FISHERY BULLETIN: VOL. 87, NO. 1 



r 



D J F 



1984/1985 



M 



Figure 2.— Monthly recovery of tagged shells and tagged shell 

 fragments from dead abalone. Results expressed as the percent- 

 age of the original number of tagged abalone. 



site B, and 7.2% at site C (expressed as a percent- 

 age of the original tagged number). 



Predation and Seasonal Variation 

 in Habitat 



Shells recovered during monthly inspections were 

 categorized by the nature of breakage. Shells pres- 

 ent on the sites prior to the transplant were not 

 categorized. These older shells were identifiable by 

 degree of shell deterioration and epiphytization. 

 Most shells were recovered whole: 68% at site A, 

 51% at site B, and 79% at site C. 



Recoveries of loose tags owing to tag loss or 

 predation ranged from 0% of the initial tagged 

 population at site C to 1.3% at site B. The relative 

 proportion of loose tags recovered at each site cor- 

 responded to the proportion of broken shells at each 

 site, suggesting that shell breakage due to preda- 

 tion may be the main cause of loose tags. 



One to three octopus dens were present at each 

 site. Abalone shells found outside the dens were un- 

 broken and not drilled. Over the course of this study, 

 four octopuses were removed from site A, two from 

 site B, and one from site C. Dens were often re- 

 occupied three to four months after removal. Red 

 rock crab. Cancer productus, were also a numeri- 

 cally important prey item of octopus at the study 

 sites. 



In July and August, the sunflower star, Pycno- 

 podia helianthoides, preyed intensively on abalone 

 at the transplant sites. This species was seen to prey 

 on weakened or stressed abalone, and starfish were 



observed actively feeding on abalone immediately 

 following the transplant. As with octopus, shells of 

 abalone eaten by P. helianthoid£s were always 

 recovered unbroken, either under actively feeding 

 stars or entirely within the stomach. 



In contrast, broken or chipped shells were pre- 

 sumed to be due to predation by red rock crabs, 

 wolfeels (Anarrhichthys ocellatus), or cabezons 

 (Scorpaenichthys marmoratus). Red rock crabs were 

 abundant during the spring and summer at all sites 

 except site C, but were rarer in the fall and winter. 

 A few abalone shells were recovered outside a wolf- 

 eel den at site A, and one or two cabezon were 

 observed at all sites throughout the study period. 



Considerable seasonal variation in the marine 

 plant community at the transplant sites was ob- 

 served. Annuals, such as Desmarestia ligulata, died 

 back in October and were completely gone by 

 November. The Macrocystis canopy was also re- 

 duced in fall and winter as a result of storm dam- 

 age. Plants at site A were stripped of most fronds 

 over the winter while losses were lower at site B, 

 the more sheltered of the two transplant sites. 

 Holdfasts remained intact and growth was renewed 

 by March. 



Recovery of Abalone 



After nine months, 72% of the transplanted north- 

 ern abalone were recovered from site A, and 39% 

 from site B (Table 2). When shells from dead north- 

 ern abalone collected during the 9-mo period were 

 included, 88% of abalone at site A and 55% of 

 abalone at site B could be accounted for. At the con- 

 trol site (C), 31% of the tagged abalone were re- 

 covered live and 40% of the original tagged abalone 

 could be accounted for by including tagged shells 

 recovered over the study period. The difference in 

 percent recovery between the two transplant sites 

 suggests that either abalone survival, abalone move- 

 ment, or the ability of divers to find abalone differed 

 between the sites. 



The recovery of tagged northern abalone was 

 6% less than recovery of untagged abalone at 

 both transplant sites (Table 2), and the ratio of 

 tagged to untagged abalone at recovery (0.20) was 

 less than the initial ratio of 0.23. This difference 

 is not significant (jc analysis, P < 0.05), indicating 

 that losses due to the tagging procedure were 

 minimal. 



The number of tagged shells recovered by divers 

 over the 9-mo study allowed estimation of minimal 

 instantaneous natural mortality (M„i„) (Ricker 

 1975). This calculation assumes that divers recov- 



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