Target strengths & baby bunnies

We've been working to understand the sizes of acoustic targets we've been detecting in Lake Geneva. These analyses will help us interpret the acoustic data properly. We make frequency distribution plots (right hand plot below) and plots of target strength versus water column depth (left hand). Here we limited the analysis to the uppermost 4-25 m of the water column. Each crosshatch is an echo that meets what we call single echo detection criteria or SED criteria. The fish have target strengths that are more or less > -60 decibels (dB). We also see a distinct mode at -75 dB, especially with the 123 kHz transducer. This is, in all likelihood, an invertebrate, but we will need to process our zooplankton samples to know for sure. At this point we are speculating it is either Leptodora or possibly Bythotrephes, but that is pure speculation. It is too large of a target to be Mysis. We also have some acoustic noise. We can tell this because it increases in magnitude with increasing depth. We remove noise before attempting to estimate abundance. The distinct trough between the noise and the "invertebrate" in the frequency distribution down to 25 m is a good situation to have because it seems the "invertebrate" may be detectable down to the greatest depth of interest (25 m).

The bunny at the lab became a mother bunny last night. The newborns are hidden in the nest. Thanks to Valentin for showing me this miracle of life. I made everyone read about boring acoustic data before getting to the bunny story.