Conservation of freshwater fishes of Sri Lanka

Biological Conserration 22 (1982) 181 195

CONSERVATION OF FRESHWATER FISHES OF SRI LANKA

F. RANIL SENANAYAKE~ & PETER B. MOYLE

Department of Wildli]e and Fisheries Biology, University of California, Davis, California 95616, USA

ABSTRACT

Sri Lank a supports a diverse jauna ojfreshwater fishes, 24 %o of which are endemic. A survey of the island's streams indicated that a number of the endemic fishes are threatened with extinction and others are depleted due to the interaction oj deforestation, urbanization, gem mining, pesticides, exploitation, water diversions, and introductions of exotic species. It is clear that these declines should be halted for ethical, economic, and ecological reasons. Methods proposed to reverse the declines include captive breeding, better watershed management, translocation, and regulation of fisheries, especially that for aquarium fishes. The depauperate Second Peneplain is proposed as a site,[or translocation of endangered species.

I N T R O D U C T I O N

The island of Sri Lanka supports a rich and varied freshwater fish fauna. While the dominant fishes are the 64 species of ' true' freshwater fishes, there are probably an equal number in its streams that are at least partially dependent upon saltwater to maintain their populations (Senanayake, 1980a). Of the true freshwater fishes, 24 ~o are species endemic to the island, 17 ~ are introduced species, and the remainder are shared with the ichthyofauna of the Indian mainland. In 1978 and 1979 a study of the distribution, ecology, and status of the fishes over the entire island was undertaken because such information was largely lacking (Senanayake, 1980a). In the course of this study, it became apparent that many of the native fishes are much less common than the limited earlier literature indicated and that a number of species are threatened with extinction in the near future. The purpose of this paper,

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182 F. RANIL SENANAYAKE, PETER B. MOYLE

therefore, is to examine the causes of the decline of the native fishes, suggest why it is important to conserve them, and then propose ways in which the threatened elements of the fauna can be preserved. We will concentrate on the 15 endemic species (Table 1) because the threats to their continued existence are most immediate. However, the analysis can also be extended to local populations of species Sri Lanka shares with the Indian subcontinent and the Malaysian Peninsula.

TABLE 1 ENDEMIC FISHES OF SRI LANKA AND FACTORS AFFECTING THEIR STATUS

Name Distribution ~ Status b Factors affecting status ~

Two spot barb Barbus cumingi Giinther Black ruby barb Barbus nigrofasciatus Giinther Cherry barb Barbus titteya (Deraniyagala) Side striped barb Barbus pleurotaenia Bleeker Blotched filamented barb Barbus sp. d Red scissortail barb Barbus sp. ~ Vateria flower rasbora Rasbora vaterifloris Deraniyagala Green carplet Horadandiya atukorali Deraniyagala Green labeo Labeo fisheri Jordan and Starks Banded mountain loach Noemacheilus notostigma Bleeker Spotted loach Lepidocephalus jonklaasi Deraniyagala Green topminnow Aplocheilus dayi (Steindachner) Comb tail Belontia signata (Giinther) Ornate paradisefish Malpulutta kretseri Deraniyagala Redtail goby Sicydium halei Day

1 V U, P*, E* 1 V D*, U*, G*, P, E* 1 T D*, U*, P*, E* 1 T D*, U*, E* 2 E D*, G* 1 T D, P*, E 1 T D*, P*, E* 1 C P*, I 2 V W* 2, 3 C P* 1 E D* 1 C P* 2,3 V G*, P, E 1 T P, E, I* 1 V G

Ichthyological regions as follows: 1 = Southwestern Province, 2 = Mahaveli Province, 3 = Dry Zone Province.

E = endangered (extinction imminent); T = threatened (may become endangered in near future): V = vulnerable (distribution limited and populations in decline but not in immediate danger); C = common and widely distributed.

D =deforestation, U = urbanisation, G = gem mining, P = pesticides, W =water diversion, I = Introduction of exotic species. E = exploitation. * indicates a strong negative impact. d Senanayake (in press). e This has been tentatively identified as B. kuda, a name which may not be valid (Senanayake, 1980a).

