Cyclic fluctuations, frequency, and levels 

 of biological sounds are investigated with 

 sound amplifying and recording equipment 

 (Noise Measuring Set AN/PQM-IA). Since 

 the tower has a low noise level (it contains 

 no generators and all small motors can be 

 stopped during critical experiments), the 

 weak biological sounds can be distinguished 

 from the background. 



YELLOWFIN CROAKER 

 Vmbrina roncctdor 



SPOTFIN CROAKER 

 Roncador Steamsi 



The long period (25- to 

 40- second) variations in 

 ambient noise observed in 

 the 300- to 800-c/s band 

 increase in intensity dur- 

 ing the late spring and 

 summer months (contoured 

 in 1, 5, and 10 dB above 

 normal background). Inten- 

 sities reach a maximum 

 just after sunrise and at 

 sunset. 



M J J A 



MONTHS 



49 



