Capture and Release of Minke Whales Offers New Research Opportunities Including Measurements of Mysticete Hearing

Abstract

Knowledge about species-specific hearing is vital to assessing how anthropogenic noise impacts marine mammals. Unfortunately, no empirical audiogram exists for any mysticete whale. We therefore developed a catch-and-release method to assess hearing in a small mysticete, the minke whale (Balaenoptera acutorostrata). Stationary lead nets were placed to intercept migratory routes and direct animals into an ocean basin enclosed by nets and islets, while another net was pulled across the entrance once a whale entered the basin. The whales were then slowly corralled into a modified aquaculture pen using a net suspended between two boats. Subsequently, the water volume available to the whales was gradually reduced by raising the pen net by hand until the whales were secured in a "hammock" between the floating pen ring and a raft. From the raft, researchers could access the whales to monitor their health, apply instruments for hearing tests, or other research objectives, and attach tags to monitor the movements and diving behavior of the whale post-release. The method is a slow and controlled procedure, allowing continuous monitoring, and quick release of the whales, if needed. In the first three field seasons employing the method, three animals were caught for research procedures. Initial hearing measurements using auditory evoked potentials were successfully completed. After release the animals resumed migration and dive behavior were considered normal. Our observations demonstrate that minke whales can be safely guided via moored net barriers, corralled into an aquaculture pen, and safely handled for research purposes, before being released back into the wild.