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Fishery Bulletin 104(4) 



mate of 13.0 abalone/ha. Densities were lower overall 

 in our surveys conducted at Tanner Bank in 2004, and 

 the most significant differences were apparent in the 

 40-50 m depth range. These lower densities in sur- 

 veys conducted only two years after initial surveys are 

 noteworthy and worrisome, especially because Tanner 

 Bank is a site where the population was thought to be 

 relatively stable. 



The density of white abalone prior to commercial 

 and recreational exploitation is poorly known, and the 

 few reported estimates are the subject of considerable 

 speculation. Tutschulte (1976) reported an estimate 

 of white abalone density of 2300 abalone/ha, based 

 on three 10-m- quadrats. Because of the small sam- 

 ple size and lack of replicate sites, caution should be 

 used when applying this estimate to all of California. 

 However, it is important to note that one cluster of 

 five white abalone was observed in the present study, 

 which would lead to a local density close to that re- 

 ported by Tutschulte (1976). It is also of interest to 

 note that Shepherd et al. (2001) suggested that once 

 populations of Haliotis laevigata reached densities 

 below 0.25 abalone/m- (2500 abalone/ha) management 

 action should be taken, and therefore estimates of 0.23 

 abalone/m^ reported by Tutschulte (1976) were not 

 extremely high. 



More recently Rogers-Bennett et al. (2002) used his- 

 torical landings data and the habitat area estimated 

 by Davis et al. (1998) and Hobday et al. (2001) in an 

 attempt to reconstruct past population densities. Ap- 

 plying the 39c rocky habitat criteria referred to above 

 (Discussion section, paragraph 1) (Thompson et al., 

 1993), Rogers-Bennett et al. (2002) calculated a density 

 of 479 abalone/ha for all of California and a density of 

 1623 abalone/ha for San Clemente Island, where 75% of 

 the landings were reported. These densities are lower 

 than those reported by Tutschulte (2300 abalone/ha; 

 1976), but the more recent estimate is also too high 

 because the proportion of rocky habitat is greater than 

 3%, as observed in the present study. The maximum 

 density observed in the present study (19.8 abalone/ha) 

 is only an order of magnitude less than Rogers-Ben- 

 nett et al.'s (2002) calculation of historic density for 

 all of California (479 abalone/ha), but is two orders 

 of magnitude less than the estimates by Tutschulte 

 (2300 abalone/ha, 1976). Regardless of the problem of 

 inflated density estimates, the densities observed in the 

 present study at San Clemente Island were less than 5 

 abalone/ha at all depths, which is astoundingly lower 

 than the 1623 abalone/ha calculated by Rogers-Bennett 

 et al. (2002). 



Whether the existing white abalone populations are 

 viewed as viable depends largely on the validity of esti- 

 mates of past population distributions and densities and 

 on establishing confidence in current density estimates. 

 Total abundance of individuals becomes irrelevant if 

 these animals are distributed such that densities within 

 a particular area are below the critical level necessary 

 for successful reproduction. The relatively deep range of 

 H. sorenseni is outside the range of dense macroalgal 



growth, and therefore we can assume that the ROV 

 does an adequate job in identifying animals within 

 its field of view (2 m). Based on the assumption that 

 we are actually sighting nearly all of the animals that 

 are within the search range, our data indicate that 

 the majority of individuals at these sites are greater 

 than 5 m (linear distance) from any other individuals 

 along and between transects, and that many are over 

 30 m away from a potential mate. These distances well 

 exceed what has been shown to be a critical minimum 

 distance (<2 m) for successful spawning and fertiliza- 

 tion in other species of abalone (e.g., Haliotis laevigata; 

 Shepherd and Brown, 1993; Babcock and Keesing, 1999; 

 Shepherd et al., 2001). The large distances between 

 individuals coupled with density estimates that are 

 several orders of magnitude lower than those necessary 

 for a viable population (Shepherd et al., 2001) would 

 indicate that white abalone populations are currently 

 in a dire state. 



Despite generally large distances between individu- 

 als, an analysis of dispersion within the population 

 surveyed at Tanner Bank in 2002 showed a large pro- 

 portion of individual sightings within 30 m of another 

 sighting. Additionally, there was a high degree of con- 

 tagion between individuals in 250-m'- subsamples at 

 depths of 40-50 m. It may be true that white abalone 

 at this site are aggregated on a larger scale, indicat- 

 ing that certain habitats within their most prevalent 

 depth range (40-50 m) may promote higher survival 

 of white abalone. However, ultimately, if animals are 

 not packed densely enough at smaller scales, successful 

 spawning and fertilization will not occur. This study 

 highlights the importance of establishing accurate den- 

 sity estimates at appropriate scales for guiding assess- 

 ments of population viability and future enhancement 

 protocols. 



The mean sizes of white abalone observed in the pres- 

 ent study varied little between sites and were compa- 

 rable to those observed during 1999 submersible sur- 

 veys at Tanner Bank and Cortes Bank (Behrens and 

 Lafferty, 2005). The size distribution of white abalone 

 did differ slightly between the two banks and island 

 location. More notable was an apparent shift in the 

 size distributions of animals observed at Tanner Bank 

 in 2002 versus those observed in 2004. Unlike in 2002, 

 there were no large individuals observed in 2004, in- 

 dicating a possible die-off of older individuals and a 

 lack of new, younger individuals to fill this size class. 

 No white abalone smaller than 9.0 cm (approximately 

 three years old; Tutschulte, 1976) were observed at 

 any of the sites. If this were a self-sustaining popula- 

 tion, smaller individuals indicating recruitment from 

 several preceding year classes would be present, al- 

 though the likelihood of sighting abalone recruits and 

 juveniles younger than three years is not very high. 

 Juvenile white abalone shells are mottled red in color 

 and settlement occurs on pink crustose coraline algae- 

 covered rocks, thus making them very cryptic during 

 the first few years of life. Even during historic periods 

 when white abalone density was much higher than cur- 



