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Lehigh River
American shad spawning run – 2010
 

The 2010 spawning run passage of American shad through the Easton fishway (RM 0.0), was suggestive of an increase in the spawning run into the Lehigh River, at least up-river of the Easton Dam. Yet the passage of shad into the adjacent reach, up-river of the Chain Dam (RM 3.0) remained low and continues to frustrate staff as well as concerned anglers.

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.

Figure 1

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.

Figure 2

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.

Figure 3

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).

Table 1. Total catch, total catch-per-unit-effort (CPUE) and percent occurrence of wild American shad recaptured from the Chain Dam plunge pool (RM 2.99) and the Palmer Township Riverview Park fishing pool (RM 2.55), Lehigh River. No sampling was accomplished in 2003.
Year Total No. Time (hrs) CPUE Total No.
Hatchery
Shad
Total No.
Wild Shad
Percent
Wild Shad
1995 33     24 9 26.4
1996 39 0.30 106.67 36 3 7.7
1997 54     51 3 5.5
1998 53     52 1 1.9
1999 104 0.61 164.45 96 8 7.6
2000 100 1.42 70.60 91 9 9.0
2001 105 0.29 364.68 96 9 8.6
2002 100 0.41 243.24 89 11 11.0
2003 0          
2004 62 0.57 109.14 50 12 19.4
2005 13     8 5 38.5
2006 55 0.62 82.74 40 15 27.3
2007 40 1.32 30.28 23 17 42.5
2008 42 1.14 36.88 21 20 47.6
2009 27 1.93 13.97 17 10 37.0
2010 97 1.00 96.51 64 32 33.3
Estimation of age and repeat spawning marks allow biologists to further characterize the shad spawning run in the Lehigh River. For the 2010 spawning run, age class 5 (2005 year class) for both female and male shad was the most frequently occurring age interpreted from scale microstructure (Table 2). Comparison across years, suggests that age class 5 is consistently the dominant class for females. However, males typically return a year earlier than females, thus age 4 is usually the dominant age class. The observation of age distribution for the 2010 spawning run is not unusual compared to previous years. Thus, the spawning run in the Lehigh River is supported by multiple age classes, yet in some years nearly half of the spawning shad can be represented by a single dominant age class. Staff would like to see the continued presence of multiple age class, however, those age classes should represent the older (more mature) shad rather than shad younger than age 5 (less mature shad, particularly for females) as is the current and past status of the age structure of the Lehigh River shad population.
Table 2. Percent frequency of age distribution as interpreted from scale microstructure for female and male shad caught electrofishing the Chain Dam (RM 2.99) plunge pool and Palmer Township Riverview Park fishing pool (RM 2.55) from 1996-2010.
  Age Class  
Year 2 3 4 5 6 7 8 9 Total
Female
1996                  
1997                  
1998     26.09 69.57 4.35       23
1999   8.57 45.71 42.86 2.86       35
2000     3.03 57.58 36.36 3.03     33
2001     13.51 54.05 21.62 10.81     37
2002     16.67 53.70 27.78 1.85     54
2003                  
2004     12.90 48.38 32.25       31
2005     20.00 20.00 40.00 20.00     5
2006   10.00 35.00 50.00 5.00       20
2007     30.77 42.31 26.92       26
2008     3.03 15.15 18.18 42.42 18.18 3.03 33
2009     33.33 0.00 44.44 11.11 11.11   9
2010     21.74 69.57 8.70       23
Male
1996                  
1997                  
1998   33.33 58.33 8.33         24
1999 1.64 14.75 77.05 6.56         61
2000   1.59 17.46 65.08 15.87       63
2001   10.45 58.21 26.87 4.48       67
2002   2.27 34.09 61.36 2.27       44
2003                  
2004   29.03 29.03 38.70 3.22       31
2005   12.50 37.50 12.50 37.50       8
2006   11.43 42.86 40.00 0.00       35
2007   21.43 42.86 28.57 7.14       14
2008   33.33 0.00 0.00 33.33 33.33     9
2009   5.56 77.78 16.67         18
2010   4.35 36.23 57.97 1.45       69
Interpretation of shad scales for the presence of repeat spawning mark(s) can provide an understanding of the contribution of returning shad to the spawning run (Table 3). Typically repeat spawning shad are from the older age classes. For the 2010 spawning run in the Lehigh River, none of the examined scales contained a repeat spawning mark, suggesting all of the shad examined (N = 92) were first-time spawners. Comparison from prior years, suggest the high occurrence of virgin or first -time spawners observed in 2010 is not uncommon. Female shad tend to have a slightly greater propensity to return in future years and spawn a second, third or more times than males, although for either sex, a first time repeat spawning shad is the most typical. In other words, once a shad has spawned in the Lehigh River, there is a very low occurrence of that shad returning to the Lehigh River for spawning in the following future years.
