STEVENSON and F'lERCE: PANDALUS MONTAGU! AND DICHELOPANDALUS LEPTOCERUS 



however, may still have been a result of mortality 

 rather than migration. The depth-area length- 

 frequency data also revealed that slightly larger 

 shrimp of both sexes and age-groups were captured 

 in deeper water further down the Bay, suggesting 

 that larger individuals are more likely to migrate 

 than smaller ones. 



Older male P. montagui also migrated down the 

 Bay into deeper water during the winter: older age-1 

 males were more abundant than younger age- 

 group males in areas 2 and 3 (moderate and deep 

 water, respectively) in November-December 1980 

 (Fig. 6A, B, C) and by late January nearly all the 

 older males were in deep water in area 3 (Fig. 6D, E, 

 F), but were not as abundant as the younger males in 

 deep water in area 4 (Fig. 6G). There was no clear 

 evidence that the larger males in either age-group 



40- 



30 

 20 

 10 



Area 2 

 Moderate Depth 

 N=255 



^^TL 



Area 4 

 Deep 

 N=ei 



■^ 



1 r1 I n 



10 11 



12 13 14 15 16 17 



CARAPACE LENGTH (mm) 



Figure 6. -Male Pandalus montagui numerical length-frequency 

 distributions by area and depth range. 



were more frequent in deeper water and not enough 

 females were collected during any single sampling 

 period to permit an analysis of differential distribu- 

 tion of different age-groups by depth. 



Allen (1963) reported an offshore migration of 

 age-1 males to deeper water in the spring and sum- 

 mer in Northumberland waters; Couture and Trudel 

 (1969a) observed the same phenomenon in Grand- 

 Rivifere in the summer as the temperature exceeded 

 6°C and reported that it was triggered by the onset 

 of maturity; earlier maturing males migrated sooner 

 than later maturing males, indicating that migration 

 was a function of size, not age. Mistakidis (1957) and 

 Allen (1963) both reported an offshore migration of 

 P. montagui females in the fall; Allen, however, 

 reported that the smaller females stay behind to 

 spawn in shallow water and that there was no 

 "massive" return migration in the spring whereas 

 Mistakidis reported a general offshore fall migration 

 of females and a return migration in the spring. 

 Allen (1963) reported that females in Northumber- 

 land which survived to spawn a third time were only 

 found in depths > 100 m. 



CONCLUSIONS 



This study of the life histories of Pandalus mon- 

 tagui and Dichelopandalus leptocerus in Penobscot 

 Bay has revealed some notable differences in repro- 

 ductive characteristics and (apparently) in longevity 

 between the two species. On the other hand, growth 

 rates and migratory behavior were similar. 



Most importantly, P. montagui is hermaphroditic; 

 D. leptocerus is not. In 1980-81, some transitional P. 

 montagui were observed during all five sampling 

 periods, but were most common in the early spring; 

 most individuals change sex at the end of their sec- 

 ond year but some do so during their first year and a 

 few may not change sex until their third year. Some 

 individuals apparently begin life as females; 15% of 

 the age-group which recruited to trawl catches at 

 5-10 mm CL in November-December 1980 were 

 females. Ovigerous P. montagui were collected over 

 a longer time period, owing, at least in part, to the 

 presence of more age-groups in the spawning popula- 

 tion. Most D. leptocerus females spawn during their 

 second year, although a few also spawn in their first 

 year; ovigerous females were collected primarily in 

 late November-early December. Pandalus montagui 

 spend 1-2 yr as males; individuals which undergo sex 

 transition in their second year may function as 

 "emales during their second, third, and fourth years 



/hile those which change sex in their third year may 

 only function as females for 2 yr. Judging from the 



231 



