Social Network Analysis of Partner Preference in Lemon Sharks, Negaprion brevirostris, During the Introduction of Strangers to Familiar Groups

Bryan Keller, School of Coastal and Marine Systems Science, CCU
Event Location: 
Event Date: 
Thursday, March 26, 2015 - 3:00pm
Event Type: 
SCMSS Seminar Series


Grouping in sharks is well-known, however there are few quantitative analyses on the mechanisms that drive their formation. In this study we use controlled semi-captive behavioral experiments to assess the potential role that familiarity plays in group formation and social behavior in a large marine vertebrate. Juvenile lemon sharks, Negaprion brevirostris, (n =23) in Bimini, Bahamas were captured, measured and tagged with external color codes for individual recognition and housed in pens that exposed them to ambient conditions. Sharks were separated by size class into four holding pens and given 14 days to familiarize themselves with their cohort. Following familiarization, pairs of sharks were taken from two holding pens and introduced in a social network pen for a total of 25 replicates. An overhead video system recorded behaviors for one hour. Tracking software transformed the movement patterns into a coordinate system. Multiple algorithms were used to analyze these coordinates and these produced a matrix of interactions between familiar and unfamiliar individuals. Social network analysis showed that that juvenile lemon sharks show a significant preference familiar individuals for the entire trial (P < 0.0005) and this preference declines over the one-hour trial. The decline in avoidance of unfamiliars supports the hypothesis that the original preference for familiars was due to the Dear Enemy effect. After prolonged interactions with unfamiliars, the focal sharks most likely determined there was no significant threat from the strangers and no further discriminatory behavior was necessary. This research advances our understanding of the mechanisms driving group formation in lemon sharks, a model species for large marine predators.

Speaker Information

Bryan grew up in the Sonoran desert and had few interactions with marine life as a child; despite these rare occurrences they still greatly influenced his career. Upon enrolling at the University of Arizona for his BSc, he pursed internships that exposed him to large marine fishes. He spent a summer at the Bimini Biological Field Station studying a variety of sharks. He returned to Bimini the following two years where he conducted research for his MSc thesis on the social behavior of lemon sharks (Negaprion brevirostris) while enrolled at Coastal Carolina University. At CCU he has continued research on topics including the physiology of deep-sea sharks, the spatial ecology and feeding preferences of sharks in Winyah Bay, and energy conservation in group behavior for juvenile lemon sharks. While in Bimini, he received a grant that allowed the Bimini Biological Field Station to give outreach presentations to every student enrolled in public school on the island. Bryan continues those presentations to students around Myrtle Beach, South Carolina as he did in Bimini.

Bryan is fascinated by spatial ecology and how the presence of offshore wind farms could impact seasonal migrations of coastal sharks. His PhD dissertation will determine the environmental impact of wind farms and if there is a way to mitigate the effect of large marine fishes.

After earning his PhD he plans to continue his career as a research scientist. In addition to his research, he hopes to be able to influence policy decisions. Tom Mullikin once compared the aphorism ‘If a tree falls and no one is around to hear it, does it make a noise?” to science and policy by saying “If you don’t influence policy with good bench science, does it matter?” Recently, Bryan worked with Tom to draft legislation to prohibit the wanton waste of sharks and the possession of shark fins in South Carolina. If passed, we will finally hear ‘the tree fall’.