DEVELOPMENT AND EVALUATION OF METHODOLOGIES FOR 



ASSESSING AND MONITORING THE ABUNDANCE OF 



WIDOW ROCKFISH, SEBASTES ENTOMELAS 



Mark E. Wilkins 1 



ABSTRACT 



Rapid expansion of a new fishery for widow rockfish, Sebastes entomelas, stocks off the Pacific coast of 

 the United States began in 1979. Within 3 years, landings rose from <1,000 t to almost 30,000 t of a 

 species for which little information on abundance or life history was available. It was known that widow 

 rockfish occurred in irregularly distributed, dense, midwater, and semidemersal schools primarily during 

 the night, which posed problems in directly assessing this resource Therefore, a project was designed 

 to further investigate the habits and distribution of the species and develop an adequate assessment 

 methodology. 



Line transect survey methods, using sector scanning sonar to estimate the number of schools per 

 unit area and standard hydroacoustic echo integration techniques to estimate school biomass, were used 

 in study areas off Washington and Oregon. The applicability of this methodology will depend on our abil- 

 ity to resolve technical problems and minimize the effects of distributional variability by refining survey 

 design. The need for more sophisticated sonar equipment to improve data collection and processing, the 

 extreme temporal and spatial variability of widow rockfish school size and location, and the difficulty 

 of identifying the species composition of observed schools are matters of special concern. 



The rockfish (genus Sebastes) of the Pacific Ocean 

 are comprised of over 65 species exhibiting a wide 

 array of colors, sizes, body forms, behavior, and life 

 history characteristics. Members of this family are 

 generally demersal or semidemersal and school over 

 hard substrate on the continental shelf and slope. 

 The widow rockfish, Sebastes entomelas, is atypical. 

 As an adult it aggregates in dense midwater schools 

 during the night. 2 These schools tend to disappear 

 from established fishing grounds at dawn or shortly 

 thereafter, becoming less vulnerable to the fishery. 



The role of this species in the Pacific coast ground- 

 fish fishery changed from an undesirable incidental 

 catch in 1978 to a major target species by 1980. Ad- 

 vances in fishing technology and product handling 

 and marketing, as well as new vessels seeking alter- 

 native fisheries, promoted an increase in landings 

 from 1,107 t in 1978 to 28,419 t in 1981 (Table 1). 



By 1981, schools were becoming more difficult to 

 locate and there was concern that the resource was 

 being overharvested. The fishery began expanding 

 into new areas to maintain profitable catch rates. 

 During late 1981 and early 1982, most of the widow 



Northwest and Alaska Fisheries Center Seattle Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, 7600 Sand Point Way N.E., 

 Building 4, BIN C15700, Seattle, WA 98115. 



2 Groundfish Management Team. 1981. Status of the widow 

 rockfish fishery. Unpubl. manuscr., 41 p. Pacific Fishery Manage- 

 ment Council, 526 S.W Mill Street, Portland, OR 97201. 



rockfish were being taken from the vicinities of 

 Bodega Bay and Monterey, CA, though fishing was 

 taking place as far north as Cape Flattery, WA. 



The rapid growth of this new fishery resulted in 

 large catches from a resource about which little was 

 known. Research on this species prior to 1979 was 

 limited to general descriptions of distribution, 

 habitat, and biological characteristics (Hitz 1962; 

 Phillips 1964; Pereyra et al. 1969). Scientists began 

 gathering data in 1978 to determine the impact of 

 the fishery on the condition of the stock, to define 

 the distribution and size of the stock, and to establish 

 a baseline of biological characteristics of the species. 

 Commercial landings have been sampled by State 



Table 1.— Landings of widow rockfish by state for 

 years 1973-83 in metric tons. 



This also included 519 1 of joint venture and foreign catch. 



Manuscript accepted July 1985. 



FISHERY BULLETIN: VOL. 84, NO. 2, 1986. 



287 



