Stone and Jessop: Seasonal distribution of Alosa pseudoharengus and A. aestivalis 



381 



*- 1 

 Q. 



O 



c5 

 o 



c 



10 n 

 8 

 6 

 4 

 2 

 



Spring 



70 

 60 

 50 

 40 - 

 30 

 20 

 10- 

 — 1 



12 



27 



302 



Summer 



12 



Fall 



10 



f- ' I 



-r-T 



302 



Bottom temperature (C) 



Depth (m) 



Figure 4 



Mean catch-per-set of river herring 

 within 1°C intervals of bottom tem- 

 perature and 18.2m (lOfm) depth in- 

 tervals from spring, summer, and fall 

 groundfish surveys, 1979-84, con- 

 ducted off the Atlantic coast of Nova 

 Scotia. Vertical bars represent ± 1 

 SE. Sample sizes are >10 sets for 

 each temperature and depth interval. 



regions where bottom temperatures from groundfish 

 surveys exceeded 5°C. 



Temperature, depth, and 

 diel effects on catch 



The relationship between catch, bottom temperature, 

 and depth was examined by plotting mean catch-per- 

 set by season for intervals of 1°C and 18.3m (lOfm) 

 (Fig. 4). Despite much variability in the data, most 

 catches occurred within the 7-1 1°C range regardless 

 of season, with maximum catches within 9-1 1°C from 

 spring through fall. An exception is the moderate 

 catches at bottom temperatures <2°C during spring 



surveys in the Bay of Fundy (Figs. 2 and 4). The depth 

 distribution of catches was more variable; spring 

 catches occurred mainly at intermediate depths of 

 101-174m, summer catches in shallow areas (46-82m), 

 and fall catches at mixed depths (i.e., 46m, 119-192m). 

 Mean catch-per-set of river herring for annual 

 (1979-84) spring, summer, and fall surveys varied 

 significantly by season and depth (Table 2, Fig. 5). 

 Season effects within depth strata were significant for 

 depths of <93m and 93-183m, but not for depths 

 >183m where all catches were low. Catches were 

 highest within the <93m strata during summer and 

 within the 93-183 m depth strata during spring. Depth- 

 within-season interaction was significant only during 



