Karakteristik bioekologi rajungan (Portunus pelagicus) di Perairan Laut Kabupaten Brebes

Abstract

Blue swimming crab (Portunus pelagicus) is commercial and exported product from Indonesia. It is usefull to make it as sustainable resource, so the research should conduct to analysis bioecology characteristic. The research was conduct from April 2008 through March 2009 in Brebes district waters with survey method. The objective of the research was to analysis biology and ecology characteristic and its relationship on crab distribution as base of sustainable fisheries management. Samples was collected by capture gear was called garok (mini beam trawl-like). In the present research, analyzed ecologycal data covered substrat texture, Carbon-organic content, Nitrogen-total content, orthoposfat (P2O5) content, pH value, salinity and water themperature. Also analyzed biological data covered morfology, anatomy, growth, reproductive performance, age assessment, length infinity, size at first maturity and legal size. Ecological data analyzed descriptively through performance of substate texture, organic content and water quality and also the parameters relationship each other. Principle Component Analysis (PCA) used to know ecology parameters relationship. Reproduction performance analized descriptively, whereas growth used regression analysis and von Bertalanffy growth formula (VBGF) from FISAT software. The result points that substrate fraction don’t give effect on crab size distribution. Ranges of male crab carapace length are 22 mm to 75 mm, while female crab carapace length are 21 mm-74 mm. Weight range male crab are 10.12 g-234.13 g, while female crab are 6.53 g to 253.24 g. This conditions demonstrate there is variation of old structure on crab population and crab which is caught is not from same cohort. Sex ratio demonstrated that number of female crab more than male along a year. Almost long a year, male crab dominated by ovarian stage I. The female crab on ovarian stage V (berried female) found out long a year. Spawning occure long a year with peak season on April and September. Generally male crab have weight increases faster than length in other hand female crab have length increases faster than weight increases. Male crab have bigger size than female. Size at first maturity for male crab is 63 mm, while female crab is 48 mm. The legal size of blue swimming crab is 65 mm. Base on ELEFAN analysis resulted that length infinity (L) is 81.10 mm for male and 81.38 for female with growth coefficient are 1.20 and 0.78 for male and female respectively. Base on VBGF resulted that maximum length occur at 5.66 and 5.63 year old for male and female respectively. From Battacharya method found there are two size class that are on mean length 47.5 mm and 59.5 mm. Result from FISAT analysis pointed that total mortality value (Z) was 2.52, natural mortality (M) was 1.53, fishing mortality (F) was 0.98. Fishing exploitation rate (E) was 0.391, indicated that fishing effort still in the range allowable catch. Substrat texture class was dominated by sandy loam. Carbon-organic content range of 1.08-4.79 %, Nitrogen-total was 0.07-0.51 % and Orthophosfat (P2O5) was 3.65-32.26 mg/100g. Acidity value (pH) of substrat range of 5.3-7.8, themperature variated on 26-30oC and salinity range of 30 - 33 ppt.

Rajungan (Portunus pelagicus) merupakan salah satu komoditas perikanan yang bernilai ekonomis penting karena permintaannya tinggi dan merupakan komoditas ekspor yang memiliki harga tinggi. Pengetahuan tentang karakteristik bioekologi rajungan sangat penting dalam upaya melestarikan sumberdaya tersebut, baik melalui upaya pengelolaan maupun budidaya. Penelitian mengenai karakteristik Bioekologi Rajungan (Portunus pelagicus) telah dilakukan di perairan laut Kabupaten Brebes Jawa Tengah sejak bulan April 2008 sampai Maret 2009. Tujuan penelitian ini secara umum adalah menganalisis karakteristik biologi, ekologi dan hubungannya dengan distribusi rajungan sebagai dasar pengelolaan sumber daya rajungan yang berkelanjutan Sampel rajungan sebanyak 844 ekor dikumpulkan dengan alat tangkap garok. Data-data biologi dan ekologi rajungan dikumpulkan secara in situ dan dianalisis secara deskriptif. Pada penelitian ini dilakukan analisis terhadap karakteristik ekologi yang meliputi komposisi tekstur substrat, kandungan C-Organik, kandungan N-total, kandungan orthoposfat (P2O5), nilai pH, salinitas dan suhu perairan. Pada penelitian ini juga dilakukan analisis terhadap karakteristik biologi yang meliputi morfologi, anatomi, pertumbuhan, distribusi TKG, pendugaan umur, panjang infinitif, ukuran pertama matang gonad, dan ukuran layak tangkap. Data karakteristik ekologi dianalisis secara deskripsi dengan menampilkan data kelas tekstur substrat, kandungan bahan organik dan kualitas air serta menampilkan hubungan antara parameter-parameter tersebut. Analisis komponen utama (PCA) digunakan untuk mengetahui korelasi parameter ekologis. Analisis terhadap morfologi dan anatomi dilakukan secara deskriptif dengan mengacu dan membandingkan dengan rujukan yang relevan dalam kajian yang serupa, dan disajikan dalam bentuk gambar-gambar morfologi dan anatomi yang dapat menjadi rujukan dalam melakukan identifikasi rajungan. Penampilan reproduksi dianalisis secara deskripsi, sedangkan pertumbuhan dianalisis secara regresi dan menggunakan pola pertumbuhan von Bertalanffy dari perangkat lunak FISAT. Hasil penelitian menunjukkan bahwa fraksi substrat tidak mempengaruhi distribusi ukuran rata-rata rajungan. Hasil analisis komponen utama menunjukkan fraksi lumpur dan liat berkorelasi positif dengan variabel C-Organik dan N-total. Nilai pH berkorelasi positif dengan C/N rasio dan fraksi pasir. Kondisi substrat didominasi oleh fraksi pasir diikuti oleh farksi lumpur dan fraksi liat. Hasil analisis menggunakan segitiga shepard didapatkan bahwa kelas tekstur substrat setiap titik sampling hampir sama yaitu didominasi lempung (loam) baik lempung berpasir maupun lempung berliat. Kandungan C-organik berkisar antara 1.08-4.79 %. Kandungan N-Total berkisar antara 0.07-0.51 % sedangkan kandungan Posfat (P2O5) sebesar 3.65-32.26 mg/100g. Kisaran nilai pH dalam substrat adalah 5.3-7.8, dan masih dalam batas toleransi bagi kehidupan rajungan. Suhu perairan bervariasi antara 27-30oC. Salinitas perairan di daerah penelitian berkisar dari 30 sampai 33 ppt. Nilai pH perairan di lokasi penelitian berkisar antara 5.2 sampai 7.1. Kedalaman di lokasi penelitian berkisar 3-12 m.