COLVOCORESSES and MUSICK: CONTINENTAL SHELF DEMERSAL FISHES 



FALL 

 I — . - 



I I 



ill 



iv 



V 



100 



200 



300 



400 



DEPTH (m) 



FIGURE 7. — Temperature-depth envelopes for pooled fall site 

 groups, Middle Atlantic Bight area, 1967-75. To avoid distortions 

 introduced by misclassified stations, points falling over two 

 standard deviations from either mean were excluded. 



tribution from year to year, the groupings were 

 largely consistent over the 9-yr period of this 

 study. Figure 8 shows the number of times the 30 

 most commonly occurring and dominant demersal 

 species occurred within the same species group 

 during the spring and fall cruises. The species are 

 arranged so as to be closest to those species they 

 occurred with most often in the clusters, i.e., so 

 that the densest cells fall along the diagonal bor- 

 der of the diagram. 



Four strongly recurring species groups are evi- 

 dent from this diagram. Myoxocephalus oc- 

 todecemspinosus, Scophthalmus aquosus, Raja 

 erinacea, and Limanda ferruginea frequently ap- 

 peared in the same group during both seasons. In 

 the spring they were often joined by Macrozoarces 

 americanus, a species generally absent from the 



FIGURE 8. — Cooccurrences within the same species cluster 

 group for major species, spring and fall NMFS Groundfish 

 Survey cruises. Middle Atlantic Bight area. 1967-76. 



NUMBER OF COOCCURENCES 



305 



