Association behavior between sand tiger sharks and round scad is driven by mesopredators.

Nicholas C Coleman,Erin J Burge

doi:10.7717/peerj.11164

Abstract

In marine systems, behaviorally-mediated indirect interactions between prey, mesopredators, and higher trophic-level, large predators are less commonly investigated than other ecologic interactions, likely because of inherent difficulties associated with making observations. Underwater videos (n = 216) from SharkCam, a camera installation sited beneath Frying Pan Tower, a decommissioned light house and platform, on a natural, hard bottom site approximately 50 km off Cape Fear, North Carolina, were used to investigate association behavior of round scad Decapterus punctatus around sand tiger sharks Carcharias taurus. Videos containing sand tiger sharks were analyzed for the simultaneous presence of round scad, and six species of scad mesopredators, with scad-shark interactions assigned to one of three categories of association: no visible interaction, loosely associated, or tightly associated. The likelihood of scad being loosely or tightly associated with sharks was significantly higher in the presence of scad mesopredators, suggesting that sharks provide a predation refuge for scad. This behaviorally-mediated indirect interaction has important implications for trophic energy transfer and mesopredator control on hard bottoms, as scad are one of the most abundant planktivorous fish on hard bottoms in the western Atlantic Ocean. Although we were not able to provide statistical evidence that sand tiger sharks also benefit from this association behavior, we have clear video evidence that round scad association conceals and attracts mesopredators, enhancing predation opportunities for sand tiger sharks. These interactions potentially yield additional trophic consequences to this unique association and highlight the value of exploring behaviorally-mediated interactions in marine communities.

Highlights

Multispecies interactions highlight the underlying interdependency between organisms that exist in all communities (Hutchinson, 1959; Paine, 1984; Beard & Dess, 1988)
We examined association behavior between sand tiger sharks (STs), round scad (RS), and scad mesopredators (MPs) using video records from a unique, long-term underwater video installation sited on a hard bottom system off the coast of Cape Fear, North Carolina
Based on SharkCam underwater video observations conducted over more than 5 years and representing over 340 h of underwater footage, we demonstrate that round scad (RS) are significantly more likely to be associated with sand tiger sharks (STs) in the presence of potential scad mesopredators (MPs), than in their absence

Summary

Introduction

Multispecies interactions highlight the underlying interdependency between organisms that exist in all communities (Hutchinson, 1959; Paine, 1984; Beard & Dess, 1988) These interactions are often categorized as direct, between two species, or indirect, where the interaction between two species affects a third species (Wootton, 1993). Some marine, demersal mesopredatory fishes access pelagic prey that are driven towards the seafloor by pelagic mesopredators, enhancing feeding opportunities (Auster et al, 2009; Auster et al, 2013; Campanella et al, 2019). Despite their importance, BMIIs are less commonly investigated than other ecologic interactions because of the difficulty attributed to quantifying changes in behavior, especially within marine habitats

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