METHODS

Between October 1978 and December 1979, fishes were collected from 362 sites on the island. An average of four collections were made at each site, to make sure all the habitats were sampled. For most collections, the upper and lower ends of a section of stream were blocked with nets and the section seined three times, without replacement, with 5 mm mesh seines measuring either 27 x 1.4 m or 5.4 x 1.4 m. The total catch data for each section were pooled and an abundance rating given to each species in addition to the absolute count. The abundance rating was on a scale of 0-5 , where 5 indicated that large numbers were taken in every haul and 1 indicated that only one or two individuals were collected. While such ratings are rather

CONSERVATION OF FRESHWATER FISHES OF SRI LANKA 183

arbitrary, they have been shown to be quite useful in evaluating the factors affecting the abundance of stream fishes (Moyle & Nichols, 1973). At each site, 34 environmental variables were measured and recorded (Senanayake, 1980a); however, only the variables that most strongly influenced fish distributions will be discussed here. Dissolved oxygen was measured as ppm using a colorimetric Winkler analysis (Model 0-12, R-7512, Chemetrics, Inc.). Current speed was measured as surface flow, by timing a 1.5 g cork float over a measured distance. Turbidity was ranked with a visual estimate, where '1' represented extremely clear water and '4' water that was nearly opaque. This variable referred to the silt load of the water only; turbidity due to organic matter was recorded separately. Human influence was rated simply as '0' when the stream flowed through undisturbed forest and '1' when there was evidence of human disturbance. Shade was recorded as percentage of the stream that was shaded by overhanging vegetation. Substrate composition was recorded using the methodology of Cummins (1962) except that the smallest particle size considered was clay (less than 0.005 mm). Each substrate type (clay, mud, sand, gravel, cobbles, boulder, bedrock) was recorded as the percentage of bottom it covered. The environmental variables and the fish abundance variables were analysed using Pearson Correlation matrices. For further details see Senanayake (1980a).

ZOOGEOGRAPHY

In order to understand why certain species are threatened, it is important to understand the zoogeography of the fishes of Sri Lanka, a subject treated in more detail in Senanayake (1980a).

Sri Lanka is a continental island lying on the southern end of the Indian continental shelf. It has a land area of 65,584 km z. Topographically, the island is divided into three peneplains. The First Peneplain, making up the majority of the island, is at elevations of 0 to 122 m. The Second Peneplain rises as a steep step (about 305 m high) from the inner edge of the First Peneplain and has elevations of 365-762m. The Third Peneplain rises as another steep step, 919 to 1219m high, from the Second Peneplain and has a general elevation of 1529 to 1828 m, rising in places to 2938 m (Cooray, 1967).

The distribution patterns of the fishes of Sri Lanka suggest that there are three distinct ichthyological provinces: the Southwestern Province, the Mahaveli Province, and the Dry Zone Province (Fig. 1). Each province has distinctive elements to its fish fauna and is separated from the other provinces by physical and ecological barriers. The Southwestern Province consists of the river basins from the Nilwalaganga (12) in the south to the Attanagalu oya (103) in the north. To the east, this province is bounded by the wall of the Second Peneplain. The Mahaveli Province consists of the drainage basin of the Mahaveli River (60) which drains most

184 F. RAN1L SENANAYAKE, PETER B. MOYLE

~///I/I////////~ c^'""'-^-tern Province

Province

Province

Zone

Fig. 1. •chthy•••gica•Pr•vinces•fSriLanka.Dashed•ineindicatesinnerb•undary•fFirstPenep•ain; dotted line indicates the approximate separation of the wet zone and the dry zone. The wet zone is west of the line. Rivers are numbered following Senanayake (1980a) and are referred to in text by number.

of the Second and Thi rd Peneplains . In the Fi rs t Peneplain, the fauna of this province is largely identical to tha t o f the Dry Zone Province, which covers all par ts of the Fi rs t Peneplain that are not within the wet zone cl imatic region. In the steep hilly par ts of the Second Penepla in (Trans i t ion Zone) the fish fauna is depaupera te .


It is the same in all provinces and consists of a few species capable of living in fast water (Table 2).

The Southwestern Ichthyological Province is the most important area for endemic fishes, as 67 ~o of them occur only in this province. Another 13 % are confined to the Mahaveli Ichthyological Province. While the remaining 20 ~o are found in all three provinces, this component consists of the species adapted to life in fast water (Table 2). Presumably the main reason for this pattern is that the Southwestern Province represents the only major refugia for the high rainfall adapted species. It is the only area of the island that has had consistently high rainfall and no major tectonic changes since the early Pleistocene (Senanayake, 1980a). Further, it remained heavily forested until the 19th century because agriculture had previously been concentrated in the dry zone (Senanayake, 1978).

