FISHERY BULLETIN: VOL. 87, NO. 1 



z 

 o 



\ 



20% RETURN \ 



~\ I I I I I T" 



3 4 5 6 07 8 0.9 



Figure 4.— Isoprofit lines drawn from internal rates of return calculated at varying seed cost and natural mortality values. Solid line 



= breakeven point, dotted line = 20% internal rate of return. 



the control and transplant sites, because growth rate 

 is inversely related to body size. Therefore the 

 growth rate differences observed in this study are 

 likely smaller than would have been observed if the 

 mean length of transplanted abalone had been equal 

 to the mean length of the control group at the ini- 

 tiation of the study. Analyzing growth rates by 

 Walford plots diminishes this bias because the anal- 

 ysis compares the length of individual abalone at the 

 beginning and end of the study period and does not 

 use pooled data to compare growth rates among 

 sites. 



In most transplant experiments, recovery follow- 

 ing transplanting depends on both abalone size and 

 source and is greatest with larger abalone collected 

 from the wild. In the present study wild-harvested 

 northern abalone of 50-100 mm length were trans- 

 planted, and recovery was 72% and 39% at the two 

 sites 9 months after the transplant. Saito (1984) 

 reported 18% recovery 9 months after transplant- 

 ing 25 mm hatchery-reared Haliotis discus hannai 



in Japan. The author also stated that commercial 

 recapture rates are 5-10% for hatchery-reared seed 

 and 20-25% for wild seed. Recovery of 45-71 mm, 

 hatchery-reared Haliotis rufescens in California was 

 less than 1% one year after transplanting (Tegner 

 and Butler 1985). Inoue (1976) reported increased 

 survival with increasing seed size up to 70 mm. 

 Tegner (pers. commun.)^ estimated an annual mor- 

 tality rate of 9.1% for mature, native green abalone, 

 Haliotis fulgens, one year after being transplanted 

 in California. The use of large, wild-harvested north- 

 ern abalone likely contributed to the relatively high 

 recovery rates observed in the present study. 



The markedly different rates of recovery between 

 the two transplant sites seemed independent of 

 handling, tagging, and transplant procedures. Shells 

 collected within two weeks of release indicated that 

 immediate posthandling mortality was similar (<2%) 



'M. J. Tegner, Scripps Institution of Oceanography. La Jolla, 

 CA 92092, pers. commun. January 1987. 



102 



