Acoustic Technology -- Summary and Recommendations

## Summary and Recommendations

In addition to the recommendations documented in the individual working group reports, several common themes evolved from the meeting.

- It was recognized that development, acquisition, and use of new sampling technology was needed to successfully address GLOBEC science issues. Acoustical and optical technologies were acknowledged as leading candidates from which the necessary tools could be drawn to support the pursuit of GLOBEC's science goals.

- Based on their quasi-continuous sampling characteristics, acoustical and optical tools deployed in various ways (e.g., towed or hull-mounted sensors vs. moored, bottom-mounted, or drifting sensors) are essential to relating small-scale processes important at the level of the individual to large-scale processes that impact populations. This concept was described as "nesting" of sensors that measure small-scale temporal and spatial phenomena within measurements at incrementally increasing temporal and spatial scales up to those that include populations and their dynamics.

- Several groups stressed the importance of the mode of deployment of any acoustical, optical, or integrated sensor package. The same mode is not, in general, appropriate for all the different kinds of GLOBEC science questions. The ability to use an instrument in a diversity of deployment modes, e.g., cast, towed, hull-mounted, bottom-moored, etc., was considered a valuable sensor characteristic, substantially enhancing the usefulness of a particular instrument.

- Each of the working groups recognized the value of examining the same distribution of animals with more than one frequency of sound. It was recognized that the range and numbers of frequencies required depends on the sizes of the animals present, which animals present are of interest, their abundances, their physical characteristics, their distribution, and the mode in which the sensor is to be used.

- Several groups noted that modularity, standardization of instrumentation, and simplicity of operation and deployment were important. At the same time, arguments for versatility, flexibility in deployment mode and signal processing algorithms, sophisticated internal data processing, and low cost were presented. On the surface some of these criteria seem conflicting, thus requiring thoughtful tradeoffs when designing instrumentation.

- It was determined that the integration of acoustical and optical technology could yield synergistic benefits and that the technologies are complementary. Acoustic sensors could place optical measurements in the context of larger scale biological distributions. They may also be used to detect rare organisms that may prey on the relatively small and more numerous animals under study with the optical system. Acoustic sensors could also contribute data on vertical migration and swimming behavior to aid in better understanding optical observations. Optical data could provide important measurements of animal orientation, provide independent information on particle size spectra, and offer a potential for taxonomic identification of acoustically sensed individuals and distributions (e.g., aggregations, schools, patches, layers).

- There was a strong sense that sampling of both the biological environment (e.g., with acoustics and/or optics) and the physical environment (temperature, salinity, light, currents, turbulence, etc.) should be done synoptically rather than serially. There was also a sense that traditional methods will remain important in sampling the marine environment, but that the use of alternative sensors will result in major improvements in the efficiency of these conventional sampling tools.

- The establishment of data archiving protocols to facilitate long term (10's of years) use of data is explicitly recognized as a particular problem for acoustical data as it is for GLOBEC data in general.

- In some cases, access by the community of biological oceanographers to complex bioacoustic instrumentation is limited by acquisition cost and the multidisciplinary talents (electronics, acoustics, and machine level programming) required to operate, calibrate, adapt, and maintain such gear. The establishment and staffing of a limited number of "facilities" or "teams" to provide and maintain bioacoustic devices for data collection under the direction of individual or groups of investigators, is recognized as a viable approach to expansion of the biological communities' access to such devices.

- Finally, there was a consensus that there was a need for continued basic research and development in order to advance the state-of-the-art in remote underwater sensing of marine animals. Specifically, advances would be welcomed in the following areas:

  1. Development of new methods for quantitative combination of multifrequency acoustic data;

  2. Continued analytical research and supporting measurements directed towards the development of better and more comprehensive descriptions of acoustic scattering from all marine genera (e.g., adult fish, larval fish, micronekton, macrozooplankton and small zooplankton); and

  3. Development and validation of methods for quantitative combination of multisensor data (i.e., data fusion).