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Fishery Bulletin 102(4) 



refitting them to Hall's (2000) integrated models for 

 the three adult assemblages on the south coast of WA. 

 The integrated model is tuned with B SPDEPM estimates. 

 Therefore, replacing B SPDEPM estimates with B SP _ 0PTI _ 

 MAL estimates will result in a model that better simu- 

 lates the size of the Sardinops stocks off southern WA. 

 Although the changes may appear trivial, it is impor- 

 tant that re-estimating the most deviant estimates of 

 Bspdepm can De undertaken in a manner that satisfies 

 demands by stakeholders, including industry, for open- 

 ness and clarity in the provision of scientific advice. 



As further DEPM surveys are conducted to assess the 

 status of the Sardinops stocks in the five to six years 

 following the 1998-99 mortality event, more reliable re- 

 lationships between PPS and B sp DEPM will be developed. 

 To assist this process, the relative merits of the data 

 for individual DEPM surveys can also be re-examined, 

 particularly those data that this study has indicated to 

 have resulted in poor estimates of B SPDEPM . An ongoing 

 iterative approach that employs retrospective analyses 

 will be undertaken in an attempt to continuously re- 

 duce the variance of the PPS-B SP _ DEPM relationship. 

 This approach will permit further refinement of Hall's 

 (2000) integrated model, a process already in prog- 

 ress (Stephenson et al. 5 ) and will therefore contribute 

 to increased confidence in the scientific advice that is 

 provided for management of the Sardinops fisheries in 

 WA. Eventually, PPS alone may be sufficient to provide 

 an indication of spawning biomass with an acceptable 

 level of precision. 



Besides contributing to the integrated model, the B SP 

 optimal point estimates obtained over nearly a decade in 

 each of four management regions now provide a clearer 

 indication of potential maximum biomass levels against 

 which industry members can plan their businesses. Be- 

 cause of the highly variable recruitment of many small 

 pelagic fish, purse-seine businesses that target fish such 

 as Sardinops should not invest at levels that require an 

 economic return based on maximum biomass sizes. For 

 the purse-seine fishing zones in southern WA the maxi- 

 mum spawning biomass from which purse-seine indus- 

 try members can expect their TAGS to be determined 

 are as follows: west coast 40,000 t, Albany 29,000 t, 

 Bremer Bay 37,000 t, and Esperance 30,000 t. Although 

 these values provide an upper limit to business plan- 

 ning, maximum biomasses should not represent invest- 

 ment targets. These values provide an indication of 

 the maximum size for the industry but, because of the 

 "natural and social disarray" that can result "from har- 

 vesting marine fish species at the crest of their produc- 

 tion" (Smith 2000), the industry should be structured 

 at a level that focuses on longer-term average biomass 

 and that includes industry's ability to survive during 

 periods of low stock size. Maximum and average B sp 

 for Sardinops at each of the four management regions 



Stephenson, P., N. Hall, and D. Gaughan. 2004. Unpubl. 

 data. Department of Fisheries. Western Australian Ma- 

 rine Laboratories, North Beach, Western Australia 6920, 

 Australia. 



in southwestern Australia will be further investigated 

 during ongoing development of the integrated model and 

 as more information becomes available. 



Conclusion 



Even large numbers of plankton samples can result in 

 imprecise estimates of egg production for use in DEPM 

 calculations (e.g., Mangel and Smith, 1990). Relative 

 trends in spawning area that can be obtained from the 

 same survey by using egg presence-absence analysis 

 provide a secondary means of assessing trends in the 

 status of stocks. This egg presence-absence analysis 

 will be particularly useful for stocks already assessed 

 by using DEPM surveys and more so for those that do 

 not have large amounts of ancillary information, such 

 as long time-series of catch-at-age data, or meaningful 

 effort data. 



Detection of either upwards or downwards bias in 

 estimates of B sp will be considered in the integrated 

 model and also communicated to industry members to 

 increase their understanding of the stock in each region. 

 Although this review of biomass trends of Sardinops 

 during the 1990s cannot change how Sardinops were 

 managed during that period, an increased understand- 

 ing of both the stock sizes and the science behind the 

 biomass assessments will facilitate ongoing manage- 

 ment processes. 



Acknowledgments 



The authors sincerely thank all Department of Fish- 

 eries staff involved with the collection and analysis 

 of historical ichthyoplankton-survey data, in particu- 

 lar Stuart Blight, Gary Buckenara, Cameron Dawes- 

 Smith, Rick Fletcher, Kieren Gosden, Matt Robinson, 

 Rob Tregonning, Ken White, Bruce Webber, and other 

 personnel on PV Baudin and PV McLaughlan. We also 

 thank Kevern Cochrane (FAO) for a detailed review of 

 an earlier version of this manuscript. We are grateful 

 to the Fisheries Research and Development Corporation 

 (Canberra) that provided funding through Project 92/25 

 for the earlier DEPM surveys. 



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