CHITTENDEN: PRESENT SPAWNING GROUNDS OF SHAD 



stretch from Torresdale, Pa., to the Delaware 

 Memorial Bridge, the most severely affected area 

 being from Chester, Pa., to the Benjamin 

 Franklin Bridge (Chittenden 1969). Minimum 

 daily dissolved oxygen levels of about 2.5-3.0 mg/ 

 liter are needed to permit mere survival of shad, 

 and this is not a reasonably normal existence 

 (Chittenden 1973a). 



Some spawning probably occurs in fresh water 

 seaward of Philadelphia when low oxygen pre- 

 vents upstream passage of part of the run. There- 

 fore, this area would be a nursery. The area is 

 limited in extent, however, and survival of fish 

 may be precarious because of daily dissolved oxy- 

 gen fluctuations due to photosynthesis or tidal 

 movement of polluted water, de Sylva et al. (1962) 

 collected larval shad, but no juveniles, in the Del- 

 aware River estuary shore zone even though the 

 euryhaline young can and do utilize brackish 

 nurseries (Chittenden 1973b). Production of shad 

 seaward of Philadelphia, at best, apparently is 

 small because landings in the Delaware Basin 

 have been low for more than 50 yr. 



The West Branch is apparently no longer an 

 important nursery. Young shad were repeatedly 

 collected at Hancock in 1963, but none were cap- 

 tured in two collections with lights in 1964 and 

 1966. Cold water releases from Cannonsville Res- 

 ervoir, which began after summer 1963, may ac- 

 count for the apparent absence of young in the 

 West Branch thereafter (Chittenden 1972). If so, 

 the East Branch and possibly the Delaware below 

 Hancock may be of precarious suitability for 

 spawning and nursery purposes, because Pepac- 

 ton Reservoir on the East Branch is also designed 

 for water release from the hypolimnion. 



Tributaries act as nurseries and possibly 

 spawning grounds but are probably not impor- 

 tant to production today in the Delaware River. 

 Compton (1963) captured 38 young on 23 July 

 1962 in Big Flat Brook, nearly 1.6 km from the 

 Delaware, and adults have been observed in sev- 

 eral tributaries. Tributaries in nontidal water are 

 too small to support many fish, however, except 

 for the Lehigh River (km 168) which is dammed 

 near its junction with the Delaware. Those in 

 tidal water near or upstream of the Philadelphia 

 area are dammed, affected by tidal movement of 

 low oxygen water, or the young produced therein 

 reach Philadelphia too early in summer or fall to 

 successfully pass seaward (Chittenden 1969). 



The present findings on spawning and nursery 

 areas agree with Sykes and Lehman's (1957) ob- 



servations and with their descriptions of unpub- 

 lished findings of Cable: plankton tows were 

 taken in May 1944 from Bordentown, N.J., to 

 Equinunk, Pa.; the greatest concentration of eggs 

 was above Lackawaxen and no eggs were found 

 below Lumberville, Pa. Therefore, it would ap- 

 pear that the chief spawning grounds and nur- 

 series have remained about the same for at least 

 the last 30 yr and probably since about 1910-20. 



Areas Contributing to 

 Successful Production of Adults 



It appears that there has been a fundamental 

 shift in the chief spawning grounds and nurseries 

 since the decline of the Delaware River shad 

 runs. Historically the chief spawning grounds 

 were downstream of Delaware Water Gap and in- 

 cluded the tidal area. These areas are now of little 

 importance; since the decline, the chief spawning 

 grounds have been upstream of Delaware Water 

 Gap. The most important spawning grounds and 

 nurseries for the last 60 yr or more have seem- 

 ingly been near the Hancock area. 



Implications of the shift in spawning and nur- 

 sery areas include the existence of an intrastream 

 homing tendency which brings the fish back to 

 spawn in their general area of birth. Chittenden 

 (1969) discussed in detail causes of the decline in 

 abundance of Delaware River shad and why 

 abundance has remained low. I suggested 

 (1969:424) that the shift in spawning and nursery 

 areas occurred because pollution near Philadel- 

 phia has selected for an upstream-spawning stock 

 based upon the time when the young reach 

 the Philadelphia area; fish produced farthest 

 downstream have the greatest probability of 

 reaching Philadelphia before dissolved oxygen 

 improves sufficiently to permit successful sea- 

 ward passage. This implies intrastream homing. 

 Interstream homing exists in shad (Hammer 

 1942; Hollis 1948; Talbot and Sykes 1958; Nichols 

 1960), but direct evidence of intrastream homing 

 is desirable. 



Spawning and nursery areas near Hancock are 

 apparently the key to maintenance of the rem- 

 nant Delaware River shad runs, because Chit- 

 tenden (1969) demonstrated that the last fish to 

 move seaward were, in general, those produced 

 farthest upstream. The extent of the spawning 

 and nursery area since about 1910-20 or earlier 

 has probably expanded and contracted depending 

 upon the size of the run and spawning success. 



349 



