Distribusi Spasial Rajungan (Portunus pelagicus) pada Musim Timur di Perairan Pulau Lancang, Kepulauan Seribu

ABSTRAK

Penelitian ini mengkaji kondisi terkini sumber daya rajungan (Portunus pelagicus) di Pulau Lancang yang meliputi identifikasi daerah penangkapan ikan, serta penilaian lingkungan perairan dan biometri rajungan. Pengumpulan data hasil tangkapan dilakukan setiap bulan pada Juni September 2015 di tiga pengumpul rajungan, menggunakan kuesioner dan pengukuran morfometri dari sedikitnya 30 individu yang dipilih secara acak. Survei batimetri dilakukan untuk menghasilkan peta kontur kedalaman yang dikombinasikan dengan sejumlah parameter oseanografi (suhu permukaan laut-SPL, salinitas, kecerahan, total padatan tersuspensi-TSS, oksigen terlarut-DO, dan nitrat-NO) yang diukur di 15 stasiun. Peta grid dihasilkan untuk mengidentifikasi area kunci yang menjadi daerah penangkapan ikan, habitat rekrutmen, dan habitat pemijahan. Selama musim timur, daerah penangkapan ikan utama terdapat di perairan sebelah barat dan selatan Pulau Lancang (grid C3, C4, dan D5). Secara umum, hasil tangkapan nelayan didominasi oleh rajungan betina (66,9%) dan 43,8% di antaranya mengerami telur. Empat kelas 3 ukuran ditetapkan berdasarkan sebaran frekuensi lebar karapas rajungan (Kelas 1 = 7,0-10,6 cm; Kelas 2 = 10,7-14,2 cm; Kelas 3 = 14,3-17,8 cm; dan Kelas 4 = 17,9- 21,5 cm), dengan Kelas 2 sebagai komponen utama hasil tangkapan. Mengacu sifat migrasi ontogeni yang dimiliki spesies ini, maka grid A6 diduga merupakan habitat rekrutmen karena terdapat kelimpahan juvenil yang tinggi dan pengaruh oseanik kuat dengan rentang kedalaman  24-30 m. Keselarasan spasial antara sebaran rajungan betina bertelur dengan beberapa parameter lingkungan (suhu permukaan laut, salinitas, dan oksigen terlarut-DO) mengindikasikan dibutuhkannya pengaruh estuaria untuk habitat pemijahan rajungan di C3 dan D5.

Kata kunci: daerah penangkapan ikan, distribusi spasial, musim timur, Pulau Lancang, rajungan

ABSTRACT

A study was carried out to assess the present status of blue swimmer crab (Portunus pelagicus) in Lancang Island, incorporating identification of fishing ground, also measurement of environmental condition and crab biometry. Monthly catch assessment was performed on June- September 2015 at three landing bases using structured questionnaire and morphometric sampling of minimum randomly selected 30 crabs. Bathymetric survey was conducted to produce depth-contoured maps combined with certain oceanographic parameters (sea surface temperature, salinity, water clarity, total suspended solids, dissolved oxygen, and nitrate-NO) measured at 15 sampling sites. A grid map was produced to identify key areas of crab fishing grounds, recruitment habitat, and spawning habitats. During southeast monsoon, main fishing ground was distributed in the western and southern part of Lancang Island (grid C3, C4, and D5). In general, crab yields were dominated by female (66.9%) and 43.8% of them were bearing eggs. Four size classes were determined from frequency distribution of carapace width (Class 1 = 7.0-10.6 cm; Class 2 = 10.7- 14.2 cm; Class 3 = 14.3- 17.8 cm; and Class 4 = 17.9-21.5 cm), with Class 2 as the most prominent catch. Referring to ontogenetic migration trait of the species, presumed recruitment habitat for blue swimmer crab in Lancang Island is located at A6, where abundant juveniles were harvested in the area with strong oceanic influence and depth range of 24-30 m. Spatial coherence on the distribution of bearing egg female with several environmental parameters (sea surface temperature, salinity, and dissolved oxygen) indicates strong estuarine influence is required for crab spawning habitat at C3 and D5.

Keywords: blue swimmer crab, fishing ground, Lancang Island, southeast monsoon, spatial distribution

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