PENGKAJIAN STOK DAN MODEL PENGELOLAAN SUMBERDAYA IKAN LEMURU (Sardinella lemuru) DI SELAT BALI Peneliti: Ir. Daduk Setyohadi, MP Ir. Tri Djoko Lelono, M.Si Ir. Martinus Ali Muntaha, A.Pi., S.ST., MT Dibiayai oleh Direktorat Jenderal Pendidikan Tinggi, Departemen Pendidikan Nasional, Melalui DIPA Universitas Brawijaya No. 0174.0/023-04.2/XV/2009 tanggal 31 Desember 2008, dan berdasarkan SK Rektor Nomor: 160/SK/2009 tanggal 7 Mei 2009
UNIVERSITAS BRAWIJAYA 2009
RINGKASAN Di Indonesia khususnya di Jawa Timur jenis ikan Lemuru yang khas dominan ditemukan di Selat Bali, sehingga khusus ikan lemuru di Selat Bali diidentifikasikan sebagai Sardinella lemuru, sangat spesifik dan satu-satunya di Indonesia. Di perairan Selat Bali terjadi proses penaikan air pada musim Timur, sehingga perairan ini menjadi kaya akan bahan makanan yang sangat dibutuhkan oleh ikan-ikan lemuru. Jenis ikan lemuru ini biasanya mendiami daerah-daerah dimana terjadi proses penaikan air, sehingga dapat mencapai biomassa yang tinggi. Oleh karenanya akan tergantung sekali kepada perubahan-perubahan lingkungan perairannya. Lemuru yang tertangkap di Selat Bali memiliki keunikan yaitu produksinya dapat mencapai rata-rata hampir 80% dari total produksi (dalam berat) per tahun (1976-2007). Sejak diperkenalkannya alat tangkap pukat cincin atau jaring kolor (purse seine) pada tahuan 1972 oleh Lembaga Penelitian Perikanan Laut (dahulu Balai Penelitian Perikanan Laut) di Muncar Jawa Timur, perikanan lemuru di Selat Bali berkembang dengan pesat. Pesatnya perkembangan ini seharusnya mendapat perhatian yang serius. Jika sumberdaya itu rusak maupun kelestarian sudah tidak terjaga memerlukan waktu yang lama dalam perbaikannya. Walaupun sumberdaya ikan lemuru cukup berlimpah, tetapi kalau penangkapannya dilakukan secara besar-besaran baik terhadap ikan-ikan dewasa maupun yang kecil, maka lama kelamaan dapat terjadi lebih tangkap (over-fishing). Indikasi terjadinya lebih tangkap untuk perikanan lemuru di Selat Bali cukup kuat. Hal ini dapat dilihat dari penurunan produksi ikan lemuru di Jawa Timur yang puncaknya terjadi pada tahun 1986/1987 dan nampaknya ada indikasi terjadi penurunan produksi lagi di tahun 1992 dan 1997 serta tahun 2002. Tujuan penelitian ini adalah: (1) mengetahui beberapa parameter biologi dan dinamika populasi ikan lemuru; (2) menduga potensi stok ikan lemuru; (3) menduga status perikanan lemuru berdasarkan tingkat pengusahaan kaidah biologi, ekonomi dan sosial; (4) membuat simulasi dinamika stok cadangan dan hasil tangkapan terhadap perubahan upaya penangkapan sampai dengan tahun 2020. Data sekunder produksi dan alat di Selat Bali diambil dari Laporan Statistik Perikanan Propinsi Jawa Timur dan Bali tahun 1976-2007. Pengambilan data primer untuk penelusuran penyebaran ikan lemuru melalui wawancara dengan nelayan purse seine. Sedangkan pengukuran parameter biologi dan dinamika populasi diambil dari contoh hasil tangkap alat purse seine di Muncar pada bulan April-September 2009. Data dianalisis dengan pendekatan holistik yaitu Model Produksi Surplus menurut Schaefer (1954) untuk kaidah biologi dan Gordon Schaefer (1959) untuk kaidah ekonomi dan sosial, serta pendekatan analitik dengan bantuan program FISAT II. Sedangkan simulasi dinamika stok lemuru menggunakan metode Walter & Hilborn (1976). Hubungan panjang dan berat ikan lemuru total contoh adalah W = 0.0069 L3,06 , lemuru jantan W = 0.0080 L3,00, dan lemuru betina W = 0.0067 L3,07. Lemuru betina pertambahan beratnya lebih cepat dari pada lemuru jantan. Rasio lemuru jantan dengan betina tidak berbeda nyata. Puncak kematangan gonad terjadi pada bulan Juli (67%). −
Ukuran panjang pertamakali tertangkap (Lc) 14,3cm dan ukuran panjang rata-rata ( L ) 15,9cm, sedangkan panjang ikan matang gonad untuk pertama kali (Lm) 17,3cm.
