The sociality of Atlantic sturgeon and sand tiger shark in dynamic bay environments

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Robert E. Roose II and Aaron Carlisle, College of Earth Ocean and Environment, University of Delaware, Lewes, DE, Matthew Breece, Earth, Ocean, and Environment, University of Delaware, Lewes, DE, Dewayne A. Fox, Delaware State University, Dover, DE, Danielle Hasulsee, Stanford University, Matthew J. Oliver, College of Earth, Ocean, and Environment, University of Delaware, Lewes, DE

Background/Question/Methods
Social network analysis (SNA) provides a method to quantify and visualize animal interactions. Utilizing biotelemetry data, we produced social networks of two study species, the Atlantic sturgeon (Acipenser oxyrhynchus oxyrhynchus) and sand tiger shark (Carcharias taurus). In this study we compare the sociality of these species within the Delaware Bay. To supplement our SNA, we identified the total distance individuals consecutively traveled together. The recent transmission from terrestrial to aquatic networks has prompted discussion about network structure and the tools implemented for their generation. When developing an SNA, ecologists should consider the environment from which their data is derived. The influence environmental variables have on acoustic listening conditions is well documented, but there has been little research regarding their influence on marine social networks. Using spectral analysis and linear models, we analyzed four network metrics and three environmental variables on an hourly timescale.
Results/Conclusions
Our networks revealed little evidence for sociality amongst Atlantic sturgeon. Conversely, sand tiger sharks exhibited evidence for both preferential co-occurrence and maturity assortment in three out of five years (p < 0.05). Atlantic sturgeon were not recorded traveling together, while sand tiger shark often moved between receivers in pairs (n = 3,154 pairs). From these analyses, we conclude that sand tiger sharks exhibit a higher degree of sociality than Atlantic sturgeon while in the Delaware Bay. The spectral analysis revealed the considerable role environmental variables have on network metrics. The most prominent periodicities were that of 6.2 and 12.4 hours, indicating a correlation to sea breeze and tidal regime. Thus, we suggest caution when producing marine networks. Researchers should consider the periodicity of any predominant environmental variables when generating SNA.