TABLE 2 DISTRIBUTION OF THE FRESHWATER FISHES OF SRI LANKA BY ICHTHYOFAUNAL PROVINCES.

Transition Southwestern Mahaveli Dry Zone Zone common to

Province Province Province all Provinces No. °//o No. °/o No. °/o o No. %

Totals No. %

Endemic species 13 23 5 10 3 7 3 27 15 23 Native resident species 35 61 35 73 35 79 3 27 40 63

(shared with India) Introduced species 9 16 8 17 6 14 5 46 9 14

Total 57 100 48 100 44 100 11 100 64 100

CAUSES OF DECLINES

The decline of the native fish populations can be attributed to the interaction of a number of factors, but foremost among them are (1) deforestation, (2) urbanization, (3) water diversion, (4) gem mining, (5) pesticides, (6) exploitation, and (7) introduction of exotic species.

Dejorestation Although Sri Lanka has been densely settled for several thousand years, much of

the Southwestern Province was forested until recently, especially in the upland areas. In the past 150 years, however, extensive deforestation has taken place. Although some of the deforestation has been the result of logging, which can result in rainforest being replaced by open areas dominated by the bracken fern Gleichenia linearis Clarke, the principal cause of deforestation has been clearing to create tea and rubber plantations. The streams in such areas change from being heavily shaded with extensive cover provided by overhanging vegetation and fallen trees to exposed

186 F. R A N I L S E N A N A Y A K E , P E T E R B. M O Y L E

streams with comparatively little cover. Elsewhere it has been well documented that the removal of riparian vegetation may affect stream flow, increase erosion and turbidity, and increase temperature fluctuations (e.g. Burns, 1972; Moyle, 1976). These changes were noted to hold true in the Sri Lankan situation. Many of the endemic species show negative correlations with turbidity and stream modification (Table 3) while others reflect the same tendency by showing a positive correlation with shade and riparian vegetation. These two variables are negatively correlated with turbidity and stream modification.

Alfred (1966) noted that in Singapore, when open country streams replaced forest streams, the absolute numbers of fish often increased but the diversity was reduced. In this study a negative correlation between the abundance of threatened species and loss of riparian forest (shade) has been demonstrated (Table 3). The overall abundance offish, however, seemed fairly consistent. The loss in threatened species is apparently being compensated for by an increase in 'generalist' species. It should be noted that some species of the threatened fauna successfully inhabit plantation forests or rubber plantations, habitats that possess a high (10-m) canopy that may give over 50 ~o shade to the streams. In this study many populations of Barbus cumingi, B. nigrofasciatus, B. titteya and Belontia signata were recorded in such streams.

T A B L E 3 CORRELATIONS (r) BETWEEN SELECTED ENVIRONMENTAL VARIABLES AND THE ABUNDANCE RATINGS OF THE ENDEMIC FISHES. ALL COEFFICIENTS ARE SIGNIFICANT ( P > 0 ' 0 1 ) UNLESS FOLLOWED BY AN ASTERISK

(P > 0.05)

Species Turbidity Oxygen % Mud Human Shade Flow bottom influence

Barbus titteya - 0 . 6 2 - 0 . 8 9 * - 0 . 8 6 - 1 - 0 0

Barbus pleurotaenia - 0 - 8 3 0 . 3 6 0 . 5 3

Barbus nigrofasciatus O, 3 2 - 0 . 3 3 0 . 9 3 - 0 . 2 1 *

Barbus cumingi - 0 3 7 *

Noemacheilus botia - 0 - 4 5 - 0 - 4 2 0 . 4 3

Urbanization Like most other 'developing' countries, Sri Lanka has a rapidly growing

population (2~ per year). This growth has led to increased urbanization, especially in the Southwestern Province which has a population density over twice that of the rest of the island (564 persons per km 2 compared with 222 per km 2 in 1976; Anon., 1979). In addition, the recent increase in industrialisation further concentrates people in urban areas and produces many pollutants. Thus, the streams that flow through urban areas are increasingly being subject to heavy pollution and habitat degradation. The fish species that inhabit such areas are largely exotic forms, such as Poecilia reticulata and Trichogaster pectoralis, or widely distributed air-breathing species, such as Anabas testudineus and Channa


(Ophiocephalus) gachua kelaarti. These species can all tolerate high tempera- tures and low oxygen levels. It is worth noting, however, that small isolated populations of endemic species still occur whenever there is a stand of trees and the water is clear. In particular, refuges for some of these fishes are provided by the older villages that have mature trees and that maintain the water quality of their streams.

