Decline of the Leatherback Population in Terengganu, Malaysia, 1956
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'*'"w,'###;,;i1";: j'"il,';;*ff li''"' Decline of the Leatherback Population in Terengganu, MalaysiarL956-1995 ENc-Hrnc Cnaur alu Hocr-Cnlm Lrnwr TSEATRU (SeaTurtle ResearchUnit), Faculty of AppliedScience andTechnology, Universiti KolejTerengganu, 21030 KualaTerengganu, Malaysia [Fax:609-669-6694; E-mail: [email protected]] Ansrr-acr. - The Rantau Abang leatherback population in Terengganu, Malaysia is now severely depleted, with current nestings representing less than l7o of levels recorded in the 1950s. Major causes of decline are mortalities attributed to fisheries operations in the high seas as well as within the territorial waters of Malaysia, and a long history of egg exploitation. These problems have been compounded by loss of suitable nesting habitat due to tourism-related development, marine pollution, and sub-optimal hatchery practices leading to reduced hatch rates and sex-biased hatchling production. The global moratorium on driftnet fisheries and complete protection of eggs to ensure optimal hatch rates and production of hatchlings with balanced sex ratios offer some hope for the eyentual rehabilitation of the depleted population. Kuy WoRDs. - Reptilia; Testudines; Dermochelyidael Dermochelys coriaceai sea turtle; nesting trendsl threats; hatchery practicesl conservation; management; Terengganu; Malaysia The leatherback population of Rantau Abang, from 1919 to 1984. The Fisheries Department of Terengganu Terengganu, Malaysia, was celebrated as the only remaining initiated systematic collection of nesting statistics in 1984, leatherback population of importance in the world in the and thereafter data became available for different tendered 1950s (Wyatt-Smith, 1960). However, the once healthy total beaches on a yearly basis. of over 10,000 nests per year (in 1956) has collapsed to fewer After collating data from the various sources, popula- than 100 (averaged from 1993-95) in recent years. This tion trends became apparent (Fig. 1). The decline from 1956 tragic decline is a classic example of the plight of a modern- to 1995 has been precipitous, with 1995 nestings (37) day endangered species. representing only 0.4 Vo of the levels recorded for 1956 The dramatic decline of the Rantau Abang population (10,155). The annual decline averaged 260 nests per year spanning the last several decades has been well documented over the 39 year period. by Malaysian scientists (Brahim et al., 1987; Chan, 1987 a, Three-year running averages of nestings have been 1987b, l99I; Chua, 1988a). This decline, brought to the calculated to smooth out yearly differences in the declining attention of local authorities in the late 1980s, has caused trends (Fig. 2). The single data-year of 1956 has been much concern, resulting in the intensification of conserva- omitted here. As shown in the histogram, there have been tion efforts. Whether or not attempts to save the population two periods of especially sharp declines, one from 1972-7 4 from extirpation bear fruit remains to be seen. and the other from 1918-80. This paper collates available information on the Rantau Between 1972 and I97 4, the rate of decline averaged Abang leatherback population to date, analyzes causes of 723 nestings per year or 2IVo annually. This period coin- population decline, and discusses the developmenJ and evolu- cided with the period of rapid development in the fishing tion of conservation measures for the leatherback in Malaysia. industry in Terengganu. Trawling was first introduced to the state in the early 1970s and thereafter, marine fish landings NESTING TRENDS increased dramatically (Ministry of Agriculture Malaysia, I978). The negative impact of fishing gear on leatherbacks Temporal Trends from 1956-95 The earliest quan- and other turtles in Terengganu has been documented by tification of leatherback egg production in Terengganu re- Chan et al. (1988). sulted from a survey conducted by Hendrickson and Alfred B etween 1 97 8 and 1 9 80, nestings dropped at an aver age in 1956. The estimated annual egg production was 853,000 rate of 469 nests per year or 3IVo annually. This coincided e-s,_qs (Hendrickson and Alfred, 1961) or 10,155 nestings, directly with the introduction of the Japanese high seas squid assuming an average clutch size of 84 eggs (Chua and driftnet fishery of the North Pacific in 1978 (Yatsu et al., Funado, 1988). Between 1956-66, no records were avail- 1991). This fishery is presumed to have impacted the Malay- able. In 1967, the Fisheries Department of Terengganu sian leatherback population, since tagged individuals from initiated a tagging program which lasted ten years, providing Rantau Abang have been recovered from as far away as records of annual nestings between196T-76 (Chua, 1988b). Taiwan, Japan, and Hawaii (Leong and Siow, 1980). Similar [.