Persamaan pertumbuhan von Bertalanffy adalah
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Lt = 22,1 1 − e −1, 29 (t + 0, 08) . Laju
mortalitas total (Z), alami (M), dan penangkapan (F) sebesar masing-masing 6,33, 2,29 dan 4,03. Rekruitmen pertama mulai bulan Januari-Mei dan puncaknya terjadi pada bulan Pebruari (15,3%) dan Maret (16,4%), sedangkan rekruitmen kedua mulai bulan Juni-Nopember dan puncaknya terjadi pada bulan Agustus (16,1%). Panjang maksimum (Lmax) sebesar 21,0 cm pada umur maksimum (tmax) 2,4 tahun atau 28,8 bulan. Laju eksploitasi (E) yang memaksimumkan Y/R (Emax) sebesar 0,64. Upaya penangkapan yang memaksimumkan hasil tangkapan fmax (f0.0) diduga sebesar 14.444 trip, sedangkan f0.1 sebanyak 13.000 trip purse seine tiap tahun. Jumlah alat tangkap maksimum berimbang lestari secara biologi (fMSY), ekonomi (fMEY), dan social (fOA) berturut-turut 22.792 trip, 20.186 trip dan 40.372 trip per tahun. Sedangkan volume hasil maksimum lestari secara biologi (fMSY), ekonomi (fMEY), dan social (fOA) berturut-turut 47.235,63 ton, 46,618 ton dan 19.132,63 ton per tahun. Keuntungan maksimum lestari secara biologi ( π MSY) dan ekonomi ( π MEY) sebesar Rp. 68,9 milliar dan Rp. 70,1 milliar per tahun. Tingkat pengusahaan dengan pendekatan analitik berdasarkan nilai f0.0 dan f0.1 diperoleh sebesar 233,4% dan 258,3%, sehingga status pengusahaannya sudah deplesi (depleted). Berdasarkan pendekatan holistik kaidah biologi (MSY), JTB, dan ekonomi (MEY) tingkat pengusahaannya berturut-turut sebesar 147,9%, 267%, 167% sehingga status pengusahaannya sudah over exploited dan depleted. Sedangkan berdasarkan kaidah social diperoleh tingkat pengusahaan sebesar 83,5% yang menunjukkan perikanan pada kondisi tereksploitasi penuh (fully exploited) atau maksimum berimbang lestari (MSY). Potensi cadangan lestari (Be) sumberdaya ikan lemuru Selat Bali diduga sebesar 126.242,15 ton per tahun, sedangkan potensi stok cadangan ikan lemuru pada tahun 2007 (B2007) tinggal 71.479,78 ton, atau sekitar 56,6% dari Be. Jumlah produksinya (Pd2007) sebesar 43.352,89 ton, sedangkan hasil tangkapannya (Y2007) sebesar 46.711,58 ton. Faktor kritis terhadap kelestarian sumberdaya lemuru adalah: (1) tertangkapnya ikan ukuran pertamakali (Lc=14,3 cm) jauh lebih kecil dari ukuran ikan matang gonad (Lm=17,3 cm) menunjukkan bahwa alat tangkap purse seine yang ada saat ini menangkap ikan-ikan muda yang belum matang gonad; (2) besarnya tekanan penangkapan yang menyebabkan status pengusahaan sumberdaya lemuru terdeplesi. Jumlah alokasi alat tangkap yang boleh beroperasi untuk memaksimalisasi keuntungan jangka panjang (th 2020) dan mencegah tangkap lebih dan terkurasnya sumberdaya ikan lemuru Selat Bali disarankan sebanyak 22.792 trip per tahun atau 95 trip purse seine per hari. Selanjutnya penelitian tentang selektifitas alat tangkap perlu dilakukan sebagai dasar pengaturan ukuran mata jaring terkecil.
