FISHERY BULLETIN: VOL, 87, NO. 1 



20 



16 

 12 J 



C 



ID 



-.3 



,1 .1 



60 



40 . 



20 . 



1985 

 n = 365 



-O- 



-.5 -.3 -.1 .1 .3 



Residual from Ln- linear 



Figure 13.— The distribution of residuals about the semilog regression of In total length 

 against age of Macruronus novaezelandiae for 1984 and 1985, based on growth trajec- 

 tories pooled by year. 



whereas those for the slower growing larvae col- 

 lected off the west coast exhibit a significant posi- 

 tive skew (^2 = 0.68, t = 2.76, P < 0.01). We con- 

 clude, therefore, that the data are consistent with 

 the constrained growth hypothesis, that variations 

 in rates of larval growth documented in this study 

 are likely to be real, operating within whatever fac- 

 tors constrain the limits of larval growth for the 

 species, and that they reflect variations in environ- 

 mental conditions that affect growth rates. 



Exactly what these environmental conditions are 

 is still not clear, though it is likely they relate to 

 water temperature and food availability. That lar- 

 vae <15-20 d postfirst-feeding grew faster off the 

 west coast of Tasmania than off the south and east 

 coasts could, for example, reflect the presence of 

 the relatively warm Zeehan Current off the west 

 coast. Growth rates of gadoid larvae increase with 

 water temperature (Lawrence 1978) and tempera- 

 tures in this current near the spawning grounds 



were 1°-2°C warmer than off the south and south- 

 eastern coasts. Circumstantial evidence suggests 

 that regional differences in growth rates of older 

 larvae, in turn, were related to differences in food 

 availability. As noted above, larvae older than 25 

 d postfirst-feeding grew faster off the east coast 

 than off the west coast early in the spawning sea- 

 sons. This difference between coasts narrowed later 

 in the season and disappeared altogether late in the 

 spawning season (September). This pattern of 

 spatial and temporal differences in growth was 

 matched by variations in coastal productivity. Harris 

 et al. (1987) reported that in winter (August, re- 

 ferred to by them as "early spring"), autotrophic 

 water column productivity was higher off the east 

 coast in 1985 than off the west coast; reported 

 values for shelf waters ranged from 1.71 to 4.5 mg 

 C-m"^-h"^ for the east coast versus 0.06 to 0.84 

 for the west coast. In September, however, (Harris 

 et al.'s "late spring"), differences in water column 



44 



