NOAA PROFESSIONAL PAPER 11 



feature of the shelf is the Hudson Shelf Valley, a broad, 

 shallow channel extending from the Bight Apex seaward 

 to the outer shelf and Hudson Canyon (fig. 1-1). The 

 surface of the shelf is a gently rolling plain that gradually 

 increases in depth from the Apex at the mouth of the 

 Hudson River to the edge of the shelf, a gradient of about 

 60 m in 100 km. North of the Hudson Shelf Valley the 

 surface is veneered with sand. To the south, the surficial 

 sediments are sand and gravel. Within the valley, nutrient- 

 rich muds have accumulated since the postglacial sea be- 

 gan to rise. Barrier beaches, bluffs, and estuaries are 

 prominent coastal features of the Bight. 



Water movements in the Bight are highly variable in 

 space and time. Over the middle and outer portions of the 

 shelf, waters generally move to the southwest, parallel to 

 the bathymetric contours. In the inner (nearshore) portion 

 of the Bight, water movement and structure of the water 

 column vary greatly with dominant seasonal influences. 

 Boundaries between the regimes of the inner and outer 

 Bight are poorly defined and constantly changing. Never- 

 theless, the inner Bight has two major features: 



1. A two-layer flow near the Hudson-Raritan estuary 

 is dominated by the outflow of these rivers. In the 

 surface layer, less dense water flows seaward, gen- 

 erally parallel to the New Jersey coast. In the lower 

 part of the water column, the denser water of the 

 Bight flows into the estuary. Evidence for this two- 

 layer flow is found in current meter measurements, 

 which show a slight imbalance between the much 

 stronger ebb and flood tidal components of cur- 

 rents in the respective layers. 



2. A clockwise circulation gyre (at least in the sta- 

 tistical sense) persists outside the region of strong 

 river influence. Its western edge tends to be 

 aligned with the Hudson Shelf Valley. 



The importance of the Hudson Shelf Valley to oceanic 

 processes on the shelf is just beginning to be realized. The 

 flow of water can be either up or down valley. Over ex- 

 tended periods of time, the flow has been measured up 

 valley (Beardsley et al. 1976). However, in the inner Bight 

 particulate material tends to be transported seaward and 

 concentrated on the valley floor. 



Oceanic conditions in the Bight are largely controlled 

 by the temperate, middle-latitude climate, which is dom- 

 inated by maritime air from the tropics or subtropics for 

 9 or 10 months and by arctic air for 2 or 3 months (Lettau 

 et al. 1976). Waters of the Bight undergo pronounced 

 seasonal changes in temperature, salinity, and density. In 

 winter, they are characterized by considerable horizontal 

 and vertical homogeneity. In spring, freshwater outflow 

 begins to establish a pycnocline, particularly over the inner 

 shelf. In summer, heating of the surface layer produces 

 thermal stratification and intensifies the pycnocline. Sea- 

 sonal variations are great and changes are most rapid in 



the inner Bight. They decrease seaward over the midshelf 

 region. 



A summer feature of deeper midshelf waters is the "cold 

 pool," thought to be relict winter surface water (Bowman 

 and Wunderlich 1977) of local or distant origin. However, 

 the low dissolved oxygen content of this water suggests 

 considerable modification at depth on the shelf (Gordon 

 et al. 1976); and its southwest flow at speeds equal to or 

 exceeding those of adjacent waters (Beardsley et al. 1976) 

 indicate the pool is not stagnant. 



Atmospheric and oceanic processes and their variations 

 play an important role in the chemical and biological proc- 

 esses in the Bight. Also, human activities are known to 

 have altered some chemical and biological phenomena. 

 Knowledge about the extent and magnitude of these in- 

 teractions is important in understanding oxygen depletion 

 in the Bight. 



FISH AND SHELLFISH STOCKS 



The abundant fish and shellfish populations of the Mid- 

 dle Atlantic Bight are important to the Nation's economy. 

 Oceanic species of bivalve mollusks — surf clams, ocean 

 quahogs, and scallops — are more numerous here than in 

 any comparable coastal area in the United States. Surf 

 clams harvested from the Middle Atlantic Bight constitute 

 over 50 percent of the total landed weight of molluscan 

 shellfish in the United States; the fishery for ocean qua- 

 hogs is expanding rapidly, and populations of sea scallops 

 are fished regularly in deep waters of the Bight. 



The National Marine Fisheries Service (NMFS) has con- 

 ducted surveys of surf clam, ocean quahog, and scallop 

 distribution and abundance in the Middle Atlantic Bight 

 for a number of years. Results of April 6 to May 13, 1976, 

 surveys by the RV Delaware 11 are given in figures 1-2, 

 1-3, and 1-4. Total estimated biomass of offshore surf 

 clams in the Bight was 875,000 t of meats, with the New 

 Jersey sector containing 207,000 t. Coastal stocks of surf 

 clams in New Jersey (within 5 km of shore) were estimated 

 at 34,000 t. Total estimated biomass of ocean quahogs in 

 the Bight was 2.450,000 t of meats, with the New Jersey 

 sector containing 818,000 1. Biomass estimates for sea scal- 

 lops in the Bight are not available, but much of the stocks 

 are composed at present of a single strong year class 

 (1972). Scallops occupy about 11,500 km- of the shelf off 

 New Jersey. 



Significant finfish species in the Middle Atlantic Bight 

 include cod, summer flounder, bluefish, striped bass, 

 mackerel, sea bass, and weakfish. A number of these spe- 

 cies are taken by recreational as well as commercial fish- 

 ermen; often the recreational catch predominates. Some 

 species (such as striped bass) are estuarine-dependent; 

 others, such as summer flounder and bluefish, migrate 

 across bathymetric contours to and from the coast, or 



