Feeding Ecology of the Sandbar Shark in South Carolina Estuaries Revealed through δ13C and δ15N Stable Isotope Analysis

David S Shiffman,Bryan S Frazier,Gorka Sancho,Jay Brandes,John R Kucklick,Daniel Abel

doi:10.1080/19425120.2014.920742

Abstract

AbstractStable isotope ratios of carbon and nitrogen (δ13C and δ15N) from muscle samples were used to examine the feeding ecology of a heavily exploited shark species, the Sandbar Shark Carcharhinus plumbeus. Two hundred and sixty two Sandbar Sharks were sampled in five South Carolina estuaries. There were no significant differences in average δ13C or δ15N signatures between estuaries, between sampling years, or between male and female Sandbar Sharks, suggesting that these variables do not affect diet. A potential ontogenetic diet shift between young‐of‐year and juvenile Sandbar Sharks in South Carolina, similar to a shift previously described in Virginia and Hawaii populations, is suggested by significant differences in average δ13C and average δ15N signatures between these age‐classes. Results confirm that Sandbar Sharks in South Carolina are generalist predators and that juvenile Sandbar Sharks have a wider diet breadth than young‐of‐year sharks, a pattern common in elasmobranchs. Sandbar Shark diet in South Carolina is similar to that found in previous stomach content analysis studies. This study also demonstrates that nonlethal sampling methods can be applied to sharks to obtain diet and trophic information, including the detection of ontogenetic shifts in diet.Received September 17, 2013; accepted April 1, 2014

Highlights

Stable isotope ratios of carbon and nitrogen (δ13C and δ15N) from muscle samples were used to examine the feeding ecology of a heavily exploited shark species, the Sandbar Shark Carcharhinus plumbeus
The U.S National Marine Fisheries Service plans to eventually institute a new ecosystem-based fishery management plan to improve the management of U.S shark species (SEDAR 2006)
Ecosystem-based fisheries management plans differ from traditional fishery management by focusing not just on a target population and on diet, trophic interactions, and environment (Pikitch et al 2004)

Summary

Introduction

Stable isotope ratios of carbon and nitrogen (δ13C and δ15N) from muscle samples were used to examine the feeding ecology of a heavily exploited shark species, the Sandbar Shark Carcharhinus plumbeus. An alternative method to study elasmobranch diet is stable isotope analysis (Hussey et al 2011; Hussey et al 2012; Shiffman et al 2012) This method utilizes the isotopic signatures of carbon and nitrogen isotopes in tissues to examine trophic status and other relevant ecological relationships, such as sources of carbon to the food web (Peterson and Fry 1987). This technique can provide long-term, temporally integrated diet estimates compared with stomach content analysis, which reflects only recently ingested prey (Pinnegar and Polunin 1999). Gathering samples for stable isotope analysis can be nonlethal and minimally invasive when restricted to the use of certain tissues (Sanderson et al 2009)

Objectives

Methods

Results

Conclusion