Continuous Monitoring of Fish Population and Behavior by Instantaneous Continental-Shelf-Scale Imaging with Ocean-Waveguide Acoustics

Transcription

1 Continuous Monitoring of Fish Population and Behavior by Instantaneous Continental-Shelf-Scale Imaging with Ocean-Waveguide Acoustics Principal Investigator Nicholas C. Makris Massachusetts Institute of Technology Department of Ocean Engineering 77 Massachusetts Avenue, Room Cambridge, MA Partners Nicholas C. Makris, Massachusetts Institute of Technology Purnima Ratilal, Northeastern University Redwood W. Nero, Naval Research Laboratory J. Michael Jech, National Marine Fisheries Services Lilimar Ruhlmann, WaveTech Engineering, LLC John R. Preston, Penn State University Edward K. Scheer and John Kemp, Woods Hole Oceanographic Institution Edward Rynne, Space and Naval Warfare Systems Command Michael Einhorn, Naval Facilities Engineering Services Center William Metzger, Marine Acoustics Inc. Duration of Effort: 3 years ABSTRACT A new lower frequency acoustic method is proposed for (1) instantaneously detecting, imaging and spatially charting fish populations over continental-shelf scales, and then (2) continuously monitoring the areal densities and behavior of these fish populations over time. It is proposed that this new method be applied to explore the abundance, temporal and spatial distributions and behavior of fish populations in the Gulf of Maine on and near Georges Bank, a marine ecosystem being studied in the Census of Marine Life program. To provide verification of areal fish population density and species identification, the new method will be used in conjunction with simultaneous measurements of fish population by conventional line-transect methods that employ direct sampling with net and trawl as well as standard higher frequency acoustics. Since the new method can continuously monitor wide areas, it will be used to quantitatively assess the impact of fish behavior and distributions on conventional line transect methods, which are known to greatly under-sample fish populations in time and space. Correlation of behavior, including school and shoal formations, migrations, interactions and fragmentations, with local geologic and oceanographic habitat will be made. The

2 impact of remotely sensed fish behavior on the detection and enumeration of fish population and abundance by conventional line transect methods will be assessed. OBJECTIVES The overall goal of this project is to continue the development of a novel low to mid frequency acoustic system referred to as Ocean Acoustic Remote Sensing (OARS) to instantaneously detect, enumerate and spatially chart living marine fish populations and assemblages over continental shelf-scales and then continuously monitor the areal densities and behavior of these populations. The basic elements of the new method have recently been successfully applied to detect, monitor and enumerate fish populations and their behavior over wide areas of the New Jersey Continental Shelf in May 2003 [1, 2]. There, the new method has been shown to yield areal fish densities consistent with those simultaneously measured with conventional fish finding sonar [1]. Such continuous widearea sensing is possible because OARS relies upon the capacity of the continental-shelf environment to behave as an acoustic waveguide [3, 4] where sound at low to mid frequencies propagates over long horizontal ranges, tens to hundreds of kilometers, via trapped modes that suffer only cylindrical spreading loss with relatively low attenuation. This is in contrast to the spherical loss and extremely high volumetric attenuation suffered by conventional fish finding sonar (CFFS) which operates at much higher frequencies, tens to hundreds of kilohertz, and much shorter ranges, tens to hundreds of meters, in primarily downward directed beams [5, 6]. This enables OARS to use sound that is significantly less intense than CFFS at the fish, typically by more than three orders of magnitude [2, 6]. The primary objective of this proposal is to explore the population distributions and behavior of living marine fish in the Gulf of Maine on and near Georges Bank with the new OARS technology. The Gulf of Maine is one of the primary marine ecosystems currently under study in the Census of Marine Life [12]. It includes Georges Bank, one of the most important marine fisheries on the east coast of the United States [12]. OARS will be used to instantaneously (within 80 seconds) image fish population density in an area of roughly 120 km diameter or 11,300 km2 from central locations on the northern flank of Georges Bank. Fish population centers will be instantly detected and spatially charted in absolute spatial coordinates as well as in reference to local seafloor elevation or bathymetry, an essential element in the Gulf of Maine habitat. The morphology of large fish shoals and their spatial relationship to smaller schools and assemblages as well as bathymetry and ocean temperature, will be quantitatively described. These large areas will be continuously monitored for temporal and spatial changes in fish population density. Movies will be made of the population density of fish over these large areas by concatenating consecutive images in a manner similar to that done in New Jersey Continental Shelf applications [7-10]. Interactions between population centers, including those between smaller schools and larger shoals, will be documented. Migrations of fish populations over time will be documented.

