Fish behavior towards trawl - Universitas...
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FISH BEHAVIOR TOWARDS TRAWLOBSERVING & UNDERSTANDING FISH BEHAVIOUR
PATTERNS FOR EFFECTIVE DESIGN OF MOBILE TRAWLING
SYSTEMS
By. Ledhyane Ika Harlyan
Dept. of Fisheries Resources Utilization and Marine ScienceFisheries Faculty, Brawijaya University
27 April 2011
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TUJUAN INSTRUKSIONAL KHUSUS
Mahasiswa mampu menjelaskan pengetahuantingkah laku ikan yang dapat mempengaruhiteknologi dan keberhasilan pengoperasian trawl sebagai alat penangkapan ikan
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DESAIN TRAWL DARI MASA KE MASA
Skema lengkap BOTTOM TRAWL
Desain, bentuk & ukuran akan beragam
Tdk banyak perubahan + 20 – 50 tahun
Perubahan yg terjadi merupakan hasil dari:
peningkatan biaya bbm, selektivitas ukuran
dan jenis species, pengurangan bycatch, &
kebutuhan utk mengurangi efek negatif thd
lingkungan.
Rangsangan suara dan visual ikan
merupakan respon dari:
•kapal,
•pintu bukaan jaring (otter boards),
• pasir, pemberat (tickler), dan
• jaring trawl
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ILUSTRASI ZONA IKAN DALAM PROSES PENANGKAPAN
DENGAN BOTTOM TRAWL
Zona 1: pre-trawl zone mendeteksi & bereaksi thd frekuensi rendah yg dihasilkan oleh kapal termasuk tingkah laku menghindari tali selambar (warps)
Zona 2: tingkah laku ikan dlm merespon pintu trawl (otter boards), sapuan trawl dan jaring bukaan
Zona 3: tingkah laku ikan saat berada di dalam badan trawl
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ZONA 1 (PRE-TRAWL ZONE)
Ikan merespon frek. rendah yg dihasilkan oleh kombinasi dari mesin kapal, getaran tali selambar (warps), pintu bukaan (otter boards) yang bergesekan dgn dasar laut, dan kontak jaring trawl dgn air.
Frekuensi (Hz) yg rendah ≈ rentang kemampuan ikan mendengar (hearing range)/ ambang pendengaran (db)
Hasil dr variasi selection pressure dari waktu ke waktu (Popper,2004):
a. Hearing Specialist dpt mendeteksi >3000 Hz
b. Hearing Generalist dpt mendeteksi <1500 Hz
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Audiogram fish hearing sensitivity
Frek. paling rendah
mampu
mendeteksi jarak yg
relatif jauh
Detect vs React??? beda• Detect ditentukan dr telinga bg.dalam & dpt diprediksi utk species/ukuran ttt;
pada ambang noise di air; dan berbagai partikel dlm air)
•Response/reaction trade off antara (-) kerugian & (+) keuntungan
mendekati pemangsa atau mangsa
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RESPON IKAN JIKA BERTEMU MANGSA
Menentukan: 1. melarikan diri atau tdk; kapan?
2. ke arah mana?
3. seberapa cepat?
4. seberapa jauh?
Model ekonomi dari jarak reaksi (reaction distance “D”) utk ikan dalam
“pemangsaan” Trawl
2 pilihan TLI saat bertemu
mangsa:
• melarikan diri (fleeing) “F”
• tetap tinggal (remaining) “R”
Jarak saat ikan hrs melarikan diri
keseimbangan antara “F” & “R”
High F kehilangan kesempatan
utk memijah, mencari makan &
energi yg dikeluarkan
High R kematian
Source: Ydenberg and Dill ’ s (1986)
Distance of predators
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AVOIDANCE PATTERN
Deteksi + Bereaksi (pada jarak tertentu) 1. Ke arah mana 2. seberapa cepat
“Ikan lambat menjauh (secara horisontal) dari rangsangan yg datang” namun
“ikan pelagik juga bisa bergerak vertikal thd dasar laut –kebisingan kapal”
Pergerakan vertikal akan mulai terjadi saat mulainya towing dimana kebisingan kapal mereda.