Water diversion The Mahaveli river (60) is presently the focus of a large engineering scheme,

where the waters will be impounded on the Second Peneplain and then diverted northwards through a tunnel and associated channel systems. An effect of this project will be a reduction of downstream flow along the main channel of the Mahaveli river. The area of river to be most affected by the reduction in flow coincides with the only known habitat of Labeofisheri, an endemic species. These fishes utilise the deeper pools below cascades and fast-water streams and have been recorded to have a preferred microhabitat in the fast-flow areas (Senanayake, 1980a). Thus a reduction in flow through previously fast-water pools below the diversion dams will quite probably cause a decline in the population of this species.

Gem mining While deforestation and urbanisation have by themselves been major causes of

the decline in numbers of native fishes, their impact has been greatly increased by gem-mining activities, which cause streams already denuded of cover and shade to become turbid and silty. Unfortunately, the major gem fields are located on or near streams inhabited by endemic species. The richest gem fields are found in the Southwestern Ichthyofaunal Province. The second most important are around the Mahaveli Pleistocene refugia, the habitat of Barbus sp. (Senanayake, in press). In these regions the mining of gemstones takes place in the alluvial plains between the hills, in upland areas. The stones are mined by sinking a 3 x 4 m 2 pit and bringing up the mud and gem gravel from depths of 1 to 15 m (Wadia & Fernando, 1945). The excavated gravel is then put into baskets and washed in the nearest stream. The result is a massive input of mud, clay and silt into the streams. During the last eight years there has been a tremendous boom in the gemstone market and mining activity has increased over 600 ~ over the 1962 levels (State Gem Corp., pers. comm.). There has also been an increase in river bed mining, where the gravel from the river beds is dug up and washed, either manually or with the use of hydraulic equipment.

As the gem-bearing gravel occurs as a 'lens' with a thickness of less than 70cm (Cooray, 1967), each mine is abandoned when the excavation of the 'lens' is complete. Thus gem mines are transitory phenomena both in space and time, a situation analogous to the relationship between 'swidden' cultivation and tropical forests. In the past, this process has meant that no individual stream would be silted constantly and in every valley some would run clear while some were silty. As the gem mining industry has been in existence for over 500 years, this may have been the


mechanism that enabled the continued co-existence of clearwater-loving fishes and the gem-mining industry in the drainages of all the rivers of the Southwestern Province. However, the recent exponential increase in gem mining is making a majority of the waterways run turbid and is thereby greatly reducing the number of clear water refugia for the fishes. The potential that gem mining has for reducing the number of species in the streams becomes apparent when the impact of the industry is examined in the the light of biogeographic theory. The species area curve (MacArthur & Wilson, 1963) indicates that there is a negative relationship between the number of species in a bounded area (island) and the area of that island. Thus, if a large ecosystem is broken up into disjunct parts, each part will act as an island, resulting in many local extinctions. For the terrestrial animals of Sri Lanka, these islands are mainly patches of rainforest 10-20ha in size and rapid declines of the populations of many species have been noted (Senanayake, 1980b). These islands of rainforest are also important refuges for the native fishes but in areas not affected by gem mining, the declines observed for the terrestrial vertebrates have not been observed for the fishes. Some such 'islands' within cleared tea plantations have been in existence for over 75 years and yet seem to possess the full complement of native species expected for the habitat. There are two reasons for this. First, many of the fishes seem to be able to persist in islands of degraded habitat that are associated with villages and secondary growth forests. Second, and most important, is that the many streams in each drainage system are interconnected, especially during the rainy season, so recolonisation of disturbed areas is possible. Thus, traditional gem mining had little impact on the fish fauna because a relatively smaller number of streams would be silted at any given time and the siltation of any one stream would not last long. However, the recent increases in volume and mechanisation of gem mining have not only reduced the total amount of habitat available for the fishes but have also greatly increased the distances between 'islands', in effect isolating many of them from future colonisation. In such small isolated islands, local extinction of endemic species is highly probable (Terbough & Winter, 1980). It therefore appears that the gem-mining industry has the capability of severely depleting the native fish fauna of Sri Lanka in a relatively short period of time. In the United States, fishes that have been reasonably abundant have become extinct, owing to the activities of man in as short a space as 35 years (Pister, 1974).

