Studi Upwelling dan Implikasinya Terhadap Produktivitas Tangkapan Ikan Lemuru di Perairan Selat Bali

Abstract

Selat Bali termasuk kedalam Wilayah Pengelolaan Perikanan (WPP No. 573), dimana potensi perikanan di selat ini, utamanya komoditas ikan lemuru sangat melimpah. Produktivitas primer dan kelimpahan ikan pelagis yang tinggi tersebut berhubungan erat dengan kejadian upwelling pantai musiman. Penelitian ini bertujuan untuk mendeskripsikan proses fisik dan dinamika upwelling pantai serta implikasinya terhadap fluktuasi produksi perikanan lemuru, dengan menggunakan multi-dataset dari observasi satelit dan keluaran model sirkulasi laut INDESO. Data pendukung berupa data angin dari ECMWF dan hasil tangkaan ikan lemuru dari Pelabuhan Perikanan Pantai Muncar. Metode analisis data dengan diagram Taylor, analisis data deret-waktu, estimasi transpor Ekman, indeks upwelling, serta korelasi-silang upwelling dan produksi perikanan. Hasil penelitian menunjukkan bahwa puncak upwelling di Selat Bali terjadi dalam periode Monsun Tenggara dari bulan Juni sampai Agustus, dimana transpor Ekman sekitar 5,5 x 10-3 Sv (1 Sv = 106 m3/s) yang mengalir ke arah baratdaya (menuju lepas pantai), sehingga angkutan ini menjadikan defisit massa air di dekat pantai yang kemudian diisi oleh naiknya massa air dingin dan kaya nutrien dari lapisan lebih dalam ke permukaan. Rona permukaan laut pada peristiwa upwelling di Selat Bali dicirikan dengan suhu minimum (24.93 0C), tinggi muka laut minimum (0.75 m), tetapi klorofil-a maksimum (1.33 mg/m3). Selanjutnya, ciri upwelling di kolom bawah permukaan adalah tersingkapnya kontur isotherm 26 0C dan isohaline 33.7 psu dari kedalaman sekitar 80 m permukaan laut di pusat zona upwelling. Retata indeks upwelling berdasarkan berdasarkan perbedaan suhu adalah sekitar (1.19 ± 0.19 0C). Peristiwa upwelling berdampak positif terhadap tingginya kelimpahan produksi ikan lemuru sekitar 2 bulan setelah puncak upwelling atau sekitar bulan Oktober.

The Bali Strait has fishery potential and is included in the Fisheries Management Area (WPP No. 573), where the abundant commodity is lemuru fish. Primary productivity and high abundance of pelagic fish is closely related to seasonal coastal upwelling. This study aims to described the physical processes and dynamics of coastal upwelling and their implications for fluctuations in lemuru fish productivity, used multi-datasets from observations satellite and model outputs of ocean circulation from INDESO models. Supporting data that used in this research are wind data from ECMWF and lemuru fish catched data from Muncar coastal fishing port. Data analysis method used Taylor diagram, time-series data analysis, Ekman transport estimation, upwelling index, and cross-correlation of upwelling and fishery production. The results showed that peak of upwelling in the Bali Strait occurs during the Southeast Monsoon period (June to August), where the value of Ekman transport was about 5.5 x 10-3 Sv (1 Sv = 106 m3/s), which flows to the southwest (towards the offshore). Therefore could caused water masses deficit near the coast which would be filled by the cold rising water mass that contained nutrient-rich from the deeper layers up to the surface. The upwelling event in the Bali Strait is characterized by minimum temperature (24.93 0C), minimum sea level (0.75 m), and maximum chlorophyll-a (1.33 mg/m3). Furthermore, the feature of upwelling in the subsurface column is the outcropped contour of the isotherm 26 0C and isohaline 33.7 psu from a depth of about 80 m sea level in the center of the upwelling zone. Upwelling events have a positive impact on the high abundance of lemuru productivity for 2 months after the peak of upwelling, around October.