Moltschaniwskyj and Doherty. Distribution and abundance of juvenile Photololigo 



307 



tololigo species can be described. 

 Identification of Photololigo spe- 

 cies using allozyme electrophore- 

 sis suggests that the two species 

 are separated geographically 

 across the Great Barrier Reef 

 Lagoon (Yeatman and Benzie, in 

 press). This separation occurs in 

 a region of the coastal lagoon 

 where temperature-salinity data 

 indicate heterogeneity. High num- 

 bers of juvenile Photololigo sp. A 

 at stations close to the mainland 

 suggests that spawning grounds 

 for this species may be close to the 

 coast, a feature typical for 

 loliginid squid (Mangold, 1987). 

 Furthermore, the presence of 

 small and large individuals dur- 

 ing summer and winter months 

 indicates that spawning, hatch- 

 ing, and recruitment are not sea- 

 sonal events. This characteristic 

 may be more common for tropical 

 species that tend to have shorter 

 lifespans than temperate species 

 (Jackson and Choat, 1992). Large 

 numbers of small juveniles col- 

 lected during the winter may be 

 a function of slower growth dur- 

 ing the winter (Jackson and 

 Choat, 1992). Little is known 

 about Photololigo sp. B adults; 

 however, the presence of juveniles 

 in this region suggests that an 

 adult population does occur in the 

 Townsville region and that 

 spawning occurs throughout the 

 summer. The identification of ju- 

 venile Photololigo was confirmed 

 on a subsample of specimens cap- 

 tured during the summer. Conclu- 

 sions drawn from this study are 

 based upon the assumption that 

 the offshore distribution pattern 

 of the two species was consistent 

 in all other months of sampling. 

 Juvenile squid are not easily 

 sampled with towed nets (Vecchione, 1979; 

 Vecchione and Gaston, 1985; Holme, 1974). They 

 have highly developed sensory and locomotor sys- 

 tems (Boletzky, 1974) and it is likely that these 

 animals are often undersampled because of net 

 avoidance. Choat et al. (1993) have shown that 

 plankton nets select for small larval fish, but larger 



fish are captured from the same water column by 

 using light attraction. Thorrold (1992), as well as 

 this study, showed that light-traps are a useful tech- 

 nique for capturing juvenile squid. However, like 

 most sampling techniques, the light-traps have bi- 

 ases. One problem is that light-traps sample an 

 unknown volume of water. Nonetheless, they have 



