kepadatan stok ikan demersal dan beberapa parameter kualitas perairan di perairan tegal dan sekitarnya

Penelitian sumber daya ikan demersal dan parameter kualitas perairan dilakukan dengan menggunakan Kapal Riset Sardinela (68 GT) pada bulan April, Juli, dan Nopember 2009 di perairan Tegal dan sekitarnya. Penghitungan kepadatan stok menggunakan metode swept area dengan panjang tali ris atas dari jaring trawl 21 m, kecepatan kapal waktu menarik jaring berkisar 1,5-2,0 knot dan lama penarikkan jaring di setiap stasiun penangkapan maksimal 1 jam. Posisi stasiun penangkapan dan oseanografi relatif sama pada kedalaman berkisar 10-50 m. Laju tangkap pada 41 stasiun penangkapan rata-rata 10,86 kg/jam dengan kepadatan stok 0,498 ton/km2 dan biomassa 23.082 ton. Sepuluh famili dominan tertangkap, yaitu Leiognathidae, Apogonidae, Sciaenidae, Nemipteridae, Pomadasydae, Synodontidae, Tetraodontidae, Carangidae, Teraponidae, dan Priacanthidae. Dibandingkan dengan hasil penelitian terdahulu (tahun 1976-2005), terdapat kecenderungan laju tangkap yang meningkat bagi famili Sciaenidae, Nemipteridae, dan Pomadasydae. Kelompok ikan yang cenderung menurun terdapat pada famili Synodontidae. Sementara famili Leiognathidae selalu mendominansi hasil tangkapan trawl. Kepadatan stok tertinggi (1,0 ton/km2) terdapat pada strata kedalaman 40-<50 m dan terendah (0,2 ton/km2) terdapat pada strata kedalaman antara 10-<20 m. Biomassa tertinggi (15.059 ton) terdapat pada strata kedalaman 30-<40 m dan terendah (1.410 ton) pada strata kedalaman 10-<20 m. Korelasi positif yang nyata terjadi antara kepadatan stok ikan demersal dengan kepadatan makrozoobentos, kedalaman perairan, suhu, dan oksigen terlarut pada dasar perairan. Penyebaran kepadatan stok tidak dipengaruhi oleh salinitas dan pH dasar perairan.   Research on the demeral fish resources and some parameters of water quality using Sardinela Research Vessel (68 GT) were carried out during April, July, and November 2009 in Tegal and its adjacent waters. Stock density was estimated by swept area method. The trawl used has 21 m head rope, trawling speed of 1.5-2.0 knot, and the maximum towing time was 1 hour. The main fishing ground was 10-50 m water depth. Sampling position of trawling and oceanography parameters were set up relativelly the same position. Based on the result of 41 successful haul’s station, the average of catch rate of demersal fish was estimated to be 10.86 kg/hour with stock density of 0.5 ton/km2 and biomass of 23,082 ton. The ten dominant families were Leiognathidae, Apogonidae, Sciaenidae, Nemipteridae, Pomadasydae, Synodontidae, Tetraodontidae, Carangidae, Teraponidae, and Priacanthidae. Compared with research in the previous years (1976-2005), the catch rates familiy of Sciaenidae, Nemipteridae, and Pomadasydae tend to increase. Meanwhile, catch rate family of Synodontiade tend to decrease. The family of Leiognathidae in the overall years were always dominant. According to the depth stratum, the highest stock density of 1.8 ton/km2 was found in the depth between 41-50 m, while the lowest density of 0.2 ton/km2 was found in the depth between 10-20 m. Meanwhile, the highest biomass of 15,059 ton was found in the depth between 30-40 m, and the lowest of 1,410 ton in the depth between 10-20 m. A high correlation occured significantly between stock density of demersal fish and the water’s depth, temperature, and dissolved oxygen on the bottom. Meanwhile, correlation between stock density of demersal fish with pH and salinity on the bottom did not significantly different.