THRESHER ET AL.: LARVAE OF GADOID, MACRURONUS NOVAEZELANDIAE 



with a cross-shaped radar reflector and a flashing 

 light. The buoy's position, determined by radar fixes 

 on coastal features, was recorded at 3 h intervals. 

 Surface temperature and salinity were recorded 

 continuously during all cruises, using a Grundy 

 thermosalinograph. The readings were calibrated 

 against measurements taken during routine hydro- 

 graphical sampling using depth-profiled CTD and 

 Niskin bottle casts. 



RESULTS 



Distribution of Larvae 



In both 1984 and 1985, M. novaezelandiae larvae 

 were caught almost entirely in the winter, peaking 



in abundance in July and August, and primarily 

 along the western and southern coasts of Tasmania. 

 The highest densities were caught off the midwest 

 coast (Fig. 3). Larvae were collected in largest num- 

 bers at nearshore and midshelf stations (Fig. 4), i.e., 

 at bottom depths of 30-100 m and well inshore of 

 the shelf break, a pattern consistent across all 

 transects. 



During depth-stratified sampling, relatively few 

 larvae were caught on tows made at depths <20 m 

 (Fig. 5). Samples taken with the ring net suggest 

 that larvae occurred predominantly between 20 m 

 and 90 m (at a maximum depth of 100-120 m) and 

 that the depth of peak abundance was greater at 

 night (60 m and below) than during the day (approx- 

 imately 40 m). In a two-factor analysis of variance. 



11 a 



o 



o 2: 

 >> 



o 

 C 



3 



Nearshore Midshelf Shelf Edge Offshelf 



FiGUEE 4.— The proportion (percent of total for cruise) of larvae caught on each cruise dur- 

 ing the spawning season at each of the four typical sampling positions across the continen- 

 tal shelf. 



20 



40 60 



Depth (m) 



80 



100 



FiGtmE 5.— Number of larvae caught during day (open circles) and night (closed circles) periods 

 by oblique tows made to ma.\imum depths ranging from 10 to 90 m. Numbers caught are 

 standardized to 1,000 m' of water filtered. 



35 



