750 



Fishery Bulletin 100(4) 



that avoidance or attraction of fish in response to the 

 submersible was minimal, and thus did not affect counts 

 substantially. This assumption was tested by Hixon et al.'' 

 by observing the local distribution and abundance of fish 

 around the submersible just before and after the 10-15 

 minute "quiet periods'" on the bottom, during which all 

 motors and lights were turned-off Quiet periods were con- 

 ducted for all transect dives, and there was no indication 

 that fish behavior was altered by the presence of the sub- 

 mersible. However, midwater schools of yellowtail rock- 

 fish sometimes circled the submersible during transects, 

 which could have affected counts if fish were counted more 

 than once. The final assumption was that transect width, 

 which varied as a function of the altitude of the submers- 

 ible above the seafloor, was constant. Certainly, there was 

 some variation in altitude, yet the error introduced was 

 presumably insubstantial except perhaps in areas of ex- 

 tremely heterogeneous vertical relief 



This study provides an expanded view of the groundfish 

 habitat of Heceta Bank in areas adjacent to the histori- 

 cal Delta transects. In order to perform a full assessment 

 of the bank it will be important to groundtruth habitat 

 types for the entire extent of the bank. The new sonar da- 

 ta have indicated areas on the bank that contain unique 

 habitats that have not been identified. The best study 

 plan would have been to gather the sonar data first, then 

 use the detailed imagery to define patches of uniform 

 bottom type for planning subsequent stratified random 

 sampling and groundtruthing using submersibles. The 

 next phase of our project was initiated in June 2000 and 

 involved operations with the manned submersible used 

 in the original study and an advanced remotely operated 

 vehicle (ROV) to conduct transects on unsurveyed areas, 

 as well as to repeat the original historical transects. Not 

 only will this approach optimize the techniques developed 

 in our project but may also provide the opportunity to es- 

 timate changes in fish density on Heceta Bank over the 

 past decade. 



Conclusions 



In this exploratory project we have demonstrated how sonar 

 and submersible data can be combined to allow habitat- 

 based stock assessments of multiple species of groundfish. 

 Despite its limitations, this method provides the possibility 

 for a detailed look at fish abundance using habitat associa- 

 tions. This approach could be used to address the problem 

 of the high number of groundfish species that are currently 

 unassessed. It offers the prospect of examining multiple 

 species of fish and may provide a better indication of fish 

 abundance estimates, particularly for multiple species, 

 than is possible using current methods. 



The method presented in our study provides an alter- 

 native for assessing these ten groundfish species and ad- 

 ditional groundfish species that are currently unassessed, 

 as well as for monitoring species that are considered to 

 be overfished. Of the groundfish species examined in this 

 study using the 1988-90 submersible observations, the 

 status of all, but the pygmy, rockfish has been reported 



recently (NMFS, 1999). In the NMFS report on the sta- 

 tus of fisheries in the United States, only the lingcod was 

 reported as "overfished." Yellowtail rockfish, shortspine 

 thornyhead, sablefish, and Dover sole were listed as 

 "not approaching overfished," and the status of rex sole, 

 greenstriped rockfish, rosethorn rockfish and sharpchin 

 rockfish was reported as "unknown" (NMFS, 1999). In 

 addition to the ten species that were examined here, the 

 method described in our study would be important for 

 assessing species of rockfish found on Heceta Bank that 

 are considered overfished, such as the canary rockfish, Pa- 

 cific ocean perch, and darkblotched rockfish. It should be 

 stressed, however, that this method would be useful only 

 for those species that are closely associated with seafloor 

 habitats and spend most of their time near the bottom. For 

 example, yellowtail rockfish are found as high as 25-35 

 m off the seafloor, so that transect data collected on the 

 seafloor may not accurately reflect their true abundance 

 (Pearcy, 1992). 



The preliminary work in this study is a step toward 

 creating a model approach for characterizing and quanti- 

 fying groundfish and their habitat associations on a scale 

 meaningful to the stock assessment of commercial species 

 and the conservation of benthic communities. Traditional 

 stock assessment methods for groundfish have been inad- 

 equate. Our study is the first step in the development of 

 a new quantitative method of assessing groundfish stocks 

 that is independent of traditional trawl surveys. Overall, 

 this habitat-based approach to stock assessment has par- 

 ticular recommendation for defining and mapping essen- 

 tial fish habitat, as well as providing important data for 

 designing and managing marine reserves and protected 

 areas. 



Acknowledgments 



We would like to thank all who were involved in the col- 

 lection and analysis of both the Delta submersible data 

 and the Simrad EM.300 multibeam sonar data. We espe- 

 cially thank D. Stein, B. Barss, R. Methot, B. Malouf and 

 J. Auyuong. W. Wakefield provided advice and support 

 with this project. The high-resolution multibeam survey 

 of Heceta Bank would not have been possible without the 

 efforts of the captain and crew of the MV Ocean Alert, and 

 the personnel from C&C Technologies. Also, D. Clague 

 and Monterey Bay Aquarium Research Institute pro- 

 vided valuable support for the EM300 survey with both 

 the onboard processing system and in allowing us to use 

 some of their survey time to complete the Heceta Bank 

 survey. J. Reynolds generously stayed on board Ocean 

 Alert for the Heceta Bank survey and provided invaluable 

 expertise in data collection and processing. We also thank 

 N. Maher for valuable technical advice on EM300 pro- 

 cessing. This research was funded by Oregon Sea Grant 

 (NOAA), NOAA's National Undersea Research Program 

 through NURP Headquarters and the West Coast and 

 Polar Regions Undersea Research Center. The submers- 

 ible and sonar portions of the work were funded through 

 the U.S. Department of the Interior Minerals Manage- 



