Juvenile American shad were collected by haul seine at Columbia, in lift nets at Holtwood, in cooling water intakes at Peach Bottom Atomic Power Station, and in strainers at Conowingo Dam. Haul seine GM CPUE (combined daily lifts) of 0.01 was the lowest recorded for that gear type since 1990. Lift-net GM CPUE (combined daily lifts) of 0.03 was among the lowest recorded for that gear type for the period of record. Lift net AUC was the second lowest recorded for the period of record. Otoliths from the four sites combined were 10% wild and 90% hatchery. Fewer eggs were delivered to the Van Dyke Hatchery, resulting in decreased production of hatchery larvae, and decreased production of juvenile American shad in the Susquehanna River basin.
The Conowingo West Fish Lift continued to be used as a source of adult American shad and river herring to support monitoring activities and tank spawning. A total of 3,970 adult shad were collected at the Conowingo West Lift. The majority were released back into the Conowingo tailrace, with 1,516 retained for tank spawning.
Since the completion of fish passage facilities at Holtwood and Safe Harbor in 1997, the Conowingo East Lift has operated in fish passage mode. American shad had access to the Fabri-Dam on the Susquehanna main stem, and Warrior Ridge or Raystown Dams on the Juniata. Portions of large tributaries including Muddy Creek, West Conewago Creek, Conestoga River, Conodoguinet Creek, and Swatara Creek were also accessible to American shad.
During the 2006 spring migration, Conowingo East Lift passed 56,899 American shad while fishways at Holtwood, Safe Harbor, and York Haven passed 35,968, 24,929 and 1,913 American shad, respectively. No river herring were passed at Conowingo, Holtwood, Safe Harbor or York Haven Dams. Four hickory shad were passed at Conowingo Dam, but none were passed at upstream dams.
Juvenile American shad in the Susquehanna River above Conowingo Dam are derived from two sources, natural reproduction of adults passed at the lower river hydroelectric projects, and hatchery produced, marked larvae from Pennsylvania Fish and Boat Commission’s (PFBC) Van Dyke Hatchery in Pennsylvania. Juveniles occurring in the river below Conowingo and the upper Chesapeake Bay may result from natural spawning below or above dams and hatchery fry stockings either in Maryland or from upstream releases in Pennsylvania.
During the 2006 production season, the PFBC Van Dyke Research Station for Anadromous Fish produced 4.3 million shad larvae which were released in the Susquehanna Basin in Pennsylvania. Most larval releases occurred from May 22 to May 29 and June 7 to June 12 to avoid an episode of high flow from May 31 to June 6 (Figure 1). Larvae were released in the following locations and numbers:
|Juniata River (various sites)
|North Branch Susquehanna River (NY)
|Chemung River (NY)
|North Branch Susquehanna River (PA)
|West Branch Susquehanna River
|West Conewago Creek
Insert figure 1 here
The production goal of 10 million larvae was not met, primarily due to fewer eggs shipped from the Hudson River.
Sampling for juvenile American shad was conducted at locations in the Susquehanna River Basin during the summer and fall in an effort to document in-stream movement, out-migration, abundance, growth, and stock composition/mark analysis. Juvenile recoveries from all sources were provided to the PFBC for otolith analysis. Otoliths were analyzed for tetracycline marks to determine hatchery versus wild composition of the samples.
Geometric mean catch-per-unit effort (CPUE) was calculated as an index of juvenile abundance for haul seine and lift net collections. Ideally, CPUE would be calculated using data from individual lifts or seine hauls. Unfortunately, this data is not available prior to 1995 for lift netting and prior to 1997 for haul seining. As a result, geometric means could not be computed in the usual way for those years. Combined daily catch for each gear is available and was used as a surrogate to compute GM means. ASMFC stock assessment (due to be released in 2007) recommends use of area-under-the-curve (AUC) methods in cases where sampling is targeted at migrants moving through an area (Andy Kahnle, NY Dept. of Conservation, personal communication). Because the Holtwood dam lift net collects juvenile shad during the directed outmigration, (AUC) measures of juvenile abundance were also calculated for lift net collections.
Haul Seining - Main Stem
Haul seining in the lower Susquehanna River was scheduled once each week beginning mid-July and continuing through October. High river flows in July postponed initial sampling until the first week of August. Fifteen weekly sampling events were planned for 2006, however, high river flows during September and in late October, coupled with the low number of juvenile shad being collected, resulted in postponement and eventually cancellation of sampling events. A total of 11 sampling events occurred. Sampling was concentrated near the Columbia Borough boat launch since this location proved very productive in past years. Sampling consisted of 6 hauls per date beginning at sunset and continuing into the evening with a net measuring 400 ft x 6 ft with 3/8 in stretch mesh.
Holtwood Dam, Peach Bottom Atomic Power Station, and Conowingo Dam
Sampling at the Holtwood Dam inner fore-bay began on September 12 and continued every third day through November 2006. A total of 30 sampling events was planned for 2006, but by mid- November it was apparent from the low collection numbers that further sampling efforts were not warranted. Therefore, the program was terminated after completion of 23 of the 30 scheduled events.
Sampling at the Holtwood Dam inner fore-bay was conducted using a fixed 8-ft square lift-net. Sampling began at sunset and consisted of 10 lifts with a 10-minute interval between lift cycles. The lift-net was placed on the north side of the coffer cell in the inner fore-bay. A lighting system was used to illuminate the water directly over the lift-net similar to that employed in previous years.
A comprehensive program to monitor intake screens for impinged alosines at Peach Bottom APS was conducted in 2006. Sampling was conducted on a 24-hour basis, once per week from September 5 to October 17. After the first shad was collected on October 23, the sampling regime changed to daily until Nov. 17. A total of 59 samples was collected during October through November. Conowingo Hydroelectric Station’s cooling water intake strainers were also sampled for impinged alosines twice weekly from October 13 to November 20 for a total of 4 samples.
