A minimum of 1,935 adult American shad passed the Easton fishway in 2010. The passage of the first recorded American shad in 2010 was on 7 April with shad being recorded through 28 June. A significant number of shad (N = 79) passed very early in the season (7 April – 9 April). The greatest movement occurred from May through mid- June with multiple peaks in passage: May 1 – 9 May (N = 631 shad), May 14 – 17 May (N = 315 shad), and May 21 – 7 June (N = 657 shad). The final surge of adult shad occurred during the period from June 11 – 15 June (N = 123 shad; Figure 1). The “second” run of shad, known as the May shad run, which generally occurs in the last weeks of May, was not discernable in our passage counts.

A minimum of 169 adult American shad passed the Chain fishway in 2010. The passage of the first recorded American shad was on 25 April with shad being recorded through 26 June. Generally passage of shad through the Chain fishway was sporadic with low numbers (N < 10) of shad passing on any given date. Greatest passage occurred May 15 – 16, June 1, and June 14 when at least 52, 10, and 38 shad passed, respectively representing 59.5 % of the total passage above the Chain Dam (Figure 1).

Figure 1. Plot of daily passage of American shad at the Easton and Chain fishways and Lehigh River average daily water temperature (oC) from 1 April through 30 June 2010. Average daily river temperatures were obtained from the USGS Easton, PA station 01454720, data classified as provisional. From 2 June through 30 June, 2010 water temperature was unavailable from Easton gage.

The 2010 passage of shad through the Easton fishway represents a substantial increase relative to recent observed passage 2008 and 2009 (Figure 2). Since the completion of fishway modifications for the 2001 spawning run, shad passage was suggestive of two peaks of passage observed in 2001 (N = 4,740 shad) and 2006 (N = 2,023 shad); whereas observed passage during the years of 2003 (N = 422), 2008 (N = 408) and 2009 (N = 425) represented poor passage runs through the Easton Fishway. The observed passage during the 2010 spawning run into the Lehigh River is suggestive of at least the same magnitude as observed during the 2006 spawning run peak, but not a return to the strong passage years observed during 2001-2002.

Figure 2. Annual passage of American shad through the Easton (RM 0.0) and Chain (RM 3.0) fishways on the Lehigh River.

Passage of shad through the Easton fishway is most likely confounded by multiple factors. First, total passage of shad into the Lehigh River could simply be a reflection of the magnitude of the returning spawning population. The apparent peaks of annual total passage most likely representing the return of successful young-of-the-year production that has recruited to the adult spawning population. Second, density-dependent factors may play a role, such that an increase in shad abundance in the Delaware River may force shad to seek other spawning grounds potentially above the Easton Dam. Third, passage may be significantly correlated with environmental factors such as water temperature and perhaps flows (Figure 1 and 3). Shad tend to pass both fishways when water significantly warms. Indeed the exceptionally warm weather during the 2010 run in early April appeared to encourage shad to pass the Easton fishway in abundance. The steadily decreasing river flows may have emphasized the attraction flows leading into the Easton fishway. However, the influence of flow on shad passage through the fishways is not well known. Correlations between shad passage and river flow were non-significant suggesting that flow is unrelated to shad passage; however, it most likely has a confounding influence with other water quality parameters such as temperature and pH. Finally, all these factors, and others may play a role in passage counts and each may have greater or lesser influence depending upon the year.

The 2010 passage of shad through the Chain fishway was lackluster compared to the passage through the Easton fishway. Only 8.7% of the shad that passed the Easton fishway actually passed the Chain fishway. American shad are known to utilize Riverview Park pool (RM 2.55) located below the Chain Dam (RM 3.0), for spawning. Thus, these shad may not behaviorally attempt to pass through the Chain fishway.

Figure 3. Plot of daily passage of American shad passage at the Easton (RM 0.00) and Chain (RM 3.0) fishways, and mean daily flow (cfs) for the Lehigh River (USGS Glendon, PA 01454700) from 1 April through 30 June 2010. Flow was classified as provisional by the Unites States Geological Survey.

Interestingly, a total of 379 shad were observed in the viewing window located at the top (upstream end) of the Chain Dam fishway but failed to successfully pass out of the fishway in 2010. In other words, these shad successfully navigated through all of the various chambers and obstacles inherent with the fishway and failed to successfully exit the viewing chamber – the last chamber in the fishway. This behavior has not been typically seen in past years of monitoring. It is perplexing as to what would prevent shad from swimming out of this final chamber. One can only speculate as to cause. Field notes indicated the Chain Dam fishway’s attraction flow was generally adequate and any occurrence of excessive aeration in the entrance chamber was minimal. The most reasonable explanation is that continued sedimentation in the backwater that the fishway exits into above the Chain Dam has altered conditions in such a way as to affect shad behavior. The Chain fishway is located on river-left just downstream of an island (RM 3.1 – RM 4.4) that is part of the Hugh Moore Park. Over the years sediments have been depositing off the downstream tip of the island in such a manner as to fill in the existing legacy canal or channel on river-left and advance towards the fishway exit. The potential exists that the sedimentation has finally encroached, or altered the flow close enough to the fishway exit to inhibit shad exiting the viewing chamber and into upstream reaches of the Lehigh River. From field notes, the sediment encroachment is essentially only leaving 1-2 feet of clearance from the fishway exit forcing the shad to immediately turn back towards the Dam ogee to successfully find the deep channel water above the Dam. Unfortunately, it appears that the majority (68.9%, N = 379) of shad observed in the viewing chamber are unable to negotiate this last obstacle.

The restoration of a sustainable spawning run of wild American shad in the Lehigh River is a fisheries management goal of the PFBC. Researchers at PFBC Van Dyke hatchery facilities produce a florescent mark on fry shad otoliths (ear bones of a fish), that when excised from harvested adult shad, the mark on the otolith can be used to identify shad that were stocked as fry by PFBC. Staff from Area 5 & 6 have been electrofishing the Chain Dam plunge pool (RM 2.99) and Palmer Township Riverview Park fishing pool (RM 2.55) to provide an estimate of the percent contribution of wild shad to the spawning run. The percent of wild shad (unmarked otoliths) has been increasing in recent years, such that for the 2008 spawning run, nearly half (48.7%) of the captured adult shad were of wild origin (i.e., not stocked by PFBC as fry; Table 1).