SUMMARY Oil sardine, Sardinella lemuru, is an economically important, dominant and endemic fish species inhabiting Bali Strait, East Java, Indonesia. During monsoon season, the sea current increased the sea water level and the abundance of natural food needed by oil sardine fishes in the Bali Strait. This species schooling areas which are the sea levels are increased and reach highest biomass. Major importance of oil sardine fisheries was the annual production up to 80% of the total fisheries production in Bali Strait during 19762007. Since the purse seine fishing gear firstly introduced in 1972, oil sardine fisheries production has become dramatically increased. It should be seriously noticed, since depletion of natural resources needs longer time to recover. Although oil sardine were heavy abundant, strong fishing pressure to the adult as well as smaller fishes will lead to the phenomenon called “overfishing”. Bali Strait has been indicated to be overfished according to the production data which are decreased overtime. The lowest production of oil sardine fisheries was occurred in 1986/1987 and repeated in 1992, 1997 and 2002. Aims of this study were: (1) to estimate biological parameter and population dynamic of oil sardine; (2) to assess the oil sardine fisheries stock; (3) to estimate the status of oil sardine fisheries based on the exploitation level in term of biological, economical and social parameters; and (4) to simulate the dynamic of standing stock and fisheries production to the dynamic of the number of fishing effort until 2020. Secondary data of production and fishing gear in Bali Strait were obtained from annual fisheries statistics of East Java and Bali province from 1976-2007. Primary data were obtained from interview with local purse seine fisherman in order to trace the distribution of oil sardine. Measurement of biological parameters and population dynamics were obtained from sampling data of the oil sardine caught by purse seiner in Muncar Banyuwangi during April - September 2009. We used both holistic and analytic approaches for data analysis. In holistic approach, we used surplus production model (Schaefer, 1954) and Gordon Schaefer (1959) to reveal biological and socio-economic analysis, respectively. In analytic approach, we utilized the FAO-ICLARM Stock Assessment Tool (FISAT) II program. Simulation of stock dynamics of oil sardine was conducted by using Walter and Hilborn method (1976). Total length and weight relationship of oil sardine sampled was W = 0.0069 L3,06 , the relationship for male individuals was W = 0.0080 L3,00, and for female individuals was W = 0.0067 L3,07. Females had faster growth than males. The ratio of male and female individuals was not significantly different. Peak of maturity season occurred at July (67%) −
Length at first catch (Lc) was 14.3 cm with average length L = 15.9 cm, while length at first maturity (Lm) was 17.3 cm. The von Bertalanffy Growth Formula was Lt = 22,1 1 − e −1, 29 (t + 0, 08) . Total mortality rate (Z), natural mortality (M) and fishing
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mortality (F) were 6.33, 2.29, and 4.03, respectively. First recruitment starts from January to May with peaks season on February (15.3%) and March (16.4%), while second recruitment starts from June to November with peak season on August (16.1%). The maximum length (Lmax) was 21.0 cm at maximum age (tmax) 2.4 years or 28,8 months. The exploitation rate maximizing Y/R (Emax) value was 0.64. Fishing effort that maximizing fishing yield fmax (f0.0) was approximately reached 14.444 trips, while f0.1 was approximately 13.000 trips of purse seine each year. Equilibrium sustainable fishing
effort in term of biology (fMSY), economic (fMEY), and social (fOA), respectively, were 22,792 trips, 20,186 trips and 40,372 trips each year. Equilibrium sustainable yield in term of biology (fMSY), economic (fMEY), and social (fOA) were 47,235.63 tonnes, 46.618 tonnes and 19,132.63 tonnes each year, respectively. Maximum sustainable benefit in term biological ( π MSY) and economic ( π MEY) were Rp. 68.9 billion and Rp. 70,1 billion each year, respectively. Based on f0.0 and f0.1 values in analytic approach, the exploitation rate were 233,4% and 258,3%, respectively. According to holistic approach in term of biological (MSY), Total Allowable Catch (TAC), and economic (MEY), the exploitation rate respectively were 147,9%, 267%, 167%. Both approaches suggested that the exploitation status of oil sardine fisheries in Bali Strait was over exploited or depleted. However, according to social term, we found that the exploitation rate was 83.5%, suggesting the oil sardine fisheries were fully exploited, or were in Maximum Sustainable Yield (MSY). Potential sustainable reserve (Be) of oil sardine resources in Bali Strait was approximately 126,242.15 tonnes per year. In 2007 (B2007), however, potential standing stock was only 71,479.78 or about 56.6% from Be. Total production (Pd2007) was 43,352.89 tonnes and total yield (Y2007) was 46,711.58 tonnes. Critical factors affecting the sustainability of oil sardine in Bali Strait are : (1) Length at first catch (Lc = 14.3 cm) considerably less than length at first maturity (Lm = 17.3 cm), indicating the existing purse seines are capable to catch fishes before they reach at maturity age; (2) high fishing pressure causes depletion in oil sardine resources. To prevent resources depletion and maximizing long term benefit (until 2020), we suggest the total fishing effort allowed to fish in Bali Strait should be 22,792 trips per year or 95 trips per day. Further study is needed to determine selectivity of fishing gear in order to provide scientific reference for minimal mesh size regulation.
