Spatial and behavioral ecology of the sand tiger shark Carcharias taurus in the Northwestern Atlantic 

Date
2017
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Publisher
University of Delaware
Abstract
Quantifying the biogeography of coastal marine species is difficult and requires innovative study designs. These challenges are the motivation behind this dissertation. The Sand Tiger shark (Carcharias taurus) is an important apex predator in the coastal oceans along the Eastern Coast of the United States. I conducted a study in the Delaware Bay and Mid-Atlantic coastal Ocean, which used historical species location records from acoustic telemetry matched to static and satellite-measured dynamic environmental predictor variables, to create a near-real time predictive species distribution model. Notably we found Sand Tigers were predicted by water temperature, water depth, day length and ocean color absorption in the near-infrared, which likely relates to turbidity in the coastal ocean. In this study I identified the timing and location of migratory corridors used by Sand Tigers, as well as how the timing and location of migration differed between juvenile, mature male and mature female Sand Tigers. ☐ In my second study, I investigated the timing and migration of Sand Tigers along the Delmarva Peninsula on much smaller spatiotemporal scales during their fall migration south, a time during which Sand Tigers are susceptible to anthropogenic threats. For the first time, I used an autonomous underwater vehicle to concurrently detect Sand Tigers carrying acoustic tags, and measure fine scale environmental properties of the sub-surface ocean to determine habitat selectivity. I found that Sand Tigers migrated rapidly and en masse through the coastal ocean off the Delmarva Peninsula and were selecting for waters near-shore, lower in salinity, and higher in color dissolved organic matter. These results support the larger scale patterns in environmental predictors I found in my first study, as well as prove that using autonomous underwater vehicles is an effective method for extending our capabilities of detecting acoustically tagged marine species. ☐ Finally, I developed a novel tagging method that implanted an archival acoustic receiver into the body cavity of Sand Tigers, which were released alive and continued to conduct their annual migration before they were recaptured and the tags were removed. This tagging method allowed me to record associations between Sand Tigers and other acoustically tagged species for one year of the Sand Tigers life. Analysis of that dataset revealed potential fission-fusion behavior, or the change in size and composition of groups, in the Sand Tiger population depending on where the Sand Tigers were along the East Coast, and what they were likely doing during that time (i.e. feeding, searching for mates, migrating, etc.). I observed Sand Tiger aggregations change from mixed groups of male and female juveniles and adults, to groups of only adult males, to solitary phases where Sand Tigers were completely dispersed for weeks at a time. This study is important because it suggests the potential for social behavior in a shark species, but also identifies the possibility of anthropogenic impacts disproportionally impacting one sector of the Sand Tiger population as the composition of their aggregations changes in time and space. This dissertation uses advances in remote sensing and animal tagging methods to provide insights into the species distribution, habitat selection, and the migratory and grouping behavior of a coastal shark species under threat of population decline due to anthropogenic impacts along the East Coast of the United States and provides insights into the ecology and biogeography of this species that will assist managers and researchers in future conservation efforts for this and other imperiled species.
Description
Keywords
Biological sciences, Behavior, Marine biology, Oceanography, Remote sensing, Robotics, Spatial ecology
Citation