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ABSTRACT-Autonomous underwater vehicles (AUV's) are increasingly used to collect physical, chemical, and biological information

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.

Featured Application: Using autonomous underwater vehicles equipped with telemetry-based payload control to locate marine fish tagged with acoustic transmitters.Abstract: An autonomous underwater vehicle (AUV) under payload control (PC) was used to map the movements of juvenile Chinook salmon (Oncorhynchus tshawytscha) tagged with acoustic transmitters. After detecting a tag, the AUV deviated from its pre-programmed route and performed a maneuver designed to enhance the location estimate of the fish and to move closer to collect proximal environmental data. Nineteen fish were released into marine waters of southeastern Alaska. Seven missions with concurrent AUV and vessel-based surveys were conducted with two to nine fish present in the area per mission. The AUV was able to repeatedly detect and estimate the location of the fish, even when multiple individuals were present. Although less effective at detecting the fish, location estimates from the vessel-based surveys helped verify the veracity of the AUV data. All of the fish left the area within 48 h of release. Most fish exhibited localized movements (milling behavior) before leaving the area. Dispersal rates calculated for the fish suggest that error associated with the location estimates was minimal. The average movement rate was 0.62 body length per second and was comparable to marine movement rates reported for other Chinook salmon stocks. These results suggest that AUV-based payload control can provide an effective method for mapping the movements of marine fish.Autonomous underwater vehicles (AUVs) are increasingly being used to supplement the use of surface vessels for measuring the physical, chemical, and biological characteristics of the marine environment, and when equipped with acoustic receivers can be used to determine the distribution and movements of fish tagged with acoustic transmitters [13,14]. This approach has definite advantages over tracking fish from surface vessels, particularly for demersal or deep-water pelagic species [15]. Proximal data obtained from AUV-based sensors and sonar also make it possible to compare the spatial and temporal distribution of the fish with the associated environmental conditions, benthic characteristics, and the presence of other fish species and untagged con-specifics.Despite these advantages, AUVs have their own constraints. Unlike a piloted vessel that can easily deviate from its existing course to enhance location estimates, AUVs mapping the movements of acoustically tagged fish were initially programmed to simply follow a predetermined route and record the transmitters detected. Position estimates were limited to kernel density or sound-pressure-level (SPL) estimates of proximity, which were often bimodal [16,17]. Positioning errors frequently resulted from the presence of tagged fish on the periphery of the pre-programmed route and the unfavorable geometry of the hyperbolic curves used to estimate fish locations [15]. Survey routes for unmanned vehicles (both surface and submerged) have become much mor...

Dredging is one of the most common human modifications of estuaries and although its effects have often been studied, there has been little effort in evaluating the effects on mobile macrofauna, such as fishes and crabs. We evaluated the response of fishes and crabs to 4 d of dredging in a small boat basin within a polyhaline marsh creek of a New Jersey estuary. We used several measures, including fish and crab species composition, abundance, and size from trap collections and movements of marked mummichogs Fundulus heteroclitus before, during, and after dredging. In general, the fauna changed little during the 4 d of dredging relative to the 1.5-month sampling period. Species composition variations that did occur may have been due to seasonal changes that are typically observed during the fall based on annual sampling at this site. The movement of tagged mummichogs was minimal, with most recaptures taking place in the boat basin. Individuals that left the boat basin moved into pools in an adjacent marsh for the winter. These results suggest that the short-term effect of this low-sediment-volume dredging project was negligible for the benthic fishes and crabs studied, which we believe are representative of the high-salinity portions of estuaries in the northeastern United States.