The white abalone was listed by NMFS as an endangered species on May 29, 2001, effective June 28, 2001, after a comprehensive status review of the species. The decline of white abalone was attributed to overutilization by commercial and recreational fisheries in the absence of adequate regulatory mechanisms. The status review identified an urgent need for human intervention in the recovery of white abalone, because subthreshold densities of the animals in nature make it unlikely that the species will recover on its own. Without intervention, it is estimated that the approximately 1,600 remaining white abalone in the wild will disappear by 2010.
Implementing a captive-breeding program for white abalone is difficult for several reasons, including the depths at which white abalone occur (20-60 m) and the fragility of the animals. In an effort to design a safe and effective collection protocol, John Butler, a fishery biologist at the Southwest Fisheries Science Center, organized the July cruise aboard the research vessel David Starr Jordan. His goal was to locate white abalone, record their positions, and produce high-resolution habitat maps of Tanner Bank, using acoustic remote-sensing tools in combination with an ROV equipped with a GPS (global positioning system)-integrated directional hydrophone.
ROV and Acoustic Remote-Sensing Operations
Tests done without the sidescan-sonar system indicate that the multibeam-sonar system could have collected better data and at twice the speed. Future surveys should dedicate several days to 24-hour multibeam-sonar surveying, followed by alternating daytime ROV operations and nighttime high-resolution sidescan-sonar surveying.
Preliminary data from Tanner Bank suggest that the density of white abalone is approximately 0.003 abalone per m2, several orders of magnitude lower than the density of 1 abalone per m2 estimated for the area before intensive harvesting began in the 1970s. Approximately 194 individuals were identified during 60 hours of ROV searching, and their GPS coordinates were logged. It is unknown whether the white abalone on Tanner Bank are a self-sustaining population, because the larval period of white abalone is 8 to 10 days and currents faster than 1 knot sweep over the bank. Thus, larvae from any successful reproduction may be swept out to sea. None of the observed abalone were juveniles.
Preliminary Recovery Plans
Butler hopes to return to Tanner Bank in the near future with a team of scuba divers that have been trained in deep diving and are skilled in the safe removal of white abalone from their substrate. These animals will serve as broodstock for a captive-breeding program based out of the Southwest Fisheries Science Center.
Establishing multiple culture facilities is essential for creating a successful captive-breeding program. To this end, NMFS is partnering with the Channel Islands Marine Resources Institute and the University of California, Santa Barbara, which currently hold 11 broodstock and 100,000 juveniles resulting from a spawning attempt made during spring 2001.
The captive-breeding program will not only serve to rebuild white-abalone stocks through the outplanting (release to the wild) of cultured individuals, but will also advance scientists' understanding of the biology of the species. Critical research initiatives will include the examination of white-abalone genetic-stock structure, recruitment dynamics, growth and survival patterns, and habitat preferences.
The success of an outplanting program for white abalone will depend upon previous knowledge of the animal's preferred habitat, the ability to locate suitable outplanting habitats in the wild, the ability to monitor these sites, and the ability to protect these sites against poaching. To this end, the high-resolution habitat maps produced by Guy Cochrane and Rikk Kvitek, director of the Seafloor Mapping Lab at CSUMB, are critically important to the recovery effort for white abalone.
Effective Survey Methods
By superimposing both the real-time ROV and support-vessel positions on these three-dimensional maps, the ship captain and ROV pilot were able to effectively navigate and focus their search efforts within specifically targeted habitat types. The efficiency of this combined approach was demonstrated dramatically during the July 2002 cruise, when ROV pilots found, on average, 24 white abalone per day by using the new sonar maps generated the night before, in comparison with previous attempts that lasted as long as 1 month and resulted in the identification of fewer than 8 white abalone per day.
Preliminary mapping results from the July cruise indicate that Tanner Bank is an anticline composed of folded sedimentary rocks. Differential erosion of the rock layers has created a relatively large habitat for white abalone and a good habitat for many types of rockfish (Sebastes spp.), as well as a depression in the center of the bank, giving it a shape similar to that of an atoll or volcanic crater. During low sea level, Tanner Bank was probably an island with a large central lagoon.
The techniques employed during this cruise should prove valuable for the recovery and conservation of white abalone. The extension of ROV and acoustic remote-sensing technology to other areas along the coast of Southern California, the Channel Islands, and Baja California will be crucial for reestablishing white abalone throughout its historical range.
In addition, the potential for addressing other Federal and State agency initiatives exists. The marriage of ROV and acoustic remote-sensing technologies can help to advance ocean exploration through nondestructive sampling techniques, to determine critical habitat for endangered and threatened species, to aid in establishing marine reserves, and to aid in managing fisheries resources.
For example, Tanner Bank is part of the cowcod (Sebastes levis, a rockfish) conservation area, and bottom fishing on the bank is restricted to depths of less than 20 fathoms (120 ft, or about 40 m). This area has been designated by the Pacific Fishery Management Council as part of the rebuilding plan for cowcod. The high-resolution habitat map of Tanner Bank will be used to direct the recovery monitoring for cowcod and, possibly, other exploited species.
in this issue:
Endangered White Abalone