DINAMIKA POPULASI Rhinoclavis sinensis GMELIN 1791 (GASTROPODA: CERITHIIDAE) DI PANTAI KRAKAL, YOGYAKARTA

Felicia Zahida, Dra.,M.Sc., Prof. Jusup Subagja, Ph.D.,

2012 | Disertasi | S3 Biologi

Penelitian ini bertujuan mendapatkan data dasar dinamika populasi Rhinoclavis sinensis di Pantai Krakal Yogyakarta, berupa: (1) mempelajari cacah populasi, berat, umur, struktur umur, dan rasio seks serta rentang hidup R. sinensis secara temporal, (2) mempelajari proses-proses dalam populasi seperti kecepatan pertumbuhan, pola reproduksi, pola rekrut, rentang hidup, serta mortalitas populasi, baik alami maupun penangkapan R. sinensis (3) mempelajari pengaruh penangkapan pada populasi siput R. sinensis. Penelitian lapangan meliputi pengumpulan siput hasil penangkapan penduduk per bulan selama empat tahun dari 2005 hingga 2008, serta penelitian laboratorium yang meliputi kharakterisasi sIstem reproduksi, yaitu penentuan ukuran matang kelamin, monitoring pola reproduksi dengan menggunakan indeks gonad, serta penentuan umur jenis dengan operkulum. Data frekuensi panjang cangkang dianalisis secara tahunan dan empat tahunan menggunakan analisis stok yang meliputi: parameter pertumbuhan ( K, t0, L00) mortalitas alami (M) dan penangkapan (F), pola rekrutmen, dan estimasi komposisi umur, prediksi hasil per rekrut (Y’/R) dan biomassa per rekrut (B’/R) menggunakan program FiSAT II. Hubungan antara variabel penelitian yang diamati (cacah individu, berat panenan dan indeks gonad) dan data fisik lapangan dianalisis secara grafis menggunakan program Excell dan ordinasi (redundancy analisis (RDA) dan canonical correspondence analysis (CCA)) menggunakan program Canoco. Hasil penelitian menunjukkan populasi R. sinensis meningkat per tahun, dengan kisaran cacah individu 28-55 individu per bulan atau 248-1627 individu per tahun dan rata-rata 661 ± 647,24 individu per tahun. Hasil panenan ini berkisar antara 519,89-5762,43g, rata-rata 2203,3 ± 2399,23g per tahun. Hasil sebesar ini termasuk rendah. R. sinensis mencapai umur dewasa dalam tiga tahun dengan ukuran panjang cangkang 28mm. Rentang hidup yang ditunjukkan pada umur dan struktur umurnya menunjukkan usia rata-rata 5+ tahun dan maksimal 7+ tahun. Ini berarti waktu reproduksi dua hingga empat tahun. Reproduksi berlangsung sepanjang tahun, dengan pola bimodal yang khas daerah tropis dan indeks gonad dua puncak yaitu pada bulan April dan November dengan puncak tertinggi pada bulan April. Nisbah betina:jantan adalah sebesar 100:150. Populasi menunjukkan kecepatan pertumbuhan, yang meningkat per tahun dengan kisaran K, 0,41-0,49 dengan K empat tahun 0,47. Pola rekrut juga memiliki dua puncak pada bulan Mei dan September. Mortalitas alami, M, berkisar 0,917-1,016; mortalitas pemanenan, F, sebesar 0.093-1,064, dan mortalitas total, Z, 1,01-2,08, ini berarti dapat dipanen lebih jauh sebab kematian alami lebih besar dibanding kematian penangkapan dengan kisaran eksploitasi 0,2-0,89 atau rendah, namun demikian karena nilai K rendah, maka jenis ini rentan jika dieksploitasi terlalu tinggi. Laju sintasan S, sebesar 0,125-0,364 atau 12,5-36,4% dengan tipe sintasan III, rendah. Penangkapan R. sinensis direspons dengan peningkatan populasi, oleh karena itu MSY diperkirakan secara holistik (MSY Cadima).

This research has a purpose to elucidate basic informations of the Rhinoclavis sinensis population dynamics at Krakal Beach, Yogyakarta, such as: (1) Studying the characteristics of population such as density, biomass, reproductive pattern, age, age structure, sex ratio, life span of R. sinensis temporarily from 2005 to 2008. (2) Studying the processes within population such as growth rate, reproductive pattern recruitment pattern, mortality (natural mortality and catch mortality) of R. sinensis. (3) Studying the respons of catching to the population of R. sinensis. The field research was basically collecting snails from residents every month, for the duration of four years from 2005 to 2008. Further the laboratory researches were including characterization of reproductive system such as the size of maturation, reproductive pattern based on gonad index, and age determination using operculum. Length frequency data were analized yearly and total four years using stock analysis such as: growth parameter (K, t0, L00) natural mortality (M), fishing mortality (F), recruitment pattern, age structure, yield per recruit (Y’/R) and biomass per recruit (B’/R) prediction using FiSAT II. The relationship among research variables (density, biomass, and Gonad Index) to physics and chemics of beach environment were analyzed using ordination (Redundancy Analysis (RDA) and Canonical Correspondence Analysis (CCA)) using Canoco. The research showed that the population’s character of R. sinensis apparently increase year by year, with the density of 28-55 individual per month with a range of 248-1627 individual per year with an average 661 ± 647,24 individual per year. This was equal to yield’s range of 519.89g – 5762.43g with an average of 2203,3 ± 2399,23 g per year. The ages of first maturity snails were three years with the size of shell length about 28mm. The lives span which are refrected by the operculum and age structure with an average of 5+ years and maximum of 7+ years. This means that there are at least two-four years for the snails to reproduce. Reproductive pattern of the species was all year round, bimodal, with the gonad index reached its peak on April and November with April as the highest. The sex ratio of female: male was about 100: 150. Population processes elucidated were include the growth rate, which was increased year by year with VBGF’s curvature, K, 0.41-0.49 with K 0.47 for four years. Recruit pattern had its peak on May and September. The natural mortality, M, about 0.917-1.016 catch mortality, F, about 0.093-1.064, and total mortality, Z, about 1.01-2.08, which means more snails can be yielded, with exploitation ratio 0.2-0.89 or low, however since the K value was low, it is risky to yield more. The survivorship rate, S, was about 0.125-0.364 or 12.5%-36.4% for invertebrate with survivalship type III, this is categorized low. The effect of catching of R. sinensis during four years of research was increased in number or density of population, as a consequence, the value of MSY has predicted using analisis holistic (Cadima formula).

Kata Kunci : R. sinensis, VBGF, mortalitas, sintasan, dan dinamika populasi.