## 2 Materials and Methods
### Fish Tracking
Although the reception range for the tagged fish could not be determined, reference transmitters deployed at known locations within the study area were consistently detected at 500 m and infrequently detected at distances up to 980 m [23]. An aluminum boat (5 m in length with an enclosed cabin) was used to deploy and recover the AUV, and to conduct concurrent vessel-based surveys (Figure 2). The boat was instrumented with an acoustic receiver (Model MAP 600 RT: Lotek Wireless) and stereo hydrophones (Model LHP, Lotek Wireless) capable of detecting, identifying, and recording CDMA transmitter signals. Hydrophone struts were attached on the port and starboard side of the vessel (spaced 1.6 m apart). The struts were lowered into the water and vertically oriented during the survey with the hydrophones submerged to a depth of 1 m. The struts were hydrodynamic in shape, making it possible for the boat to maintain speeds up to 2.6 ms\({}^{-1}\) (5 knots) without cavitation. Similar to the AUV missions, SYNAPS software (Lotek Wireless) was used to calculate a series of location estimates from the telemetry data collected for each fish detected and to provide diagnostic variables that measured the overall quality of the estimates. These data were treated the same as the information obtained by the AUV. Positioning information for the boat was collected with a GPS receiver (Model GPSMap-76 CSX, Garmin, Olathe, KS, USA). Paired AUV and vessel-based location estimates with an offset time (i.e., difference in the time of detection between the two estimates) <20 min were examined and compared. We examined the dispersal rate of the fish based on the best location estimates made by the AUV over the entire tracking period. The rate between any two points, distance moved (m) divided by time elapsed (s), represents the movement of the fish plus any error in the location estimate (combined as \(\gamma\)). These factors cannot be parsed because the actual position of the fish is unknown, but \(\gamma\) can be compared to possible swimming rates and the distribution of \(\gamma\) described. This distribution represents the movement behavior of the fish (directed movements vs milling) over time, ranging from hours to days, and helped quantify expectations related to emigration and residence within the area. Further, quantification of the distribution, especially the extent and frequency of large numbers in the distribution tails relative to possible swimming rates, indicates the extent to which error may be problematic in the filtered/selected solution set. To do this, we calculated the rate of movement between each pair of best location estimates \(jk\) for a given fish, for individuals with more than two estimates. Distance calculations were made using the Pythagorean theorem assuming a flat plane, because curvature of the geoid surface is negligible at such small distances and because sound underwater is not constrained to follow the surface. We calculated the mean and standard deviation of \(\gamma\) within and among fish and fit the distribution of all fish combined using an appropriate estimator in MATLAB (MathWorks Inc., Natick, MA, USA). \[\delta\mathrm{x/t}=\mathrm{distance}_{jk}/(\mathrm{T}_{k}-\mathrm{T}_{j}), \tag{1}\]