FISHERY BULLETIN: VOL. 82, NO. 2 



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42° 00 



FIGURE 3.— Bottom isotherms for fall 1973 (A) and 1971 



During 1973 bottom-water temperatures were less 

 stratified and 2°-4°C warmer throughout most of 

 the study area. Inshore temperatures exceeded 

 16° C along the entire Bight, with temperatures 

 above 18°C occurring only south of Chesapeake 

 Bay The coolest temperatures were found again 

 on the mid-shelf off New Jersey and Long Island, 

 but the "pocket" was much less clearly defined and 

 was composed of waters between 10° and 12°C, 

 indicating that turnover had already occurred. 

 The other fall cruises showed thermal regimes 

 intermediate to those of 1971 and 1973 (Davis 

 1979). 



Site Groups 



Spring Cruises 



Station groups based on cluster analysis were 

 300 



determined for the nine spring cruises (Col- 

 vocoresses and Musick 1979). Most groups were 

 geographically contiguous and tended to be ther- 

 mally and bathymetrically restricted. Site groups 

 were not precisely comparable from one year to the 

 next, but could, however, be categorized on the 

 basis of faunal similarity, geographic location, 

 bathymetry, and temperature. 



During all nine cruises there was a group of site 

 clusters of similar depth and temperature regimes 

 which were contained between the shore and ap- 

 proximately the 8°C isotherm. The geographic ex- 

 tent of these groups varied from year to year, but 

 generally covered the inner- and mid-shelf out to 

 about 70 m from Cape Cod south to between Dela- 

 ware Bay and Cape Hatteras, depending upon the 

 southward extent of waters cooler than 8°C. These 

 site groups were assigned to site group I ( Fig. 4 ) for 

 the pooled analyses. Adjacent to this group were 



