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



619 



which accuracy was suspect. However, because of the 

 small size of the fishery and the difficulty in secur- 

 ing additional research funds, no fishery-independent 

 method of estimating biomass other than the DEPM 

 was undertaken. We recognized that this study could 

 not, therefore, unequivocally determine whether or not 

 any improvement in accuracy had been achieved; there- 

 fore, we focused on improving the consistency between 

 available data sets (in terms of the broader economic 

 environment) in order to improve the decision-making 

 process for what is a small-scale fishery. 



We examine the relationship between relative trends 

 in the B 



SP-DEPM 



and spawning area of Sardinops in each 

 of four regional fisheries. We propose a method of using 

 the relationship between spawning area and egg pres- 

 ence-absence data as an indicator of B sp that is simpler 

 than the methods of Mangel and Smith (1990) and 

 Zenitani and Yamada (2000). We specifically chose to 

 keep the retrospective analysis simple in recognition of 

 data limitations, i.e., short time series and low numbers 

 of samples for some DEPM surveys. In particular, our 

 analyses did not rely on substantial knowledge of vari- 

 ous parameters associated with estimating B SPDEPM . 



This investigation (an objective re-assessment of Sar- 

 dinops B sp DEPM ) was undertaken because of the con- 

 trast provided by the significant collapse in distribu- 

 tion, coupled with the sudden and substantial decrease 

 in B sp DEPM that followed mass mortality in 1998-99. 

 Although problems in obtaining accurate B SP estimates 

 with the DEPM will not be resolved by the present 

 study, greater consistency between indicators of the 

 magnitude of B sp and the development of a transparent 

 and objective technique to identify apparent discrepan- 

 cies between the two will facilitate better management 

 of this key pelagic resource. 



Methods 



Estimates of spawning biomass with the DEPM 



The estimates of B sp used in this study (Table D were 

 obtained by using the DEPM, which relies on ichthyo- 

 plankton surveys to estimate egg production and tem- 

 porally concurrent samples of adult fish to estimate the 

 adult parameters of fecundity, sex ratio, and weight. 



