MUSICK: SEASONAL DISTRIBUTION OF SIBLING HAKES 



AVERAGE SUMMER BOTTOM TEMPERATURES <°C) 

 ALBATROSS IV GflOUNDFISH SURVEYS 63-5. 64-10. 65-10 





Figure 3. — Average summer bottom temperatures compiled 

 from RV Albatross IV groundfish surveys 63-5, 64-10, 65-10. 



reduces correlation between the mean and the 

 variance (Pereyra, Heyamoto, and Simpson, 1967). 

 An index of numerical abundance of U. chuss 

 and U. tenuis was computed for each stratum 

 by applying the above logarithmic transformation 

 to each catch and calculating the transformed 

 mean catch per stratum. Catch data from all 

 3 yr were pooled by season of collection, because 

 U. tenuis did not occur frequently enough or in 

 large enough numbers to allow calculation of 

 reliable estimates of mean abundance in some 

 strata on the basis of single cruises. Thus the 

 analysis estimates average seasonal distribution 

 for a 3-yr period probably with little distortion 

 because hydrographic conditions in the principal 

 areas of hake concentration did not differ drasti- 

 cally among the 3 yr. 



AVERAGE FALL BOTTOM TEMPERATURES (°C) 

 ALBATROSS IV GROUNDFISH SURVEYS 63-7,64-13,65-14 



Analysis of Temperature and Distribution 



The mean catch per tow at each 1°C temperature 

 interval was computed by species, life history 

 stage, subarea, and season. A few temperature 

 intervals were not sufficiently sampled to provide 

 reliable estimates of mean abundance. 



RESULTS AND DISCUSSION 



Seasonal Distribution of U. chuss 



Juvenile («14 cm) U. chuss were rarely cap- 

 tured during summer cruises because young-of- 

 the-year were pelagic and unavailable to the 

 trawl, and most yearlings had grown larger than 

 14 cm and were classified as immature fish 

 (Figure 5). In the fall juvenile U. chuss were 

 most abundant off southern New England at 

 depths shoaler than 60 fm (Figure 6). Their 

 distribution coincides with that of the sea scallop, 

 Placopecten magellanicus, which serves as a host 

 to the young inquiline U. chuss (Musick, 1969). 

 The shoreward distribution of Placopecten is 

 limited by temperature off southern New Eng- 

 land. Dickie (1958) found the upper lethal range 

 to be 20° to 23.5°C, temperatures which occur 

 normally in the summer in the shallow bays 

 and sounds of southern New England. In the cooler 

 Gulf of Maine, Placopecten are most abundant in 

 inshore areas shoaler than 30 fm and occur com- 

 monly in shallow bays (Dow and Baird, 1960; 

 Bourne, 1964). Thus in the Gulf of Maine, the 



SUMMER 

 < 14 cm. Total length 







□ <-0.24 



□ 0.25-0.99 



Figure 4. — Average fall bottom temperatures compiled from 

 RV Albatross IV groundfish surveys 63-7, 64-13, and 65-14. 



Figure 5. — Distribution and abundance of juvenile Urophycis 

 chuss during the summer. Abundance in each sampling stratum 

 is indicated on a log scale. 



485 



