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



631 



very poor fit for Esperance may reflect the low sample 

 size or may be indicative of a certain level of decoupling 

 of B SP and PPS not evident in the other south coast 

 regions. 



The 1996 estimate for the west coast was hampered 

 by poor estimation of adult parameters resulting from 

 a low number of adult samples obtained; the B sp DEPM 

 estimate for that year appeared to be much too high 

 and, intuitively, was not used as the basis for making 

 management decisions at that time. The precautionary 

 decision to use the lower bound rather than the "best" 

 estimate from the 1996 west coast DEPM survey was 

 therefore justified. In contrast, the estimate of B^ pDEP!il 

 of 8714 t in 1994 for the west coast Sardmops stock 

 appears to have been too low. The lack of an obvious 

 collapse in distribution off the west coast was partly 

 due to the marked changes in the intensity and dis- 

 tribution of sampling after 1996. Another contributing 

 factor may have been a change in the distribution of 

 the spawning adults because of the anomalously warm 

 water in the Indian Ocean in the late 1990s (Webster 

 et al., 1999) during the last major La Nina. The PPS 



of only 0.10 in 1998, before the epidemic mortality, may 

 therefore have been the result of behaviorally mediated 

 changes in the distribution of Scuxlmops in response to 

 the warmer than average water temperatures (Gaughan 

 et al., 2000). We recognize that other factors may also 

 have influenced the distribution of Sardinops off the 

 west coast but our relatively short time series of data 

 precluded development of more definitive, alternative 

 hypotheses at this time. The potential for unusual en- 

 vironmental conditions to influence spawning behavior 

 applies equally to the south coast Sardinops; interpreta- 

 tion of PPS data therefore also requires consideration 

 of environmental conditions in each case. As our time 

 series of biomass estimates is extended through further 

 DEPM surveys, hypotheses regarding the influence of 

 the environment will be further developed. Prelimi- 

 nary hypotheses have already been presented to the 

 Management Advisory Committee and thus form part 

 of current management deliberations. 



The results from this retrospective analysis will im- 

 mediately be used to reassess the B sp estimates ob- 

 tained for Sardinops in WA during the 1990s before 



