STEVENSON and PIERCE: PANDALUS MONTAGUI AND DICHELOPANDALUS LEPTOCERUS 



JULY 16 -SEPT 18 1981 



Males 

 N»52 7 



Non-ovlgaroua Females 

 Stage II 

 N-24 



M 



1 OCT 5-6 1981 



Males 

 N-83e 



N 



Non-ovlgeroua Females 

 Stage I 

 N> 7 1 5 



-_X 







-1 — — ^ 



Non- o vigerous Females 



Stage II 

 N>2 3 



—n . r^ 



—r 1 1 1 r- 



a 9 10 11 12 13 14 15 16 

 CARAPACE LENGTH (mm) 



— I » 



17 ia 



were collected between November and April). A few 

 females were still carrying eggs the following June. 

 Hatching began in the winter and continued through 

 June. Pandalus montagui populations studied in 

 Penobscot Bay and Grand-Riviere spawned primari- 

 ly in their second and third years. Females in the 

 North Sea, on the other hand, were fully mature dur- 

 ing their first year (Mistakidis 1957; Allen 1963), but 

 there was no evidence that individual age-groups 

 spawned more often there than at Grand-Riviere or 

 in Penobscot Bay. 



At least two age-groups of ovigerous P. montagui 

 were apparent in the winter samples (Fig. 30, G), 

 whereas only a single age-group of ovigerous D. lep- 

 tocenis was observed (Fig. 2D). Length-frequency 

 data suggested that older female P. montagui (age 

 2 + ) spawned before younger females (age 1); 57% of 

 the ovigerous females collected in November- 

 December were > 15 mm CL (Fig. 30), whereas only 

 30% remained in the same size group in late January 

 (Fig. 3G). Sample sizes were much too small, 

 however, to clearly indicate how many spawning 

 age-groups were present or whether older femaleo 

 spawned earlier than younger ones. Earlier comple- 

 tion of spawning by older females was reported by 

 Mistakidis (1957) in the Thames estuary. In 

 Penobscot Bay, the relative abundance of ovigerous 

 females was higher in moderate and deep waters and 

 in areas 2, 3, and 4 (Tables 5, 6). 



The capture of a single 10 mm OL ovigerous 

 female P. montagui in January (Fig. 3G) indicates 

 that a few females mature and reproduce during 

 their first year. This shrimp could have started life as 

 a female or could have changed sex in the first year 

 and therefore never functioned sexually as a male. 

 Mistakidis (1957) reported that some age-group 

 males in the Thames estuary changed sex and func- 

 tioned as females during their first year. Some in- 

 dividuals in both the Thames estuary and North- 

 umberland began life as females and matured in 

 their first year (Mistakidis 1957; Allen 1963). 



Sex Transition 



Unlike most other Pandalid species, the Penobscot 

 Bay population of D. leptoceru^ was not her- 

 maphroditic. Not a single transitional individual was 

 identified in the over 7,000 shrimp which were ex- 

 amined. Furthermore, males and females recruited 

 to the > 5 mm OL population in October of their first 

 year in nearly equal numbers (Fig. 2N, P). The ratio 

 of males to females for the entire survey period was 

 53:47 (Table 3). Pandalus montagui, on the other 

 hand, is a protandric (sequential) hermaphrodite. 

 Nearly 7% of the 2,475 individuals examined ex- 

 hibited external morphological characteristics typical 

 of transitional P. borealis (Allen 1959). The sex ratio 

 was 69% males to 7% transitionals to 24% females 

 (Table 6). Although P. montagui is clearly protan- 

 dric, some individuals in Penobscot Bay either begin 

 life as females or assume external female character- 

 istics by late November of their first year.^ These 



^Individuals of protandric pandalid shrimp species which begin life 

 as females are referred ta as primary females; those which change 



225 



