| ABUNDANCE AND DISTRIBUTION OF JUVENILE AMERICAN SHAD IN THE SUSQUEHANNA RIVER, 2004 |
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| Michael L. Hendricks and R. Scott Carney Pennsylvania Fish and Boat Commission |
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INTRODUCTION This report summarizes the results of bio-monitoring activities for adult and juvenile alosines conducted in the Susquehanna River and its tributaries in 2004. 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. Some 3,426 adult shad were collected at the Conowingo West Lift. The majority of these were released back into the Conowingo tailrace. Some 550 were retained for tank spawning. Unlike previous years, no alosids were transported and released upstream. 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 2004 spring migration, Conowingo East Lift passed 109,360 American shad while fishways at Holtwood, Safe Harbor, and York Haven passed 3,428, 2,109 and 219 American shad, respectively. Only 190 river herring were passed at Conowingo Dam. Two herring were passed at Holtwood, however, these were small fish, probably not anadromous migrants. 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 2004 production season, the PFBC Van Dyke Research Station for Anadromous Fish released 4.7 million shad larvae in the Susquehanna Basin, Pennsylvania. Larvae were released coinciding with receding flows between 17 May and 22 June in the following locations and numbers:
METHODS 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. Haul Seining - Main Stem Haul seining in the lower Susquehanna River was scheduled once each week beginning mid-July and continuing through October. Fifteen weekly sampling events were planned for 2004, however, high river flow in late July through early August, again in mid-August, and through much of September necessitated postponement of sampling during these periods. Attempts to re-schedule the missed events later in the year were thwarted by additional high river flow 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 APS, and Conowingo Dam Sampling at the Holtwood Dam inner fore-bay began on 14 September and continued every third day through 1 December 2004. A total of 30 sampling events was planned for 2004. Once initiated, high river flow in late September necessitated postponement of three sampling events. By early December, it was apparent that a continuation of the program would not result in any improvement in the catch. Therefore, the program was cancelled after completion of 24 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. Intake screen sampling for impinged alosids at Peach Bottom Atomic Power Station was conducted three times per week from 6 October to 3 December for a total of 23 samples. Conowingo Hydroelectric Station’s cooling water intake screens were also sampled for impinged alosids twice weekly from 3 October to 8 December for a total of 16 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. RESULTS Haul Seining - Main Stem A total of 25 juvenile American shad were captured by haul seine resulting in a Geometric Mean Catch-Per-Unit-Effort (GM CPUE, individual haul) of 0.17 (Tables 1 and 2). Juvenile American shad were captured on August 31 (16), September 7 (5) and September 9 (4). All shad captured were of hatchery origin. Table 3 lists weekly catches of American shad by haul seine from 1989 to 2004. Catches generally peaked in August and September except in 1989 and 1992 when catches peaked in July.
Holtwood Dam, Peach Bottom APS, and Conowingo Dam Lift-netting at Holtwood Dam inner fore-bay resulted in no juvenile American shad captured in 240 lifts (Table 4). Catch per unit effort was 0.00 (Table 5). Historical weekly catches peaked in October, except in 1985, 1997, 2000, and 2001 when catches peaked in November (Table 5). One alewife was captured by lift-net on 14 September, 2004. Peach Bottom intake screens produced no juvenile American shad or blueback herring, and 6 alewives (Table 7). Cooling water strainers at Conowingo produced no juvenile American shad or blueback herring, and 1 alewife (Table 8). Susquehanna River Mouth and Flats In 2004, 151 juvenile American shad were captured at seven permanent sites by Maryland DNR’s juvenile finfish haul seine survey during fourteen hauls, and 53 juvenile American shad were captured at the auxiliary sites (Table 9). These fish have been sent to a federal facility for OTC and otolith microstructure analysis but results are not yet available. Juvenile American shad indices for the upper Chesapeake Bay have increased exponentially since 1980 (Figure 5; r2 = 0.32 P<0.001). Otolith Mark Analysis Results of otolith analysis are presented in Table 10. A total of 25 juvenile American shad were collected in haul seine collections. All 25 were analyzed for hatchery marks and all 25 were of hatchery origin. Twenty-two (88%) were larvae from Hudson River eggs stocked in the Juniata or middle Susquehanna River. The remaining three (12%) were larvae from Susquehanna eggs stocked in the Juniata or middle Susquehanna River. DISCUSSION Spring river conditions for the Susquehanna River basin during 2004 could be characterized by relatively high and variable flows in May and June (Figures 1 and 3). Water temperatures at Conowingo Dam were generally between 60 and 65F during late April and early May, then increased rapidly from 62.3 on May 9 to 75.6 on May 19 (Figure 2). Temperatures then remained above 70F for the remainder of the spawning season. This rapid and sustained rise in water temperature had the effect of shortening the length of the spawning season and contributed to a reduction in eggs delivered to the hatchery. Variable flows in the watershed during stocking season may have contributed to poor survival of larvae, since many of the stocking events were followed by increases in flow resulting in conditions that are not optimal for larval survival (Figure 1). River flow was consistently high for the entire season due to abundant rainfall. Flows in 2004 dropped below the 72-year mean for short periods, but the polynomial trend line for 2004 flow was consistently above the mean except for a short period during April (Figure 3). In interpreting Figure 3, it should be noted that mean flows are skewed from “normal” due to the influence of very high, flood waters on the mean. A better measure of “normal” flows would be median, however, median flows are not readily available from USGS. Fish passage at Holtwood and York Haven was severely impaired by persistent high river flows and constant spilling which adversely affected attraction at the fishway entrances. Abundance – Main Stem Comparison of relative abundance of juvenile alosids 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. Based on river haul seine and lift-net catch rates, abundance of juvenile American shad in 2004 was among the lowest recorded in recent history. GM CPUE for haul seine (both individual lifts, and combined daily lifts, Table 2) was the second lowest value ever recorded for that gear type since 1990. Lift net collections in the Holtwood Dam forebay have been ongoing since 1985. In 240 lifts, over an 11-week period, no juvenile shad were collected by lift net in 2004, a first in the history of the program (Table 5). Low juvenile shad abundance in 2004 is most likely attributed to a combination of limited natural reproduction resulting from poor fish passage performance and poor recaptures of hatchery fish. High river flows appeared to have a negative impact on capture of stocked hatchery larvae. This may be due to a direct negative impact on survival of hatchery larvae or early out-migration resulting from high flow events in late July and September, 2004. Low abundance of juvenile shad has been observed for 3 years in a row (Tables 2 and 5). Poor hatchery performance was responsible for decreased abundance of hatchery reared juvenile shad in 2002. High river flows were responsible for decreased abundance of hatchery reared shad in 2003 and 2004. High river flows also negatively impacted fish passage in 2002 to 2004, resulting in low abundance of wild juvenile shad. Poor juvenile production in 2002 to 2004 will likely impact adult returns in 2006 to 2010. Stock Composition and Mark Analysis All otoliths analyzed from haul seine collections at Columbia were hatchery fish (Table 10). In 2003, 24 juvenile shad were captured at Columbia, including 2 wild and 22 hatchery fish. SUMMARY
ACKNOWLEDGMENTS RMC/Normandeau Associates (Drumore, PA) was contracted by the PFBC to perform juvenile collections. Many individuals supplied information for this report. Ken Woomer and Coja Yamashita processed shad otoliths. |
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