 19pp.Castillo, B. & Gonzales, C. 1976. Hydrology of Taal Lake. Fish. Res. J. Phil. 1: 62-75.Enriquez, E. 2001. Taxonomy, distribution and temporal changes in the abundance of phytoplankton

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Hargrove, T.R. 1991. The mysteries of Taal. Bookmark Publishing Manila, 204pp.Herre, A. 1927a The fi sheries of Lake Taal (Bombon), Luzon, and Lake Naujan, Mindoro. Phil. J.

Sci. 34(3): 287-306. Herre, A. 1927b. Four new fi shes from Taal Lake (Bombon). Phil. J. Sci. 34(3): 273-278.Hilario, J. 2000. Predicting transport of nutrients from three tributary rivers of Taal Lake,

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Hutchinson, G.E. 1975. A treatise on limnology Vol 1. John Wiley & Sons, New York.Jorge, J. & Pacamara, A. 2000. Infl uence of abiotic factors on dinofl agellate dominance in Lake

Taal, Philippines. B.S. thesis. Institute of Biology, College of Science, University of the Philippines, Diliman, Quezon City.


Lewis, W.M. 1978. Dynamics and succession of the phytoplankton community and a new measure of succession rate. Am. Nat. 112: 401-414.

National Water Resources Council, 1983. Taal Lake Basis. Report No. 24-4B. June 1983.Offi ce of the Provincial Planning Development Coordinator, Batangas City, 1996. Socio-economic

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of Batangas. Province by Municipality as of July 2001.Philippine Institute of Volcanology and Seismology (PHIVOLCS); unpubl. Report.Presidential Commission on Tagaytay-Taal. 1997. Tagaytay-Taal Integrated Master Plan Phase II

(1996-2016), parts 1-3. Manila.Ramos, E. 1986. Lakeshore landslides: unrecognized hazards around Taal Volcano. Phil. J. Volcanol.

3: 28-53.Reynolds, C. 1984. The ecology of freshwater phytoplankton. Cambridge University Press.

Cambridge, U.K. 384pp.Rott, E., Kling, H. & Perez, T. 2001. Planktonic centric diatoms from the volcanic Taal Lake.

Philippines. in: Jahn, R., Kociolek, R., Witkowski, A. & Compere, P. (eds), Lange-Bertalot-Festschrift, Gantner, Ruggell: 39-52.

University of the Philippines Los Banos Foundation Inc. (UPLBF). 1997. Rapid resource appraisal of Taal Lake. Report submitted to the Department of Agriculture Fishery Sector Program. 242 pp.

Villadolid, d.V. 1937. The fi sheries of Lake Taal, Pansipit River and Balayan Bay, Batangas Bay, Luzon. Phil. J. Sci. 63(1): 191-226.

Vuorinen, I., Kurki, H., Bosma, E., Kalangali, A., Mls, H. & Lindqvist, O.V. 1999. Vertical distribution and migration of pelagic Copepoda in Lake Tanganyika. Hydrobiologia 407: 115-121.

Zafaralla, M. 1993. Limnological assessment of Taal Lake. Research Project Report, University of the Philippines at Los Baos, College, Laguna. 281pp.

Zafaralla, M. & Orozco, R.P. 1989. Benthic and algal fl ora of Volcano Island in Taal Lake: Cyanophyta and Chlorophyta. Phil. Agric. 72(2): 191-200.

Zafaralla, M., Santos, R., Torreta, N., Regalado, M. & Orozco, R. 1992. Infl uence of water quality and phytoplankton community structure in Taal Lake. Fish. Res. J. Phil. 17: 75-91.

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