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Samantha Velasco1, Haley K. Glasmann2, & Dr. Kevin Boswell2
1Eckerd College
2Department of Biological Sciences, Florida International University
Diel vertical migration is the movement of animals between the surface and mesopelagic layers. It is a ubiquitous feature across the global ocean and is considered the largest daily mass movement of animals in addition to playing a pivotal role in the biological carbon pump of oceanic ecosystems. The adaptive driver of diel vertical migration is to avoid visual predation as animals are concealed in the darkness of night. Therefore, the metabolic cost of this movement outweighs the risk of mortality for these animals. The isolume hypothesis suggests that organisms follow a preferred or optimal level of light to begin diel vertical migration. Moonlight has been rarely studied as a contributing factor for this hypothesis. The DEEPEND Consortium conducts yearly research cruises to monitor the deep-water community in the northern Gulf of Mexico. Using the DEEPEND data, we investigated the correlation between lunar phase and diel vertical migration in the northern Gulf of Mexico with 18kHz echosounders. For each night of the research cruises, we created echograms and quantified migrating layers using Echoview software. We then correlated those nights with moon phase data made available by NASA. We were able to determine a strong correlation between moonlight (%) and Sv (volume backscatter), in addition to differences regarding the speed and amplitude of migrating fish on nights with a full moon versus nights with a new moon. As there is an increasing global interest in harvesting mesopelagic organisms, the implications of this study will not only add to the isolume hypothesis, but it can also be used in tandem with other diel vertical migration research to inform deep-sea resource management and to understand the potential ramifications of exploiting the deep-sea.
What is the field of active acoustics? Will it endanger marine organisms?
Active acoustics means producing a pulse of sound and listening for the echoes resulting from that sound being backscattered. The backscattered sound is a proxy for biomass in the water column. In other words, when sound travels through a water column, it bounces off of anything in its path. The more times it bounces and scatters, the higher we can estimate the number of organisms in the water column. This makes active acoustics a non-invasive way of studying diel vertical migration.
Why should this study be of interest to you?
There is currently a vested interest in harvesting deep-sea organisms, such as those pictured. This study can be used in tandem with other diel vertical migration research to better inform deep-sea resource management. If we have an estimation of when and where these mesopelagic organisms migrate in the water column, we will be better prepared to utilize them in the future.
For more information, contact: srvelasc@eckerd.edu
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