522 



Fishery Bulletin 104(4) 



can allow for detailed and accurate estimates of abun- 

 dance of marine organisms. 



The white abalone (Haliotis sorenseni) is one of six ab- 

 alone species (red, green, pink, pinto, black, and white) 

 that have been exploited commercially on the west coast 

 of North America. The species ranged historically from 

 Morro Bay, California, USA, to Punta Rompiente, Baja 

 California, Mexico (Geiger, 1999). Serial depletion of 

 stocks of congeneric, relatively shallow-dwelling aba- 

 lone species led to the exploitation of white abalone, 

 the deepest living abalone species in the North Pacific 

 (Karpov et al., 2000). During a ten-year period from 

 1969 to 1978, approximately 360,000 white abalone 

 were harvested (Hobday et al., 2001). After 1978, the 

 mandatory reporting of white abalone landings was no 

 longer required, and although abalone fishing effort has 

 remained high, there are (at present) no data on the 

 numbers taken (Tegner, 1989). 



In surveys conducted in the late 1990s in suitable 

 habitat, very low numbers of white abalone were re- 

 ported (Davis et al., 1996, 1998; Haaker et al.^; Hobday 

 et al., 2001). Densities at many localities were less than 

 1 abalone/ha, and the entire population of white abalone 

 was estimated at less than 3000 individuals (Hobday et 

 al., 2001). Reproductive efforts of the remaining adults 

 are believed to have been seriously hindered by poten- 

 tial AUee effects (AUee, 1931) because of low densi- 

 ties. Concern for the survival of the species prompted 

 a status review and the white abalone was listed as an 

 endangered species by the Department of Commerce on 

 29 May 2001 (Federal Register. 2001). 



Postexploitation estimates of abundance and available 

 white abalone habitat need revision because the spatial 

 coverage of sampling in the 1980s and 1990s was lim- 

 ited in the case of determining abundance estimates 

 and virtually nonexistent in the case of determining 

 habitat classification (Lafferty et al., 2004). Accurate 

 estimates of density and the amount of suitable habitat 

 are critical for making informed decisions regarding 

 how to prioritize recovery actions and where to focus 

 population enhancement efforts. In addition, identifi- 

 cation of the specific locations of white abalone in the 

 wild will help both to focus efforts to protect areas 

 where the species remain and to locate potential brood 

 stocks for captive breeding. Information on the recruit- 

 ment potential of the remaining individuals cannot be 

 directly assessed, but an examination of the temporal 

 trends in size distributions may be helpful in address- 

 ing questions of population viability and sustainability. 

 The present study was conducted with recovery efforts 

 in mind, and therefore included intensive sampling of 

 offshore banks and islands where white abalone abun- 

 dance was high historically. We used a combination of 

 advanced mapping technology (multibeam sonar and 



side-scan sonar) and a remotely operated vehicle (ROV) 

 to quantify the total amount of available habitat at each 

 location, in order to examine the size distributions of 

 surviving populations, and to derive new estimates of 

 white abalone abundance. 



Materials and methods 



Habitat mapping 



Habitat was surveyed during three cruises on the NOAA 

 ship RV David Starr Jordan at Tanner Bank (July 2002 

 and September 20041, Cortes Bank (July 2003), and 

 San Clemente Island (August 2004) with multibeam 

 (all years, Fig.l) and side-scan sonar techniques (2002 

 only). The multibeam sonar system, which was installed 

 on the RV David Starr Jordan for the Tanner Bank 

 2002 and Cortes Bank 2003 cruises, included a Reson 

 8101 multibeam sonar (Reson Inc. Goleta, CA) supple- 

 mented with a side-scan sonar option, and was used in 

 conjunction with a Triton-Elics Isis System (Triton Elics 

 International, Portland. OR) for data logging and sonar 

 control. The San Clemente Island 2004 habitat survey 

 was conducted by using the same sonar system aboard 

 a smaller vessel, the RV VenTresca, in conjunction with 

 ROV operations conducted aboard the RV David Starr 

 Jordan. Delphmap and BathyPro software (Triton Elics 

 International, Inc., Portland. OR) were used to create 

 real-time side-scan mosaics and to generate digital 

 elevation models. The pitch and roll motion of the vessel 

 used for mapping was corrected for using a TSS HDMS 

 (heading and dynamic motion sensor) (pitch, roll and 

 heading accuracy ±0.02°; heave accuracy ±5% or 5 cm). 

 Hypack Max software (Hypack, Inc., Middletown, CT) 

 was used for survey planning and navigation. Position- 

 ing information was provided by a Trimble 4700 GPS 

 receiver and NavBeacon for receiving U.S. Coast Guard 

 RTCM (radio technical commission for maritime com- 

 munications) corrections. Sound velocity profile data 

 were collected with an Applied Microsystems (Sydney, 

 British Columbia, and CA) SVPlus sound velocimeter. 

 Multibeam data were processed with CARIS HIPS soft- 

 ware (CARIS USA, Ellicott City, MD), and all final GIS 

 products were derived from shoal-biased data. 



Microhabitat analysis 



Habitat type and algal cover were examined for surveys 

 conducted at Tanner Bank in 2002. Habitat was charac- 

 terized by broad type (e.g., bank, seamount), modifiers 

 (e.g., faulted, eroded), microhabitat (e.g., sand, boulders), 

 seafloor slope (by degree), seafloor complexity (5 levels), 

 and algal cover (species identification and four levels of 

 coverage), after Greene et al. (1999; Table 1). 



2 Haaker, P. L., D.V.Richards, and I. Tanaguchi. 2000. White 

 abalone program October 9-25, 1999, cruise report, 

 p. 1-17. California Department of Fish and Game, 330 

 Golden Shore Suite 50, Long Beach, CA 90802. 



Abalone surveys 



Abalone surveys were conducted with a Phantom HD 

 2-1-2 (2002 and 2003) and a Phantom DS4 (2004) 



