544 



Fishery Bulletin 92(3), 1994 



Changes in depth distribution with 

 ontogeny 



There was considerable variation in the mean depths 

 of occurrence and in the abundance of eggs of differ- 

 ent stages among the 13 tows of series one, two, and 



three (Table 3). Stage groups one and six were sig- 

 nificantly deeper than stage groups three, four, and 

 five; stage group two was intermediate in depth (Fig. 

 5) (ANOVA, multiple comparisons test P<0.05). 

 Almost all of the larvae collected deeper than 100 

 m throughout the study were <5 

 mm, while the length of larvae in 

 the upper part of the water column 

 appeared to increase later in the 

 season (Fig. 6). In several tows of 

 series four through eight, a bimo- 

 dal depth distribution was evident; 

 most larvae were found in the up- 

 per 60 m, almost no larvae found 

 between 60 and 100 m, and larvae 

 again were present deeper than 

 100 m. Mean lengths of larvae in 

 the nets of the tows of series nine 

 ranged from 4.8 to 9.8 mm, with 

 an overall mean of 7.8 mm. There 

 was no indication of length strati- 

 fication of larvae within the upper 

 100 m. The mean lengths of larvae 

 among tows in series nine were rela- 

 tively homogeneous (7.2-8.6 mm). 



Relationship of depth 

 distribution and 

 hydrography 



The temperature of the water col- 

 umn measured concurrently with 

 the tows in series one through 

 three increased with depth from 

 about 4.0° to 5.0°C near the sur- 

 face to 5.0 and 5.5 C at 150- 

 250 m, where most of the eggs oc- 

 curred (there is no hydrographic 

 data from tows 3 and 5 of series 

 two). Temperature at the mean 

 depth of occurrence of eggs varied 

 from 4.7 to 5.4'C among the tows 

 in series one through three 

 (Fig. 7A). Since temperature in- 

 creased with depth, among the 

 tows of series one through three 

 there was a positive linear rela- 

 tionship between mean depth of 

 occurrence of eggs and tempera- 

 ture (P<0.001, r 2 =0.7619). The re- 

 lationship between the depth dis- 

 tribution of eggs and water den- 

 sity among tows of series one 

 through three was not significant 

 (P=0.632l(Fig. 7B). 



