144 



Fishery Bulletin 90|l|. 1992 



ment overfishing, as does an annual catch quota. 

 However, size limits introduced to the California aba- 

 lone fishery were also conservative but failed to arrest 

 the decline of the fishery (Tegner 1989, Tegner et al. 

 1992). The combination of high commercial effort and 

 intense recreational and illegal harvest resulted in a 

 removal of surplus stocks in the California (Tegner et 

 al. 1992) and Mexican (Guzman del Proo 1992) abalone 

 fisheries. Unrestrained recreational and illegal harvest 

 remains a threat to the Victorian fishery, but with a 

 comparatively low human population and a relatively 

 inaccessible coastline the Victorian abalone fishery is 

 less vulnerable to noncommercial overfishing than 

 the California or Mexican abalone fisheries (McShane 

 1990). 



While fishing can deplete stocks, there are a multi- 

 tude of other factors that affect the abundance of aba- 

 lone. For example, overfishing could not explain the 

 recruitment failure which occurred in the abalone 

 fishery of British Columbia (Breen 1986, Sloan and 

 Breen 1988). Recruitment failure in various species of 

 abalone has been attributed to sea temperature anom- 

 alies (Hayashi 1980, Forster et al. 1982, Shepherd et al. 

 1985) or natural variation (Sainsbury 1982b; see also 

 McShane and Smith 1991). The collapse of the Califor- 

 nia abalone fishery for H. rufescens coincided with 

 predator release (Lowry and Pearse 1973, Hines and 

 Pearse 1982, Tegner 1989, Tegner et al. 1989, 1992). 

 The importance of predation in controling abalone 

 abundance is further exemplified by the recovery of 

 stocks of H. cracherodii concomitant with a reduction 

 in the abundance of major predators (Davis et al. 1992). 

 The decrease in abundance of some California popula- 

 tions of abalone (H. rufescens, H. cracherodii) was 

 attributed to low food availability caused by El Nino 

 events (Tegner and Dayton 1987, Tegner et al. 1989), 

 competition with other herbivores, and kelp harvest 

 (Davis et al. 1992). Starvation in abalone causes a 

 decrease in reproductive effort (Cox 1962) and an in- 

 creased susceptibility to disease, both of which can 

 cause a severe decline in stocks (Haaker et al. 1992, 

 Tissot 1992). A major factor in the reduced abundance 

 of abalone stocks in Japan is nearshore pollution 

 (I. Hayashi, Igarashi-Jutaku 2-205, Niigata, Japan, 

 pers. commun. 1990), a factor also implicated in the 

 decline of California abalone stocks (see Tegner et al. 

 1992). 



Variation in abiotic factors such as temperature have 

 demonstrable effects on the survival and growth of ex- 

 ploited species (Cushing 1988). Such factors, apart from 

 seasonal variation, vary stochastically and introduce 

 uncertainty in fisheries management (Megrey and 

 Wespestad 1988, Walters and Collie 1988). Faced with 

 this uncertainty, fishery managers must proceed 

 cautiously and gain a better understanding of the 



ecology of exploitable species, particularly of abalone 

 which have a history of unexplained stock collapse. 



Acknowledgments 



I thank Dr. Paul Breen for helpful discussion and con- 

 structive comments on the manuscript. Drs. Linda 

 Jones and Scoresby Shepherd offered helpful sugges- 

 tions as did an anonymous reviewer. 



Citations 



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