Pesticides The increasing use of pesticides and herbicides in Sri Lanka is another factor

contributing to the decline of fish populations in the habitat islands, although the impact of these poisons is poorly understood. There are few restrictions placed on their use and good records are not kept. However, Johnson (1973) noted that the use of herbicides in rubber plantations causes severe depletions of fish populations in long stretches of stream. In Sri Lanka, a large kill of Barbus cumingi occurred following the application of herbicides to rice fields near the stream (Senanayake, 1980a).


Exploitation The stream fishes of Sri Lanka are exploited both for food and for the aquarium

trade, although the impact of both kinds of exploitation is poorly known. The capture of stream fishes for food has a long tradition in Sri Lanka, but the fishing effort has tended to concentrate on the larger streams, on the larger fishes, and during the dry season (when fish are trapped in pools). The fishes have obviously withstood this kind of exploitation for centuries but increased demands for fish and new methods of capture may be depleting populations in many areas. Particularly alarming has been the increase in the use of explosives and poisons (typically insecticides) for the capture of fish because such methods kill many more fish than the individuals actually keep for consumption. Both methods were commonly observed in the survey of the island's fish fauna.

The exploitation of stream fishes in Sri Lanka for export for the aquarium trade has been going on for about 40 years, but increases in the extent of the trade in recent years make it likely that it is now having a detrimental impact on the highly prized endemic species. Despite the value of the trade (Conroy, 1975), all the fish exported are collected from the wild. There is no company that breeds any of the native fishes for export (personal survey, Senanayake). During this study, the catches of five professional collectors were noted at the time of capture and accompanied down to the city where they were sold to exporters. A minimum of 20 % loss in transport was recorded for species such as Barbus nigrofasciatus from time of capture to delivery. In more delicate species, such as Rasbora vaterifloris, a 40 % loss seemed to be typical. No records are currently kept on the number or kinds of fish exported, but today there are over 45 companies registered to export aquarium fish from Sri Lanka. Visits to two of the larger firms indicated that between 5000 and 10,000 individuals of the commoner endemic species are currently being exported each year by each company.

The impact of the collecting of aquarium fishes has generally been ignored in studies of tropical freshwaters. One of the few studies is that of Johnson et al. (1969) for Malayan streams, in which the authors conclude that if the aquarium fish industry is to continue to flourish, artificial rearing will have to be used because wild populations are being depleted. Johnson (1973) noted that a number of Malayan streams that were once good habitats for common aquarium fishes have been denuded of their fishes by over-exploitation. One reason for this is that entire streams may at times be poisoned in order to collect a few saleable fishes.

Introduction of exotic species Exotic species do not yet seem to have had much of an impact on the native

stream fishes because they have become established mainly in highly disturbed areas, in reservoirs, or in high elevation areas where few or no native fishes exist (Senanayake, 1980a). However, increasing emphasis is being placed in Sri Lanka on the use of exotic species to increase fish production in freshwater (files, Department of Fisheries), so their potential for having a negative impact on the native fish fauna


is high. In other parts of the world, decreases in native fish populations have been associated with increases in exotic species (e.g. Moyle, 1976).

REASONS FOR PROTECTING NATIVE FISHES

The reasons for preserving the native fishes of Sri Lanka are ethical, economic, and ecological.

Ethical reasons

Many of the fishes needing protection in Sri Lanka are small inconspicuous species that have no known economic value. The conservation of such non-resource species has proved a major problem in western countries (Ehrenfeld, 1976). Sri Lanka, however, has historically been a nation well disposed towards conservation. For instance, in the 12th century laws were passed by King Kirti-Nissanka-Malla that no animals, fish or birds could be killed within a radius of 35.7 km from the city of Anuradapura (Wickramesinghe, 1928). This law (edict) probably was the first recorded instance of a sanctuary being created that included fishes. An ethic where natural resources form part of the heritage of mankind has been proposed by Train (1974), and forms part of the philosophy of the global bodies such as IUCN. In Sri Lanka, UNESCO has begun supporting a series of reserves as part of the Man and Biosphere Programme. The criteria and guidelines of this programme (UNESCO, 1974) make it amenable to setting aside reserves for the threatened ichthyofauna.

