Moltschaniwskyj and Doherty: Distribution and abundance of juvenile Photololigo 



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in each month of the 1991/92 sampling period the 

 19- and 24-km stations were sampled both early and 

 late in the night. The samples were separated into 

 early (captured before 2400 hrs) and late (captured 

 after 2400 hrs). By combining data from stations, 

 across nights and months, it was possible to com- 

 pare the size distributions between depths and time 

 of night. A multiway-frequency analysis was used to 

 determine the effect of time of night and depth on 

 the size-frequency distribution. 



Results 



Distribution patterns 



Juvenile Photololigo individuals were predominantly 

 caught within 52 km of the mainland (Fig. 2). The 

 few individuals found farther offshore were in the 

 Magnetic Passage (five individuals) and on the reefs 

 (six individuals). Photololigo species were not found 

 in the Coral Sea. Photololigo sp. A was numerically 

 the most abundant of the two species during both 

 summers (Fig. 2); 856 individuals were caught in 

 181 hours of light-trapping (4.73 individuals caught 

 per hour), compared with 379 Photololigo sp. B 

 caught in 348 hours of light-trapping ( 1.09 individu- 

 als per hour). Catch per hour of light-trapping was 

 greatest for Photololigo sp. A, especially at the 24- 

 km station. The catch per unit of effort for Photo- 

 loligo sp. B was greater at the 33-km station (Table 



2). Overall, Photololigo sp. A juveniles were present 

 in higher numbers at the 24-km station in the sur- 

 face waters (Table 3). This pattern was consistent 

 in both years, but higher numbers were caught in 

 1991/92 (Table 3), largely because of very high 

 catches in December 1991 (Fig. 2). In comparison, 

 highest numbers of Photololigo sp. B were consis- 

 tently found at the 33-km station and abundance 

 levels tended to decrease farther offshore (Fig. 2). 

 Overall, Photololigo sp. B demonstrated no differ- 

 ence in abundance levels between the two years 

 (Table 4). In contrast to Photololigo sp. A, juvenile 

 Photololigo sp. B was more abundant deeper in the 

 water column (Table 4). Farther offshore, Photololigo 

 sp. B juveniles were present in very low numbers and 

 were caught only in the deep light-traps (Fig. 2). 



Photololigo sp. A ranged in size from 2.6 to 47.9 

 mm. The size-frequency distributions at the two 

 depths were not significantly different between the 

 19-km and 24-km stations (x 2 =12.28; df=9; 

 P=0.1979) (Fig. 3). There was no systematic change 

 in the size-frequency distribution of Photololigo sp. 

 A during either summer (Fig. 4). A modal shift in 

 the size-frequency distribution in January 1992 

 suggested that fewer small individuals were avail- 

 able to be caught. However, catches were very low 

 in this month. 



Photololigo sp. B ranged in size from 3.6 to 61.6 

 mm (Fig. 3). From the size-frequency distributions 

 it was clear that larger juveniles were found farther 

 offshore and deeper in the water column (Fig. 3). No 