-,]]Lxing this. Siow and Moll (1982) reported an annual fisheries operating within the South China Sea must have prrrtlus-titrn of 194.000 eggs (or 3500 nestings) in 1978, compounded the problem. After these two periods, rates of b;-3d rro inten'ieu's with licensed egg collectors. Subse- decline averaged64nests per year or 167o annually, suggest- :r--:tr .un.i\.s ( Siti and de Silva, 1985) yielded nesting data ing continuing threats from fisheries operations. CHnN AND LrEw Leatherbacks - in Terengganu r97 not shown the same decline, but instead appears to har e be e n t roughly stable between 1984 to 1994.This anal1'sis poinrs ro 10000 lU two possibilities; either only the population within the sAnc- tuary area is suffering the bulk of the decline, or rhe deciine U)t o 8000 is uniform in Terengganu, but is manifested only' u ithin the 1 F sanctuary area because of emigration of turtles to beuche . a located south of the sanctuary. Although leatherback.. l.U 6000 lik: z other sea turtle species, exhibit some reproductive philop.lrn lJ- o (nest site fidelity), straying or switching to other ne rri:S 4000 & beaches ranging from a few to over 100 km apan have t e lU ::r 6 documented. Pritchard ( 1973) reporte d 14 cases of learhe:- f backs which displayed counter-current intra-seas11r.;. z internesting shifts between Surinam and French Gui;L; beaches 100- I20 km apart. Likewise, Eckert et al. r I 9 S q 1e6o 1e64 1e68 1e80 1e84 1 ,rtirlxh reported that 0-27.37o of the nesting population in the \\'es: Indies shifted to other beaches or islands each year. ,,,...: Figure 1. Nesting trends in the Terengganu, Malaysia, leatherback distances ranging from 30-90 km. once a switch had t e ::. population from 1 956-95. made, the turtles did not subsequently return to the beach ,_ . initial choice (Eckert et a1.,1989). In the Rantau Abu:l The pattern of decline from 1967 to 1995 can be population, Chan et al. (1991) found one radio-track:: represented by a quadratic equation (Fig. 3) : leatherback straying more than 20 km to lay a subsequi:^: clutch of eggs. y = 80.662 - 3.526t + 0.0371t2 Since the entire Terengganu leatherback popularion :. subject to similar pressures in the open-ocean environmen:. with a mean square error of 64.989 and where y = J"^tt"gt it is more likely that the overall population has suffered the and 1 = (year - 1966). Based on this equation, it is predicted decline exhibited, rather than just the animals nesting in th; that population extirpation may occur in the year 2003 if sanctuary. Based on the additional evidence of nesting beacl. present trends persist. However, trend reversals in leather- switches, we hypothesize that nesting beaches south of the back populations of St. Croix (Dutton and McDonald, 1992; sanctuary are also losing turtles at similar rates, but that the rr Boulon et al., 1996) and Tongaland (Mrosovsky, 1983; rates of decline are buffered by arrivals of sanctuary turrles Hughes, 1996) following beach protection offer some hope which have switched nesting location. In Terengganu, onlr to the depleted Rantau Abang population. the sanctuary area is subject to tourism and hence human Spatial Trends from 1984-95. - Locations of leather- disturbance. The Government Reserve area, once the site of back nesting beaches are shown in Fig. 4 while Table I highest nesting activity (Chan, 1987b) is now an open-access provides nesting statistics for the beaches between I 984-95. areawhere vendors and tourists are allowed free access. Beach The Rantau Abang Turtle Sanctuary ( 14 km long) comprises Rantau Abang I and II and the Government Reserve, which is a 0.5 km stretch reserved for egg collection by the Fisheries Department. 5000 Cumulative nesting data from 1984 to 1995 show that G, the sanctuary is the most important nesting site, accounting r! 4000 for over 707o of the total nestings in Terengganu. However, (n L9 a year to year analysis shows that sanctuary nesting contri- = 3000 F U) butions have declined in recent years. Between 1992-94, lJ.J sanctuary nestings accounted = 2000 for only 2948Vo of the total LL nestings, compared to 80-847o from 1984-86 (Table 1). In C) &, 1 000 1995, however, sanctuary nestings accounted for 68Vo of €r! total nestings. Nestings north of the sanctuary are relatively = = 0 insignificant, accounting for only 3-157o of total nestings. Beaches south of the sanctuary, however, have shown in- -1000 1965 1968 1971 1974 1s77 1980 1983 1986 19E9 1ss2 19e5 cre a s i n.-s pe rcentage contribu tion s, parti c u I arly from 1992 to YEAR 1994 when contributions have ranged from 43-67 Vo of total nestin-us for the state. Figure 2. Declining trends in the Terengganu, Malaysia, leather- The overall decline in the Terengganu leatherback back population based on 3 year running averages of nestings. Line population is due primarily to nesting trends within the graph shows the average number of nestings per year while the histogram depicts rates of annual decline by average number of sanctuary area, and to a lesser extent, along the beaches north nestings per year, with negative numbers indicating population of the sanctuary.