Economic reasons

The heavy exploitation of many stream fishes is an obvious indicator of their economic value, although little attention has been paid to stream fisheries in Sri Lanka. In particular the aquarium trade has been almost completely ignored, despite its considerable value and recent growth. While recent records of the value of the aquarium trade in Sri Lanka seem to be lacking, Conroy (1975) found that from 1961 through 1966, the value of the exports ranged from US $26,445-44,089, figures which did not include the black market trade that undoubtedly also existed. Since then the trade has increased enormously, as it has worldwide. Conroy (1975) estimated that the worldwide aquarium trade in 1966 was worth US $4000 million. While this figure reflects the trade in all aquarium products, as well as fishes, it does suggest the magnitude of the fishery for tropical species. In Southeast Asia, the trade in aquarium fishes is considered to be one of the most profitable 'aquaculture enterprises', even though most of the fish exported are caught in the wild (IDRC, 1973).

Ecological reasons

One of the least appreciated values of the endemic fishes is their value as indicator species. Healthy populations of these species generally mean that there has been


adequate protection of local habitats of all species and that water quality is high. The latter factor may be particularly important as the lower reaches of many of the clearwater streams that flow through estates have been classified as potable (Sirimanne, 1953). In the case of the Kelani River the water is used to augment the supply to the city of Colombo. Thus clearwater streams in rubber estates should be maintained as 'clean' waterways. Some of the threatened species will serve as admirable indicator species for such a project. The survey of Sri Lanka fish distribution (Senanayake, 1980a) suggests that Rasbora vaterifloris and Barbus titteya are particularly susceptible to such environmental degradation as loss in water quality. Both species were found to be most abundant in pristine conditions, but large populations were also recorded around settled villages or estates, having high shade and clear water. In more degraded environments, such as more modern urban areas, the abundances decrease, until there is a complete lack of the species in polluted streams. The potential of organisms for biological monitoring has been shown by Patrick (1972) for algae, by Brandt (1972) for lichens, by Bauerle et al. (1975) for snakes, and Hillaby (1975) for fish and amphibians.

METHODS FOR PRESERVING ENDEMIC FISHES

Legal machinery for protecting the fishes already exists in Sri Lanka, under sections 34 and 37 of the Fauna and Flora Protection Ordinance (Chapter 469), as amended by Act 44 of 1964 and approved by the National Assembly in 1972. These sections give legal protection to any elements of the fauna deemed threatened, although no fishes are at present on the list. Three species that seem to need immediate protection are Barbus sp. (Senanayake, in press), Rasbora vaterifloris, and Lepidocephalus jonklaasi, although other species may also need protection in the near future. Two such species (B. cumingi and B. nigroJasciatus) are already listed by the International Union for the Conservation of Nature (1977) as vulnerable and endangered, respectively. However, legal protection by itself is not enough to save these fishes; positive steps need to be taken to increase depleted populations and to prevent further declines. Some of the steps that should be considered are (1) captive breeding, (2) watershed management, (3) translocation, and (4) regulation of fisheries.

Captive breeding The breeding and rearing of endemic fishes under artificial conditions could have

two major benefits: reducing the need to exploit wild stocks of aquarium fishes, and preserving species in immediate danger of extinction. Worldwide, captive breeding of aquarium fishes is already an important source of fish for the trade (Axelrod, 1969, 1971), But this is not the case for the endemic species in Sri Lanka. Presumably, captive breeding of endemic forms could reduce the need to exploit the wild populations, especially the rarer species. Captive breeding, however, is not a


substitute for protecting the habitats of threatened species so that wild populations can be maintained, even though it could be used to save species threatened with immediate extinction due to habitat degradation. Present work in conservation biology suggests that propagation of a species cannot be carried out indefinitely without seriously altering the characteristics of the species (Campbell, 1980). The reasons advanced have been mainly genetical, such as the development of inbreeding depression in the captive stock (Senner, 1980) or ethological, such as behavioural changes in captive stock (Kleiman, 1980). Work on captive propagation of fishes has shown that some element of selection occurs at the hatchery, by the fish breeders. This may be unintentional or intentional (Bennett, 1970) but will in some manner alter the gene frequency. Workers with trout (Salmonidae) have long recognised the profound morphological, physiological, and behavioural changes that take place in captive populations after only a few generations of captivity. Such changes generally make the fish less well adapted for surviving in the wild (Vincent, 1960; Moyle, 1969).

