Assessing the Retention Rates of External Acoustic Transmitters in Atlantic Sturgeon

Typical studies involving acoustic telemetry surgically implant transmitters to ensure long term tag retention.  In certain studies, such as those examining post-release mortality or involving protected resources, the use of external acoustic transmitters may be preferred for a variety of reasons including diminished stress levels, shortened handling times, and reducing the confounding negative effects generally caused by surgical complications/healing.  Since retention rates of external acoustic tags are unknown for the federally protected Atlantic sturgeon, we conducted a tag retention study to validate and estimate external acoustic tag shedding rates.  A total of 40 Adult Atlantic Sturgeon were captured off the coast of Delaware and each fish had a VEMCO V16-6H acoustic tag surgically implanted as well as an external VEMCO V16-4H acoustic transmitters were affixed to the base of the dorsal fin.  Atlantic Sturgeon were monitored for a minimum of seven months from coast-wide VEMCO VR2-W acoustic receivers.  Based upon their detection histories from the acoustic receivers we estimated shedding rates of external transmitters using a maximum likelihood approach.  The results of this study strongly suggest that the less invasive external tagging approach may be appropriate for short-term projects, such as those examining post-release mortality in commercial fisheries.