JoURNAL oF TRoprcAL Brorncy Alro CoNsswATrol{,2 (l) : L7 -26,2006 t7

Research article

Iluman exploitation and conservation of sea snakes in Sabah

AmaWONG

School of Science and Tbchnology, U niv ersiti M alay sia S ab ah, Locked bag 2073, 88999 Kota.Kinabalu, Sabah, Malaysia

ABSTRACT. This study looks into the insufficient existing data. The aquatic and exploitation of sea snakes in relation to fish secretive habits of these snakes probably harvesting where sea snakes are frequently minimize their contact with humans. On the caught in fishhg nets, on the west coast of other hand, local abundance of populations, Sabah. Commercial fishing operations have their movements, and the need to breathe air increased remendously, with a 36-fold periodically render sea snakes potentially increase of marine fish landing by using trawl vulnerable to exploitation. There are two areas nets since 1988 to 1997. This study found that of concern regarding the conservation of sea mean number of sea snakes caught per trawl snakes from rhe subfamily Hydrophiinae: one was 23 specimens, and 46 sea snakes per is the direct exploitation of the snakes by trawler per landing. For the last ten years, a killing; the other is the indirect destruction total of I .3 million sea snakes are estimated to attributable to depletion of the quantity and have died. It is remarkable that trawlen killed quality of habitat. more tlnn six hundred thousand sea snakes per year recently, yet the sea snakes continued This study looks into tlle tbreat to sea snakes to survive. Compared with the previous study from fish harvesting for commercial purposes, (carried out 10 years ago before this study), as sea snakes are frequently caught in fishing the species diversity and abundance of sea nets used by fishermen on the west coast of snakes on the west coast of Sabah is still high. Sabah. Commercial operations have This might be explained by the presence of increasingly invested in large, efficient trawls suitable habitats. adequate food resources and and dredges. Although this gear is deployed healthy environment. to catch fish and prawns, it scoops up everything in its path as it plows the ocean INTRODUCTION floor (Raloff, 1999). Also, the fishermen generally use nets with small mesh size for At present, it is difncult to ascertain the impact catching prawns and fish, and sea snakes of human activities on sea snakes due to appear to be attracted to the txapped prawns and hsh. The heads of snakes get caught in the mesh and are squeezed, pulled or crushed Key y)ords: by-catch, Bomeo, Malaysia, trawling 18 Huu,qN rtclorrattoN AND coNsERvATIoN or sEe sNmrs tN Seaarr

when the fishermen extract the snakes ftom hours and there was only one pull per clay for the nets. Survival of sea snakes caught by this study. A colour video sounder was used prawn-hawler n€ts is about 600lo (Wassenberg to obtain depth data at each site of pull. er a/., 1994). These trawlers generally haul nets for 2 lz to 3 hours. The chances that a sea RESUT]TS AND DISCUSSION snake would survive depend on when it enters the ne! the duation ofthe trawl, and how it is There were 12 locations designatad randomly treated on the deck. Under natual conditions, for all the pulls throughout the year within the the sea snakes may remain submerged for up study area and each pull was represented by to 213 minutes (Heatwole 1975; Rubinoff er a lett€r to indicate the exact location of the a/. 1986). In a trawling net, frsh are buffeted pull, with the depth measurements as shown and tossed around, which result in injuries in Figure 2. and death (Maclean, 1972; Juhl & Drunnond, 1976; Saila, 1983). Sea snakes are very likely A total of 277 specimens representing 1l to suffer the same trauma ftom trawling as fish, species of sea snakes (subfarnily: suffering stress and lack of oxygen that often Hydrophiinae) were caught in approximately result in death. 30 hours of trawling throughout the year with

