796 



Fishery Bulletin 91|4), 1993 



non-tidal river. Presumably, expansion of the spawning 

 and nursery grounds is a first step in recovery of the 

 stock. 



There was little difference in M. americana abun- 

 dance in the Delaware River between our study and the 

 historical data (Tables 1 and 3), suggesting that the 

 poor water quality may have had little impact on M. 

 americana spawning and nursery activities in the Dela- 

 ware River. We observed that most M. americana lar- 

 vae were concentrated upstream of Philadelphia in an 

 area where water quality was not as seriously impacted 

 as below Philadelphia (Albert, 1988). Unlike A. 

 sapidissima, which leave the estuary and must return 

 through the Philadelphia region to spawn, M. americana 

 remain in the estuary throughout their life cycle. Pre- 

 sumably, these life history characteristics have allowed 

 M. americana to avoid effects of the poor water quality 

 of the Philadelphia area more effectively than shad. 



We found that larval M. saxatilis were primarily con- 

 centrated in the area downstream of Philadelphia. Since 

 this area historically had the worst water quality, the 

 M. saxatilis population should have benefitted from wa- 

 ter quality improvements. The Delaware River beach 

 seine monitoring survey, conducted annually by the State 

 of New Jersey, showed a consistent increase in young- 

 of-year M. saxatilis abundance throughout the 1980s 1 . 

 However, we did not find the density of eggs to be higher 

 in our study than in the 1970s, and the density of 

 larvae was only slightly higher. We did find that present 

 densities of M. saxatilis eggs and larvae in the Dela- 

 ware River are considerably less than in the Hudson 

 River 1 " or the Chesapeake Bay ( Setzler-Hamilton et al., 

 1981; Grant and Olney, 1991). This may be due, in part, 

 to a year effect, since juvenile abundance in the Dela- 

 ware River in 1988, as measured by the beach seine 

 survey, was lower than in any other year since 1985. 

 However, it is possible that higher juvenile abundance 

 in the late 1980s resulted from better survival of larvae 

 as water quality improved (Burton et al., 1992), rather 

 than from increased egg production. 



We found that the density of M. saxatilis eggs was 

 considerably higher in the C&D Canal than in the 

 mainstem Delaware River. This finding seems to sup- 

 port studies suggesting that the mechanism for main- 

 tenance of the Delaware River M. saxatilis population 

 is transport of eggs spawned in the Chesapeake Bay 

 through the C&D Canal (Chittenden, 1971; Johnson 

 and Koo, 1975). Our data, however, are probably more 

 consistent with that of Kernehan et al. (1981), who 



18 Lawler, Matusky, and Skelly Engineers iLMS). 1989. 1986 and 

 1987 year class report for the Hudson River estuary monitoring 

 program. Prep, bv LMS. Pearl River. NY, for Consolidated Edison 

 Co., New York, NY. 



suggested that most of the eggs transported through 

 the canal are not viable. In spite of finding consider- 

 ably elevated densities of eggs in the C&D Canal, no 

 larvae were found there, and we collected fewer than 

 10 larvae within 10 km of where the C&D Canal emp- 

 ties into the Delaware River estuary. Most of the M. 

 saxatilis larvae we found in the Delaware River were 

 collected between the Delaware Memorial (rkmlll) 

 and Commodore Barry (rkml32) bridges, more than 

 30 km upstream of the C&D Canal. This distance rep- 

 resents about three tidal excursion distances, and while 

 upstream transport of eggs is possible in some estua- 

 rine systems (Norcross and Shaw, 1984), it is unlikely 

 to occur in this portion of the Delaware because of the 

 lack of a well-defined thermocline or pycnocline that 

 would allow for two-layer circulation. Thus, it is more 

 likely that most of the M. saxatilis larvae found in the 

 Delaware River were actually spawned in the river. 



Acknowledgments 



We would like to thank P. Kazyak, J. Gurley, A. Brindley, 

 J. McGroder, M. Young, and C. DeLisle for their consid- 

 erable efforts in both the field and laboratory aspects of 

 this project. We would also like to thank W Richkus, J. 

 Frithsen, S. Beck and C. DeLisle for helpful comments 

 on the manuscript, and J. Miller for his help in all 

 aspects of the project. This work was funded as part of 

 a continuing striped bass management effort by the 

 Delaware Basin Fish and Wildlife Management Coop- 

 erative, which includes the Delaware Division of Fish 

 and Wildlife, Pennsylvania Fish Commission, New Jer- 

 sey Division of Fish, Game and Wildlife, New York Di- 

 vision of Fish and Wildlife, U.S. Fish and Wildlife Ser- 

 vice, and the National Marine Fisheries Service. 



Literature cited 



Albert, R. C. 



1988. The historical context of water quality manage- 

 ment for the Delaware estuary. Estuaries 11:99-107. 

 Burton, W. H., S. B. Weisberg, A. Brindley, and J. A. 

 Gurley. 



1992. Early life stage survival of striped bass in the 

 Delaware River, USA. Archives for Environmental 

 Contamination and Toxicology 23:333-338. 

 Chambers, J. R., J. A. Musick, and J. Davis. 



1976. Methods of distinguishing larval alewife from lar- 

 val blueback herring. Chesapeake Science 17:93-100. 

 Chittenden, M. E. 



1971. Status of the striped bass, Morone saxatilis, in 

 the Delaware River. Chesapeake Science 12:131-176. 

 1974. Trends in the abundance of American shad, Alosa 

 sapidissima, in the Delaware River basin. Chesa- 

 peake Science 15:96-103. 