KECEPATAN RENANG
“ Perubahan kecepatan renang terjadi saat perubahan arah renang tdk cukup utk mengurangi makin dekatnya ancaman”
Jika kapal makin mendekat, ikan akan menambah kecepatan renangnya
(kurva “F” semakin curam)
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ZONA 2 (TLI ANTARA OTTER BOARD & BUKAAN JARING)
Posisi Ikan: (1) Langsung berada pada jaring; atau(2) Berada di zona sapuan (antara sayap dan otter boards)
Area jaring: area hingga berakhirnya jaring (codend) area siap tangkapArea zona sapuan: harus digiring agar ikan terarah ke area siap tangkap
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HERDING PATTERN
1. Round Fish: salmon, cod, trout
Habitat: dekat dgn dasar lautRespon: bereaksi thd otter boards yg dilihatnya“Ikan cenderung memilih utk mempertahankanancaman dgn menjaga visual range thd ancaman”Meningkatkan kerentanan mereka thd
penangkapan (vulnerable to capture)
IN
OUT
Keberadaan Pelampung & pemberat-Out visual range: ikan tdk bereaksi-In visual range: bereaksi
!!!! Herding efficiency tali selambar antara otter boards & sayap
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2. Benthic species: flat fish
HERDING PATTERN
Giringan terjadi krn kontak dgn gumpalan pasir (dekat dgn sea bed), sapuan dan otter boards.
Ikan akan bereaksi dlm jarak pendek(tegak lurus thd sapuan)
atau
Ikan akan mengubah lintasan renang, namun tdk akan pernah menuju area jaring(capture zone)
Jaring bag. sayap
Otter board
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RELEVASI KECEPATAN TOWING DAN TLI
Kontak ikan dgn dasar laut, ikan akan:
1. Renang Ikan < towing speed (sapuan)
2. Renang Ikan = towing speed
3. Renang Ikan > towing speed melambat berdiam di dasar laut
poin 2, 3 memiliki possibility utk masuk ke trawl
Recommended Towing speed = 0.2 – 0.6 m/s
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TLI DI DEPAN BUKAAN TRAWL
Bergantung pada TLI di zona 1: avoidance behavior
zona 2: herding behavior
Respon paling umum berenang di depan pemberat (foot gear)
Foot gear
Foot gear
Intensitas cahaya rendahreaksi ikan cepat, jarakperpindahan pendekkontak dgn footgear
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Ikan kelelahan & memiliki kemampuan yg terbatas utk tetap berenang berusaha menghindari kontak dgn jaring & ikan lain
Ikan perenang lambat : mengurangi gerakan langsung menuju codend (kontak dgn ikan lain atau jaring menyebabkan respon baru)
Ikan perenang cepat: tetap berenang sebelum akhirnya menuju codend atau tetap berenang sepanjang jaring trawl escape/lolos
ZONA 3 (TLI DI DALAM JARING)
Konstruksi codend + jumlah ikan yg terkumpul dicodendMempengaruhi durasi ikan dapat berenang
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DESAIN CODEND YG DILENGKAPI BY-CATCH REDUCTION DEVICES (BRD)
A. Super shooter TED (Turtle Excluder Devices)B. Radial Escape Section utk melepaskan ikan perenang cepat dari codendC. Square mata jaring utk lolosnya ikan kecil dari codendD. Square – mesh window/escape panel meloloskan ikan kecil dari codend
Sumber: Eayrs (2007)
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BEBERAPA PENELITIAN
YANG BERKAITAN
DENGAN DESAIN BRD
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REACTION OF JUVENILE FLOUNDER TO GRID
SEPARATORS
Main species : conger eel
By-catch : Japanese flounder
By-catch Reduction Devices (BRD) mengeluarkan by-catch & menahan main species
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BACKGROUND
• Berenang ke bagian belakang codend
• Habitat di dasar laut
• Daya apung rendang
By-catch behavior
• Designed codend with grid separatorGrid Separator
• Vertically/Horizontally oriented bars
• Light/Dark condition
New trawl net design
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BACKGROUND (DISAIN TRAWL NET)
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FUNGSI GRID DALAM DISAIN TRAWL NET
Menghalangi masuknya ikan ke dalam codend
Sebagai “escape vent” (pintu keluar) ikan harus melewati grid
METHODS
FISHING TRIAL mampu menahan main target tapipelepasan by-catch tidak maksimal jumlahnya
UNDERWATER TANK EXPERIMENT menguji grid separator kunci pengembangan BRD yang paling efektif dan praktis
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UNDERWATER TANK EXPERIMENT
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REACTION PATTERNS OF FLOUNDER TO GRID
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THE RESULTS
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NOTES Muncul 3 perilaku ikan yang tidak normal, yaitu :
1. swimming over the grid
2. sticking on the grid
3. passing through the grid , karena :
Model selalu membuat ikan berada pada posisi kelelahan sehingga akan kontak langsung dengan grid
“Forward swimming” sebagai perilaku yang normal tetap mendominasi.