a 1 2 m net in Pulau Tiga and adjacent area. MATERIAISAI\DMETIIODS These were Airysurus eydoutii, Hydrophis Marine suweys were carried out in coastal klossi, H. btookii, H. caerulescens, H. seas in Pulau Tiga Park and its adjacent areas ctanocinctus, H. fasciatus, H, ornatus, off the west coast of Sabah, from Kota Keriliajerdoni, Lapemis curtus, H. gracilis, Kinabalu in the east to Labuan in the west, and Praescutata viperina. P viperina is anew within the area demarcated by latitudes 5 ' 36' record for Sabah. In this strdy, Lapemis curtus N to 6' 00' N and longitudes I 15' 15' E to 115' was the most abundant species encountered 50' E (Fig. 1). The range ofdepth was between (43.7%), followed by Aipysurus eydouxii 20 to 50 metres and the distance to the (17%), Hydrophis brookii (14.4%), H. shoreline was between 10 to 50 km. Pulau cy anocinctus (7 .6%o), Kerilia j erdoni (5.8%), Tiga Park and its adjacent area is where the H. fasciatus (4.O%o), H. caerulescens (3.2%o), fishing boat tawlers normally trawl for fish H. gracilis (2.2%), H. ornatus (1.4%o), H. and prawns, klossi, and Praescutata viperino (0.3yo). T\e total number ofspecimens for each species is The samplings were carried out once a month shown in Figure 3. Sinpsont Index ( 1949) was for twelve months from March 1998 to used for diversity ofsea snakes for the entire February 1999 by using individual trawler sample, registering a high diversity index (Ds boats. There were two fishing boats used to = 0.74) as compared to IIKMS collections (Ds catch sea snakes, boat numbers 2828/F and :0.61; Han 1988). andmaximum diversity was

1 7/F, with trawls measuring 40 m long and 122 0.91; evenness was 0.82 aod the dominance m wide each (30 to 60 cm mesh) but reduced to was quite low (ds = 0.18), as shown in I 0% or I 2 m wide (8 cm mesh), when pulled. Appendix A. Ihe following trawl pull data were recorded: date, time of start and end of each pull, with No samplings were mad€ at night. Most were the GPS reading 0atitude and longitude) at done in the moming between 0800 to 1200 hls. the start and end of each pull, respectively. Mean number of sea snakes caught p€r traud Each pull took approximately two and a half throughout the year was 23 specimens and at A.rleWONG t9

116. U!' lt7'

Figure 1. Map showing the west coast of Sabah

E r15. 50' N6.m. a -i;r4H.j':/$ ?-" lst . _ t15r'

..-. ,1, o 92 0 z;,- i'".. 3t :e:@38:9 .,.'' "....\... ;",7 sS A' D n st .....i_ cot*l,rrn )r-\ _ nsr.@J6 -/ 'f I r,P lGbryulnm ./.

25*--;-." i .-.",._.,,' @ rJ ./) \, o o n/"'o f 4t \ KTMAM' Ga a / ) l. *]*\ \ 8ar N 5.35' -'ctn

Figure 2. Location (A-L) of start and end of each trawl per month with depth (m) in Pulau Tiga area Hullex rxpLortltlou AND coNsERvATIoN oF seA. sNlres { SlglH

Thble 1. Catch rates of sea snakes Per hour in Pulau Tiga area by commercial trawlers during March 1998 - February 1999.

Date NetDimension Hours of Numbers of Catch ftn) Trawling Sea Snakes Rate

March 1998 12.0 2A5Q.75) 57 L1n April 1998 12.0 3.30(3.50) 14 0.333 May 1998 12.0 2.30 Q.s0) 11 0367 June 1998 12.0 7.30Q.50) 1) 1.000 July 1998 12n 2.52(2.87) 4 0.116 August 1998 120 2.4s (2.7s) A 0:7n September 1998 12.0 3.00(3.m) ry 1.361 October 1998 12n 2.s0(2.83) 8 0236 November 1998 124 2.30 (2.50) 4 0.133 December 1998 12.O 2.30 (2.s0) a 0.933 January 1999 12.o 3.4(3.67) 12 0.272 February 1999 12.0 2.45 (2.7s) % 1.@1

