FishwayLehigh River American Shad:
The First Six Years

The 1999 American shad migratory run marked the sixth year that the Lehigh River has been open to most migrating fishes. Currently, the Lehigh River contains five functional dams. Only the three most downstream dams have fishways, the Easton, Chain and Hamilton Street dams. The Easton Dam is right at the mouth of the Lehigh River, or river mile 0.0. A river mile designation shows how far upstream the dam is from the river's mouth. Chain and Hamilton Street dams are at river miles 3.0 and 17.0. Cementon and Francis E. Walter dams are at river miles 24.0 and 76.5. The Hamilton Street fishway was constructed in 1983, and the fishways at the Easton and Chain dams were built in 1993. Only the Easton and Chain dam fishways contain a private observation room with a viewing window to monitor fish passage. In addition, two public viewing windows were installed at the Easton fishway.

We have been monitoring fish passage through the Easton Dam fishway since 1994, and the Chain Dam fishway since 1996. Fish passage was monitored via time-lapsed video recording.

Operating a fishway

Operating a fishway sounds simple and should be, but it is not, at least for the Easton fishway. Mother Nature has flooded the Easton fishway to some extent nearly every year it has been open. Fishways that are completely in one river system, such as the Chain and Hamilton Street fishways, are hardly ever negatively affected by flood waters.


How many shad have passed through the Easton and Chain dam fishways?

Easton Fishway: American shad passage showed a steady increase from 1994 (87), 1995 (873), 1996 (1,141) and 1997 (1,428) to 1998 (3,293). But passage decreased in 1999 with a total passage of at least 2,346 shad. However, this decrease in passage is applicable only when compared to 1998's passage, because it is still higher than 1997's and that of preceding years. The passage of 1,141 in 1996 could have been higher, if it were not for the "Flood of 1996." The subsequent increase in passages, since 1994, was the result of fine-tuning the fishway's operation, and the more frequent cleaning of the attraction flow system by the Delaware Canal State Park and Commission staff.

Chain Dam Fishway: In contrast to the Easton fishway, passage varied greatly. The highest and lowest passages occurred in 1998 and 1997 with recordings of 698 and 126. Passage in 1996 and 1999 were similar with recordings of 696 and 674. The passage of 496 shad in 1996 was outstanding, because it represented a passage rate of 43 percent of Easton's total passage. However, in 1997 it passed only nine percent of Easton's total passage. A prolonged period of low river flows may have negatively affected passage. With more moderate flows in 1998, passage increased to 21 percent of Easton's total passage. However, even with low flows in 1999, passage was similar to 1998's at 20 percent. During periods of low flows, a sand bar partially cuts off the calm resting pool created near the fishway entrance. To compound this even further, its entrance and attraction flow are pointed directly downstream along the shoreline. In addition, during these conditions, the dam's undertow becomes the attraction force for the shad. Thus, they move close to the dam and avoid finding the fishway's entrance. Temporary modifications addressing these factors made near the fishway's entrance in 1999 may have increased passage.

How long does the shad run last?

Many factors influence the shad's use of the fishway. Their passage through the Easton Dam fishway in 1995, 1996, 1997, 1998 and 1999 commenced on April 20, April 27, April 14, April 6 and April 15, respectively. The last day of recorded passage for each year occurred on June 27 (1997), June 30 (1995 and 1998), July 5 (1999) and July 11 (1996). Changes in mean daily river temperature appear to affect their movement. Generally, an increase in river temperature during May corresponds to increases in passage. Conversely, decreases in river temperature correspond to periods of decreased passage.

Shad passage through the Chain Dam fishway in 1996, 1997, 1998 and 1999 began on May 11, April 26, April 13 and May 1. The last day of recorded passage for each year occurred on July 3, July 2, July 4 and July 6 (taping ended). The lag time in initial passage between the two fishways has ranged from seven to 15 days.

Best viewing time

Hourly passage through both fishways is similar. They are most active from 6:00 a.m. to 8:00 p.m., and are least active from 9:00 p.m. to 5:00 a.m. With respect to their active period, the 1998 and 1999 passage suggests that the best time to view them is from 2:00 p.m. to 7:00 p.m.

The 1999 shad run marked the first time in Fisheries Management history when known-age shad have returned. This is possible based on the distinctive tagging patterns developed by the Commission's Division of Research. Our Division of Research expects the millennium run to contain known age three-, four-, and five-year-old shad. The development of the returning run comprised of various known-aged shad will greatly aide the management of this species throughout the Atlantic region, and perhaps worldwide. The Commission is in the lead in American shad management.

This is important, because aging work in fisheries is done through scale analysis, which is less invasive to the monitored species. Furthermore, for American shad, scales are the only structure used to determine the incidence of repeat spawning. Thus, it is also important to determine at what ages repeat spawning had occurred.

Determining the ages of American shad and other marine fishes through scale analysis is unlike that for freshwater species above or below the equator. In North America, aging freshwater fish is possible because of the seasons. Those fish with scales, such as bass, walleyes and trout, lay down a pattern of growth on their scales similar to rings of a tree. Growth is greatest during the late spring through early fall. Thus, the rings are generally spaced farther apart. However, through the winter, growth slows and the rings become compressed.

