618 



Fishery Bulletin 102(4) 



114° 



116° 



118° 



J Fremantle 



•Dunsborough 

 If" Bremer Ba 



Albany 



Figure 1 



Map of southwestern Australia showing Pacific sardine fishing ports. North of Dunsborough to 

 Fremantle constitutes the west coast fishery and the other regions constitute the south coast 

 fishery. WA = Western Australia, SA = South Australia. 



1996 1 ; Cochrane 2 ). A population model that integrates 

 age-structure information and DEPM-derived estimates 

 of B sp (B S p. DEPM ) has recently been developed by Hall 

 (2000) for each of the three south coast regions. 



Although the DEPM is able to provide relatively ro- 

 bust estimates of B SP for a variety of species (Alheit, 

 1993; Hunter and Lo, 1997), it is not without problems 

 (Cochrane, 1999; Ward et al., 2001). The B sp _ DEPM es- 

 timates for Sardinops in WA are presented at Manage- 

 ment Advisory Committee (MAC) meetings and, in turn, 

 are provided to the relevant government minister. The 

 B sp DEPM estimates therefore undergo critical scrutiny 

 by industry representatives. The shortcomings of the 

 DEPM (e.g., sensitivity of precision for small sample 

 sizes) are well understood by the members of the man- 

 agement committee; industry recognizes that onshore 

 infrastructure and fleet capacity must be matched to 

 long-term average B sp and that industry should not 

 capitalize at levels that require maximal stock sizes to 

 meet financial expectations. Inasmuch, a level of conser- 

 vatism has been adopted by the Management Advisory 

 Committee when setting quotas. Nonetheless, the accu- 



1 Fletcher, W. J., K. V. White. D. J. Gaughan, and N. R. 

 Sumner. 1996. Analysis of the distribution of pilchard 

 eggs off Western Australia to determine stock identity and 

 monitor stock size. Final Report to Fisheries Research and 

 Development Corporation. Project No. 92/95. 109 p. De- 

 partment of Fisheries, Government of Australia, 168-170 

 St. Georges Tee, Perth, WA 6000, Australia. 



2 Cochrane, K. L. 1999. Review of Western Australia pil- 

 chard fishery, 12-16 April 1999. Fisheries Management 

 Paper 129, 32 p. Department of Fisheries, Government 

 of Western Australia, 168-170 St. Georges Tee, Perth, WA 

 6000, Australia. 



racy of estimates has been a contentious issue; industry 

 members typically believe that the scientific advice 

 presented often underestimates the B SP . Likewise, wide 

 confidence intervals around biomass estimates introduce 

 doubt in the minds of industry members regarding the 

 reliability of scientific advice, which can therefore stall 

 the implementation of management measures. However, 

 the lack of a formal and objective means of dealing with 

 suspect and imprecise B sp _ DEPM estimates (e.g., because 

 of problems with sampling spawning fish) has previ- 

 ously not been rigorously addressed. 



Following the progression along the southern WA 

 coast in early 1999 of a mass mortality of Sardinops, 

 estimates of the quantity killed at Albany appeared 

 to be very low (Gaughan et al., 20001. That is, very- 

 few dead Sardinops were found in comparison to the 

 other regions where fisheries occur. Mortality rates 

 for Esperance and Bremer Bay were 69. 6 r A and 74.59f 

 of the B sp , respectively, whereas that for Albany was 

 estimated to be only 2.4'7 f . Estimates of the mortality 

 rate of Sardinops in South Australia (SA. Fig. 1) for 

 the same epizootic event were independently found to 

 also be around 70* (Ward et al., 2001). The inconsis- 

 tency with Albany could not be attributed to different 

 weather conditions; the weather conditions at Albany- 

 were similar to those at Esperance and Bremer Bay and 

 would be expected to result in equally visible evidence 

 of mortality. Gaughan et al. (2000) contended that the 

 true epizootic mortality rate of Sardinops in Albany was 

 similar to that for the other regions, but that the very 

 low mortality estimate was likely seen as such in view 

 of the previous overestimation ofB sp - 



In this study we aimed to address the problem of poor 

 precision, while also developing a technique to identify- 

 particularly poor estimates of B SPmDEPM , i.e., those for 



