LAUSR

Autonomous underwater vehicles (AUVs) have demonstrated superior performance for tracking marine animals tagged with individually coded acoustic transmitters. However, AUVs engaged in mapping the distribution of multiple tagged fish have not previously been able to alter search paths to achieve precise position estimates. This problem is solved by the development of payload control software (Synthetic Aperture Override, SAOVR) that allows the AUV to maneuver with trajectories favorable for solving the tag’s location from a synthetic aperture. Upon tag detection during a default mission search path, SAOVR (running on an embedded guest computer) seeks permission to take over navigation from the vehicle’s native system after checking constraints of geography, timing, tag identification, signal strength, and current navigation state. Permitted maneuvers are then chosen from a template library and executed before returning the AUV to the point of first deviation for continued searching of other tags. Field evaluation on moored reference tags showed a high level of predictability in the AUV’s behavior at SAOVR initiation and through maneuvers. Trials suggest that this logic system is highly beneficial to AUV use for fish telemetry in challenging environments such as narrow, deep fjords, or among reefs. Any mission programmed with the AUV’s native software can be run with the SAOVR package to allow scientists to easily implement and manipulate synthetic aperture geometries without altering any of the software. Further modeling can help improve template design specific to expected movements of different fish species and relative to the designation of signal strength-defined execution thresholds. Autonomous underwater vehicles (AUVs) have demonstrated superior performance for telemetering marine animals (fish and crabs) tagged with coded acoustic transmitters (Eiler et al. 2013). Telemetry, specified for this paper as acoustic tag detection by a hydrophone distinct from telemetry as messages between a remote vehicle and user, has become an important tool for ecological and stock assessment research. Telemetry typically utilizes fixed arrays of moored omnidirectional hydrophones to detect passage or general area of space use (Heupel et al. 2006; Reynolds et al. 2010; Eiler and Bishop 2016) or if closely spaced to calculate sequential fine-scale positions (tracks) by trilateration. (Cooke et al. 2005; Espinoza et al. 2011). Surface vessels are also used to sequentially occupy fixed listening stations (Ng et al. 2007), actively search an area for the tagged fish (Holland et al. 1999; Sims et al. 2001; Nielsen et al. 2012), or to follow a tagged individual (Wetherbee et al. 2004). Moored hydrophones are useful for experimental designs meant to synoptically detect the presence or passage of multiple tagged animals over long periods, but must defer to costly and laborious vessel-based tracking for information on animals beyond the array detection limits on the order of km. AUVs can perform some of these tasks (Grothues et al. 2008; Oliver et al. 2013; Haulsee et al. 2015; Breece et al. 2016), which then benefit from deeper, quieter hydrophone positioning (Eiler et al. 2013; Oliver et al. 2017). The application is further justified because other onboard sensors can provide proximal information on the surrounding habitat, making it possible to integrate fish telemetry data with geomorphic and environmental data (Grothues et al. 2010; Oliver et al. 2013; Haulsee et al. 2015, see Lennox et al. 2017 for a review of telemetry challenges and projections). AUVs have previously been designed and used to track (follow) individual fish. One such solution involved the use of a REMUS-100 (Hydroid, Pocasset, MA) AUV proprietary native homing/docking system (Skomal et al. 2015). A short baseline system (SBL) hydrophone array in the nose cone determined the bearing and distance toward a large (~ 9 cm × 30 cm) native homing beacon, which was on a suitably large great white shark (Carcharadon carcharias) (Packard et al. 2013; *Correspondence: [email protected]