Analisis sebaran dan kelimpahan ikan kemuru (sardinella lemuru bleeker 1853) di perairan selat Bali: kaitannya dengan optimasi penangkapan

Abstract

lkan lemuru ( Sardine/la /emuru) merupakan sumber daya perikanan taut yang sangat penting dan spesifik di perairan Selat Bali, dengan rata-rata produksi tahunan mencapai 80% dari produksi total perikanan laut. Produksi perikanan lemuru di perairan Selat Bali ternyata sangat berfluktuasi baik secara musiman ataupun tahunan. Untuk menangkap ikan lemuru di perairan Selat Bali digunakan alat tangkap pukat cincin dan dilakukan oleh nelayan yang berasal dari dua propinsi, yakni Jawa Timur (Muncar) dan Bali (Pengambengan). Perairan Selat Bali mempunyai bentuk unik yang menyerupai corong yaitu menyempit di utara dengan lebar sekitar 1 mil dan melebar di selatan sekitar 28 mil. Perairan sebelah utara berhubungan dengan Laut Bali, sedang di sebelah selatan berhubungan dengan Samudera Hindia. Dengan topografi seperti ini, karakteristik perairan Selat Bali sangat dipengaruhi oleh massa air yang berasal dari Samudera Hindia dan diperkirakan sangat bervariasi baik secara spasi,al ataupun temporal (musiman). Terjadinya variasi parameter oseanografi, baik secara spasial maupun temporal akan berpengaruh langsung atau tidak langsung terhadap penyebaran dan kelimpahan ikan lemuru. lkan lemuru juga memiliki sifat seperti kebanyakan jenis ikan clupeids lainnya yaitu senang hidup bergerombol, membentuk gerombolan besar yang dinamakan schooling. lnformasi tentang karakteristik (panjang, tinggi, densitas, dan kedalaman) gerombolan ikan lemuru ini sangat penting bagi keberhasilan penangkapan dengan pukat cincin yang dioperasikan dengan cara berburu tanpa menggunakan alat bantu pengumpul ikan. De_mikian juga dengan informasi tentang ukuran ikan lemuru yang akan ditangkap sangat diperlukan untuk penentuan pola penangkapan yang optimum sehingga tidak mengganggu kelestarian sumber dayanya. Penelitian ini dilakukan dengan tujuan: (1) mengkaji penyebaran dan kelimpahan ikan lemuru berdasarkan musim dan hubungannya dengan parameter oseanografi, (2) mendapatkan informasi tentang karakteristik gerombolan ikan lemuru berdasarkan waktu (musim dan tengah harian), (3) mengetahui pola pengelompokan ukuran ikan berdasarkan daerah penangkapan dan waktu (bulan), dan (4) menyusun pola penangkapan ikan lemuru yang optimum dengan memperhatikan kaidah-kaidah pengelolaan sumber daya perikanan.

small pelagic resources in Bali Strait waters. Some factors have played important roles in the variation of lemuru production, among others, are the oceanographic parameters. The objectives of this research are: (1) to study the distribution and the abundance of lemuru specifically their relationship to oceanographic parameters, (2) to analyze the size structure of lemuru caught by the purse seine, (3) to evaluate the characteristics of lemuru schools in different seasons, (4) to develop an optimum fishing pattern for lemuru purse seine fisheries. This research was carried out in two years, from 1996 to 1998 in the Bali Strait waters, applying acoustic methods and the analysis of its abundance index (catch per unit effort, CPUE). Oceanographic observations were also carried out along cruise tracks using research vessel. The analytical hierarchy process was applied for determining the optimum fisheries pattern. In Bali Strait, lemuru was abundant at the end of southeast monsoon (August) and transition season-2 (September-November) which was indicated by a high CPUE. The acoustic data analysis showed that during transition season-2 the abundance pelagic fish was higher than during transition season-1. Upwelling was occurred during southeast monsoon in Bali Strait, characterized by low temperature, high salinity, and phytoplankton was abundant. · Using factorial correspondence analysis, it can be identified four groups of fish size correspond to the months: (1) August-September: 7.5-10.5 cm group, (2) October-December: 11.5-12.5 cm group, (3) January-February: 13.5-14.5 cm group, and (4) March-July: 15.5-18.5 cm group. The spatial distribution indicated that juvenile fish were found abundantly in the northern part of the strait, while the large size lemuru were more abundant in the middle and southern areas. The characteristics of lemuru schools were different significantly between transition season-1 (May) and transition season-2 (September), especially for their length and density. During transition season-2, the schools were larger and denser than during transition season-1. Most of the lemuru schools distributed in the water layer of 29 to 54 m deep. During the day time, the schools were in the deeper layer of more than 75 m, while in the night they merge to sub surface, within the depth of 38-52 m. The best fishing ground for lemuru located in. the waters adjacent to the coast of Bali, with large size of schools. During August and September when juvenile fish, locally called, "sempenit" was abundant in the northern part of the strait, it is recommended not to exploit them intensively. By implementing a closed area measure to protect the juvenile, the yield could be increased about 1, 165 tons for a month and 2,441 tons for two months.