FISHERY BULLETIN: VOL. 70. NO. 2 



appeared asymptotic while the average length 

 fluctuated above and below 32 mm in the Booth- 

 bay area from March through May in 1965 and 

 1966. Differences in the average length also oc- 

 curred between the eastern and western sectors 

 of the coast. In late September to mid-October, 

 the mean lengths did not differ greatly along the 

 coast (Figure 8) . By early November the mean 

 length was larger in the eastern sector than in 

 the western sector, but this difference diminished 

 in winter; by spring mean lengths were similar 

 along the coast. 



z 

 z 



z 



UJ 



< 

 > 



< 



Z 

 < 

 UJ 



•. 20 



10 .•' 



•Nov. 1-17, 1966, 

 N=I,0I2 



40 r Mor. 16-23, 1966 

 N=l,844 



30 



40 r Mar. 28-Apr. 13, 1967 

 . N = 87l 



ll I I L_ L I I 1_ 



WEST 



c.«>V c.<>V 



EAST WEST 



EAST 



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C.«>V'^ r&V 





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STATIONS 



Figure 8. — Variations in the average length of larval 

 herring from west to east along western coast of the 

 Gulf of Maine. 



The seasonal change in mean length (Figure 

 7) was influenced by the movements of larvae, 

 their avoidance of our sampling gear, and their 

 departure from the vicinity of our sampling sta- 

 tions after metamorphosis. Broods of larval 

 herring moved shoreward in the autumn from 

 the coastal water, but the size at which they in- 

 itially entered the Boothbay area varied. This 

 is illustrated by data from 1964 and 1965 ; data 

 from 1966 were similar to those of 1965. In 

 autumn 1964, two broods of larvae (labeled a 

 and b in Figure 9) initially entered the Boothbay 

 area; the more abundant had a size mode of 

 13 mm, the other was recently hatched and had 



a size mode of 9 mm. By mid-October these two 

 broods were of equal abundance. In November 

 a third brood (c) was detected, during a coastal 

 cruise, that had a modal length of 13 mm, equal 

 to the modal length of larvae initially entering 

 the Boothbay area. Presumably, the addition of 

 this group in part slowed the shift in modal 

 length to only 3 mm from mid-November to late 

 December. These variations in size resulted 

 from the location of the Boothbay area within 

 an east-west coastal zone of transition for hatch- 

 ing time. Also, some of the larvae hatched in 

 the eastern sector of the coast at an earlier time 

 and were carried westward along the prevailing 

 currents (Graham, 1970b) and then into the 

 Boothbay area. 



In autumn 1965, a single brood (d) of re- 

 cently hatched larvae with a modal length of 

 7 mm initially entered the area. In October, 

 this brood was still the most important contrib- 

 utor to the inshore area, since the modal size 

 from a coastal cruise in October coincided with 

 the seasonal progression of larval size within 

 the Boothbay area. A second group (e) of re- 

 cently hatched larvae entered the area in early 

 November. 



In the spring it was obvious that we were 

 failing to catch the larger larvae and the spring 

 peak in catch rates should have been consider- 

 ably larger than that recorded for daytime tows. 

 We assumed that this failure was due to their 

 avoidance of our gear because we captured more 

 of these larger larvae at night when they could 

 not see the gear. Day and night cruises were 

 alternated in the Boothbay area from January 

 through April during 1965 and 1966. The size 

 ranges of larvae captured during these cruises 

 were the same, but the modal length was much 

 larger for larvae captured during the night 

 cruises. The length-frequency curves for all 

 larvae from the day and night cruises showed 

 two distinct modes, one at 33 mm and the other 

 at 40 mm (Figure 10). At 36 mm the percent- 

 ages of larvae in the day and night catches 

 were identical. For larvae larger than 36 mm 

 the percentages increased for night catches and 

 decreased for day catches, indicating that avoid- 

 ance increased progressively until the larvae 

 grew to 40 mm. Initial nighttime catches of 



314 



