790 



Fishery Bulletin 91(4), 1993 



tinguished from M. saxatilis larvae based on the 

 smaller size of M. americana at this stage and on gut 

 morphology, which in M. americana parallels the noto- 

 chord for about six myomeres before turning down- 

 ward. Post yolk-sac M. americana and M. saxatilis lar- 

 vae less than 8 mm in length were separated by size 

 and the formation of fin rays, (formation of fin rays 

 occurs at about 5 mm and 8mm, respectively). Post 

 yolk-sac larvae of 8 mm and longer were identified by 

 clearing and staining the specimens and examining 

 the pterygiophore/neural spine interdigitation patterns 

 (Olney et al., 1983). A. sapidissima larvae were sepa- 

 rated from Alosa spp. by counting post-anal myomeres 

 (Lippson and Moran, 1974 :i ; Chambers et al., 1976). 



For the purpose of data presentation, the Delaware 

 River sampling effort was post-classified into lower 

 river, mid-river, and upper river regions (Fig. 1). These 

 regions corresponded to Artificial Island (rkm 87) to 

 the Christina River (rkm 114), Christina River to the 

 Schuylkill River (rkm 148), and Schuylkill River to 

 Trenton, NJ (rkm 214), respectively. Density estimates 

 were calculated for each region during each week as 

 the simple average of all samples collected in that re- 

 gion. A Friedman's rank-sum test, blocked on week, 

 was used to test for differences in density among re- 

 gions (Conover, 1980). 



Data from over 2,000 ichthyoplankton samples col- 

 lected from the Delaware River during the 1970s were 

 obtained from reports submitted as part of regulatory 

 requirements or environmental impact studies (ANSP, 

 1974 4 ; Anselmini, 1974 5 ; Anselmini 1976 K ; Potter et al., 

 1974, a and b 78 ; Harmon and Smith 1975 9 ; PECO, 1977, 

 a _eio,ii.i2.i3,i4. ^ 197 9 > a an d buue. RMC, 1979 17 ). While 



none of these studies individually provided coverage of 

 the entire tidal river, collectively they provided excel- 

 lent coverage. To compare present ichthyoplankton com- 

 position and abundance with that in the 1970s, these 

 data were digitized and summarized. 



To maximize comparability of data between periods, 

 we extracted for analysis from the historical reports 

 only those samples which were collected between mid- 

 April and mid-June with a 500-(im mesh gear that was 

 towed for at least five minutes and filtered at least 40 

 m 3 . Where studies differed in taxonomic level of identi- 

 fication, data from all studies were restated to the higher 

 taxonomic group. From these data, weekly average den- 

 sities were estimated for each region and year. Historic 

 abundances for each region were taken as the simple 

 averages of weekly estimates. We included data for only 

 years in which collections were taken in at least eight 

 weeks between April and June to ensure that our com- 



parison was not biased by data sets with limited tempo- 

 ral coverage. Comparisons of average abundance with 

 the present study were accomplished separately for each 

 region by using a Friedman's test blocked on week. 



Results 



Water quality 



Water temperature during the 1987 and 1988 survey 

 ranged from 11 to 26° C. Differences in temperature 

 between regions were less than 1°C in both years. 



' Lippson, A. J., and R. L. Moran. 1974. Manual for identification of 

 early developmental stages of fishes of the Potomac River estuary. 

 Available from Maryland Department of Natural Resources. Ref. 

 No. PPSP-MP-13, 282 p. 



I ANSP (Academy of Natural Sciences of Philadelphia). 1974. Eco- 

 logical studies in New Jersey, Oldman's Creek, Raccoon Creek, Birch 

 Creek, and the Delaware River 1972-1973. Prep, by ANSP, Phila- 

 delphia, Pennsylvania for the Shell Oil Company, Philadelphia, PA. 



5 Anselmini, L. D. 1974. An ecological study of the Delaware River 

 in the vicinity of the Mercer Generating Station, Trenton, NJ. Prep, 

 by Ichthyological Associates, Inc., Ithaca, NY, for Public Service Elec- 

 tric and Gas Co., Newark, NJ. 



h Anselmini, L. D. 1976. An ecological study of the Delaware River in 

 the vicinity of Newbold Island. Prep, by Ichthyological Associates. 

 Inc., Ithaca, NY, for Public Service Electric and Gas Co., Newark, NJ. 



; Potter, W. A., D. C. Smith, and P. L. Harmon. 1974a. An ecological 

 study of the Delaware River in the vicinity of Chester Generating 

 Station. Chester Progress Rep. 1. Prep, by Ichthyological Associates, 

 Inc., Ithaca, NY, for the Philadelphia Electric Co., Philadelphia, PA, 

 94 p. 



"Potter, W. A., D. C. Smith, and P. L. Harmon. 1974b. An ecological 

 study of the Delaware River in the vicinity of Eddystone Generating 

 Station. Eddystone Progress Rep. 3. Prep, by Ichthyological Associ- 

 ates, Inc., Ithaca, NY, for the Philadelphia Electric Co., Philadel- 

 phia, PA, 42 p. 



" Harmon, P. L., and D. C. Smith. 1975. An ecological study of the 

 Delaware River in the vicinity of Eddystone generating station. 

 Eddystone Progress Rep. 4 to Philadelphia Electric Co., Philadel- 

 phia, PA. 



1,1 PECO (Philadelphia Electric Company). 1977a. Chester Generat- 

 ing Station, 316(b) Rep., Permit No. PA 0011614. Rep. to the EPA, 

 Philadelphia, PA. 



" PECO. 1977b. Richmond Generating Station, 316(b) Rep., Permit 

 No. PA 0011649. Rep. to the EPA, Philadelphia, PA. 



12 PECO. 1977c. Southwark Generating Station, 316(b) Rep., Permit 

 No. POA 00116-65. Rep. to the EPA, Philadelphia. PA. 



1:1 PECO. 1077d. Delaware Generating Station, 316(b) Rep.. Permit 

 No. PA 0011622. Rep. to the EPA, Philadelphia, PA. 



II PECO. 1977e. Eddvstone Generating Station, 316(b) Rep., Permit 

 No. PA 00137-14. Rep. to the EPA, Philadelphia, PA. 



'' Ichthyological Associates (IA). 1979a. Effect of the cooling water 

 intake structure, intrainment and impingement of fishes. Burlington 

 Generating Station Demonstration for Section 316(b) of the Federal 

 Water Pollution Control Act Amendments of 1972, PL 95-500. Prep, by 

 IA, Ithaca, NY, for Public Service Electric and Gas Co., Newark, NJ. 



16 Ichthyological Associates (IA). 1979b. Effect of the cooling water 

 intake structure, intrainment and impingement of fishes. Mercer Gen- 

 eration Station Demonstration for Section 316(b) of the Federal Wa- 

 ter Pollution Control Act Amendments of 1972, PL 95-500. Prep, by 

 IA, Ithaca, NY, for Public Service Electric and Gas Co., Newark, NJ. 



17 Radiation Management Corporation (RMCl. 1979. An evaluation 

 of the cooling water intake at the Edge Moor Power Station. Edge 

 Moor Power Station section 316(b) Evaluation. Permit No. DE- 

 000058. Prep, by RMC, Pottstown, PA, for Delmarva Power and 

 Light Co., Wilmington. DE. 



