PERIKANAN DAN DINAMIKA POPULASI RAJUNGAN (Portunus pelagicus Linnaeus, 1758) DI TELUK JAKARTA

Abstract

Teluk Jakarta merupakan salah satu daerah penangkapan dan habitat rajungan (Portunus pelagicus) di Indonesia. Permintaan pasar yang terus meningkat dan bersamaan dengan penurunan kualitas perairan mengakibatkan stok rajungan mengalami tekanan eksploitasi dan degradasi habitat. Agar pengelolaan sumberdaya rajungan di Teluk Jakarta tetap lestari, maka diperlukan penelitian mengenai perikanan dan dinamika populasi. Tujuan penelitian memperoleh data dan informasi mengenai daerah tangkapan, alat dan musim penangkapan, indeks kelimpahan, produksi dan komposisi, struktur ukuran, nisbah kelamin, kematangan gonad, musim pemijahan, ukuran panjang pertama tertangkap, ukuran panjang pertama matang gonad, laju pertumbuhan, laju kematian dan laju eksploitasi. Data dan informasi diperoleh dengan eksplorasi, observasi, enumerasi, wawancara dan perunutan pada tempat pendaratan ikan dan instansi lain yang terkait dengan perikanan, selama tahun 2016. Hasil penelitian didapatkan karakteritik daerah penangkapan rajungan; substrat lumpur berpasir dengan perairan dasar yang mempunyai salinitas 30,5-32 ppt, oksigen 6,5-6,9 ml/l, pH 7,5-8,01, kecepatan arus 0,08-0,24 m/dt. Alat tangkap utama berupa jaring insang dasar bermata 3-3,5 inchi, musim penangkapan Mei-Agustus dan paceklik November-Januari. CPUE rajungan tahun 2016 sebesar 7,2 kg/tarik/trip/hari dan mengalami penurunan 55,22 % tahun 2007. Rajungan berkontribusi 69,11 % terhadap hasil tangkapan jaring insang dasar, sumberdaya ikan lainnya 30,89 %. Modus lebar karapas 85-90 mmCW, lebar karapas pada perairan dekat pantai 84,3 mm dan kearah lepas pantai 99,4 mm. Rajungan di Teluk Jakarta mempunyai tipe pertumbuhan alometrik negatif. Nisbah kelamin jantan : betina = 1 : 0,83, betina dominan pada perairan kearah lepas pantai dan jantan dominan kearah pantai (salinitas rendah). Musim pemijahan rajungan di Teluk Jakarta sepanjang tahun, mempunyai dua puncak pada bulan Maret dan September dengan pusat sebaran gonad ovigerous di sekitar perairan P. Damar. Rata-rata ukuran pertama tertangkap (Lc) = 93,87 mmCW lebih besar dari rata-rata ukuran pertama matang gonad (Lm) = 68,8 mmCW. Laju pertumbuhan (K) = 1,08 mmCW/tahun dengan lebar karapas maksimal (L”) = 142,5 mmCW. Laju kematian total (Z)= 4,87/tahun, penangkapan (F) = 3,63/tahun, alami (M) = 1,24/tahun dan laju pengusahaan (E) = 0,75/tahun. 

Jakarta Bay is one of the fishing areas and habitat of blue swimmer crabs (Portunus pelagicus) in Indonesia. Market demand that continues to increase and along with the decline in water quality results in crab stocks experiencing pressure from exploitation and habitat degradation. So that the management of crab resources in the Jakarta Bay remains sustainable, research on fisheries and population dynamics is needed. The purpose of the study was to obtain data and information; fishing ground, fishing season and main gears, abundance index, production and composition of catch, size structure, sex ratio, gonad maturity, spawning season, first length of catch, length of first gonad maturity, growth rate, mortality rate and exploitation rate. Data and information were obtained by exploration, observation, enumeration, interviews and tracing at fish landing sites and other institutions related to fisheries, during 2016. The results of the study obtained the characteristics of the crab fishing ground; sandy mud substrate with bottom waters which have a salinity of 30.5-32 ppt, oxygen 6.5-6.9 ml / l, pH 7.5-8.01, flow velocity 0.08-0.24 m / sec. The main gears are bottom gill nets with mesh size 3-3.5-inch, the fishing season in May-August and famine in the November-January. CPUE of blue swimmer crabs in the 2016 was 7.2 kg / pull / trip / day decreased 55.22% in 2007. The blue swimmer crabs contributed 69.11% to the catch of bottom gill nets, other fish resources 30.89%. Carapace width frequency have mode is 85-90 mmCW, carapace width in waters near the coast is 84.3 mm and offshore is 99.4 mm. The blue swimmer crabs in Jakarta Bay has a negative allometric growth type. Sex ratio male: female = 1: 0.83, female dominant in offshore and male dominant direction towards in shore and (low salinity). The spawning season of blue swimmer crabs in Jakarta Bay has two peaks in March and September with an ovigerous gonad distribution center around the waters of P. Damar. The average size of the length first catch (Lc) = 93.87 mmCW is greater than the average size of the length first gonad maturity (Lm) = 68.8 mmCW. Growth rate (K) = 1.08 mmCW / year with length infinity of carapace width (L”) = 142.5 mmCW. Maturity rate are total (Z) = 4.87/year, capture (F) = 3.63/year, natural (M) = 1.24/year and explotation rate (E) = 0.75/year.