Table 3. Frequency of occurrence of repeat marks as interpreted from scale microstructure by sex from shad collected in the Lehigh River Chain Dam plunge pool (RM 2.99) and Palmer Township Riverview Park fishing pool (RM 2.55), 1996-2010.
  Repeat mark  
Year 0 1 2 3 4 5 Total
Female
1996              
1997              
1998 78.3 21.7         23
1999 97.4 2.6         38
2000 90.9 6.1 3.0       33
2001 100.0           37
2002 77.8 22.2         54
2003              
2004 96.8 3.2         31
2005 20.0 40.0 40.0       5
2006 95.0 5.0         20
2007 92.3 7.7         26
2008 39.4 18.2 21.2 18.2   3.0 33
2009 11.1 33.3 44.4 11.1     9
2010 100.0           23
Male
1996              
1997              
1998 87.5 4.2         24
1999 97.0 3.0         66
2000 84.1 12.7 3.2       63
2001 94.0 6.0         67
2002 86.4 13.6         44
2003              
2004 96.8 3.2         31
2005 37.5 37.5 25.0       8
2006 87.9 12.1         33
2007 100.0           14
2008 66.7 11.1 11.1 11.1     9
2009 72.2 27.8         18
2010 100.0           69
In addition to passage of American shad, a variety of other fishes were observed successfully passing both the Easton and Chain fishways (Table 4). By far, white suckers (N = 2,986 ind.) and sea lamprey (N = 1,537 ind.) were the most commonly recorded for the 2010 monitoring period.
Table 4. Fishes observed migrating through the Easton (RM 0.0) and Chain (RM 3.0) fishways, 2001-2010.  Note monitoring at the Chain fishway in 2004 was terminated in early April due to equipment failure.
Fish
Species/Type
Easton Fishway
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
American shad 4740 3314 422 754 675 2023 1397 408 425 1935
Herring sp. 0 0 0 1 11 0 0 0 0 0
Gizzard shad 392 121 6 16 21 720 472 192 206 62
Striped bass 0 1 0 1 3 1 3 2 0 9
American eel * 12* * 1* 35 20* 6* 24 1 1
Sea lamprey 894 490 233 6936 1882 1366 5657 4674 1738 1537
Trout 267 309 75 199 313 282 160 129 170 354
Muskellunge 8 7 2 11 3 2 6 9 8 1
Chain pickerel 0 0 0 0 0 0 0 0 0 0
Walleye 1 2 0 1 37 0 7 20 10 13
Yellow perch 3 1 0 0 1 6 0 0 0 0
Bass 377 584 221 147 161 1026 398 592 719 349
Sunfish/Crappie 504 346 77 83 225 893 167 491 513 437
Carp 651 726 558 437 679 1322 600 640 567 334
Quillback 21 22 8 24 26 34 28 31 29 37
Catfish 367 381 122 262 340 830 378 525 573 490
Minnows/Fallfish 279 109 66 351 258 257 14 15 55 500
Sucker 2292 1156 1867 3797 688 2549 9408 6960 3045 2986
Unknown 32 177 72 142 123 81 334 58 95 64
Total 10828 7746 3729 13162 5471 11392 19029 14770 8154 9109
  Chain Fishway
American shad 2057 1479 40 . 324 588 215 84 60 169
Herring sp. 0 0 0 . 0 0 0 2 0 0
Gizzard shad 416 72 3 . 38 383 188 71 76 24
Striped bass 0 0 0 . 0 0 0 0 0 1
American eel * 80* 5* . 401 30* 66* 1,923 59 403
Sea lamprey 570 1321 163 . 2346 4194 384 1,318 1,477 3296
Trout 205 321 106 3 352 124 71 212 194 292
Muskellunge 0 2 2 . 4 6 0 0 1 1
Chain pickerel 0 0 0 . 0 0 0 0    
Walleye 1 0 4 . 54 13 3 7 8 3
Yellow perch 59 2 0 . 10 0 0 0 2 1
Bass 575 876 298 . 221 824 140 484 692 444
Sunfish/Crappie 1089 850 215 . 605 617 186 502 350 472
Carp 193 244 138 . 266 247 94 220 208 86
Quillback 0 0 0 . 0 2 0 0 0 0
Catfish 318 210 93 . 184 337 193 298 341 271
Minnows/Fallfish 320 158 84 . 793 245 30 15 62 64
Sucker 1143 621 1227 254 1741 1621 1812 862 9,533 3873
Unknown 10 65 346   167 407 336 96 59 80
Total 6956 6221 2719 257 7506 9608 3652 6094 13122 9500
Area 5 staff would like to pass on one encouraging parting thought. During routine fall sampling in various pools throughout the non-tidal reaches of the Delaware River, Area 5 Biologists observed numerous schools of young-of-the-year (YOY) American shad dimpling the water surface. The extent of this dimpling created an effect similar to a “light” rain striking the water’s surface. These observations tend to be suggestive of a solid YOY production year from the 2010 spawning run. Hopefully, this will translate into a strong return of spawning adults in future years.

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