Habitat Loss: Predator-Prey Interactions

Predators influence prey behavior, feeding rates, movement patterns, habitat use, morphology and population structure as a result of both direct and indirect interactions.  Antipredatory behavioral responses are major factors influencing habitat use in many marine vertebrates. Although mangrove shorelines are often major components of juvenile sharks’ nursery habitat, the hypothesis that juvenile sharks use mangroves to avoid predators has never been empirically tested using experimental manipulations. The objectives of this study were to investigate the small-scale use of artificial mangrove structure by small juvenile lemon sharks as an antipredatory response to predation risk, and to examine the relationship between body size and fine-scale habitat use in the presence of a predator.

1. Is a large juvenile lemon shark perceived as a predation threat by small juvenile lemon sharks?

2. Do small juvenile lemon sharks use artificial mangrove structure within the experimental configuration as a habitat-specific refuge in the presence of a potential predator more than when solitary or when with a size-matched conspecific?

3. Is there a relationship between body size and use of artificial mangrove structure in the presence of a potential predator?

This study suggests the importance of mangrove structure as a habitat-specific escape tactic within a lemon shark nursery.  The sharks’ use of artificial structures mimicking natural mangrove shorelines may have important management and mitigation implications, particularly in environments such as Bimini, where mangrove habitats within nurseries have been lost due to coastal development.  Natural habitats are desired for optimal ecosystem function, but if development does occur, it is important to consider restoration of the refuge function of mangrove shorelines, perhaps by requiring developers to add structural complexity to modified habitats.

1. Is a large juvenile lemon shark perceived as a predation threat by small juvenile lemon sharks?

Yes. When in the presence of a large lemon shark, smaller juveniles exhibited a significantly higher number of fright responses than when they were solitary or with a size-matched juvenile. 

2. Do small juvenile lemon sharks use artificial mangrove structure as a refuge in the presence of a predator more than when solitary or when with a size-matched conspecific?

Yes and no.  When two similar-sized juveniles were together, they used the artificial mangroves much less than when the test shark was with a predator.  However, when the test shark was alone, it still used the artificial mangroves for a large portion of time.  This result suggests that there is increased boldness due to shared vigilance when similar-sized sharks group together

3. Is there a relationship between body size and use of artificial mangrove structure in the presence of a potential predator?

Yes.  The larger the juvenile, the less is used the artificial mangrove, indicating less perception of a predation risk from the larger lemon shark. 

Principal Investigator:

Dr. Kristine Stump – University of Miami

 

Collaborators:

CJ Crooks, B.Sc. – University of Manchester, UK

Dr. Tristan Guttridge – Cardiff University, UK

Dr. Samuel Gruber – Bimini Biological Field Station

Stump K, Crooks CJ, Guttridge TL, Gruber SH. (2014) Hunted hunters: an experimental test of the effects of predation risk on juvenile lemon shark habitat use. In review. Marine Ecology Progress Series

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