Abstract
We examined the affects of selected water quality variables on the presence of subadult sharks in six of nine Georgia estuaries. During 231 longline sets, we captured 415 individuals representing nine species. Atlantic sharpnose shark (Rhizoprionodon terranovae), bonnethead (Sphyrna tiburo), blacktip shark (Carcharhinus limbatus) and sandbar shark (C. plumbeus) comprised 96.1% of the catch. Canonical correlation analysis (CCA) was used to assess environmental influences on the assemblage of the four common species. Results of the CCA indicated Bonnethead Shark and Sandbar Shark were correlated with each other and with a subset of environmental variables. When the species occurred singly, depth was the defining environmental variable; whereas, when the two co-occurred, dissolved oxygen and salinity were the defining variables. Discriminant analyses (DA) were used to assess environmental influences on individual species. Results of the discriminant analyses supported the general CCA findings that the presence of bonnethead and sandbar shark were the only two species that correlated with environmental variables. In addition to depth and dissolved oxygen, turbidity influenced the presence of sandbar shark. The presence of bonnethead shark was influenced primarily by salinity and turbidity. Significant relationships existed for both the CCA and DA analyses; however, environmental variables accounted for <16% of the total variation in each. Compared to the environmental variables we measured, macrohabitat features (e.g., substrate type), prey availability, and susceptibility to predation may have stronger influences on the presence and distribution of subadult shark species among sites.
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Reference to trade names does not imply Government endorsement of commercial products.
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Acknowledgements
The University of Georgia Marine Extension Service provided field support and personnel needed to conduct this project. Robert Cooper, Gary Grossman, and Randy Walker provided useful comments to an earlier draft of this manuscript. We would like to extend our appreciation to the three reviewers who provided additional comments and edits to this manuscript. Funding for this project was administered through the National Marine Fisheries Service’s Apex Predator Program in Narragansett, RI as part of a larger cooperative grant sponsored by National Marine Fisheries Service’s Highly Migratory Species Division in Silver Spring, MD. The Georgia Cooperative Fish and Wildlife Research Unit is sponsored jointly by the US Geological Survey, the U.S. Fish and Wildlife Service, GA Department of Natural Resources, the University of Georgia, and the Wildlife Management Institute.
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Belcher, C.N., Jennings, C.A. Utility of mesohabitat features for determining habitat associations of subadult sharks in Georgia’s estuaries. Environ Biol Fish 88, 349–359 (2010). https://doi.org/10.1007/s10641-010-9648-3
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DOI: https://doi.org/10.1007/s10641-010-9648-3