This pattern allows the biologist to age freshwater fish species with scales. Marine-dwelling species usually do not display this pattern because they follow thermal currents of a specific temperature region.

In addition, shad also have an additional groove line, called the transverse groove. Transverse grooves are laid in a half-moon pattern beginning at the base of the scale to its edge. The current aging methodology is to count the number of transverse grooves and look for what appear to be annulus markings on the scale. The combination of these two factors currently allows shad to be aged.

American shad also lay down a distinctive mark on the scale, called a freshwater mark. This mark is laid down when the young-of-the-year shad (Age 0) leave fresh water and enter the ocean. Once in the ocean, they follow the thermal currents of the Gulf Stream from Florida to Nova Scotia. Because they live in roughly the same water temperature year after year until they return to fresh water to spawn, their scale aging pattern is not the same as that displayed by freshwater species. Thus, the above tagging method developed by the Commission Division of Research is a vital key to understanding and managing the American shad inland and marine fisheries.

Sampling the migratory runs

Adult shad were sampled during the migratory runs of 1995 through 1999. Hatchery stocked fry returning as adults dominated the samples. Thus, the Commission's stocking program has greatly aided the American shad's restoration process in the Lehigh River. The incidence of wild shad was low. The term "wild shad" includes strays from other rivers, and/or those resulting from spawning in the Lehigh River. For returning wild Lehigh River fish, we expected this because not enough years had lapsed for such fish to have attained sexual maturity and return in good numbers. Thus, the wild component mostly consists of straying shad. Their source may be the Delaware River or other coastal rivers. Shad mingle while traversing the Florida-to-Nova-Scotia circuit, following the Gulf Stream.

Repeat spawning

To assess this aspect, we detected what is known in fisheries jargon as a "repeat spawning rate." Adults returning to fresh water from the ocean go through demanding physiological changes. Additional stress is placed on the shad because they do not eat during their spawning run. They must use stored energy to sustain themselves. This stored energy lies in body fat reserves, muscles and protein structures, such as scales. The use of these reserves causes the scales to reabsorb partially, leaving what we call a spawning mark.

The repeat spawning mark means that the adult has spawned once, went back to the sea, and returned to spawn again. Multiple spawning marks are possible. The Hudson River Fisheries Unit (NY Department of Environmental Conservation) has sampled shad with four to eight repeat spawning marks. In addition, research shows that the rate of repeat spawning increases with the northerly latitude of each shad's home river (that is, from St. John's River in Florida to the Delaware, and finally to St. John River in New Brunswick, Canada).

Generally, the more northerly the river system, the greater is the incidence of repeat spawning. Florida female shad have a higher fertility rate. They produce the greatest number of eggs per body weight for their given size or age. With increases in latitude of the shad's home river, the fertility rate decreases. Thus, repeat spawning is necessary for the more northern populations to sustain themselves. In time, although not necessarily in the same year, northern females spawn similar quantities of eggs as their southern counterparts do in one year.

The Lehigh's incidence of repeat spawning in 1998 and 1999 was 12.5 and 3.1 percent. These rates may seem low. However, they are comparable to those reported for Delaware River at Smithfield Beach (1996-1998: 10 percent; and 1999: 4 percent) and Raubsville (1998: 22 percent; and 1999: 10 percent) areas. Because the Lehigh is just beginning its restoration, the fact that repeat spawning is occurring is considered very encouraging.

The decrease in repeat spawning noted above for the Lehigh and Delaware rivers may reflect a lower than expected shad run in 1999. The reason for the possible decline is not fully known, but all Delaware River-bordering state fishery agencies, through the Delaware River Basin Commission's Fish and Wildlife Cooperative Technical Committee and the Atlantic States Marine Commission, are studying the matter.

However, the fact that repeat spawning had occurred in 1999 is a positive sign. The Lehigh River's decline may also be a reflection of the younger makeup of the shad run in 1999. The lower repeat spawning rate at the Delaware River Smithfield Beach site may be the result of traveling such a great distance in fresh water. Lehigh River shad have shown only one repeat spawning mark. Even though the Delaware River shad have shown mostly one mark, a few had two repeat spawning marks.

Lehigh River shad reproduction

We have assessed the young-of-the-year (YOY) shad in July, August and September during 1995 through 1998. The 1999 samples, as of print time, were undergoing analysis. We sampled hundreds of YOY during this three-month period. The percentage of wild YOY caught was one percent (1995), 11 percent (1996 and 1997) and two percent in 1998. The Commission's hatchery program is still providing the bulk of the YOY's abundance. The size of the YOY shad (wild and stocked) by September ranges from 2.6 inches to 5.4 inches. Wild YOY shad are generally larger than stocked shad.

Considering all the factors affecting the American shad migration into the Lehigh River, their restoration is going steadily well. The process is slow. However, the day will come when one can see shad steadily swimming by the observation windows of the Easton Dam fishway.

This article is dedicated to the memory of Daniel Bourke and David Chiles. Dan, a Fisheries Technician, had been with the Commission for 28 years. He spent much of his career working on restoring the Lehigh shad run. David Chiles, a private citizen, was very active in restoring American shad to the Lehigh River. He was a member of the Delaware River Shad Fishermen's Association, and the first Commission fishway worker at the Easton Dam fishway.

May/June 2000 Angler & Boater

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