Date of Award

2015

Document Type

Restricted Thesis

Terms of Use

© 2015 Sofia M. Gabriel. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Biology Department

First Advisor

Rachel Merz

Second Advisor

José-Luis Machado

Abstract

At reefs dominated by higher trophic level piscivores, variations in distribution and abundance of prey species mediate community composition. Understanding prey patchiness provides important information about the community and the presence and location of top predators in the area, and therefore aids in the interpretation of surveys monitoring the status of protected areas. We asked how density and distribution of small prey fish changed over space and time at Gray's Reef National Marine Sanctuary (GRNMS; off Georgia, USA) by comparing prey density (fishes 100m² segments) at reefs inside and outside a no-fishing zone that was designated in 2011. Surveys using data derived from Simrad EK60 split-beam sonar were conducted at dawn and dusk at 6 reefs in 2011 and 2012, and 5 reefs in 2013. Overall, while no significant differences were found between dawn and dusk within years, there were significant differences between fishing treatments, years, and sites. The year 2011 had the lowest fish density and 2012 the highest. In addition, comparison of the indices of mean crowding revealed significant changes in the distribution of the prey population along the reef, with greater clumping of prey in 2012 and 2013. Noteworthy comparisons within treatment levels revealed significantly higher prey densities in 2012-13 at sites outside of the no-fishing zone, suggesting that at least in the short term the no-fishing zone is effectively increasing predator numbers inside the no-fishing zone of the sanctuary. This initial assessment of variation in prey resources at GRNMS suggests that density and distribution of prey can provide a useful indicator for the effects of no-take fishing zones on reefs and potentially aid in the management of such ecosystems.

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