Seeing with Sound

Hi Everyone! Haley Glasmann here, and I am back on the R/V Point Sur for my second DEEPEND research cruise. I’m a PhD Student in the Marine Ecology and Acoustics Laboratory at Florida International University, and I’m here with my advisor, Dr. Kevin Boswell. Our role on this cruise is to set-up and monitor the scientific echosounders. It takes a lot of work upfront to prepare our acoustics for deployment in the field, but all the hard work is worth it!

Haley Glasmann and Dr. Kevin Boswell assembling “The Pod.” 

Dr. Kevin Boswell, Haley Glasmann, and Dr. Heather Bracken-Grissom with “The Pod” assembled after a hard day’s work.

 The use of active acoustics in otherwise hard to reach marine systems, where video data and diver surveys are infeasible, can provide information about distribution and behavior of organisms. Every 5 seconds, we get 1 pixel of information. As the ship drifts along, we get an echogram, which allows us to visualize our data in real time! An 18kHz echogram is shown below, with depth on the y-axis and time on the x-axis. The brighter colors are indicative of the deep scattering layer community, and the yellow line represents the CTD track. Around 19:45 you can see the upward diel vertical migration, where organisms are moving into the upper water column for the night to feed. Mounted on the CTD is our Wide-Band Autonomous Transceiver (WBAT), which allows us to send an echosounder to depth. Integrating the ship mounted echosounders with that of the WBAT allows us to discern individual organisms within the deep scattering layer. 

Although the image below may just look like a bunch of rainbow blobs, the community in question is generally referred to as mesopelagic micronekton, ranging in size from 2-20cm, comprising fishes, siphonophores, crustacea, and other zooplankton. Many of these organisms take part in the diel vertical migration and play a key role in oceanic carbon cycling, moving between two to six billion tons of carbon per year. Mesopelagic micronekton are also valued for their use as “potentially consumable protein,” some countries already target them for use for aquaculture fish feed, and for use in pet food. 

18kHz echogram with WBAT echogram inlaid.

The Gulf of Mexico is a mesopelagic diversity hotspot, and I aim to further investigate how these organisms are arranging in space and how that changes as they move vertically. Learning more about the mesopelagic micronekton will allow us to develop a better understanding of niche partitioning in the deep-sea, as well as being informative for fisheries management.

A few mesopelagic micronekton that were caught in the MOCNESS (Multiple Opening-Closing Net and Environmental Sensing System). 

To keep up with more of my acoustic adventures, follow @scubahaleykat and @boswelllab on Instagram!