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Integrating multiple techniques to identify stock boundaries of common bottlenose dolphins (Tursiops truncatus)

Balmer, Brian C., Wells, Randall S., Schwacke, Lori H., Schwacke, John H., Danielson, Barbara, George, R. Clay, Lane, Suzanne M., Mclellan, William A., Pabst, D. Ann, Sparks, Kate, Speakman, Todd R., Townsend, Forrest I., Zolman, Eric S.
Aquatic conservation 2014 v.24 no.4 pp. 511-521
Tursiops truncatus, case studies, dolphins, estuaries, issues and policy, monitoring, radio telemetry, surveys, Georgia
Under US policy, a stock is a group of animals shown to be demographically independent from other such groups. Evidence of demographic delineations for marine mammal stocks is gained primarily through genetic analysis. However, additional techniques play an important role in determining fine‐scale ranging patterns that can be used to define a stock's geographic boundaries. In cases where genetic studies have not yet been performed, movement and ranging pattern data are essential in identifying a targeted geographic region for tissue sampling and genetic studies. Photo‐identification surveys, vessel‐based radio telemetry, automated radio telemetry systems (ARTS), and satellite‐linked telemetry are sampling techniques that have been used to determine common bottlenose dolphin ranging patterns and provide detailed insight into stock boundaries. The results of near simultaneous use of these sampling techniques are compared using data from a case study of bottlenose dolphins within the estuaries of southern Georgia. Satellite‐linked and radio telemetry were determined to be useful sampling techniques for identification of short‐term ranging patterns. Satellite‐linked telemetry had the second lowest cost per location ($122) and identified dolphin ranging patterns within and outside of the study area boundaries. Vessel‐based radio telemetry was more costly ($195 per location) and had relatively limited tracking coverage. However, this sampling technique permitted visual observations of animal and tag condition. The combination of vessel‐based radio telemetry and ARTS, which had the lowest cost per location ($34), was an effective method for determining ranging patterns of tagged individuals within and outside of the study area. Photo‐identification surveys, relative to satellite‐linked and radio telemetry, were not as efficient for determination of targeted individuals’ short‐term ranging patterns and had the highest cost per location of the four sampling techniques ($292). However, photo‐identification is more effective than any other technique for compiling data on large numbers of individuals within a designated study area. Photo‐identification surveys are essential for long‐term monitoring and provide additional insight into dolphin stock structure that cannot be determined through telemetry alone. Copyright © 2013 John Wiley & Sons, Ltd.