COLVOCORESSES and MUSICK: CONTINENTAL SHELF DEMERSAL FISHES 



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(B) extrapolated from NMFS Groundfish Survey cruises. 



two other categories of groups: Northern outer 

 shelf groups extending from the cold-water group 

 to the shelf break (150 m) (pooled group II), and 

 southern groups (pooled group III) which occupied 

 the remaining shelf both outward and south of the 

 8°C isotherm. The boundary between these two 

 categories was generally off the New Jersey coast, 

 at which point there was often considerable over- 

 lap. The remaining outermost groups were located 

 along the shelf break at depths of 150-350 m 

 (pooled group IV). 



In general, areas of geographic overlap between 

 site groups can be related to variations in the 

 thermal regime. For example, there is consider- 

 able overlap between groups I and III on the inner- 

 and mid-shelf south of Delaware Bay. This area 

 showed the greatest temperature variation among 

 years, with group I station clusters predominating 

 in the area in colder years and group III station 



clusters in warmer years. Hydrographic parame- 

 ters and basic catch data for each stratum are 

 summarized in Table 1. The hydrographic 

 parameters (depth, temperature) within a site 

 group are much better represented by the mean 

 and standard deviation than by the range of val- 

 ues encountered. At a small percentage of stations 

 only a few species were taken, and in cases where 

 these species occurred within all or several strata, 

 some misclassifications occurred. Because the in- 

 cidence of these obvious misclassifications was 

 low, they have been ignored rather than introduc- 

 ing an arbitrary system of reclassification. Virtu- 

 ally all extremely variant values of depth and 

 temperature and strong deviation in geographic 

 location within a site group were attributable to 

 stations where only a few ubiquitous species were 

 taken. Figure 5 illustrates temperature-depth en- 

 velopes for each site group. In order to reduce dis- 



301 



