Primary Secondary Existing 1976

Municipal Effluent Scenario

Figure 7-18 Model simulation of DO under July 1976 "normal" streamflow conditions at the critical oxygen sag location (River Mile 96) in the Delaware estuary for primary, secondary, and existing (1976) effluent loading scenarios. Source: Lung, 1991.

ical to the spawning success of anadromous species, have been converted into docks, wharves, industrial sites, and oil refineries (Stutz, 1992).

Decades of discharge of untreated municipal and industrial waste resulted in severe declines in the once-abundant fishery resources of the Delaware estuary. In 1836, commercial landings of the American shad (Alosa sapidissima), an important anadromous fish that spawns in the Upper Delaware River, were estimated at 10.5 million pounds. By the turn of the twentieth century, the average annual harvest of shad was 12 to 14 million pounds (Frithsen et al., 1991). Historically, the commercial shad harvest from the Delaware River fishery was the largest of any river system along the Atlantic coast (Frithsen et al., 1991). Primarily as a consequence of overfishing, water pollution, and low levels of DO that created a "dead zone," construction of dams, and other obstructions in the river, shad populations declined drastically in the early 1900s (Frithsen et al., 1991).

In a pattern similar to that for shad, annual commercial landings of striped bass (Morone saxatilis) have also dropped from hundreds of thousands of pounds per year in the early 1900s to only thousands of pounds per year by 1960. In 1969, a fishery survey showed a complete absence of striped bass larvae and eggs along the Philadelphia-Camden waterfront, which had been an important spawning and nursery area for striped bass; by 1980 there was no commercial catch of striped bass (Himchak, 1984).

The historical abundance of shortnose sturgeon (Acipenser brevirostrum), once prized for caviar that rivaled imported Russian caviar, also followed the same precipitous decline as shad as overfishing and water pollution took their toll on this once-thriving fishery. Historically, the range of the shortnose sturgeon was from the lower

Delaware Bay as far upstream as New Hope, Pennsylvania (RM 149) (Frithsen et al., 1991). Historical records from 1811 to 1913 document 1,949 sturgeon captured, primarily as a bycatch of the shad gill net fishery. During the period from 1913 through 1954, no documented catches of sturgeon were reported. From 1954 through 1979, 37 sturgeon were reported in fishery and ecological surveys. From 1981 to 1984, 1,371 sturgeon were collected between Philadelphia and Trenton (Frithsen et al., 1991). Using data collected from the early 1980s surveys, Hastings et al. (1987) have estimated populations of approximately 6,000 to 14,000 adult shortnose sturgeon in the upper tidal river near Trenton, with a smaller population estimated for the section of the river near Philadelphia (Frithsen et al., 1991).

Although it is difficult to assess the relative importance to these species of each of the major industrialization factors that contributed to the declines, Summers and Rose (1987) identified a connection between water quality, especially DO concentrations, and wastewater loading and shad population levels. Using records collected during the twentieth century from the Delaware, Potomac, and Hudson estuaries, historical fluctuations in American shad populations have been strongly correlated with waste-water discharges that increased biochemical oxygen demand levels and depleted oxygen resources (Summers and Rose, 1987). Albert (1988) and Sharp and Kraeuter (1989) also noted the importance of adequate oxygen concentrations to successful shad migrations. Little correlation between water quality and striped bass populations was found, but Summers and Rose (1987) noted that larval survival for both shad and striped bass is tied to DO and other water quality factors.

Beginning in the mid-1970s, however, the water pollution control efforts of the 1970s and 1980s have paid off with a dramatic recovery of once moribund fishery resources. Estimates of the American shad population fluctuated from a low of 106,202 in 1977 to a high of 882,600 in 1992 (Santoro, 1998) (Figure 7-19). As a result of im-

0 0

Post a comment