Abstract
In previous literature it was proposed that Atlantic sharpnose sharks, Rhizoprionodon terraenovae, from the western Atlantic Ocean (WAO) population exhibited differences in their reproductive timing when compared to the northern Gulf of Mexico (GOM) population. The objective of the current study was to examine the reproductive cycle of mature male sharpnose sharks from the northern GOM population. Plasma testosterone (T) and estradiol (E2) were measured from 76 mature male sharpnose sharks sampled from 1999 to 2001, and the gonadosomatic index (GSI) was determined for 53 additional mature males sampled from 2007-2008. Plasma T, E2, and GSI exhibited similar cycles with peak values occurring in late spring (April/May) and lowest values occurring during the summer. These results suggest that male sharpnose sharks in the northern GOM are reproductively active one to two months earlier than previously reported, which now brings them into synchrony with the WAO population. Interestingly, this shift in reproductive timing corresponds with a 3.0°C (13.4%) increase in spring sea surface temperature (SST) from the Mississippi Sound over a 29 year period, which could translate into GOM male sharpnose sharks becoming reproductively active earlier in the year thus explaining the late spring peak in GSI.
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Acknowledgments
Financial support for this project was partially provided by The U.S. Fish and Wildlife Service to E. Hoffmayer and by the National Marine Fisheries Service (MARFIN # NA77FF0548) to G. Parsons. We would like to thank C. Foran for use of the EIA equipment and supplies, and B. Peterson for assistance with the assay itself. This project would have been impossible without the help of many volunteers. We are indebted to G. Gray, W. Dempster, J. Tilley, J. Bartlett, K. Larsen, M. Sandrene, D. Martinovic, and A. Haggard for their assistance in the field. We also thank J. McKinney for her assistance generating the map of the study area, and W. Driggers for his critical review and advice on this manuscript.
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Hoffmayer, E.R., Sulikowski, J.A., Hendon, J.M. et al. Plasma steroid concentrations of adult male Atlantic sharpnose sharks, Rhizoprionodon terraenovae, in the northern Gulf of Mexico, with notes on potential long term shifts in reproductive timing. Environ Biol Fish 88, 1–7 (2010). https://doi.org/10.1007/s10641-010-9603-3
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DOI: https://doi.org/10.1007/s10641-010-9603-3