Susquehanna River Mouth and Flats
Maryland DNR sampled the upper Chesapeake Bay using haul seines in the summer and fall.
Disposition of Samples
Sub-samples of up to 30 juveniles per day were used for otolith analysis. Samples of shad from most collections were returned to PFBC's Benner Spring Fish Research Station for analysis of tetracycline marks on otoliths. Otoliths were surgically removed from the fish, cleaned and mounted on slides, ground to the focus on the sagittal plane on both sides, and viewed under ultraviolet light to detect fluorescent rings indicating tetracycline immersion treatments.
Haul Seining - Main Stem
One juvenile American shad of hatchery origin was captured by haul seine on October 18, resulting in a Geometric Mean Catch-Per-Unit-Effort (GM CPUE, individual haul) of 0.01 (Tables 1 and 2). Table 3 lists weekly catches of American shad by haul seine from 1989 to 2006. Catches generally peaked in August and September, except in 1989 and 1992 when catches peaked in July, and in 2005 and 2006 when there was no peak.
Holtwood Dam, Peach Bottom APS, and Conowingo Dam
Lift-netting at Holtwood Dam inner fore-bay resulted in 8 juvenile American shad captured in 300 lifts (Table 4). All shad were captured on October 24. Geometric Mean CPUE (individual lift) was 0.01 while GM CPUE (combined daily) was 0.03 (Table 5). Area under the curve (AUC) was 2. Historical weekly catches peaked in October, except in 1985, 1997, 2000, and 2001 when catches peaked in November (Table 6, Figure 2).
Peach Bottom intake screens produced 59 juvenile American shad and one blueback herring between October 23 and November 10 (Tables 7 and 8).
Cooling water intake strainers at Conowingo produced 4 American shad, collected between 26 October and 8 November, but only 2 specimens were suitable for analysis (Tables 9 and 10). Four alewifes were collected in strainer samples in 2006.
Susquehanna River Mouth and Flats
In 2006, 20 juvenile American shad were captured at seven permanent sites by Maryland DNR’s juvenile finfish haul seine survey during 24 hauls, and 3 juvenile American shad were captured at the auxiliary sites during 36 hauls (Table 11).
Otolith Mark Analysis
Results of otolith analysis are presented in Table 12. A total of 70 juvenile American shad were collected in haul seines, lift nets, Peach Bottom intakes and Conowingo strainers. Of the 70 specimens evaluated for hatchery tags, 10% were wild and 90% were hatchery. Represented in the catch were YOY shad from releases in the Juniata River (Potomac River egg source), Juniata River (Susquehanna River egg source), Conodoguinet Creek, Swatara Creek, Conestoga River, Chemung River, and the West Branch Susquehanna River. No shad were recaptured from releases in West Conewago Creek, or the North Branch Susquehanna River.
River conditions for the Susquehanna River Basin during 2006 could be characterized by relatively stable flows in May, August and October, with a peak during the first week of June (Figure 1), a severe flood during the end of June and early July (Figure 3), and additional peaks during early September and late October through November (Figures 3 and 4). Water temperatures at Conowingo Dam increased gradually from 50F on April 5 to 77F on June 3. In response to the peak in Juniata River flow on May 31 (Figure 1), we postponed stocking until June 7. When stocking was resumed, we stocked the remainder of our production fish at Huntingdon, upstream from a severe storm which had a greater impact on the lower river (Figure 1).
The extremely high flows in the watershed during late June (403,000 cfs on June 29, 2006) probably had a negative impact on survival of both hatchery and wild juvenile shad and accounted for the low catches of juvenile shad by haul seine and lift net.
Fish passage at Holtwood (35,968) was better than average with 63% passage, based on counts at Conowingo and Holtwood (long-term mean = 33%). Fish passage at Safe Harbor (24,929) was 69%, close to the long-term mean of 74%, based on counts at Holtwood and Safe Harbor. Fish passage at York Haven (1,913) was 8%, lower than the long-term mean of 13%, based on counts at Safe Harbor and York Haven.
Abundance – Main Stem
Comparison of relative abundance of juvenile alosines in the Susquehanna River from year to year is difficult due to the opportunistic nature of sampling and wide variation in river conditions, which may influence catches. In 2006, haul seine and lift net CPUE were among lowest ever recorded. GM CPUE for haul seine (both individual lifts, and combined daily lifts, Table 2) was the lowest value ever recorded for that gear type since 1990.
GM CPUE for lift net collections (Table 5) in the Holtwood Dam forebay was also close to an all-time low. Juvenile shad abundance has been below normal for five consecutive years, a disturbing trend that may impact upstream fish passage counts during 2007 to 2011. In 2002, problems at the Van Dyke Hatchery resulted in release of comparatively few healthy larvae. In 2003 and 2004, high river flows had a negative impact on survival of stocked hatchery larvae and on fish passage efficiency. Poor catch rates for juvenile shad in 2005 may have been due, in part, to fewer larvae stocked. In 2006, poor catch rates can be attributed to fewer larvae stocked (compared to the decade of the 1990’s) and the late June flood which, undoubtedly, impacted survival.
Stock Composition and Mark Analysis
Hatchery contribution was 90% for all sites combined and exceeded wild contribution at nearly every collection site in 2006. Contribution of hatchery fish from Columbia, Holtwood, Peach Bottom and Conowingo was 100%, 100%, 90% and 50%, respectively.
Normandeau Associates (Drumore, PA) was contracted by the PFBC to perform juvenile collections. Many individuals supplied information for this report. Ken Woomer processed shad otoliths.