Abstract. — This study quanti- 

 fied the temporal and spatial 

 abundance of juveniles of two 

 Photololigo species on the conti- 

 nental shelf off Townsville, Austra- 

 lia with the use of light-traps. The 

 two Photololigo species (A and B) 

 showed very distinct and separate 

 spatial distribution patterns. 

 Photololigo sp. A was found close 

 to the coast and was the smaller 

 and more abundant of the two spe- 

 cies. This species was most abun- 

 dant in surface waters, although 

 larger individuals were generally 

 caught deeper. There was no evi- 

 dence of vertical movements dur- 

 ing the night. The presence of 

 small and large juvenile 

 Photololigo sp. A during summer 

 and winter months suggests 

 spawning and recruitment occur 

 throughout the year. In contrast, 

 Photololigo sp. B was caught pre- 

 dominantly offshore. All sizes of 

 Photololigo sp. B were caught both 

 near the benthos and at the sur- 

 face in the mid-lagoon, but farther 

 offshore juveniles were deeper and 

 larger. The presence of small juve- 

 nile squid of both species through- 

 out the summer suggests that 

 these species spawn for an ex- 

 tended period during the summer. 

 This study demonstrates that 

 light-traps are an effective way of 

 sampling small cephalopods. 



Distribution and abundance of two 

 juvenile tropical Photololigo species 

 (Cephalopoda: Loliginidae) in the 

 central Great Barrier Reef Lagoon 



Natalie A. Moltschaniwskyj 



Department of Marine Biology, James Cook University of North Queensland 

 Townsville, Queensland 481 I, Australia. 



Peter J. Doherty 



Australian Institute of Marine Science, PMB 3 

 Townsville, Queensland 4810, Australia 



Manuscript accepted 8 November 199.3 

 Fishery Bulletin 92: 302-312 (1994) 



The current poor state of knowl- 

 edge about processes important in 

 squid population dynamics is 

 mainly due to limited information 

 about the juvenile phase (Voss, 

 1983; Boyle, 1990). Life-history 

 characteristics have largely been 

 derived from information about the 

 adult phase. Our limited informa- 

 tion about young squid is demon- 

 strated in attempting to define the 

 life-history phases (Young and 

 Harman, 1988). Jackson and Choat 

 ( 1992) suggest, given the compara- 

 tively short life time of tropical 

 squid (<250 days), that a propor- 

 tionally long period of the life cycle 

 is spent as small individuals. In the 

 case of Loligo chinensis, with a 

 summer life time of 120 days, indi- 

 viduals less than 60 days old (<50- 

 mm mantle length) have not been 

 studied. Hence, for almost half the 

 life history of most squid there is 

 not even the most basic informa- 

 tion. Temporal and spatial abun- 

 dance patterns of juvenile squid 

 will provide a basis for understand- 

 ing the processes of mortality, 

 growth, and recruitment. However, 

 such information has traditionally 

 been difficult to obtain because of 

 problems in capturing and identify- 

 ing a sufficient size range of juvenile 

 cephalopods (Vecchione, 1987). 



To examine the ecology of juve- 

 nile squid it is necessary to use 

 techniques that catch a size range 

 of individuals, hatchlings to juve- 

 niles, in good condition. Pelagic 

 squid produce either benthic or 

 pelagic eggs and have a planktonic 

 juvenile phase (Boletzky, 1977). 

 Juvenile squid are alert, mobile 

 organisms that easily avoid capture 

 by towed nets (Vecchione, 1987). 

 The use of a combination of differ- 

 ent towed nets to sample an area 

 enables the collection of a wider 

 size range of juvenile squid (Rod- 

 house et al., 1992). However, it is 

 difficult to obtain replicates needed 

 to provide density estimates from 

 towed nets. In this study we have 

 employed an alternative technique 

 based on light-attraction that is 

 effective in sampling pelagic juve- 

 nile fishes. Automated light-traps 

 (Doherty, 1987) can overcome the 

 problems of net avoidance and en- 

 able sampling at discrete depths in 

 the water column. The ability to 

 sample concurrently within an area 

 ensures that estimates of variabil- 

 ity in abundance are not con- 

 founded by time. This technique 

 also collects live material in good 

 condition, which can facilitate taxo- 

 nomic identification. However, 

 sampling an unknown volume of 



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