Isakseen (1999) ikan berenang ke mulut/bukaan trawl beberapa saat sebelum lelah dan tidak mampu berpindah dari gris
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NOTES Kondisi terang mendominasi, karena:
Ikan akan lebih mudah untuk mengenali secara visual dan bereaksi terhadap grid yang terus mendekati.
Orientasi bar secara horisontal mendominasi
Glass (1993) TLI dalam melewati grid didasarkan pada bentuk bar dan bentuk tubuh ikan.
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FISHING TRIAL VS TANK EXPERIMENT
Keadaan tank experiment yang berbeda dari the real fishing trial:
1. Semua ikan akan kontak dengan grid
2. Tidak ada tangkapan yang menghalangi bukaan grid
3. Visibility sangat tinggi
GRID SELECTIVITY
Modifikasi alat tangkap (solusi 1 & 2)
Menigkatkan korelasi tank dan fishing trial
Pengenalan bukaan jaring dan grid yang lebih besar.
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GRID SELECTIVITY: PENGARUH JARAK KISI TERHADAP PELOLOSAN
IKAN MELALUI JUVENILE AND TRASH EXCLUDER DEVICE (JTEDS) PADA
SKALA LABORATORIUM (WAHYU, 2008)
Background:
Pemanfaatan SD secaraseimbang
Konservasi
Fisheries Sustainability
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BACKGROUND
PemanfaatanSD secaraseimbang
Selectivitasalat
tangkap
Mengurangihasil
tangkapansampingan(by-catch)
BRD (By-catch reduction Devices)
- JTED(Juvenil & Trash Excluder
Devices)
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PROBLEMS
JTED tidak efektif : hasil tangkapan masih didominasi oleh ikan dengan ukuran tidak layak tangkap.
OBJECTIVES
Perbedaan kisi terhadap tingkat pelolosan ikan skala laboratorium dapat diperoleh jarak kisi yang sesuai untuk meloloskan ikan non target sebagai bahan masukan bagi aplikasi penggunaan JTEDs di lapangan.
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METHODS
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SEBARAN IKAN PADA TIAP KISI
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POSISI JTED TERPASANG PADA
KANTONG JARING
Skala = 1: 3
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TINGKAT PELOLOSAN IKAN
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Dari grafik tersebut juga terlihat perubahan tingkat pelolosan ikan nila. Tingkat pelolosan akan semakin tinggi dengan semakin lebar kisi, hal ini berarti terdapat hubungan linier antara jumlah ikan nila yang lolos dengan penambahan lebar kisi.
Hanya pada ikan patin, perbedaan kisi mempengaruhi pelolosan ikan.
Mahiswara et al., (2004) menyatakan bahwa bentuk tubuh ikan sangat mempengaruhi kemampuan ikan untuk melewati kisi, ikan yang mempunyai bentuk pipih memiliki kemampuan melewati kisi lebih besar dibandingkan dengan yang memiliki bentuk lain.
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bentuk tubuh ikan patin yang secara keseluruhan memiliki perbedaan dengan kedua jenis ikan sebelumnya yang berbentuk pipih. Berdasarkan hasil pengamatan ikan patin memiliki pola renang yang berorientasi keatas sehingga peluang ikan patin keluar melalui kisi JTED bagian front part atau base part lebih besar dibandingkan dengan ikan nila dan bawal.
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MATUR
SUWUUUN….