FISHERY BULLETIN: VOL. 75, NO. 1 



N.C., in December 1966, 40 km from shore and 

 estimated their age at 8 to 55 h. Theodore N. Gill 

 cruises resulted in the location of larval menhaden 

 up to 220 km off Cape Fear, N.C., in February 

 1954, although most larvae taken during the Gill 

 cruises were over the shelf. Cruises of the RV 

 Undaunted during the winter of 1970-71 also 

 yielded larvae 170-175 km off Cape Fear. 



PHYSICAL OCEANOGRAPHY OF 

 THE SPAWNING REGION 



An excellent summary of the oceanography of 

 the coastal waters of the U.S. east coast was re- 

 cently prepared by Bumpus ( 1973) and the reader 

 is referred to that for detailed information. Bum- 

 pus identified three distinct subdivisions as the 

 Gulf of Maine, Middle Atlantic Bight (Cape Cod to 

 Cape Hatteras), and South Atlantic Bight (Cape 

 Hatteras to Cape Canaveral). Although menha- 

 den are periodically taken north of Cape Cod, 

 Mass., migratory intrusions do not occur there 

 routinely and the area is not one of significant 

 menhaden spawning activity. A brief summary of 

 oceanographic conditions in the other two regimes 

 of significant menhaden spawning activities 

 follows. 



In the Middle Atlantic Bight the Gulf Stream 

 diverges abruptly toward the northeast, passing 

 Cape Hatteras, and the space between the Shelf 

 Water masses and the Gulf Stream left by this 

 divergence is occupied by the Slope Water mass. 

 Flow in the Shelf Water and Slope Water is 

 generally slow and southward, more or less 

 parallel to the isobaths except for portions of the 

 Slope Water mass near the Gulf Stream which 

 have a northward to northeastward motion im- 

 parted by transfer of momentum from the Gulf 

 Stream. At Cape Hatteras the southward flowing 

 waters generally turn to flow northward and an 

 unknown fraction of these waters becomes en- 

 trained within the Gulf Stream. The southward 

 drift of Shelf Water is partly driven by the pres- 

 sure field developed around river effluent plumes, 

 and in times of low runoff and southeasterly winds 

 the flow may be reversed. Menhaden spawning 

 takes place throughout the Middle Atlantic Bight 

 and oceanographic conditions there should have a 

 major influence on the distribution and survival of 

 eggs and larvae. 



In the South Atlantic Bight the Gulf Stream 

 current forms the seaward boundary of the region 

 of intensive Atlantic menhaden spawning. The 



current's mean position is parallel to and a short 

 distance (37-74 km in Carolina coastal waters) 

 from the edge of the continental shelf (180-m 

 isobath). A mass of Shelf Wa^er which has lower 

 salinity and lower temperature, except in sum- 

 mer, than the Gulf Stream water is found 

 shoreward of the Gulf Stream. Motion of the Shelf 

 Water mass is generally slow and variable, re- 

 sponding to local winds, but not customarily 

 flowing southward, unlike the pattern of flow of 

 the Shelf Water in the Middle Atlantic Bight. 

 Occasionally southward flows have been identified 

 near the coast, and the cuspate formations of 

 Raleigh Bay, Onslow Bay, and Long Bay suggest 

 southward flow nearshore as part of a large 

 counterclockwise eddy in each bay. The existence 

 of these eddies, although suspected, never has 

 been conclusively demonstrated. Stefansson et al. 

 (1971) found, based on geopotential topography 

 from six cruises in 1966-67, that there was always 

 an indication of a counterclockwise eddy in 

 Onslow Bay. The pattern found in Raleigh Bay 

 was less permanent and influenced by the influx of 

 Virginian Coastal Water from the north. 



LARVAL TRANSPORT 



Menhaden larvae, spawned offshore, move into 

 estuaries before metamorphosing to juveniles, 

 after traversing long, open ocean distances. The 

 larvae are 18-22 mm in length when they enter 

 estuaries after an oceanic phase of IV2 to 2 mo. 

 Very few small larvae (<12 mm) have been taken 

 in estuaries along the central and southern U.S. 

 Atlantic coast, even though eggs and young larvae 

 have occasionally been taken near shore. The 

 timimg of larval entrance is apparently controlled 

 to some extent by the larvae and is somewhat 

 independent of water movement. During earlier 

 larval stages, however, there is a passive drift 

 period in which larval movement is the result of 

 ocean currents. Based on the rate of fin de- 

 velopment, the completely passive phase probably 

 ends when a length of 10-12 mm is reached. 

 Depending on water temperature, menhaden 

 reach that length in 30-45 days (William F. Het- 

 tler pers. commun., Atlantic Estuarine Fisheries 

 Center). 



Currents with an onshore component, par- 

 ticularly during the passive larval phase, would 

 seem to be important for transportation of the 

 larvae from offshore spawning areas to estuarine 

 nursery grounds. There are no documented 



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