TEGNER ET AL.: BIOLOGY AND MANAGEMENT OF RED ABALONES 



self-regulation of the fishery does not occur. Thus 

 the fishery can remove a high fraction of the accu- 

 mulated stock in a short time (e.g., Kojima et al. 

 1978), leading to greatly reduced breeding poten- 

 tial and thence recruitment failure. Although this 

 mechanism is an attractive explanation for unex- 

 pected declines in exploited abalone populations, 

 Harrison (1986) pointed out that recruitment failure 

 has never been convincingly demonstrated in an 

 abalone fishery. Such a demonstration would be dif- 

 ficult, because the stock-recruit relationship is not 

 known for any abalone species. Without knowing 

 the relation between stock and subsequent recruit- 

 ment, one canot know how much breeding stock 

 must be maintained. However, egg-per-recruit anal- 

 ysis can provide clues as to whether egg production 

 is adequate (e.g., Sluczanowski 1986; Praeger et al. 

 1987). 



For California red and pink abalones, the decline 

 in fishery landings may have many causes (Burge 

 et al. 1975; Cicin-Sain et al. 1977; Tegner 1989). The 

 declines occurred after large increases in fishing 

 pressure, so one is tempted to conclude that recruit- 

 ment overfishing as described above was a contrib- 

 uting cause. Our analysis does not support that 

 conclusion, at least for red and pink abalones in 

 southern California. Our egg-per-recruit analyses 

 suggest that, with the present minimum legal sizes, 

 egg production would be maintained at healthy 

 levels for both species, even at very high fishing 

 mortality rates. For red abalones, with our estimate 

 of M = 0.15, egg production would be maintained 

 at about 50% even if the population were fished 

 down to the recreational size limit. It is hard to im- 

 agine recruitment failure happening at this level of 

 egg production. 



We conclude that simple recruitment overfishing 

 is not a satisfactory explanation for the decline in 

 red and pink abalone landings. Some possible quali- 

 fications should be noted. First, the results of egg- 

 per-recruit analysis are sensitive to the growth 

 parameters used as input. Underestimation of either 

 L„ or the Brody coefficient leads to overestimation 

 of relative egg production. Because growth in aba- 

 lones varies greatly among habitats (Sainsbury 

 1982; Shepherd and Hearn 1983; Breen 1986) and 

 varied considerably from year to year in this study 

 (P. Haaker fn. 3), egg production analyses based on 

 growth data from one site might not reflect the 

 situation at other sites. The paucity of published 

 growth data for California abalones, and the impor- 

 tance of such data in assessing the fishery, point to 

 a need for further growth studies. 



Second, the mortality caused by handling sublegal 



abalones (picking and replacing them) has the same 

 effect on egg production as a reduction in minimum 

 legal size. Thus estimates of egg production at the 

 present minimum legal size are known overesti- 

 mates. However, egg production is still good well 

 below the present legal sizes (Fig. 8C, D) so this 

 problem is unlikely to affect our conclusion. 



Third, simple analyses such as this ignore spatial 

 and ecological complexities. At a particular site, 

 fishing mortality might be much higher than the 

 population-wide rate. If dispersion of larvae is 

 limited, as Prince et al. (1987) suggested, locally in- 

 tense harvesting events could cause long-lasting 

 changes in local populations. Another complexity is 

 that abalones may aggregate to spawn (Shepherd 

 1986), thus becoming far more vulnerable to fishing 

 mortality than the nonbreeding population. Final- 

 ly, populations reduced to low densities may not be 

 able to realize their potential egg production because 

 of reduced fertilization efficiency. 



Although this study does not support the idea that 

 recruitment overfishing has been a serious problem, 

 it does support the idea that reproductive factors 

 should be considered along with yield estimates 

 when fishing strategies are developed. The strate- 

 gies which lead to the best yields in red abalones 

 (Fig. 7A, B) are strategies that lead to lower egg 

 production than others (Fig. 8A, B). As Sluczanow- 

 ski (1984, 1986) found for South Australian aba- 

 lones, egg production can be greatly increased with 

 small reduction in yield-per-recruit by choosing dif- 

 ferent combinations of minimum legal size and 

 fishing mortality rate. 



If recruitment overfishing cannot be invoked to 

 explain declining landings, what happened? Some 

 of the explanations offered by Burge et al. (1975) 

 may remain valid. Many sublegal abalones may be 

 killed by handling. In at least the early years of the 

 fishery, the stock was being "fished down" as years 

 of accumulated production were removed; the land- 

 ings may have been higher than sustainable levels 

 during this period. However, it seems unrealistic to 

 argue that the fishing down process lasted from 

 1950 through 1970 (e.g.. Cox 1962). Sea otters have 

 effectively removed abalones from parts of the coast 

 that contributed to the fishery. Fishing closures 

 have eliminated access to other areas. 



Direct and indirect environmental effects may also 

 be partly responsible, especially for species near the 

 end of their range, such as pink abalones on the 

 northwestern Channel Islands. Abalones do not 

 necessarily spawn every year (e.g., Sainsbury 1982). 

 Temperature appears to be a major controlling in- 

 fluence on spawning (Pearse 1978; Uki and Kikuchi 



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