Mean=0.691

least twice (two trawls) per trip for commercial . was found that there was an optimum depth fishing, and there were 46 sea snakes per of approximately 45 m below sea level for sea trawler for each time of landing. The number snakes in the Pulau Tiga area and fewer caught of sea snake specimens and species caught in shallower areas (Figs. 5,6). per month is shown in Figure 4. The overall catch rates of sea snakes by commercial Based on rhe annual fisheries statisrics ffawlers was 0.691 sea snakes per meue of (Department of Fisheries Sabah; 1997), the headrope length per hour of trawling (Table trawl net comprised 147o ofthe total of 9,836 i). Thoughout the year, the highest catch rate fishing vessels by gear group in Sabah in 1997. of sea snakes per hour was in March (1.727), The production of marine fish landing in i997 followed by September (1.361), February was 174,300 metric ton with wholesale value (1.091), June (1.000), Decenber (0.933), August of RM 569,163,000 which had increased (0.727), whereas July and November had the tremendously with about three and a half times lowest catch rates, 0.116 and 0.133, compared to 1988 when it was just 46,200 respectively. metric ton and RM 1 83,300,000.

In a11,269 of the 277 sea snakes were captured In 1997, the number of fishing gear by trawl between 33 to 50 metres below sea level, the nets on the west coast of Sabah was 168 in remaining eight, two juveniles and six adults, Kota Kinabalu, 14 in Beaufort, two in Kuala in 23-33 m. There was a correlation between Penyu, two in Kota Belud, five in Sipitang, the number of sea snakes caught and the and none in Papar and Tuaran. The trawlers depth, with r= 0.40. However, in this study, it landing in Sipitang are operating in Brunei Bay A,TeWONG 21

a Praescutato tipefina I Hydrophis klossi

E Hydrophis ornatus

E Hydrophis Eracilis

a Hydrophis c ae rul es c ens

a Hydrophis fasciatus

a Kerilia jerdoni

E Hydrophis clanoc inctus I Hydrophis brookii lAipysurus eydouxii

B Lapemis curtus Fig, 2: Total number of specimens and species of sea snakes caught Per month

60 E Number of Specimen I Number of Species 50

40

30

20 z 10

0 Mar-98 Apr-98 May-98 Jur-98 Jul-98 Aug-98 Sep-98 Oct-98 Nov-98 Dec-98 Jan-99 Feb-99 Mooth

Figurt 4. Total number of specimens and species of sea snakes caught per month D HUMAN E)el,onAfioN AND coNsERvATIoN oF sEA sNAKEs nI SABAH

as 15 Number of a2 E indiYidud a3 l

: ta !! Dopth{trrt of Pu[ (n) L Depth-End of ,a Pul (m)

M{ri aF40 Mllit Jrltl J.r4 r!a-s 844 O.r.! N.tJtl D6';l I.l, r...t Motrth

Figure 5. Total number of specimens caught per month according to depth

+Numb.rof indMdud -ts Me.! Dcptb (m)

/r-4s14s u plo tt; ,J{ *, !m

E20 z10

Mrr- ApF98 May- Jun- Jul- Aug- SeF Oct- Nov- Irec- Jrn- X'cb. 9t 98 98 98 98 9B 9898989B9D

