INTRODUCTION 



Since November 1964, the U. S. Naval Oceanographic Office has been 

 conducting an intensive investigation of volume reverberation caused by marine 

 organisms in the oceans. Practically speaking, volume reverberation can be 

 defined as the masking of desired target returns by marine organisms which, by 

 virtue of their sound scattering properties, intrude upon the acoustic domain of 

 the Navy. The volume scattering strength of the water column is required to 

 evaluate sonar performance in a given area. Our goal, however, is ultimately 

 to provide a prediction scheme which will take into account the fact that scatter- 

 ing strength values show geographic, diel, and seasonal variations, reflecting 

 the biological character of the phenomenom. Implicit in this requirement for 

 prediction, then, is the need to understand the environmental and biological 

 factors which cause variability in scattering strengths. 



The results presented in this report are based on biological, environmental, 

 and acoustic data collected during the preliminary research cruises conducted by 

 this Office in the western North Atlantic Ocean before May 1967 (Figure 1). 

 Most of the acoustic data, and some environmental data have already been 

 reported (Gold, 1966; Farquhar, 1966; Gold and Van Schuyler, 1966; Van Schuyler, 

 1967; Van Schuyler and Hunger, 1967). The limitations imposed by collecting 

 methods do not permit firm conclusions about causal relationships. However, 

 analysis of the data can indicate guidelines for future work on this problem. We 

 have also indulged in some speculative considerations based on one series of 

 measurements east of the Bahama Islands (Gold and Van Schuyler, op. cit.). A 

 list of the operations and stations at which biological collections were made is 

 included (Appendix A) along with a check list of the species of fishes collected 

 (Appendix B). 



METHODS 



The biological collections before March 1967 were made with a B6 Multiple 

 Plankton Sampler (MPS). Collections taken during a cruise in March-April 1967 were 

 made using a six-foot Isaacs-Kidd Midwater Trawl (I KMT) with a General Motors 

 Mark III Discrete Depth Plankton Sampler (DDPS) attached to the cod end. The 

 Be MPS is pressure actuated and has three open-closing plankton nets, each pro- 

 grammed to open and close at specified depths (Be, 1962). The General Motors 

 DDPS is an electrically operated four-chambered sampling device which permits 

 samples to be taken at discrete depths (Aron et al., 1964). Electronics housed 

 in the spreader bar of the net telemeter information back to the ship about the 

 depth of the net and m situ temperature, but because the pressure sensor was 

 limited to a depth of 500 meters, all of the tows taken were shallow. 