3 A specific objective of this exploration will be to monitor the temporal and spatial population densities of herring, a fish of major ecological and commercial importance, on the northern flank of the George's Bank, where they are known to congregate in large quantities [13]. This will include an attempt to continuously monitor the southern migrations of herring from the deeper waters of roughly 200m where they feed to the shallower waters of roughly 50-m where they spawn in the September to October time frame [13]. An attempt will be made to monitor the vertical migration of herring to depths near the sea surface at night and back to much deeper feeding depths during the daytime, since this is expected to be associated with a significant increase in the target strength per individual due to swim bladder resonance changes [14]. Many other fish species inhabiting the same area, such as haddock, various species of hake, pollock and redfish [15], and possibly mackerel, are also expected to be detected and imaged by the OARS system. Initial species identification will be made by the concurrent net and trawl surveys as well as CFFS. Another objective will be to investigate the limits of taxonomic resolution inherent to the OARS system, and to use OARS imagery to assess the taxonomic limits of more conventional systems that rely upon sparse line-transect surveys that significantly undersample fish populations in time and space. Interspecies interactions could then be monitored since widely separated population centers can easily be identified by the continuous spatial coverage of OARS imaging but are easily missed by conventional line transect approaches. The spatial distributions and behavior detected by OARS could then be used to more quantitatively calibrate abundance estimates made by under-sampled line transect methods and to determine optimal temporal and spatial scales of sampling. References 1. N. C. Makris, P. Ratilal, D.T. Symonds and R.W. Nero, "Fish population and behavior revealed by instantaneous continental-shelf-scale imaging,'' submitted to Science. 2. N. C. Makris (Editor), Geoclutter Acoustics Experiment 2003 Cruise Report, MIT Cambridge MA (2003). 3. G. V. Frisk, Ocean and Seabed Acoustics, A Theory of Wave Propagation, Prentice Hall, New Jersey, (1994). 4. L. M. Brekhovkikh and Y. P. Lysanov, Fundamentals of Ocean Acoustics, Springer, New York (1982). 5. O. Sund, Nature, Echo sounding in fisheries research, Vol 135, 953 (1935). 6. O. A. Misund, ''Underwater acoustics in marine fisheries and fisheries research,'' Review in Fish Biology and Fisheries, Vol. 7, 1-34 (1997).

4 7. N.C. Makris, P. Ratilal, Y. Lai, S. Lee, D. T. Symonds, L.A. Ruhlmann, R.W. Nero, J.R. Preston, E.K. Scheer and M.T. Garr, "Long-range acoustic imaging of the Continental Shelf Environment reveals massive fish schools: 2003 Main Acoustic Clutter Experiment," J. Acoust. Soc. Am., Vol. 114, 2375 (2003). 8. D.T. Symonds, P. Ratilal, R.W. Nero and N.C. Makris, "Fish schools are the dominant cause of long-range active sonar clutter in the New Jersey Continental Shelf: Quantitative correlations," J. Acoust. Soc. Am., Vol. 114, 2375 (2003). 9. D. T. Symonds, P. Ratilal, R.W. Nero, and Nicholas C. Makris, ''Inferring fish school distributions from long range acoustic images: Main acoustic clutter experiment 2003,'' J. Acoust. Soc. Am., Vol. 115, 2618 (2004). 10. N. C. Makris, P. Ratilal, D. T. Symonds and R. W. Nero, ''Continuous wide area monitoring of fish shoaling behavior with acoustic waveguide sensing and bioclutter implications,'' J. Acoust. Soc. Am., Vol. 115, 2618 (2004). 11. L. Mayer, Y. Li, and G. Melvin, ''3D Visualization for pelagic fisheries research and assessment,'' J. Marine Science, Vol. 59, , (2002) J. M. Jech, W. Michaels, W. Overholtz, W. Gabriel, T. Azarovitz, D. Ma, K. Dwyer, and R. Yetter, ''Fisheries acoustic surveys in the Gulf of Maine and on Georges Bank at the Northeast Fisheries Science Center,'' Proceedings of the Sixth International Conference on Remote Sensing for Marine and Coastal Environments, Charleston, South Carolina, 1-3 May J. H. S. Blaxter, ''The Herring: A Successful Species?,'' Can. J. Aquat. Sci., Vol. 42, (1985) R. W. Nero, C. H. Thompson and J. M. Jech, ''In situ acoustic estimates of the swimbladder volume of Atlantic herring (Clupea Harengus,'' J. Marine Science, Vol. 61, (2004). 17. J. S. M. Rusby, M. L. Somers, J. Revie, B. S. McCartney, A. R. Stubbs, ''An experimental survey of a herring fishery by long-range sonar,'' Marine Bio. Vol. 22, (1973). 18. N. C. Makris, ''Imaging ocean-basin reverberation via inversion,'' J. Acoust. Soc. Am. 94, (1993). 19. N. C. Makris and J. M. Berkson, ''Long-range backscatter from the Mid-Atlantic Ridge,'' J. Acoust. Soc. Am. 95, (1994).

5 20. N. C. Makris, L. Avelino, R. Menis, ''Deterministic reverberation from ocean ridges,'' J. Acoust. Soc. Am. 97, (1995). 21. N. C. Makris, C. S. Chia and L. T. Fialkowski, ''The bi-azimuthal scattering distribution of an abyssal hill,'' J. Acoust. Soc. Am. 106, , (1999). 22. C. S. Chia, L., N. C. Makris and T. Fialkowski, ''A comparison of bi-static scattering from two geologically distinct abyssal hills,'' J. Acoust. Soc. Am. 108, (2000). 23. P. Ratilal, Y. Lai, D.T. Symonds, L.A. Ruhlmann, J. Goff, C.W. Holland, J.R. Preston, E.K. Scheer, M.T. Garr and N.C. Makris, "Long range acoustic imaging of the Continental Shelf Environment: The Acoustic Clutter Reconnaisance Experiment 2001," J. Acoust. Soc. Am. 117, (2005). 24. N. C. Makris (Editor), Geoclutter Acoustics Experiment 2001 Cruise Report, MIT Cambridge MA (2001). 25. Purnima Ratilal, ''Remote Sensing of Submerged Objects and Geomorphology in Continental Shelf Waters with Acoustic Waveguide Scattering,'' MIT Doctoral Thesis, Makris Supervisor, June N. C. Makris, ''The effect of saturated transmission scintillation on ocean acoustic intensity measurements,'' J. Acoust. Soc. Am. 100, (1996). 27. N. C. Makris, "A foundation for lgarithmic measures of fluctuating intensity in pattern recognition," Optics Letters 20, (1995). 28. N. C. Makris and P. Ratilal, "A unified model for reverberation and submerged object scattering in a stratified ocean waveguide," J. Acoust. Soc. Am., Vol. 108, (2001).