Sex and social networking: the influence of male presence on social structure of female shark groups

Abstract

Marine predators such as sharks often form single-sex aggregations as part of their diel behavioral cycle. Such aggregations are potentially driven by contrasting reproductive and behavioral strategies between the sexes, leading to distinct sexual segregation. There is, however, no experimental evidence that such predator aggregations are governed by intrinsic social systems, demonstrating long-term temporal stability. Social network structure, temporal stability, and activity profiles were analyzed to examine the impact of introduced males on social structure of 4 captive groups of female catshark (Scyliorhinus canicula). Aside from foraging and habitat selection pressures, we question whether individual female sharks manage additional social demands that potentially influence activity budget and susceptibility to male harassment. Shark groups demonstrated marked differences in their tendency to aggregate in a unisex environment and concomitantly showed significant differences in social response to male presence. Dichotomy in social structure of the 4 groups revealed that well-connected individuals demonstrated greater resilience to male disturbance. Socially isolated females experienced greater levels of partner exchange, reduced temporal stability, and increased activity levels in the presence of males and control females. These results are the first to demonstrate the disruptive influence that male and novel females have on weak female shark social interactions; conversely, aggregations demonstrating relatively strong temporally stable social bonds (at least by some individuals) are particularly resilient to potential male harassment and novel (female) intruders. We highlight that additional ‘social constraints’ may have disparate influence on individuals occupying different structural positions within a network and may thus impact individual fitness unequally. Key words: aggregation, behavior, fish, network analysis, sexual segregation, shark, social structure. [Behav Ecol]