300 
Fishery Bulletin 113(3) 
the water column than the other 2 species, regardless 
of body size. 
The highest potential for resource competition exists 
between southern kingfish and Atlantic croaker on the 
basis of the simplified M-H index. Morisita-Horn index 
values exceeding 0.60 are generally accepted as biologi- 
cally significant in the literature (Zaret and Rand, 1971; 
Labropoulou and Eleftheriou, 1997; King and Beamish, 
2000; Graham et al., 2007; Rodrigues and Vieira, 2010). 
Assuming this value is significant, southern kingfish 
and Atlantic croaker showed significant diet overlap by 
mean percent weight, at 0.74, but not on the basis of 
mean percent number, at 0.56 (Table 3). Most southern 
kingfish and Atlantic croaker that were sampled had 
prey in their stomachs, indicating that sufficient prey 
were readily available to both species and the general- 
ized (opportunistic) feeding strategy employed by these 
benthivorous species likely reduces any competition for 
resources, even when there are relatively high levels of 
diet overlap. 
Ecosystem-based management is dependent on 
defining interactions among species and, in particu- 
lar, on identifying trophic links for priority species 
(NMFS 6 ). Weakfish, southern kingfish, and Atlantic 
croaker are swept up regularly in commercial shrimp 
trawl nets, are targets of bait fisheries, and play im- 
portant roles in the nearshore food web. If exploita- 
tion increases, their large-scale removal could alter 
some fundamental ecosystem processes (Kumar and 
Deepthi, 2006). The sciaenids in this study over- 
lap spatially; therefore, ecosystem-based principles 
require that we determine whether competitive in- 
teractions occur among them for prey resources. Ig- 
norance of predator-prey relationships will result in 
fisheries managers overlooking important ecosystem- 
based complexities that could drive population trends 
(Ruckelshaus, 2008). 
Acknowledgments 
We would like to extend our gratitude to members of 
the SEAMAP-SA Coastal Survey team: P. Webster, J. 
Boylan, and the scientific and vessel crews of the RV 
Lady Lisa who have contributed to collection of samples 
for this study. We also thank S. Goldman, D. Knott, D. 
Burgess, M. Levisen and M. Pate, who played essential 
roles in diet identification. D. Wyanski, M. Reichert, D. 
Glasgow, and S. Falk provided invaluable comments on 
earlier drafts. Funding was provided by the National 
Marine Fisheries Service (Southeast Fisheries Science 
Center) grant number NA11NMF4350043. This article 
is contribution 730 of the South Carolina Department 
of Natural Resources’ Marine Resources Research 
Institute. 
6 NMFS (National Marine Fisheries Service). 1999. Ecosys- 
tem-based fishery management: a report to Congress by the 
Ecosystem Principles Advisory Panel, 46 p. [Available at 
website, accessed August 2014.] 
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