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Fishery Bulletin 102(1) 



setae. Of these, 11+12 pairs are more common than the 

 others. 



Berkeley ( 1930) described the fifth stage based on plank- 

 ton materials. In the present study, what was described by 

 Berkeley ( 1930) as the fifth stage larva turned out to be the 

 sixth stage because the larvae of this stage have fully devel- 

 oped pleopods. Although the larvae of the fifth stage have 

 somewhat natatory setose on their pleopods, they appear 

 not to be completely functional. Compared to the larvae of 

 P. japonica, P. dispar has one more stage than that of P. 

 japonica. The pleopod development of P. japonica from the 

 fourth stage to the fifth stage is very obvious, whereas that 

 off! dispar has another stage and the changes in its fea- 

 tures between the fourth and sixth stages are easily seen. 



Measurement bars represent 1 mm. 



Figure 6 



The major characteristics of the six larval stages of P. 

 dispar are summarized in Table 2. This table can be used 

 for the identification of the larval stages of this species. 

 Komai ( 1994) reviewed the morphological characters of the 

 first larval stage of three Pandalopsis spp.: P. dispar. P. coc- 

 cinata, and P.japonica.The larvae of P. dispar at this stage 

 are quite different from those of the other two species. The 

 larvae of P dispar have a triangular telson, whereas those 

 of P coccinata and P. japonica have a semicircular telson. 

 The adults of the genus Pandalopsis differ from those of 

 other pandalid shrimps by having a laminated expansion 

 on the first pereiopod (Schmit, 1921; Butler, 1980). This 

 character is also present in larvae of P coccinata and P. 

 japonica, whereas it is not present in larvae of P. dispar. 



From the third stage the is- 

 chium does indicate expansion, 

 however, it is not distinctive. It 

 is assumed that in P dispar. the 

 expansion should be distinctive 

 after the larval stages. 



In P. coccinata and P. japonica 

 f ) 'vi_— the ischium of the first pereio- 



pod has a laminated expansion; 

 however, in P. dispar it has no 

 lamination. The structure of the 

 ischium of the first pereiopod 

 can be a diagnostic feature of P. 

 dispar in addition to the shape 

 of the telson. 



Interspecific variation in the 

 larval stages of pandalid shrimp 

 is large, ranging from three to 

 thirteen stages (Rothlisberg, 

 1980; Komai and Mizushima, 

 1993). Haynes (1980, 1985) 

 assumed that P. dispar might 

 have seven pelagic stages, or at 

 least more than four. The pres- 

 ent study has determined that 

 P. dispar has five zoeal stages 

 prior to the juvenile stage. 



Pandalopsis dispar is one of 

 the four principal target species 

 of shrimp trawl fisheries in both 

 offshore and inshore areas of 

 the NE Pacific Ocean (PICES, 

 2001) but has undergone very 

 large fluctuations in abundance, 

 particularly in Alaska where it 

 was reduced to extremely low 

 levels during the late 1980s and 

 through the 1990s. These fluc- 

 tuations appear to have been 

 associated first with climate 

 fluctuations (Anderson, 2000), 

 and second with intense har- 

 vesting (Oresanz et al., 1998). 

 Anderson (2000) has suggested 

 that pandalid shrimp population 

 changes are one of the early in- 



i i< 



