EVALUATING DRIVERS OF DIEL VERTICAL MIGRATION IN FISH AND MYSIS WITH SURFACE DRONES IN LAKE SUPERIOR

Diel vertical migrations (DVM) are common in marine systems and lakes. In the Great Lakes, Mysis diluviana (hereafter Mysis) migrate upwards at night to feed on other plankton and then retreat to deeper water at dawn to avoid fish predators. Mysis migrations are closely tracked by various fish species which feed upon them. The advent of modern surface drones with multi-week endurance allows examination of DVM across large spatial scales and with high temporal resolution. We deployed two uncrewed surface vessels equipped with 120 kHz Simrad EK80 transducers in western Lake Superior from August to September of 2022. The timing of Mysis and fish migrations, their average depth throughout the night, and how close to bottom they appeared during the day were measured. We compared these to moon phase, water depth, and sunrise/sunset. After the initial ascent to within 5 to 10 meters of the surface, the mysid layer typically deepened and sometimes separated into two layers. In deep waters >200 m, Mysis remained suspended in the water column at about 220 m depth during the day. Coregonids, likely kiyi (Coregonus kiyi), migrations were tightly coupled to these mysid migrations, but the fish tended to be distributed above the maximum density mysid layer during both day and the migration phase; fish remained below the mysid layer during the night. The rate of downward fish migration at dawn was faster than the upward migration rate during dusk, mirroring the rate of the mysid migration. The use of drones allowed us to explore the details of these DVMs for the first time and their consistency across space in one of the world’s largest lakes.

Primary Presenter: Thomas Evans, Cornell University (tme33@cornell.edu)

Authors:

Kayden Nasworthy, Cornell University  (kcn33@cornell.edu)

Lars Rudstam, Cornell University  (lgr1@cornell.edu)

Suresh Sethi, Brooklyn College, CUNY  (suresh.sethi@cornell.edu)

Daniel Yule, United States Geological Survey  (dyule@usgs.gov)

David Warner, United States Geological Survey  (dmwarner@usgs.gov)

Hannah Blair, Cornell University  (hbb59@cornell.edu)

James Watkins, Cornell University  (jmw237@cornell.edu)

Peter Esselman, United States Geological Survey  (pesselman@usgs.gov)