FISHERY BULLETIN: VOL. 87, NO. 2. 1989 



1984). Food availability is also involved; when mas- 

 sive storms removed virtually all the kelp from Palos 

 Verdes in the winter of 1983, green abalones missed 

 their normal late spring spawning (Tegner and 

 Dayton 1987). Temperature also effects larval sur- 

 vival (Leighton 1974); thus variability in the repro- 

 ductive success of abalones could be intimately 

 related to variations in water temperature regimes. 

 Paine (1986) observed that purple sea urchins settled 

 successfully only four times in 20 years on the outer 

 Washington coast and suggested that settling suc- 

 cess was associated with warm-water events. 

 Similarly, Tegner and Dayton (1987) found strong 

 settlement of pink abalones into what had been a 

 red abalone bed at Palos Verdes and simultaneous- 

 ly found a near absence of young reds during the 

 1982-84 El Nino. Shepherd et al. (1985) suggested 

 that poor settlement oiH. scalaris is associated with 

 cool-water temperatures. Similar suggestions are 

 made by Hayashi (1980) and Forster et al. (1982). 

 Interannual variability in surface currents will have 

 a direct effect on larval transport; larvae which end 

 up in unsuitable habitat are not likely to contribute 

 to fishable stocks. This has been demonstrated for 

 several finfishes (Walford 1938; Nelson et al. 1977; 

 Bailey 1981; Sinclair et al. 1985). The transport 

 anomalies associated wth El Ninos (Chelton et al. 

 1982) may be responsible for purple urchin settle- 

 ment in Washington and the pink abalone event 

 described above. 



An indirect effect of hydrographic events is pro- 

 posed by Sakai (1962) who found a high correlation 

 between abalone landings and harvests of the sea- 

 weed Undaria pinnatifida. Sakai suggested that 

 seaweed growth, and consequently abalone produc- 

 tion, varies with the strength of the Kurile (Oyashio) 

 Current. Similarly, El Ninos in California involve 

 a reduced California Current and increased trans- 

 port of warmer waters from the south (Chelton et 

 al. 1982). During the major El Nino of 1957-59, Cox 

 (1962) reported that abalone growth practically 

 ceased, body tissues appeared to shrink, gonad 

 development was minimal, and there was poor re- 

 cruitment to the fishery. When Johnsons Lee was 

 sampled in 1984, few animals were found above 

 sport minimum legal size and growth was the lowest 

 observed during this study (P. Haaker fn. 3). It is 

 now clear that the warm water associated with these 

 events leads, in addition to kelp mortality, to a sharp 

 decrease in the nitrogen content of algal tissues; 

 such kelp is probably an inadequate food to support 

 herbivore growth or reproduction (Tegner and 

 Dayton 1987). 



The egg-per-recruit model we used was determin- 



istic, whereas breeding success is stochastic. Future 

 work should try to measure the degree of variation 

 in settlement and recruitment success, then evaluate 

 population responses with a simulation model incor- 

 porating the variability observed. Studies of this 

 type have shown that stochastic variation in recruit- 

 ment creates difficulties in rebuilding depleted 

 stocks (e.g., Archibald et al. 1983). If abalone lar- 

 val settlement is only occasionally successful, main- 

 tenance of the population may require a much larger 

 breeding stock than otherwise expected. 



The importance of environmental effects in ex- 

 plaining declining abalone abundance is evident in 

 several studies where abundance or recruitment 

 declined in the absence of a fishery. Breen (1986) 

 and Sloan and Breen (1988) reviewed the evidence 

 for H. kamtschatkana in British Columbia. Sains- 

 bury (1982) observed fluctuating recruitment in an 

 unfished population of H. iris in New Zealand. In 

 the English Channel Islands, H. tuberculata has 

 undergone strong fluctuations in recruitment and 

 abundance, even where not exposed to a fishery 

 (Forster et al. 1982). If unexploited stocks undergo 

 major fluctuations in recruitment caused by envi- 

 ronmental effects, then the fluctuations in heavily 

 exploited stocks may be severe under the same con- 

 ditions. As Gulland (1973) pointed out, "if the fluc- 

 tuations in year class strength, independent of the 

 abundance of adults, are large, then it is possible 

 that a serious collapse of the stock can occur before 

 the need for management is recognized and appro- 

 priate measures taken." 



To manage abalones properly, fishery managers 

 would need to know the relation between breeding 

 stock size, which they can manipulate through 

 regulation, and subsequent stock size. If there were 

 little relation, then the best strategy would be to 

 maximize the yield from whatever recruitment oc- 

 curs. At the other extreme, Prince et al. (1987) sug- 

 gested a strong relation between local stock size and 

 recruitment. In this case the manager must balance 

 the need to maximize yield with the need to main- 

 tain good egg production, and the need to maintain 

 resilience in the face of environmental uncertainty. 



In the absence of better information, we suggest 

 that prudent abalone management should follow the 

 lead of Sluczanowski (1984, 1986) and adopt the goal 

 of maintaining egg-per-recruit at the cost of some 

 potential yield. Our results support Harrison's (1986) 

 contention that the minimum size limit should be the 

 basic management tool in meeting this goal, as fish- 

 ing mortality rate is unlikely ever to fall below F 

 = 0.3. To set appropriate size limits requires good 

 information on growth patterns, fecundity and 



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