Gaughan et al.: Distribution of Sardinops sagax off southwestern Australia 



629 



1994 1996 1998 2000 



Year 



Figure 5 



Sardinops sagax B SP _ DEPM estimates Icircles with error bars) 

 and B sp qptimai estimates (squares with accompanying 95 r r 

 confidence interval boundaries! at four regions of southwestern 

 Australia. In each case the confidence intervals that extend 

 below the .v-axis have not been shown. 



Bspoptimal estimates. Notwithstanding this, the CIs for 

 the optimal estimates always encompassed the DEPM 

 point estimates. Because the CIs were so broad in rela- 

 tion to the point estimates, only the point estimates for 

 B SP _ DEPM and B SP 0PTIMAL are further compared. 



The estimated B sp .optimal indicates that for Albany 

 the spawning biomasses were underestimated in 1992 

 and 1999 and overestimated in 1997 and that the differ- 

 ence between estimates in each case was greater than 

 25% (Fig. 5, Table 4). Although the DEPM estimated 

 that the Albany B sp remained steady between 1995 

 (17,544 t) and 1997" (18,597 t), the PPS almost halved 

 from 0.33 to 0.19 for these same surveys (Tables 1 and 

 2). For Bremer Bay the estimates for B sp DEPM and the 

 Bsp-optimal were within 20% (Fig. 5, Table 4). In Esper- 



ance the B 



SP OPTIMAL 



estimate indicates that the DEPM 



underestimated B sp by 199r in 1994, but overestimated 

 B sp by 37% in 1999. 



The DEPM estimates of Sardinops B sp on the west 

 coast had the poorest fit against PPS. Thus, the optimal 

 estimates of B SP differed by >30% in four of the five 

 DEPM-based B sp estimates. In particular, the 1994 and 

 1999 DEPM estimates were too low. and those for 1996 

 and 1998 were too high. 



Discussion 



Egg presence-absence analysis, i.e., proportion of positive 

 stations (PPS), was used to objectively assess changes 

 in the spawning area of Sardinops along the south and 

 lower west coasts of WA between 1991 and 1999. The 



