FISHERY BULLETIN: VOL. 73, NO. 1 



for areal differences between strata. Area of the 

 strata are listed in Table 2. 



Indices of abundance for all stations, within 

 temperature intervals of 1°C for each of the five 

 ecological subareas, were calculated for each 

 species. Indices were not weighted. Length fre- 

 quencies were calculated for strata sets corre- 

 sponding to each of the four depth intervals 

 (27-55, 56-110, 111-183, 184-366 m) within each 

 of the subareas. This analysis gave the per- 

 centages that each 3-cm length increment con- 

 tributed to the total catch of a species within 

 each of the strata sets of the subareas. 



Hurlbert's (1969) index of association was used 

 to determine the level of cooccurrence based on 

 presence and absence of two species at the same 

 stations. Species pairs with a significant positive 

 index were compared by the product moment 

 correlation (simple correlation coefficient) to 

 determine if the two species were positively or 

 negatively related by numbers. The correlation 

 indices were computed from transformed abun- 

 dance values [log iX + 1)] at stations where the 

 two species cooccurred. According to Hurlbert 

 (1969), a negative correlation, showing an inverse 

 relationship in numbers of individuals between 

 the species, may indicate that the two species 

 compete for the same resources. 



The VIMS data included five seasonal ground- 

 fish surveys of the Chesapeake Bight (lat. 38° 

 43'N to 35°13'N) in 9 to 274 m during the four 

 seasons of 1967 and winter of 1968. This area 

 was divided into grids of lat. 15' by long. 12.5'. 

 A 1-h tow was made in each grid per survey with 

 an Atlantic western trawl without rollers (Musick 

 and McEachran 1972). 



The Chesapeake Bight was divided into two 

 areas, one north and one south of the Virginia 

 Capes (lat. 37°N) for data analysis. Index of 

 abundance (geometric mean) was computed for 

 each of the species {R. eglanteria, R. garmani, 

 R. erinacea, and R. ocellata) captured during 

 the VIMS survey, by depth zone (0-18, 19-37, 

 38-73, 74-110, 111-165, 166-274 m) and by tem- 

 perature intervals of 1°C, north and south of lat. 

 37°N separately. This index was not weighted by 

 area of the depth zone. 



The qualitative data were obtained from the 

 NMFS Exploratory Fishing and Gear Research 

 Base at Pascagoula, Miss, (now Southeast Fish- 

 eries Center, Pascagoula Laboratory) for the area 

 from the Straits of Florida to Cape Hatteras, 



Table 2. — Area of sampling strata. 



and from the Fisheries Research Board of Canada 

 Biological Station at St. Andrews, New Bruns- 

 wick for the area off northeastern Nova Scotia, 

 including Banquereau, Sable Island Bank, West- 

 ern Bank, and the Gulf of St. Lawrence. Dis- 

 tributional data from south of Cape Hatteras 

 were collected from 1961 to 1968, and data from 

 northeastern Nova Scotia and the Gulf of St. 

 Lawrence were collected from 1960 to 1970. 

 Several vessels and different types of trawling 

 gear were used. 



Small specimens of/?, erinacea and/?, ocellata 

 are difficult to distinguish (McEachran and 

 Musick 1973), and field personnel often mis- 

 identified them. Records of species not verified 

 by the authors were evaluated with discretion. 

 Records were not used when the correct species 

 could not be determined. 



RESULTS AND DISCUSSION 



Seasonal bottom isotherms were plotted from 

 the RW Albatross IV surveys of 1969 because this 

 was the only year that included a summer cruise, 

 and the winter and autumn temperature profiles 

 appeared typical. Temperatures were lowest 

 during the winter survey, and isotherms in the 

 mid-Atlantic Bight tended to parallel the coast 

 line (Figure 2), as stated by Bigelow (1933). 

 During the summer cruise a mass of cold water, 

 surrounded by warmer water, extended south- 

 ward almost to the Virginia Capes, a condition 

 previously described by Bigelow (1933). Tempera- 

 tures were warmest during the autumn survey. 



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