Month

Figurr 6. Total nunber of sea snakes versus mean depth Ar.xe WONG n while trawlers landing in Kota Belud nonnally CONCLUSIONANDRECOMMu\IDATION operate at Usukan Bay. All together the tawlers operate in Kimanis Bay and Pulau Any trawl hauls of shorter duration should Tiga Park and its adjacent areas are from Kota decrease tlle incidental catch and increase the Kinabalu, Beaufort and Kuala Penyu with a probability of survival of sea snakes. People total number of 184 trawlers including in some areas often kill sea snakes that are prawn trawlers. accidentally encountered, out of fear or ignomnce. However, such killings are considaed In 1988, trawlers that operated in Kimanis Bay to have little impact on populations. and Pulau Tiga Park and its adjacent areas were tlose trawlers landing in Kota Kinabalu The impact of commercial trawlers on sea fish market and Kuala Penlu fish market with snake populations can be minimized by a total of682 metric ton and 298.9 metric ton carrying out the trawl activities at least 50 m respectively (Department of Fisheries Sabah, depth on the west coast of Sabah. In addition, 1989). However, in 1997, those trawlen landing snakes tend to feed more readily and can in Kota Kinabalu, Beaufort and Kuala Penyu capture fish more easily in shallow waters (< 50 had marine fish landings of 36,000, 188.12 and m) than in deep sea (WasserLbery et al.,1994)- 14.23 rnetric ton, respectively (Department of Fisheries Sabah, 1997). Within ten years, the For instance, the commercial fin-fi sh-trawling marine fish landing had increased more than activities in the Gulf of Caxpentaria showed 52 times in Kota Kinabalu and new landing thar T3qo of sea snakes tend to be caught in districts such as Beaufort had been added, coastal water less than 30 m deep, and but it had decreased sharply in Kuala Penyu. commercial finfish are generally found in From 1988 to 1997, on the average, there was deeper waters further offshore (Blaber et a/., an increase of more than 36 times of marine 1994). Fish trawlers are also encouraged to fish landing by using trawl nets. Thus, this use larger mesh (100 mm) in the codend than means a lot of sea snakes were being exploited do prawn trawlers (50 mn), to allow sea snakes yearly. It was estimated that about one metric to escape. ton of marine fishes was caught per trawler for each time of landing in the market (Chua It is remarkable that fiawlers killed tens of Aik Thl pen. comm.), that is 36,202 metric ton thousands and even more than six hundred of fishes or trawlers landing on the west coast tlousands of sea snakes per year recently, of Sabah in 1997. "fhe survival rate of sea atrd yet the snakes somehow still survive in snakes from commercial trawlers was about spite of the fact that the trawlers operating on 607o (Wassenberg et al., 1994). Factors like the west coast of Sabah have increased mesh size and trawlers' capacity, which might tremendously over the years, and rates ofeven influence the catches of sea snakes, should more efficient trawling have increased. Since be excluded. Hence, it was estimated that a tlre previous study of Han et al. (1991) was tobl of 666, I 17 sea snakes in Sabah were being carried out ten years ago as compared to this exploited in 1997. For the last ten years, the study. the species diversity (ll species, marine fish landing increased exponentially, Ds=0.74) and abundance of sea snakes was the total number of sea snakes exploited by still high. This might be caused by suitable trawlers activity also increasedtremendously, habitats, adequate food resources and a with a total of about 1.3 million sea snakes healthy environment. Anyhow, a positive estimated to have died (Appendix B). finding would automatically trigger at least 24 Huulv octorutlou AND coNsERVATIoN oF sre sNnxgs IN SasnH

some awareness in conservation - a move that Han,ICH., (1988). The reproductive ecology and could bring some baseline information on diet of a sea snake (Zap emis hardteickii Grcy, these ignored marine rqfiles which can offer 1835)ftomwest coastof Sabah. B.Sc. thesis. Kebangsaan a little protection in the futwe. Sea snakes are Udversiti Malaysia, Kampus Sabah. therefore both an indicator of the marine environment and a potentially key player in Han, K.H., R.B: Stuebing & H.IC Voris. (1991). the marine food chain. Thus, they must be Population structure and reproduction in the included and considered as important as mzrine stake Lapemis hardwickii Gray, fiom marine fishes y/hile promoting sustainable the west coast of Sabah. Sqrawak Museum management of Sabah's marine resources. Journal,63:. 463-475.

