72 



Fishery Bulletin 105(1) 



years of age). We also should expect that, for similar 

 energetic reasons, not every female, which undertakes 

 a springtime up-estuary migration, will actually spawn. 

 Some mature females in a spawning run will not spawn; 

 rather, they will reabsorb final-stage oocytes (first au- 

 thor, personal observ. ). Therefore, accurate measurement 

 of spawning frequency depends on both the probability 

 of successful spawning in the field and the frequency of 

 up-estuary migratory runs. 



X-ray maps confirmed an annual cycling in otolith 

 strontium, but also showed cycles during the immature 

 period of females, contrary to patterns observed from 

 life history transects. Further, X-ray mapping and life 

 history transects indicated that many yearlings move 

 into oceanic regions — a pattern observed for Hudson 

 River striped bass (Zlokovitz et al., 2003) but not yet 

 described for Chesapeake Bay striped bass. The pos- 

 sibility that young-of-the-year or yearling striped bass 

 are present in ocean environments deserves additional 

 research in the Chesapeake Bay and elsewhere. 



Contingent migration behavior 



In past research on Hudson River striped bass, we 

 observed modalities in lifetime migration behaviors 

 (Secor et al., 2001); groups of individuals that share 

 similar migration behaviors with some, but not all, 

 members of their population are termed "contingents" 

 (Hjort, 19141; Gilbert 19172; Secor, 1999). In particular, 

 one contingent comprising a small fraction of the Hudson 

 River springtime sample was resident to freshwater and 

 oligohaline regions and was heavily contaminated by 

 polychlorinated biphenyls — an apparent consequence of 

 this lifetime migration behavior (Zlokovitz and Secor, 

 1996; Ashley et al., 2000). A similar contingent migra- 

 tion behavior has been reported for the Steweiacke 

 River population of striped bass in Nova Scotia (Morris 

 et al., 2003). In contrast, only a single Chesapeake 

 Bay striped bass (of 40 analyzed) exhibited freshwater 

 resident behavior. Small sample sizes could indicate 

 considerable error in estimates of the frequency of this 

 behavior among populations if these estimates are based 

 on research to date, but the fact that three distinct 

 populations exhibited this behavior in our study indi- 

 cates that contingent migration structuring is common 

 to Chesepeake Bay striped bass. 



Contingent migration structure has been observed 

 across diverse taxa, such as American eels (Anguilla 

 rostrata), American shad (Alosa sapidissima), white 

 perch (Morone americana), bluefish (Pomatoinus salta- 



' Hjort, J. 1914. Fluctuations in the great fisheries of north- 

 ern Europe. Rapports Conseil Permanent International Pour 

 L'exploration de la Mer, 20:1-228. Library, Chesapeake 

 Biological Laboratory, P.O. Box 38, Solomons, MD 20688. 



- Gilbert, C. H. 1917. Contributions to the life-history of the 

 sockeye salmon. Paper No. 4, report to the Commissioner 

 of Fisheries. British Columbia Fisheries Department, 48 

 p. + plates. Library, Pacific Biological Station, Fisheries 

 and Oceans Canada, 3190 Hammond Bay Road, Nanaimo, 

 V9R 5K6 British Columbia. Canada. 



trix), and Atlantic bluefin tuna (Secor, 1999, in press; 

 Fromentin and Powers, 2005). Here, a nursery or forag- 

 ing habitat associated with one contingent migration 

 behavior may make a small contribution in a given 

 year, but over a decade may contribute significantly 

 to spawning stock biomass. Thus, over generation-long 

 time scales, we should expect that minority lifetime 

 migration behaviors can contribute significantly to 

 sustained recruitment. Further research is needed to 

 determine the proximate cause of contingent struc- 

 ture, but based upon research on the sympatric white 

 perch, we advance the hypothesis that Chesapeake 

 Bay striped bass contingent migration structuring re- 

 sults from divergent early growth rates and dispersal 

 behaviors associated with early growth (Kraus and 

 Secor, 2004b). 



Acknowledgments 



We acknowledge NOAA MARFIN (Marine Fisheries 

 Initiative, Northeast Center) support for this research. 

 S. McGuire assisted with otolith preparation and data 

 analyses. Personnel at Maryland Department of Natural 

 Resources, Horn Point Environmental Laboratory, and 

 the U. S. Fish and Wildlife Service assisted in collection 

 of striped bass. The electron probe microanalyzer was 

 purchased, in part, by a grant from the National Science 

 Foundation (EAR 98-1244). 



Literature cited 



Ashley, J. T. F, D. H. Secor, E. Zlokovitz, J. E. Baker, and S. Q. 

 Wales. 



2000. Linking habitat use of Hudson River striped bass to 

 accumulation of polychorinated biphenyl congeners. En- 

 viron. Sci. Techn. 34:1023-1029. 

 Block, B. A., L. L. H. Teo, A, Walli, A. Boustany, M. J. W. 

 Sokesbury, C. J. Farwell, K. C. Weng, H. Dewar, and T. D. 

 Williams. 



200.5. Electronic tagging and population structure of 

 Atlantic bluefin tuna. Nature 434:1121-1127. 

 Chambers, R. C, and T.J. Miller. 



1995. Evaluating fish growth by means of otolith incre- 

 ment analysis: Special properties of individual-level 

 longitudinal data. In Recent developments in fish 

 otolith research (D. H. Secor, S. E. Campana, and J. 

 M. Dean, eds.), p. 155-175. Belle W. Baruch Library 

 in Marine Sciences Number 19. Univ. South Carolina 

 Press, Columbia, SC. 

 Dorazio, R. M., K. A. Hattala, C. B. McCollough, and J. E. 

 Skjeveland. 



1994. Tag recovery estimates of migration of striped bass 

 from spawning areas of the Chesapeake Bay. Trans. 

 Am. Fish. Soc. 123:950-963. 

 Fromentin, J. M., and P. E. Powers. 



2005. Atlantic bluefin tuna: population dynamics, ecol- 

 ogy, fisheries, and management. Fish and Fisheries 

 6:281-306. 

 Goodyear, C. P. 



1984. Analysis of potential yield per recruit for striped 



