FISHERY BULLETIN: VOL. 83 NO. 3 



spring since the younger age-group made up the en- 

 tire population in the summer. Most of the females 

 apparently spawn once and die after their eggs are 

 hatched since very few older females were found in 

 the winter. The presence of a few larger males in 

 October (Fig. 2N) suggested that a few survive into 

 their third fall and mate twice (or three times if they 

 mature during their first year). Further evidence 

 that most female mortality occurs following hatching 

 while male mortality is delayed until later in the 

 spring was indicated by the seasonal changes in 

 relative abundance of males and females (Table 3): 

 females decreased from 50 to 35% of the population 

 between early December and late January while 

 males decreased more slowly from 65% in January 

 to 48% in the summer. 



Age-2 P. montagui which were either in transition 

 or were still males in March had mostly become 

 females by the summer (although a few transitionals 

 and large males still remained). The single large size- 

 group of first- maturing Stage I females in the sum- 

 mer (Fig. 3M) presumably included age-1 females at 

 a modal length of 13 mm CL and age-2 females at 

 about 15 mm CL. At the same time, there appeared 

 to be at least two size-groups of Stage II females in 

 July-September (Fig. 3N) which had carried eggs the 

 previous winter (Fig. 3C, G). Ovigerous females cap- 

 tured in November-December 1980 (Fig. 3C) 

 presumably included first- time spawners at 12-15 

 mm CL and one or two groups of repeat spawners at 

 15-19 mm CL. Excluding the single female at 10 

 mm, two or three age-groups of ovigerous females 

 were apparent in January (Fig. 30). As indicated 

 earlier, the relative abundance of the different age- 

 groups in November-December and January showed 

 that repeat spawners may have accounted for a 

 larger percentage of the ovigerous females earlier in 

 the winter. 



Growth and Longevity 



Male and female D. leptocents which hatched in the 

 winter of 1979-80 reached 8.0-8.5 mm CL by Octo 

 ber of their first year (Fig. 2N, P) and grew relative- 

 ly slowly during their first winter; by March they had 

 reached 7-10 mm CL and the females were slightly 

 larger than the males (Fig. 20, H). This difference in 

 size-at-age was also discernible in January (Fig. 2E, 

 F). Orowth was rapid during the spring of the second 

 year prior to the beginning of the breeding season: 

 males increased about 3 mm in carapace length by 

 the summer while females increased by 4 mm (Fig. 

 2K, L). The difference in modal lengths between 

 males and females had increased further by October 



(Fig. 2N, P) as growth increased modal carapace 

 lengths by an additional 0.5-1.0 mm for both sexes. 

 Orowth between early October and late November 

 when ovigerous females were first sampled was 

 negligible, if October 1981 data can be compared 

 with November 1980 data. During this same short 

 period of time the relative abundance of the younger, 

 newly recruited, age-group (males and females) in- 

 creased dramatically. (A reduction in somatic growth 

 can be expected at a time of rapid egg development 

 since female growth ceases once their eggs have 

 "dropped" and they are unable to molt). This species 

 reached a maximum observed size of 19 mm CL (not 

 included in compiled length frequencies), but most in- 

 dividuals did not exceed 16 mm CL. Unless older in- 

 dividuals migrate completely out of Penobscot Bay 

 and were therefore not sampled during this survey, 

 the maximum lifespan of Z). leptocents in the Bay ap- 

 pears to be about 2 yr and 9 mo, although the bulk of 

 the population apparently survives for only 2 yr. 



The first evidence of newly recruited age-group 

 P. montagui was in November-December 1980 (Fig. 

 3A, B). Individuals which remained as males during 

 their second year grew from about 7-9 mm CL in 

 November-December of their first year to 8-10 mm 

 CL in March (Fig. 3H) and 10-13 mm CL in their sec- 

 ond summer (Fig. 3K). As was observed for D. lep- 

 tocerus, the growth rate increased in the spring. 

 Age-1 shrimp which became females during their 

 second spring reached 10-12 mm CL in March (Fig. 

 3J) and 12-15 mm CL in the summer (Fig. 3M). Com- 

 parison of November-December 1980 and January 

 1981 data (Fig. 3C, 0) with summer 1981 data sug- 

 gested that growth of mature females in the fall was 

 negligible; the same was true for the males. The 

 maximum observed size was 19.5 mm CL; females as 

 large as 17-18 mm CL were collected in the winter 

 (Fig. 3C, 0). These results suggested that P. mon^ 

 tagui in Penobscot Bay normally spend 1-2 yr as 

 males and as many as 3 yr as females. The maximum 

 lifespan is probably 4 yr since shrimp that remain 

 males for 2 yr do not complete sex transition until 

 their third year and function as females in their third 

 and fourth years. 



Growth at Grand-Rivifere was sufficiently slower 

 that males there were 2-3 mm CL smaller by the end 

 of their first year than they were in Penobscot Bay. 

 This difference in growth could be a result of lower 

 summer bottom temperatures in the Gulf of St. 

 Lawrence. A temperature range of - 1°C (in May) to 

 3°C (in October) was reported in 54 m at Grand- 

 Rivifere in 1965 (Couture and Trudel 1969a). 

 Temperatures recorded in lower Penobscot Bay dur- 

 ing the same months of the year at 40-60 m were 



228 



