Conservation of Endemic Rain Forest Fishes of Sri Lanka: Results of a Translocation Experiment

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  • Conservation of Endemic Rain Forest Fishes of Sri Lanka: Results of a Translocation Experiment ERIC D. WIKRAMANAYAKE* Department of Wildlife and Fisheries Biology University of California, Davis Davis, California 95616, U.S.A.

    Abstract: Four potentially endangered species of rain forest fishes, Barbus cumingi, Barbus nigrofasciatus, Barbus titteya, and Rasbora vateraoris, endemic to streams of southwestern Sri Lanka, were translocated in 1981 into a depauperate stream system in the central hills. By 1985 all four species had established self-perpetuating populations in these streams, and had extended their ranges into adjacent stream Barbus nigrofasciatus, a generalist, was one of the most abundant species in these stream It was widely dis- tributed throughout the stream system and in the slower sections of the Mabaveli Ganga (=Mabaveli River), and oc- cupied a wide range of macro- and microhabitat types. The other three species were more specialized in their habitat and diet, and were thus patchily distributed. The microhabitats occupied by B. cumingi, B. titteya, and R. vateritloris resem- bled the specialized microhabitats they occupy in their na- tive stream Presumably because of their specializations, these three species were not as abundant as B. nigrofasciatus. Overall, the biology and distribution of the four species will enable them to survive spatially small-scale environmental perturbations The results suggest that translocations are a feasible means of conserving other endemic fishes of Sri Lanka theatened with extinction. However, such transloca- tions must be carefully planne4 with consideration for the indigenous community as well as the ecological require- ments and genetic integrity of the target species.

    Resumen Cuutro especies de peces, potencialmente en pe- ligro de extinci6n de zonas de selvapluvial, Barbus cumingi, Barbus nigrofasciatus, Barbus titteya y Rasbora vaterifloris, que son endemicas a 10s rios del sudoeste de Sri Lanka, f u m n reubicadas, en 1981, a un sistema empobrecido y deterio- rado de nos, en las colinas centrales de esepais. En 1985 las cuatro especies habian establecido poblaciones auto- petpetuuntes en estos nos, y habian expandido su rango a nos adyacentes. Barbus nigrofasciatus, un generalist4 era unu de las especies truiS abundantes en estos rios Esta espe- cie se distribuio extensamente por todo el sistema de n,os y en las secciones truiS lentas del Mabaveli Ganga (el do Ma- haveli), y ocupo un amplio rango de tipos de macro- y mi- cro-habitats. Las otras tres especies son mciS especializadas en su habitat y dieta, y, por ello, se distnbuymn en f o m a irregulat: Los microhabitats ocupadospor B. cumingi, B. tit- teya, y R. vateriiloris se parecian a 10s microhabitats espe- cializados que ocupaban en sus rios nutivos. Sepresume de quepor su especialiazacioq estas tres especies no eran tan abundantes como B. nigrofasciatus. En general, la biologia y distribucion de las cuatro especies posibilitara su sobre- vivencia a perturbaciones ambientales de pequetia escala en lo espaciai Los resultados sugieren que la reubicacion es unu forma viablepara conservar a otrospeces endh icm de Sri Lanka amenazados de extinci6n. Sin embargo, las reubi- caciones deben ser cuidadmarnente planificados tanto en consideracion a la comunidad autoctoria, como, a las necesidades ecologicos y la integridad genetica de las espe- cies en consideraci6n.

    Present address: Department of Herpetology, me National Zoolog- ical Park, Smitbsonian Institution, Washington, D.C 20008 Paper submitted 9/14/88; revised manuscript accepted 2/13/89.

    32

    Conservation Biology Volume 4, No. 1, March 1990

  • Wikramanayake Consemtion of Endemic Elshes of Sri h k a 33

    Introduction

    The rain forests of Sri Lanka are rapidly being depleted by agriculture, mining, logging, and urbanization. Be- tween 1956 and 1980, total forest cover had been re- duced from 44 percent to 25 percent (TAMS Report 1980). Loss of rain forest is resulting in rapid declines in species abundances, and many are threatened with ex- tinction. One manifestation of rain forest loss is stream habitat degradation due to increased erosion, siltation, extreme flow fluctuations, and decreased shade and cover. Such conditions are largely unsuitable for special- ized rain forest fishes, many of which are endemic to Sri Lanka (Evans 1981; Senanayake & Moyle 1982; Moyle & Senanayake 1984).

