This panel shows the acoustic backscatter from the ADCP measured across the entire early morning transect we used to verify the features in the model and remotely sensed data (The map of our track is in the last post). Inshore at mid depth there is a region of low backscatter (purple). Offshore there are areas of high scattering (pale blue & green) at mid-depth and deep. The ship and pole arm on which the acoustic transducers are mounted make a lot of turbulence as they move through the water. As a result it is impossible to distinguish sound scattered by the turbulence or by particles at the surface.
We combine visualizations of the acoustic and CTD data to decide how deep to tow the nets. The 5 plots below overlay the CTD profiles on top of the acoustic images of the ocean made with fishery hydroacoustics right before we fish each net. In all the plots the colored lines represent the following water column characteristics: Red=salinity, dark blue=temperature, light blue=oxygen, green=Chlorophyll-A pigment of plants, and black=turbidity, or tiny particles in the water column.
After taking this CTD cast and looking at the acoustics at this station furthest offshore we decided to fish a net from 0 to 7 meters to capture plankton at the surface. We then used a second net to fish between 7 and 25 meters. This is the best we can do with the equipment we have. A 5 net electronic opening and closing net would much better but also would cost about $200k when we got through with the necessary wiring and electronics on the boat. So the net we have will have to do for a while. In the surface tow at this station we caught a baby seahorse and lobster.
Letting the tucker trawl out to fish.
Acoustic image and CTD casts at station 2 (see previous post for map) Something big (the blue streak) was rising to the surface here (No it wasn't the CTD).
Acoustic image and CTD casts at station 3 (see previous post for map)
Acoustic image and CTD casts at station 2 (see previous post for map)
And below is the acoustic image and CTD casts at station 1 closest to the beach near Sandy Hook (see previous post for map). Their often eem to be more scattering layers that coincide with steps in the density of the water along the shoreline near Sandy Hook because the flow of freshwater from the Hudson River plume pulses in with the tide. However the vertical structure of the water column in New Jersey seems to be relatively simple this year perhaps because it has been so dry (see earlier post).