FISHERY BULLETIN: VOL. 79, NO. 3 



bottom temperatures from 2° to 16° C. Catches of 

 each species were more frequent at stations where 

 both surface and bottom temperatures were 4° to 

 10° C (Figures 2, 3). 



Most stations with bottom temperatures <4° C 

 occurred in the Gulf of Maine during early spring. 

 Stations with bottom temperatures >15° C were 

 mainly off the mid-Atlantic coast during late 

 summer and early autumn. The apparent decline 

 in occurrence of alewives and blueback herring as 

 bottom temperatures increased was examined 

 further by comparing catches with total sampling 

 effort for each bottom temperature (range, l°-23° 

 C) at which trawls were fished ( Table 2). Nearly all 

 blueback herring were taken at water tempera- 

 tures <13° C. Alewives were caught at tempera- 

 tures from 3° to 17° C, and frequency of capture 

 was highest at 4° C (Table 2). 



Ocean depths at stations where river herring 

 were caught ranged from 20 to 293 m, but most 

 catches of alewives (77%) and blueback herring 

 (83%) were made at stations <100 m deep (Figure 

 4). Since trawling effort during surveys was pro- 

 portional to the area of each depth interval, the 

 number of catches within these depth strata was 

 amenable to chi-square analysis with correction 

 for continuity (Zar 1974). A comparison between 

 alewife and blueback herring catches at each 

 depth interval and catches at all other depths 

 combined indicated that both species were col- 

 lected significantly more often than expected at 



Table 2. — Total sampling effort and percent of trawl tows with 

 alewives or blueback herring at different bottom temperatures 

 during bottom trawl surveys. 1963-78, Cape Hatteras, N.C., to 

 Nova Scotia. 



Bottom temp 



rc) 



Total trawl tows 

 (no.) 



Alewives 

 (%) 



Blueback herring 



(%) 



 BLUEBACKS 

 J8 ALEWIVES 



jjjjiiil^li 



5 105 125 145 



MEDIAN DEPTHlml 



185 »200 



Figure 4. — Frequency of catches of alewives and blueback 

 herring in relation to depth at trawling stations, 1963-78, Cape 

 Hatteras, N.C., to Nova Scotia. 



depths <110 m (Table 3). Based on expected val- 

 ues, blueback herring were captured significantly 

 more often in the 27-55 m depth stratum and ale- 

 wives in the 56-110 m stratum (P<0.01). 



Seasonal Distribution 



Spring surveys were conducted primarily in 

 March and April, accounting in part for the more 

 frequent collections of alewives and blueback her- 

 ring during these 2 mo (Figures 5, 6). During the 

 spring, both species were widely distributed along 

 the Middle Atlantic Bight, and mixed catches were 

 common in this region. Alewife catches were also 

 frequent between Cape Cod, Mass., and the west- 

 ern perimeter of Georges Bank (Figure 5). No 

 spring catches of blueback herring were recorded 

 for Georges Bank (Figure 6). 



During the summer surveys of July and August, 

 neither species was captured south of lat. 40° N; 

 stations in the central Gulf of Maine were also 

 unproductive (Figure 7). Alewives were collected 

 most frequently on Georges Bank and south of 



Table 3. — Depth intervals within the survey area and associ- 

 ated catches of alewives (A) and blueback herring (B) during 

 complete bottom trawl surveys, 1967-78, Cape Hatteras, N.C., to 

 Nova Scotia. 



•p. 0.01. 



476 



