FISHERY BULLETIN: VOL. 84, NO. 2 



and Federal agencies in Washington, Oregon, and 

 California for information on size and age composi- 

 tion, sex ratio, maturity, feeding habits, morpho- 

 metries, meristics, and fecundity. 



Widow rockfish abundance was estimated by the 

 Groundfish Management Team (fn. 2, 1982 3 ) of the 

 Pacific Fisheries Management Council, using cohort 

 and stock reduction analyses (SRA) (Kimura and 

 Tagart 1982). These stocks were found to have been 

 fished down from their virgin level and were thought 

 to be approaching a biomass level which would, 

 under prudent management, produce a maximum 

 sustainable yield of about 12,000 t in the INPFC (In- 

 ternational North Pacific Fisheries Commission) Col- 

 umbia and Eureka areas. 



Research surveys were needed to complement 

 these analyses by providing independent estimates 

 of abundance, describing the distribution, and col- 

 lecting biological information not available from 

 fishery data (for example, data on prerecruits and 

 fish in areas which will not support a profitable 

 fishery). Widow rockfish present special problems 

 to those seeking to estimate their abundance 

 through research surveys. The species is not usual- 

 ly available to bottom trawls, precluding traditional 

 "area-swept" trawl surveys, and its tightly clustered 

 distribution and inconsistent schooling behavior 

 reduce the effectiveness of traditional hydroacous- 

 tic surveys. 



In 1980, the Northwest and Alaska Fisheries 

 Center (NWAFC) began developing a practicable 

 method to survey widow rockfish stocks. Scientists 

 needed to understand the distribution and behavior 

 of widow rockfish to determine which survey 

 methods might be most appropriate to measure the 

 size of the resource The first objective of the project, 

 therefore, was to study aspects of the behavior, 

 distribution, and biology of the species. The distri- 

 bution of its characteristic nighttime aggregations 

 relative to features of submarine topography was of 

 particular interest. The distribution of this species 

 is highly variable both on a diel basis and over longer 

 periods, and the reasons for this variability were also 

 of interest. Another question concerned what pro- 

 portion of the total resource is present in detectable 

 schools and how that proportion changes in space 

 and time Clark and Mangel (1979) described a 

 theoretical situation in yellowfin tuna stock dynamics 

 wherein detectable, fishable schools are constantly 

 being replenished from an undetectable portion of 



3 Groundfish Management Team. 1982. Status of the widow 

 rockfish fishery. Unpubl. manuscr., 22 p. Pacific Fishery Manage- 

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



the population. They discussed the implications of 

 this behavior in a fishery. If such a phenomenon 

 could be confirmed in widow rockfish, determining 

 the detectable proportion of the population might 

 enable us to estimate the absolute size of the 

 resource 



The second objective of the project was to inves- 

 tigate methodologies with potential for estimating 

 widow rockfish stock size, considering the species' 

 behavior and distribution patterns. The final objec- 

 tive was to evaluate the effectiveness of the chosen 

 technique when actually implemented. 



The project was conducted in three phases: 1) an 

 examination of the biology and behavior of widow 

 rockfish on commercial fishing grounds, 2) the 

 development of a practical survey method for assess- 

 ing distribution and abundance, and 3) an evaluation 

 of the feasibility and effectiveness of applying such 

 assessment methodology to widow rockfish on a 

 routine coastwide monitoring basis. Field studies 

 were initiated in March 1980 and concluded in April 

 1982. Behavior studies were conducted during 

 August 1980 and April 1981. Field work focusing 

 on methodology development took place during late 

 March 1980 and mid-March 1981, and the trial 

 assessment survey took place during mid-March to 

 early April 1982. All field work was conducted off 

 Oregon and southern Washington (Fig. 1). 



The purpose of this report is to document the work 

 done to date on the development of widow rockfish 

 assessment methodologies, to evaluate the utility of 

 those methods for routine assessment and monitor- 

 ing of widow rockfish stocks and other species ex- 

 hibiting a similar behavior, and to recommend means 

 of enhancing future assessment efforts. 



BEHAVIOR STUDIES (1980-81) 



The nature of the fishery made it apparent that 

 the behavior of widow rockfish differed from that 

 of other commercially important species of the genus 

 Sebastes. Extremely large widow rockfish catches 

 were taken by midwater trawlers operating almost 

 exclusively at night and fishing on very dense mid- 

 water schools in only a few small areas along the 

 coast. 



The first phase of the project studied the behavior 

 and habits of widow rockfish to determine their 

 distribution patterns, using demersal and midwater 

 trawls and hydroacoustic observations. This included 

 determining where the fish go when the dense, mid- 

 water schools disperse; whether there are compo- 

 nents of the stock other than the typical midwater 

 aggregations; and at what period in their daily cycle 



288 