    Following a survey of the freshwater fishes of Sri Lanka by Senanayake (1980), Evans ( 1981 ) concluded that of the 15 endemic species, 2 were rare (taxa with small world populations that are not at present endan- gered or vulnerable, but are at risk), 7 were vul- nerable ( m a believed likely to move into the endan- gered category in the near future if the causal factors continue operating), and 2 were endangered (taxa in danger of extinction, whose survival is unlikely if the causal factors continue operating) (Table 1 ). Presently, Labeo fish@ which only inhabits deep, fast-flowing sections of the mid to upper reaches of the Mahaveli Ganga (Ganga = River), may already be extinct as a result of habitat loss following the accelerated Mahaveli River Development Project (F. R. Senanayake, personal communication). Other fishes endemic to the south- western rain forest streams are now threatened with habitat loss if the proposed dammings of two major riv- ers in the wet zone, Kalu Ganga and Gin Ganga, are implemented. Because these two drainages hold most of the endemic fishes and because extinctions seem inev- itable following river development (Sheldon 1988), it is imperative that a comprehensive conservation pro-

    Table 1. Endemic fishes of S r i Lanka and their status, as listed bv Evans 11981).

    SDecies Status ~

    Cyprinidae Barbus cumingi Vulnerable Barbus nigrofasciatus Vulnerable Barbus pleurotaenia Vulnerable Barbus titteya Vulnerable Rasbora vatmyoris Vulnerable Labeo fisben Endangered

    Belontia signuta Rare Malpulutta kretseri Vulnerable

    Cbanna orientalis Rare

    Lepidocepbalus jonklassi Endangered

    Sicydium balei Vulnerable

    Belontidae

    Ophiocephalidae

    Cobitidae

    Gobiidae

    gram be initiated immediately. To conserve endemic fishes, Evans (1981) and Senanayake & Moyle ( 1982) proposed ( 1) captive breeding of commerical stocks, (2) regulation of fisheries, (3) better watershed man- agement, and (4) translocation of sensitive species to establish refuge populations.

    In 1981, Senanayake & Moyle (unpublished data) translocated four species of fishes, Barbus curningi B. nigrofasciatus, B. titteya, and Rasbora vatmporis, en- demic to the lowland rain forest (wet zone) streams, into depauperate streams in the central mountains within the wet zone (Fig. 1 ). The translocations were an experimental effort to establish refuge populations of these vulnerable species. Here, I present the status of this experiment, investigated four years following the translocations, and comment on the feasibility of further translocations to conserve other endemic fishes of Sri Lanka.

    Study Site

    Sri Lanka has centrally located hills surrounded by low- land, and presents a three-peneplain topographic profile (Fig. 1 ), with steep interpeneplain transition zones. Wet and dry zones are determined by differential rainfall

    Rasbora vateritloris -~

    Figure 1. Distribution of translocated species, Barbus cumingi, B. nigrofasciatus, B. titteya, and Rasbora va- terifloris, in streams of the upper Mahaveli Ganga (= Mahaveli River) drainage. The original transloca- tion sites are indicated by arrows The Mangles indi- cate waterfalls and the solid bar indicates a &m, both of which presumably act as barriers to the translocated fishes The relationship between Ceypo- tha Ela and the tributary network is described in the text. The inset shows the peneplain system and the wet and dry zones of Sri Lanka The location of the translocation streams is indicated by the star.

    Conservation Biology Volume 4, No. 1, March 19W

  • 34 Conservation of Endemic Fishes of Sri h k a

    from the northeast and southwest monsoons (Costa 1980). Most major rivers originate in the central hills and radiate coastward. Over 30 co-occurring species can be found in the first peneplain wet-zone streams, but the second and third peneplain streams usually have S 1 2 and S 5 native fish species, respectively (Senana- yake 1980). Except for L. fisher4 all endemic fishes are native to the wet-zone drainages.

    The fish were translocated into several small streams of the upper Mahaveli Ganga drainage (Fig. 1). The in- digenous fishes in these streams are also part of the species assemblages found in the streams to which the translocated species are native. Thus, the translocations were made into assemblages composed of fishes with which the translocated species co-occur in their native streams. The translocation streams were also selected for their similarity in physico-chemical characteristics to the native streams of the translocated species (F. R. Senanayake & P. B. Moyle, personal communication). Translocated fishes were wild-caught, either by Senana- yake and Moyle or by commercial collectors. Although the exact streams from which the fishes were collected are not known, the approximate locality and the river drainages for three species are known (Table 2). The propagule stocks ranged from 3&90 individuals each (Table 2), but the sex ratios and the proportions of juveniles to adults were not recorded.

    Indigenous fish species in the translocation streams included herbivores and carnivores; therefore, any en- demic algae, macrophytes, and invertebrates were as- sumed not to be adversely affected by the transloca- tions. Furthermore, some streams had upstream barriers preventing the translocated fishes from colonizing en- tire stream lengths. Thus, any endemic invertebrate fauna and flora would have spatial refugia from exploi- tation by these fishes.

