SUHU PERMUKAAN LAUT DAN KEDALAMAN TERTANGKAPNYA TUNA OLEH KAPAL PANCING ULUR YANG DILENGKAPI LAMPU

The movements and abundance of tuna are strongly influenced by the temperature and water depth. Bungus-based fishermen catch bigeye tuna (BET, Thunnus obesus) and yellowfin tuna (YFT, Thunnus albacares) using handlines operated on light-equipped fishing boats. Purpose of the research : (1) to measure the sea surface temperature (SST) and swimming layer bigeye tuna (BET) and yellowfin tuna (YFT) around Mentawai Island, (2) to identification the effect of light on the vertical distribution, and (3) to determine length of hookline the best catch tuna. Based on the length of the line and configuration of line, weight, hooks and live-squid baits, their hooks were at 45, 53, 60, and 68 meters below sea surface. A total of 8 YFT were caught at 45, 53 and 60 m depths; their total weight was 354 kg. One BET of 45 kg was caught at 60 m depth. This study confirmes that these large-sized tunas were caught at a swimming layer of 15-60 m depth. The sea surface temperature (SST) in the fishing ground around Mentawai Island was 28.9 oC in average where fishermen successfuly caught a total of 15 tunas consisting of 3 BETs and 12 YFT. Adult tuna were caught mostly at 23-60 m depth while the juveniles were caught at 15-45 m. This research indicated an effect of light on increasing the position of adult tuna swimming layer. Handline with line of 53 m is the best gear for catching adult tuna in the area.Sebaran dan kelimpahan ikan tuna sangat dipengaruhi oleh suhu dan kedalaman air. Nelayan tuna Bungus menangkap ikan tuna bigeye (BET, Thunnus obesus) dan tuna sirip kuning (YFT, Thunnus albacares) menggunakan pancing ulur yang dioperasikan pada kapal yang dilengkapi lampu sebagai alat abantu. Tujuan penelitian: (1) mengukur suhu permukaan laut (SST) dan kedalaman renang tuna mata besar dan tuna sirip kuning di sekitar Pulau Mentawai, (2) mengidentifikasi pengaruh cahaya terhadap sebaran vertikal tuna, dan (3) menentukan panjang tali pancing terbaik untuk penangkapan tuna. Berdasarkan panjang garis dan konfigurasi garis, berat, kait dan umpan cumi-cumi, kait mereka berada di 45, 53, 60, dan 68 meter di bawah permukaan laut. Sebanyak 8 tuna sirip kuning tertangkap di kedalaman 45, 53 dan 60 m; berat total 354 kg. Satu BET seberat 45 kg tertangkap pada kedalaman 60 m. Penelitian ini memberitahukan bahwa tuna berukuran besar tertangkap di lapisan permukaan dengan kedalaman 15-60 m. Suhu permukaan laut (SST) di daerah penangkapan ikan di sekitar Pulau Mentawai rata-rata 28.97 oC di mana nelayan berhasil menangkap 15 tuna yang terdiri dari 3 ekor tuna mata besar dan 12 ekor tuna sirip kuning. Tuna dewasa kebanyakan tertangkap pada kedalaman 23-60 m sedangkan muda tertangkap di kedalaman 15-45 m. Penelitian ini menunjukkan pengaruh cahaya dapat menaikkan posisi lapisan renang tuna dewasa. Handline dengan panjang tali 53 m adalah panjang tali terbaik untuk menangkap tuna dewasa di daerah tersebut