TEGNER ET AL.; BIOLOGY AND MANAGEMENT OF RED ABALONES 



0.4 0.6 8 12 • ; '4 



FISHING MORTALITY RATE 



Figure 9.— Con(tin«!d— 0-100 with 100 representing maximum >ield-per-recruit and at least 50% 

 of possible egg production. 



abalone shells without any shell damage and the 

 abundance of juvenile Pycnopodia and Astrometis 

 in cryptic juvenile abalone habitat, leads us to sus- 

 pect that these sea stars are important predators 

 of small haliotids. Conversely, there is more support 

 for the role of rock crab predation (Cox 1962). The 

 21% mortality assigned to Cancer predation in this 

 study was the largest proportion which could be 

 unambiguously assigned to any predator, and this 

 value is undoubtedly an underestimate of rock crab 

 importance as many cases of minor chipping were 

 considered ambiguous. Given their nocturnal activ- 

 ity pattern and tendency to bury in the sand by day 

 (Ricketts and Calvin 1968), the observed densities 

 of Cancer (Table 5) may be considerably underesti- 

 mated. 

 The predation patterns observed at Johnsons Lee 



varied considerably from the results of a study of 

 juvenOe (<100 mm) red abalones on the Palos Verdes 

 Peninsula (Tegner and Butler 1985), a mainland site 

 about 160 km southeast of Santa Rosa Island. Here 

 33% of the shells (n = 325) found in a year-long 

 study had octopus drill holes and 34% were ascribed 

 to crustacean predation, primarily by spiny lobsters. 

 The octopus density at Johnsons Lee is much lower 

 than at Palos Verdes, but these cephalopods may 

 still be important predators of juvenile red abalones; 

 9 of 21 shells recovered from a small-scale seeding 

 (size range 22-52 mm) experiment conducted at 

 Johnsons Lee in 1977 had been drilled (Tegner 

 unpub. data). The relatively low level of octopus 

 predation at Johnsons Lee may also reflect the 

 larger average size of individual animals at this 

 location; Figure 6 suggests that red abalone attain 



333 



