TEGNER ET AL.: BIOLOGY AND MANAGEMENT OF RED ABALONES 



Astrometis sertulifera consumed abalones up to 80 

 mm in aquaria experiments (Tegner and Butler 

 1989). Night dives indicated that the Pycnopodia 

 densities in Table 5 are considerably underesti- 

 mated; juveniles are cryptic during the day. Astro- 

 metis also tends to be nocturnal or at least crepus- 

 cular (MacGinitie and MacGinitie 1968; Tegner pers. 

 obs.). Because many small, empty abalone shells 

 were found without any shell damage, and because 

 juvenile Pycnopodia and Astrometis are common in 

 cryptic habitats where juvenile abalones live, we 

 suspect that these starfishes may be important pred- 

 ators of small haliotids. Pycnopodia and Pisaster 

 giganteus both attacked recently replanted adult 

 abalones from the tagging study but Pisaster does 

 not appear to be a predator of unstressed abalones 

 (Feder 1959, 1963; Tegner and Butler 1989). 



In a study of the gut contents of 87 sheephead col- 

 lected near San Diego, we found that molluscs are 

 an important part of the diet of smaller fishes and 

 found a juvenile red abalone (15 mm) in one gut 

 (Tegner unpub. data). Thus sheephead predation on 

 unstressed and undisturbed animals is probably 

 rare, but these fishes are attracted to divers and 

 probably take juvenile abalones under the spine can- 

 opies of red urchins as the urchins are fished. Sheep- 

 head and bat rays do attack recently replanted aba- 

 lones (Burge et al. 1975; Tegner pers. obs.). 



Some predators characteristic of the warmer 

 areas of the southern California Bight were rare or 

 absent at Johnsons Lee. Bat rays, which feed pri- 

 marily on emergent adult abalones (Tegner and 

 Butler 1989), were attracted to transects on two oc- 

 casions in 1978 and once in 1981 after the fish had 

 been counted. Spiny lobsters, Panulirus interrup- 

 tus, and sheep crabs, Loxorhynchus grandis, have 

 been observed to prey on juvenile and mid-sized red 

 abalones on the Palos Verdes Peninsula (Tegner and 

 Butler 1985). No lobsters and only one sheep crab 

 was seen during the 5 yr course of this study. As 

 all of our visits took place during June and July, we 

 would not have observed any seasonal variation in 

 predator populations. 



Patterns of Shell Production 



The size-frequency distributions of red abalone 

 shells from 1980 to 1982 and 1984 are illustrated 

 in Figure 5. If we assume a constant rate of mor- 

 tality independent of age (Fournier and Breen 1983), 

 then we would expect a decline in the frequency of 

 shells with increasing size above the size range 

 where shells are likely to be destroyed by predators. 

 Large modes from about 170 to 195 mm especially 



in 1980 and 1981 do not fit that expectation. These 

 modes almost certainly reflect bar cut mortality, 

 fatal injuries to abalone soft tissues caused by the 

 collecting tool (Burge et al. 1975; Tegner 1989). In 

 1981 and 1982, this increase in shell frequency can 

 be resolved into two modes: one just below sport 

 minimum size (178 mm) and one immediately below 

 commercial minimum size (197 mm). The larger 

 number of shells found in 1980 represents years of 

 accumulation; this was the first year in which the 

 tagging area was sampled. 



The large shell collections of 1980-82 were ex- 

 amined for evidence of cause of death. Some kinds 

 of shell damage could be ascribed to specific pred- 

 ator types (Cox 1962; Hines and Pearse 1982; 

 Tegner and Butler 1985, 1989) or to the boring 

 sponge Cliona celata (Cox 1962; Abbott and Hader- 

 lie 1980). Other shells were undamaged or the dam- 

 age was ambiguous and probably sometimes the 

 result of deterioration after death; for these animals 

 the cause of death was unknown. Fifty-three shells 

 (including data from 1984) had Octopus spp. drill 

 holes but, as these cephalopods do not drill all their 

 prey (Tutshulte 1976; Ambrose 1984), this is a 

 minimal estimate of the importance of octopus pre- 

 dation to this abalone population. Red abalones ap- 

 pear to attain a refuge in size (shell thickness) from 

 octopus predation; only three of the drilled shells 

 were larger than 125 mm (Fig. 6). The most com- 

 mon pattern of shell damage was the scratches, 

 chipped edges, and small breaks along the growth 

 edge characteristic of rock crab (primarily Cancer 

 antennarius but may include C. productus) preda- 

 tion (Cox 1962). Rock crabs appear to be able to 

 handle the full size range of red abalones at John- 

 sons Lee. Cliona was found in a wide size range of 

 red abalone shells but only in very large shells did 

 the degree of infestation appear sufficient to have 

 contributed to the abalones' death by weakening the 

 shells (Cox 1962). The size-frequency distributions 

 of the mortalities attributed to octopuses, rock 

 crabs, and Clioyia are significantly different from 

 each other (Kolomogorov-Smirnov tests, P < 0.01). 

 Bat ray predation can be recognized from shells frac- 

 tured into large pieces (Tegner and Butler 1989). 

 A small number of mortalities (7-10 per year) could 

 be ascribed to this predator. No shells were found 

 with the acid-etched appearance characteristic of 

 cabezon, Scorpaenichthys marmoratus, predation 

 (Hines and Pearse 1982); For the years 1980-82 

 (tagging area only, n = 986), octopuses account for 

 a minimum of about 4% of the mortalities, rock 

 crabs 21%, Cliona infestation 6%, and bat rays 2%, 

 and 67% of the deaths could not be assigned on the 



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