A review of American Shad Passage of the Easton and Chain Dams for the 2009 Season

Since the mid 1990’s, the Pennsylvania Fish and Boat Commission (PFBC) has monitored passage of American shad at the Easton and Chain Dam fishways on the Lehigh River. Both fishways were modified in 2000 and ready for the 2001 run. Enhancements to both fishways were based on PFBC observations and USFWS design updates. Ultimately construction was funded by PA DCNR Parks and included the following: 1) Easton auxiliary flow system was modified to eliminate air entrainment to provide its full complement of additional flow into the entrance chamber of the fishway to create the proper attraction flow for American shad emanating from the fishway, and 2) Chain Dam fishway was modified to reduce air entrainment in and realign the projecting attraction flow emanating from the fishway entrance to bisect the middle of the base pool below the dam. For the 2009 season, passage of shad through these fishways was poor during the monitoring period from 1 April to 26 June, 2009. A minimum of 425 adult American shad passed the Easton fishway; whereas a minimum of 60 adults passed through the Chain Dam (Table 1). These passage numbers represent the third and second lowest passage reported during the post-modification period (2001-2009), at Easton and Chain Dams, respectively. Further, the observed poor passage in 2009 continues a declining trend since 2006; and represents a 91% and 97% decrease of passage relative to 2001 when 4,740 and 2,057 shad passed through the Easton and Chain Dam fishways, respectively.

Success of the American shad run passing through the Easton and/or Chain Dam fishways are most likely influenced by multiple factors. The low passage of shad could simply reflect the declining trend in American shad stocks observed along the Atlantic coast. In other words, there are simply fewer shad returning to the Delaware River from ocean stocks. Passage through the Easton Dam is thought to be both temperature and river flow dependent, and perhaps also dependent upon density of shad in the river system. Warming river temperatures provide environmental queues to shad to cease migrating upriver and initiate spawning behaviors. High river flow in particular, has the potential to subsume fishway attraction flows decreasing the probability of shad orientating to the fishway entrance. Passage through the Chain Dam is dependent upon those shad, which pass through the Easton Dam fishway. In 2009, the Chain Dam passed 14.1% (60 of 425 shad) of Easton’s total passage. Shad are known to utilize Riverview Park pool (RM 2.55) located below the Chain Dam (RM 3.0), for spawning. Thus, shad that pass the Easton fishway may not behaviorally desire to attempt passing the Chain Dam fishway. Our vigilant monitoring continues.