306 



Fishery Bulletin 92(2). 1994 



modal shift in the size-frequency distribution dur- 

 ing the summers was apparent (Fig. 4). However, 

 catches were low in most months. 



The multiway-frequency analysis established that 

 the size-frequency distribution of juvenile 

 Photololigo sp. A at both depths changed as a func- 

 tion of time of night (Table 5). Small juveniles domi- 

 nated in the surface waters, but larger individuals 

 were generally found closer to the benthos (Fig. 5). 

 During the night, the relative abundance of small 

 individuals decreased at both depths. Close to the 



UJ 

 00 



0_ 

 5 



I 



& 

 _J 



a. 



UJ 



a. 



01 



—I 



< 



Q 

 > 

 D 



Z 



Li. 

 O 



or 



UJ 

 CD 



z 

 z 



s 



5 



SUMMER 1991/92 



10 

 8 

 6 

 4 

 7 

 



12 

 10 

 8 

 6 

 4 

 2 

 



60 

 50 



40 

 30 

 20 

 10 

 



, 



OCTOBER 



, . 



NOVEMBER 



I 



20 30 40 50 60 70 80 90 100110 

 sp A sp B 



DISTANCE OFFSHORE (km) 



Figure 2 



Catches of juvenile Photololigo sp. A (found at 19 and 24 km) and Photololigo 

 sp. B (found at 33 km and greater) from Tbwnsville, Australia. Most values 

 are averages (+ standard error) of six one-hour sets over three nights. See 

 Table 1 for replicates at each station. (Solid lines, deep light-traps; dashed 

 lines, shallow light-traps). Note the variable scale of the Y-axes. 



benthos an increase in large individuals was evi- 

 dent. There was no discernible pattern of vertical 

 migration; however, combining data across months 

 to increase the number of juveniles in the analysis 

 removed the possibility of detecting vertical migra- 

 tion in any one month. 



The number of Photololigo sp. A juveniles cap- 

 tured during the winter months was similar to most 

 of the summer monthly catches (Fig. 6); although 

 winter catches never reached levels such as those 

 seen in December 1991 (Table 6). The large num- 

 ber of small juveniles captured 

 over the winter (Fig. 6) indicates 

 that Photololigo sp. A spawns and 

 hatches in both seasons. A simi- 

 lar size range was captured at 

 each sampling during the summer 

 months (Fig. 7). 



Physical parameters 



Both temperature and salinity 

 decreased nonlinearly across the 

 lagoon; discontinuities in both 

 variables occurred midway across 

 the Lagoon (Fig. 8). Temperature 

 or salinity discontinuities were 

 detected on at least six out of nine 

 nights between the 33-km station 

 and one or both of the neigh- 

 bouring stations. This suggested 

 that in the lagoon the water mass 

 was heterogenous and may have 

 influenced the distribution pat- 

 terns of juvenile squid. 



Salinity-temperature profiles of 

 the water column at each station 

 indicated thermoclines were 

 present on some nights (Table 7). 

 A thermocline was defined as a 

 temperature change greater than 

 0.5°C between surface and bottom 

 water; differences as great as 3°C 

 were detected during January. 

 However, these thermoclines were 

 a temporally and spatially un- 

 stable feature of the water col- 

 umn, possibly due to variable 

 wind conditions and the shallow 

 body of water being sampled. 



DECEMBER 



JANUARY 



Discussion 



Light-traps have provided a tech- 

 nique by which spatio-temporal 

 distribution patterns of two Pho- 



