Our Midwater Workhorse: The MOC10

Hi Everyone, Zan here to share the workhorse of our operations....

The heart of our midwater animal sampling program is the 10-m² MOCNESS, which stands for “Multiple Opening-Closing Environmental Net and Sensing System”. That’s a pretty long name, so let’s break it down! The 10-m² part refers to the size of the MOCNESS frame: ours is pretty large, which is great for sampling the “micronekton” (animals roughly 2 – 20cm in size), but there are lots of other sizes if you prefer to sample smaller animals.

Photos:  Varying stages of the MOC prep that is involved before it is deployed.

The “Multiple” part of the name means that the MOCNESS is rigged up with several different nets. Unlike other fishing nets that might stay open the whole time you’re fishing with it, the MOCNESS has a number of different nets that can be opened and closed (the “Opening-Closing” part) at whatever depths we choose,  allowing us to sample specific depths of the water column. We have six nets on our 10-m2 MOCNESS, and one of our jobs is to decide what depths to target so that we get the best possible catches. Given that the animals we’re interested in catching all have specific depths that they prefer to live at during the day, and often migrate to different ones at night, having the ability to sample exact depth ranges is incredibly important for us to understand the ecology of our midwater animals and their behaviors. We make good use of our fisheries acoustics to help us decide where to fish!

 Photo:  Examples of Lanternfish that are caught in the MOC

The other parts of the name relate to the sensors that are mounted on the MOCNESS frame to help us understand the physical and chemical properties of the water column as we fish, and to make sure that the MOCNESS is moving correctly through the water. To make sure the MOCNESS is fishing correctly, we monitor the angle of the frame in the water, the horizontal and vertical speeds, and the depth of the gear in the water column. This last one is especially important because it tells us when to send a signal to the MOCNESS to switch to the next net. Different environmental sensors could be used, but the ones we’re mostly using include depth, temperature, and salinity, and we compare those to the CTD (conductivity-temperature-depth) casts that we’re making.

Photos:  Example of the MOC profile when nets are open/closed;  Zan's MOC monitoring station