Watershed management It is obvious that the major cause of the decline of the native fishes has been poor

watershed management involving such factors as removal of riparian vegetation and use of streams for waste disposal from gem mining, agriculture, and urban areas. It is equally obvious that the decline of the native fishes is merely an indicator of much broader problems. For example, the degradation of surface water quality makes the spread of water-borne diseases more likely and decreases the supplies of potable water. The removal of vegetation, especially rainforest, disrupts the hydrological cycle, so that rainfall runs offmore quickly, with an increase in erosion upstream and siltation downstream, and with an increase in the severity of floods followed by the drying up of many small springs and streams (Water Resources Board, 1969).

Fortunately, better watershed management, especially through the conservation of riparian forests, already has a legal basis in Sri Lanka. Government General Order No. 732 stipulates that land along either side of a stream should be retained as Crown Reserves whenever Crown lands are sold or leased. This order requires a reservation 20.12 m wide on either side of streams with a width up to 4.57 m, and a reservation 40.23m wide on both banks of streams up to 15.24m wide. Thus an enforcement of existing laws and monitoring of the water quality of the streams could confer a large degree of protection on the native fishes, in addition to producing much broader social benefits.

Translocation The transplantation of an endangered fish species from a threatened or degraded

habitat to another suitable area that is more protected has been the principal technique used to save a number of endangered fishes in the United States, such as Owens pupfish Cyprinodon radiosus (Miller & Pister, 1971), the snail darter Percina


tansi (US Fish and Wildlife Service, 1979), and greenback cutthroat trout Salmo clarki stomias (Williams & Finley, 1977). In Sri Lanka it appears that translocation may be the best way to preserve the endemic species, particularly Rasbora vater- floris, Barbus nigrojasciatus, B. titteya, B. pleurotaenia, Barbus sp. (Senanayake, in press), Lepidocephalusjonklaasi, and Malpulutta kretseri. The reason for this is that these species all inhabit the regions where the streams are most rapidly being degraded. The streams in which they live, however, are quite similar in their physical and chemical characteristics to streams of the Second Peneplain (Weininger, 1972). These streams are in many ways ideally suited for the translocation of the threatened fishes because it is unlikely that the translocated fishes will cause the extinction of fishes or invertebrates already resident in the streams. The present fish fauna of the Second Peneplain streams is depauperate and consists of species that have managed to invade in fairly recent times from the lowland areas, where these same species coexist with many other species, in much more species-rich communities. The resident fishes range in feeding habits from predators to detritivores, so the invertebrate fauna should already be adapted to fish predation. It should be emphasised, however, that no translocation should take place without first carefully selecting the translocation sites for suitability and then examining the resident fauna for possible conflicts with the translocated fishes. Also, it is not recommended that all species be transplanted at once, but that a gradual, carefully monitored, programme of transplantation be initiated.

Regulation of fisheries Presently there is a lack of data on the catch or volume of species utilised by the

aquarium fish industry, probably as a result of the lack of recognition that the industry constitutes a formal fishery. This lack of recognition is also evident in the texts of fishery science (Lagler, 1952; Rothschild, 1972). Even the texts on aquaculture, while referring to geographical areas where aquarium fishes form a large part of the culture fishery, have not mentioned the fact (Bardach et al., 1972; Huet, 1972). One reason for this seems to be that fishery science arose as a discipline in temperate countries where no fishery for aquarium species existed, and fish were, until recently, considered economically important only as food or for sport.

In order to ensure the continued existence of the threatened fishes of Sri Lanka, and a continuing tropical fish industry, the aquarium fishes must be officially designated as a formal fishery. As the government has an operative arm in the management of the inland fishery through the Ministry of Fisheries, Division of Inland Fisheries, it could be managed by this division. A programme will then need to be drawn up where tallies of the fishes exported, species exported, value, and other data relevant to monitoring a fishery can be collected. A system of licensing and setting up of annual catch limits, especially for the threatened species, needs to be established. Inducements in relaxed export licence fees can then be extended for exporters who breed and culture the fishes for export, since the industry itself stands


a great chance of losing its most valuable species if an organised, regulated fishery is not set up.

Although fishery for aquarium fishes is probably the biggest exploiter of the endemic stream fishes, there is also a need to establish the size and nature of food fisheries that occur in the same streams.

ACKNOWLEDGEMENTS

We wish to thank Professor H. Crusz of the Department of Zoology, University of Peradeniya, Sri Lanka, and Professor R. R. Miller, Museum of Zoology, University of Michigan, for their criticisms and comments on the manuscript.

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Conservation of freshwater fishes of Sri Lanka