ACKNOWI,EDGEIUENIS Heatwole, H. (1975). Voluntary submergence tim€s ofmarine snakes. Marine Biologt ,32: 205-213. Great appreciation is due to ChuaAik Tak and brother for providing logistical support and Juhl, R, & S.B. Drummond. (1976). Shrimp use of their commercial trawl€rs for the sea bycatch investigation in the United Stat€s of snake project throughout the year. Special America: stalus report. Symposium on thanks also go to their workers who assisted progress in madne research in the Carribbean me in collecting sea snakes. My highest and adjacent regions, Caracas, 12-16 July gratitude to my supervisors, Dr Harold Voris 1976- HO Fishenes Repo*, 200 213-320. of the Field Museum of Natural History, Chicago, and Dr. Fatimah Hj. Abang of Maclean,J.L. (1972). An analysis ofthe catch by Universiti Malaysia Sarawak for their trawlers in Moreton Bay (Qld) during the 1966-67 prawning season. Proceedings of the supervision of this study. Many thanks to Lin ean Society ofNew So*h Wales.g8i 3542. Shim Yen Lin of the Ministry of Agdculture Development and Food Industries for Raloff, J. (1999). Skate-ing to Exrincrion? Some providing information on frsheries hawesting long-lived fish are facing accidental in Sabah. Thanks also go to Mr. Alvin Wong annihilation. S c ie n c e N ew s, I 5 5 : 280 -282. ofthe Deparftnent ofFisheries Sabah for the support and co-operation. Rubitroff, I., J.B. craham & J. Motta. (1986). Diying of the sea snake Pelamis platurus in RtsFMENCES the Gulf of Panama. I. Dive depth and dufation. Marine Biolog,,gl: l8l - 191. Blaber, S., D. Br€wer & A. Hsrris. (1994). Saila, S.B. (1983). Importance Distribution, biomass and community alld assessment of discards in commercial fisheries. structure of dem€rsal fish€s of the Gulf of FIO Fis herie s circular,'l 65 | I -62. Carpentaria, Australia. Australia Jounal of Marine and Freshwatet Research, 45., 375- Wasserberg, T.J., 96. J.P. Salini, H. Heatwole & J.D. Kerr. (1994). Incid€ntal capture of sea snakes (Hydrophiidae) prawn Departmetrt of Fishcries Srbah. (1989).lzrra, by trawlers in Gulf of Carpentaria, Arrstralia. Australia report ofrhe Depaflment ofFisheries Sabah Journal ofMarine and Freshwater Research, .1988. Department of Fisheries Sabah, Kota 45:429-443. Kinabalu.

Depertment of Fishenes S^b^b. (1997). Antuol fishe es statistics 1997. Department of Fisheries Sabah, Kota Kinabalu. ATr,tIWONG 25

APPEI\IDD(A- Species Diversity : Sinpson Index

Divenity Index, Ds = 1 Dni(ni- 1)/N(N- I) orDs= 1-'l

MaximrurDiversity, where, zi= number of individual for a species D ar=(S-l)/S X N(N-I) N= total number ofindividual

Uniform, Es = Ds/ Dmat

Dominance, ds = 1-Es

Diversity Index: Ds = r - [ r21 (120) I 27 7 Q7 q + 47 (46) I 27 7 Q7 q + 40 Q9) I 27 7 Q7 q + 2t (20)I 27 7 (27 6) + L6 (t s) t 27 7 Q7 6) + 1 1 (t0) / 27 7 Q7 A + e G) t 27 7 (n q + 6 Q) t 27 7 87 q + 4 Q) t 77 7 (n 6) + 1 (0) t 27 7 (27 6) + t (0y 27 7 Q7 ql

Ds= 1-0.2501 = 0.7499

MaxirnumDiversity: Dnm=(S-t)/S X N/(N- 1) -(11 - ryll x 277 / (277 - 1) = 0.9124

Uniform: Es : Dx /Dmat = 0.7499 10.9124 = 0.8219

Dominance: ds=l-Es = I - 0.8219 = 0.1781 26 HUMAN DcLorrATIoN AND coNsERvATloN oF sEA sNAKEs IN SABAH

Appendix B: Fisheries statistic: data offishes and sea snakes caught in the west coast of Sabah over 10 years.

Year Quantity offishes caught by trawleB (metric ton)

1988 682+299=981 1997 36,000 + 188+ 14= 36,202

Calculation was based on assumption of geornetric progression

years period Sn = a (r ' -l)/ (r-1) ,9t = total number of fishes caught over 10 r- contmon ratio

Let 1 988 be the base year, fust number a= 98 I , af :36,202 af /a= 36,2021981 f =36,903 9lgr=1936.903

lg r= 1 .567O64/9 lgr=0.174111 r=1.493

e Sz =981 (1.493 - l)(1.493-1) = 71435 .9 metric ton

According to research, 46 sea snakes caught in I metric ton offishes Thus, 71435.9 metric ton x 46 sea snakes = 3,286,051.4 sea snakes caught survival raie d0%, died4Q% 3,286,051 .4 x 40% = 1 ,3 14,420.5 sea snakes died over 1 0 years -1.3 millions ofsea snakes died over 10 years'