72 



Fishery Bulletin 100(1) 



across the shelf to account for this spatial pattern of older 

 and larger juveniles farther offshore. The last process was 

 identified earlier as potentially important. Testing and 

 eliminating these hypotheses, however, requires spatially 

 explicit lan'al distribution data, in addition to the benthic 

 data that we collected, which would allow a comparison 

 of pre-and postsettlement distributions with abundance 

 of Prionotus propagules. Spatially explicit environmental 

 data would also be useful because we obsei-ved dynamic 

 changes in the physical parameters in our sampling area, 

 and we suspect that these could affect Prionotus sui-vival. 

 Vertical stratification of the water column was noted near 

 Beach Haven Ridge on 14 August 1991, but not during 

 cruises in September or October 1991. Low dissolved oxy- 

 gen levels near the bottom of the ridge, at about 3 ppm 

 (in contrast to >8 ppm in the upper water column) could 

 have negatively affected settlement rates near the ridge in 

 1991. Stratification near the ridge was also noted in 1992 

 with similarly depressed levels of dissolved oxygen (Hales 

 et al.^). Low dissolved oxygen offshore of New Jersey is not 

 uncommon (Falkowski et al., 1980; Glenn et al., 1996) and 

 may be another process that can contribute to geographic 

 variations in size and age of Prionotus species offshore of 

 the middle Atlantic states. We postulate that spatially ex- 

 plicit patterns of reproductive seasonality and age-0 fish 

 size for P. carolinus and P. evolans within coastal waters 

 offshore of the middle Atlantic states are related to each 

 other because the short planktonic larval durations for 

 both species limit larval dispersal. Interannual variations 

 in water temperature or vertical stratification of oxygen 

 concentrations may be proximate causes for these geo- 

 graphic variations of reproductive seasonality and age-0 

 size. These patterns could be somewhat unique to searo- 

 bins, compared with other regional fishes, because searo- 

 bins use both estuarine and shelf habitats for spawning. 



Acknowledgments 



R. Cowen, J. Hare, J. P. Grassle, R. Loveland, and C. L. 

 Smith contributed thoughtful discussions and helpful com- 

 ments on earlier drafts. S. Richards provided cultured 

 specimens of searobins and miscellaneous data that had 

 been used in P. Yuschak's research. This study was part 

 of a doctoral dissertation (R. S. M.) and was supported 

 by the Institute of Marine and Coastal Sciences (IMCS), 

 Rutgers University Marine Field Station, Anne B. and 

 James H. Leathem Fund, Manasquan Marlin and Tuna 

 Club, NOAA National Undersea Research Program for the 

 Middle Atlantic Bight, and NOAA Sea Grant Program. 

 Final preparation and revision of this manuscript were 

 made while the senior author was employed by the Florida 

 Marine Research Institute. We thank all of the above. 



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