528 



Fishery Bulletin 104(4) 



at relatively shallow (<25 m) and one shell found at a 

 relatively deep depth (72 m). 



The sizes of white abalone at all sites ranged from 

 9.0 to 19.0 cm (Fig. 4). No small abalone were observed, 

 although turban snails smaller than 6 cm were detected 

 by using ROV sampling methods. Size distributions 

 differed significantly for comparisons made between 

 Tanner Bank 2002 and Cortes Bank, and Tanner Bank 

 2002 and San Clemente Island (K-S test, P<0.01, Fig. 

 4). There was an apparent shift in size distributions be- 

 tween years at Tanner Bank; fewer large animals were 

 found in 2004 than in 2002, although the overall size 

 distributions did not differ significantly between years 

 (K-S test, P=0.19, Fig. 4). The size distribution at Cortes 

 Bank included animals in the mid size range, and no 

 abalone in the smallest or largest size ranges. Densi- 

 ties at San Clemente Island were too low to show any 

 real pattern in size distribution (Fig. 4). The mean size 

 of abalone ranged from 12.4 cm to 13.7 cm and did not 

 differ significantly between surveys (ANOVA, P>0.05). 



Site-specific white abalone population estimates were 

 based on the amount of available habitat quantified 

 from the results of multibeam sonar surveys and white 

 abalone density estimates determined from data from 

 ROV surveys. The total population of white abalone 

 on Tanner Bank based on 2002 density measurements 

 was estimated at 12,819 ±3582 (SE), whereas the total 

 population estimate based on 2004 density measure- 

 ments was 5883 ±3324. The total population on Cortes 

 Bank was estimated at 7366 ±5340 (SE), and that at 

 San Clemente Island was estimated at 1938 ±1598 (SE; 

 Table 2). 



White abalone reproductive potential 



Eighty-nine percent of white abalone at all sites were 

 observed as singletons, and only 6% were observed in 



groups. Group sizes ranged from two to five individuals 

 and the largest group was observed at Tanner Bank in 

 2002. There were no sightings of abalone in groups at 

 Tanner Bank in 2004. White abalone were not found 

 frequently in groups during any of the surveys, and the 

 observed number of individuals within 250-m- subsam- 

 ples within the 40-50 m depth range at Tanner Bank in 

 2002 did not differ from values predicted by the negative 

 binomial distribution (chi-square=4.9, P=0.67). 



The results of an analysis of distances between sight- 

 ings indicated that less than 259c of individual abalone 

 were located within 5 m of one another for all surveys. 

 The majority of individuals (60%) were over 20 m away 

 from another sighted abalone. The survey with the 

 highest proportion of abalone located within a distance 

 of 20 m of another individual was that at Tanner Bank 

 in 2002. In regard to potential mating pairs, out of a 

 possible 19,503 combinations of mating pairs, only 202 

 were within 30 m from one another at Tanner Bank 

 in 2002, 4 out of 231 pairs at Cortes Bank, 3 out of 12 

 pairs at San Clemente Island, and 10 out of 861 pairs 

 at Tanner Bank in 2004. 



Discussion 



Few areas in U.S. waters have been adequately mapped 

 to reveal detailed bathymetry or substrate character- 

 istics. Consequently, our knowledge of the amount of 

 habitat available for benthic marine organisms is so 

 inadequate that one can only speculate about overall 

 population sizes. White abalone populations in south- 

 ern California are no exception; all previous estimates 

 of the amount of suitable habitat available for white 

 abalone have been based on the assumption made by 

 Thompson et al. (1993) that 3% of the sea floor between 

 25 m and 65 m was rocky substrate (Davis et al., 1998; 



