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M arek Moszynski , Andrzej Stepnowski

ICES ASC 17-21 September 2007, Helsinki, Finland ICES CM 2007/H:08 Effects of environmental changes on the biology, physiology, and behaviour of pelagic fish.

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M arek Moszynski , Andrzej Stepnowski

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  1. ICES ASC 17-21 September 2007, Helsinki, Finland ICES CM 2007/H:08 Effects of environmental changes on the biology, physiology, and behaviour of pelagic fish The influence of fish morphological and behavioural parameters on acoustic data in algorithmic reconstruction of fish length distribution • Marek Moszynski, Andrzej Stepnowski Gdansk University of Technology Poland

  2. ICES ASC 17-21 September 2007, Helsinki, Finland ICES CM 2007/H:08 Effects of environmental changes on the biology, physiology, and behaviour of pelagic fish The influence of fish morphological and behavioural parameters on acoustic data in algorithmic reconstruction of fish length distribution Abstract The paper investigates the algorithm for estimation the fish length distribution from acoustic target strength data. The theory of scattering from a tilted cylinder is used for modelling the fish directivity pattern of swimbladdered fish. The model allows formulating the dependence of target strength on two main components:fish maximum target strength and the fish directivity pattern. As both terms depend on fish length, the inverse technique could be used to reconstruct unknown fish length distribution from acoustic data, when morphological parameters of fish are properly assumed. However, as it is shown, the algorithmic approach is very sensitive to some of behavioural parameters of swimming fish. Thus, although the effect of unknown fish tilt angle could be partially removed by statistical processing, the mean value of fish tilt angle still may produce large errors. The method and its results are verified on actual data acquired during the survey and compared to trawl catches.

  3. regression models Introduction (1) Fish echo processing chain: acoustical measures physical measures Echo Level E Target Strength TS Fish length L Fish Biomass Q • measurements: • ex situ • in situ Catch data Ei = SL+RS + TSi(li, i , zi,, fo )+ 2B(i ) - 2TL( Ri, α)

  4. Introduction (2) MEAN VALUE PROCESSING < l > • Sample catch • Regression relation Fish length L pTS INVERSE PROCESSING pl • Backscattering model • Tilt angle statistics

  5. backscattering model -tilt angle statistics -backscattering model Fish length estimation • problems: • unknown titl angle during ensonification • unknown fish directivity pattern pl pTS0 pTS

  6. Fish backscatter modelsfor swimbladdered fish simple • tilted cylinder • - Haslett (1962) • finite bent cylinder model • - Stanton (1989) • low resolution acoustic model • - Clay (1991) • Kirchhoff ray mode model (KRM) • - Clay, Horn (1994) • boundary element model • - Foote, Francis (2002) precise

  7. Haslet model for swimbladdered fish • Haslett, 1962 • swimbladder is approximated by a combination of: • a hemisphere, • a short cylinder, • a cone of fixed dimensions relative to the fish fork length. • then this shape is modified to: • a cylinder maintaining their geometrical cross section.

  8. Methods

  9. Methods (2)

  10. Backscatter theory (1)  +0 k aecb lecb

  11. Backscatter theory (2)

  12. cos  = 1/r 1: U (0,r) 1 = rup()=sin p()=2 /  (0,/2)

  13. Tilt angle dependance (1) f = 38kHz 0=8° lecb=L/4

  14. Conditional fish beam pattern PDF TS0 [dB] Df [dB]

  15. Statistical processing EMS Inversion TS pTS inversion random generator 

  16. Processing example a) b) c) d) a) acoustically measured target strength TS at 200kHz b) conditional PDF of the fish directivity pattern assuming swim bladder tilt angle 5 c) estimated maximum target strengthPDF d) reconstructed fish length distribution along with the catch histogram (in cm)

  17. Case study 1 • NOAA/Alaska Fisheries Science Center - summer 2002 -Bering Sea • provided by Neal Williamson (PMEL - Seattle)

  18. Survey data • Simrad EK500 v.5.30 echosounder • 38kHz split beam transducer • logged w/ Sonardata's Echolog 500 • 14-07-2002 8:57 – 11:22 am • 6776 pings (540MB) • 2002 tracks of walleye pollock • (Theragrachalcogramma)

  19. Survey data analysis [dB] [cm]

  20. Survey data analysis (2) [dB] [cm]

  21. Survey data analysis (3) Reconstruction of fish length PDF for different mean swimbladder tilt angle 0 along with estimate from catch data. Upper sequence for 38kHz and lower for 120kHz. X-axis represents fish length in [cm].

  22. Survey data analysis (4) Root mean square error function obtained from 38kHz and 120 kHz estimates versus assumed swimbladder tilt angle

  23. Survey data analysis (6) Estimates of length PDF for mean swimbladder tilt angle 0=7 along with catch data

  24. Tilt angle dependance (3) Target strengths as a function of tilt angle for a 31.5cm pollock at dorsal aspect at 38kHz and 120kHz Foote (1985) Walleye pollock Theragra chalcogramma (Horne - Radiograph Gallery)

  25. Case study 2 • R/V “G. O. Sars” • March 17 to April 5, 2004 • Lofoten 2004 survey • Lofoten islands, from 67oN to 70oN, • spawning grounds of North East Arctic Cod • shelf between 500 m to about 50 meters • sea temperature 6.8 – 7.1oC from 40–300m • 5 Simrad EK60 split beam echosounders

  26. Experiment • standard sphere calibration methods • CU64 (18 kHz), CU60 (38 kHz) , WC38.1 (70, 120 and 200 kHz) • transducers mounted in one of the instrument keels of the vessel • full half-power beam widths 7o, except for the 18 kHz (11o) • the transmitted pulse duration was identical on all frequencies - 1.024 ms • the Bergen Echo Integrator, BEI. • heave, roll, pitch and yaw Seatex MRU 5 -Simrad EM 1002 at 10 Hz • CTD observations (Sea-Bird SBE9). • trawling partly on fixed locations, • mostly on registrations for identification of the targets and for • biological sampling. • Campelen 1800 bottom survey trawl • Åkratrawl, a medium sized midwater trawl • Standard biological parameters were measured on all catch samples, • individual total length, weight, gonad and liver index, age and stomach content.

  27. Trawl data

  28. 70 kHz 38kHz 120kHz 200 kHz

  29. Survey data • provided by Institute of Marine Research - Bergen Norwegian cod echoes at depth range 100-160m acquired with 18kHz system

  30. Survey data • provided by Institute of Marine Research - Bergen Norwegian cod echoes at depth range 100-160m acquired with 38kHz system

  31. Survey data • provided by Institute of Marine Research - Bergen Norwegian cod echoes at depth range 100-160m acquired with 70kHz system

  32. Survey data • provided by Institute of Marine Research - Bergen Norwegian cod echoes at depth range 100-160m acquired with 120kHz system

  33. Survey data • provided by Institute of Marine Research - Bergen Norwegian cod echoes at depth range 100-160m acquired with 200kHz system

  34. Target strength data

  35. Results 38kHz 70kHz 120kHz 200kHz 2° 5° 8°

  36. Tilt angle dependance (3) TS/length relationship on tilt angle for atlantic codTS = 20log L + B20, McQuinn, Winger (2002)EK500 38kHz SB 7 Atlantic cod Gadus morhua (Horne - Radiograph Gallery) B20 

  37. Problems

  38. Conclusions

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