Butler et al Multibeam sonar mapping techniques for estimates of Haliotis sorenseni 



527 



between zero white abalone density and the 

 presence of Eiseiiia arborea, and zero white 

 abalone density and low seafloor complexity 

 (com 1 [very low]). 



Although detailed habitat analyses were 

 not completed for the 2003 Cortes Bank 

 survey, we noted the presence of the brown 

 algae Pterygophora californica and Cysto- 

 seira spp. (both absent at Tanner Bank in 

 2002), and the apparent absence of Dictyo- 

 taceae spp. in deeper waters. 



Abalone abundance, depth, and size 

 distribution 



A total of 258 individual white abalone were 

 identified in all surveys, and the highest 

 numbers were seen at Tanner Bank in 2002 

 (19.8 abalone/ha. Fig. 3, Table 2). Densities 

 ranged from 0.0 abalone/ha (San Clemente 

 Island, 50-60 m depth range) to 19.8 aba- 

 lone/ha (Tanner Bank 2002, 40-50 m depth 

 range. Fig. 3, Table 2). Very few individu- 

 als of other haliotids (5 pink and 3 red) were identified. 

 Search effort was focused on the 30-60 m depth range 

 after preliminary results at Tanner Bank indicated 

 that white abalone inhabit this depth range, but sur- 

 veys were conducted at shallower and deeper depths 

 at each site to confirm these findings. No abalone were 

 found shallower than 32 m or deeper than 61 m at any 

 site, and therefore the results of these surveys were 

 not included in the analysis. Overall densities differed 

 significantly between surveys (h = 162, Kruskal-Wallis 

 test, test statistic=23.76, P<0.0001). Densities within 



 Tanner Bank 2002 



 Cortes Banl< 



D San Clemmente Island 

 D Tanner Bank 2004 



Densi 

 Bank 

 repre 



Figure 3 



ty of white abalone iHaliotis sorenseni) by depth at Tanner 

 two years), Cortes Bank, and San Clemente Island. Error bars 

 ent standard error. 



surveys grouped by 10 m depth bins only differed sig- 

 nificantly by depth for the Tanner Bank 2002 survey 

 (7!= 33, Kruskal-Wallis test, test statistic=10.45, F<0.01. 

 Fig. 3). The total number of abalone shells ranged from 

 44 (San Clemente Island) tol54 (Cortes Bank). The 

 depth distribution of white abalone for all surveys com- 

 bined reveals that white abalone were stratified by depth 

 overall, although search effort was focused on the middle 

 depth ranges (Figs. 3 and 4). The depth distribution of 

 empty shells was similar to that of live white abalone 

 (31-61 m), although there were several (<10) shells found 



9-10 lOi: 11 C IJ Ij 13-14 14-16 15-16 16-1 17-16 18-19 



45-1 



4 

 0.35- 



03 

 0.25 



0.2 

 0.15 



0.1 

 05 



LI 



9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-1 17-18 18-19 



045-1 



04 

 35- 



03 

 0.25 



0.2 

 15 



1 

 005 



D 



9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-1 17-18 18-19 



Size class (cm) 



Figure 4 



Size distribution for white abalone (Haliotis sorenseni) at (A) Tanner Bank. 2002 («=168l, (B) Cortes Bank (;? = 12). (C) 

 San Clemente Island (n = .5), and (D) Tanner Bank. 2004 (n=35). 