    Methods

    In 1985, I surveyed the translocation streams, adjacent streams, and the section of the Mahaveli Ganga to which

    W b a n a p k e

    these streams were confluent to evaluate the status of the translocation. To determine species distributions, surveys were made by walking along the streams and observing fishes from the surface; snorkel surveys were made when necessary. For the most part these streams are shallow with clear water, making surface observa- tions a practical means of obtaining data on the fishes' presence or absence.

    I determined relative abundances of species by sein- ing twenty stations in each of two translocation streams, Horakoda Ela (ela = stream) and Ceypotha Ela. Twenty stations in Koladeniya Ela (Fig. l), a stream into which three species, B. cumingi, B. nigrofasciatus, and Rasbora vaterifloris, had expanded their ranges, were also seined. The stations were located in stream sections where I had previously documented microhabitat use by both translocated and indigenous fishes (Wikra- manayake 1988). Within these sections I sampled pri- marily in areas that were amenable to seining. The pro- cedure involved placing up- and downstream block nets three meters apart, then removing all large objects such as logs and boulders from within the enclosure to facil- itate seining. Care was taken to minimize disturbing the fish within the potential seine station while the nets were set up. Since activity in the stream tended to at- tract fish from downstream, the downstream net was always set up first. I then seined each station from bank to bank (across stream) with a 3 m seine. Each station was seined until no fish were captured. This enabled me to catch nearly all the fish within a section and also to standardize the effort. AU fishes collected were identi- fied to species, measured (standard length, mm), and released. Catches were recorded separately for each ef- fort ( = seine sweep).

    At each station I measured stream width at 0, 1.5, and 3.0 m of the station length. I then determined mean water column velocity (at 60 percent depth; see Bovee & Milhous 1978) and depth at 0.25,0.5, and 0.75 of the distance along each of the above cross-transects using a Gurley pygmy current meter (Model 625) mounted on a topsetting wading rod. The area of each station was

    Table 2. Numbers of fishes introduced (propogule stocks) into the streams (ela = stream) of the upper Mahaveli Ganga (=Mahaveli River) drainage. The drainage of the source population is also given, with the general l d i t y .

    SDecies ~ ~~

    Introduction Barbus Barbus Barbus Rasbora streams cummingi nigrofasciatus titteya vaterifloris

    - Balantota Ela - 60 31" Ceypotha Ela - 30 22 52 Ceypotha Ela tribs. - - Horakoda Ela - Kahawatura Ela 50 60 - 56 Walapita Ela - 87 91a 28" Origin of Source Population (drainage locality)

    - 31 - - 31

    Kelani Ganga; Kalu Ganga; unknown Kelani Ganga, Dehiowita Kalutara Parakaduwa

    a Indicates unsuccessful translocations

    Conservation Biology Volume 4, No. 1, March 1990

  • Conservation of Endemic Fishes 01 Sri Lanka 35

    then determined as the product of the average width (mean of cross-transect widths) and station length ( = 3 m). All values for water velocity and depths at each station were averaged to obtain mean velocity and depth for each station (data presented in Wikramana- yake 1988). Relative abundances and species densities (fish 10 m-) in each stream were also calculated. Spe- cies densities were calculated by considering only those stations where the respective species occurred.

    Results Of the 13 translocations of four species into six streams, 10 successfully established self-perpetuating popula- tions (Table 2). The translocations that did not become established were B. titteya in Balantota Ela and Walapita Ela and R vatenporis in Walapita Ela. Three species, B. cumingi, B. nigrofasciatus, and R uateriforis, ex- panded their ranges into adjacent streams (Fig. 1). All three were, for example, found in Koladeniya Ela, a stream located between Kahawatura Ela and Walapita Ela, but on the opposite side of the Mahaveli Ganga. Both R uatenporis and B. cumingi had limited and patchy spatial distributions within each stream. Rasbora vatert$!oris was more abundant in Ceypotha Ela than in Koladeniya Ela, which was a more speciose stream (Ta- ble 3).

    Barbus nigmfmciatus, however, was widely distrib- uted and utilized a wide range of habitats. In the three streams where it was found, B. nigrofmciatus was abun- dant in all stations sampled (Table 3). This species was found throughout most of the stream sections accessible to it, and in the slower sections of the river.

    Barbus titteya was present only in Ceypotha Ela and its tributaries (Fig. 1, Table 3), which consisted of a network of small (50-75 cm wide, 20-40 cm deep) ditchlike streams that drained a small grass-shrub valley. Barbus titteya had extended its range from the original translocation site to include most of the tributaries. I could not sample this network extensively because ac- cess was difficult due to hea...

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