WILKINS: ABUNDANCE OF WIDOW ROCKFISH 



var B = A 2 [(D) 2 var(MSB) + (MSB) 2 var0) 



- var (MSB) var 0)] (Goodman) 1960) 



Results 



Twenty one trawl hauls were made during the 1980 

 FRI survey aboard the Muir Milach; 6 with bottom 

 gear and 15 with midwater gear. Widow rockfish 

 were caught only in midwater hauls and comprised 

 99% of those catches. The most abundant species in 

 the bottom tows were spiny dogfish, Squalus acan- 

 thias, and black rockfish, Sebastes melanops. The 

 acoustic survey consisted of 22 systematic transects 

 covering about 550 km and employed sonar and echo 

 integration equipment. Twenty six schools were 

 sighted and measured to provide data for a line 

 transect estimate of school abundance. During the 

 nonrandom transect run on the night of 27-28 March 

 1980, 73 schools were sighted and measured for use 

 in developing line transect and line intercept esti- 

 mates of school abundance in a small subarea. 



Only four trawl hauls were attempted during the 

 1981 FRI survey due to severe gear damage. Red- 

 stripe rockfish, Sebastes proriger, comprised 90% or 

 more of the two catches which contained fish (one 

 midwater haul and one bottom haul). The midwater 

 haul was made quite close to bottom near midnight 



and contained small quantities of sharpchin rockfish, 

 Sebastes zacentrus; widow rockfish; and greenstriped 

 rockfish, S. elongatus, suggesting an association of 

 these species in nearbottom schools at night. Fifteen 

 systematic transects were covered during this survey 

 (about 400 km) during which 49 schools were sighted 

 and measured. One of the transects was replicated 

 13 times during one night to observe the behavior 

 of a group of schools over the continental shelf just 

 south of the Columbia River. These schools were not 

 gathered around a prominent bottom feature As the 

 night progressed they moved deeper and further off- 

 shore, reaching the shelf break about sunrise After 

 sunrise most of the schools dispersed, though some 

 remained on bottom at least until observations 

 ceased at 1037 (Gunderson et al. fn. 7). 



During the 1981 NMFS cruise, quantitative hydro- 

 acoustic data were collected from 21 transects on 

 the Nelson Island, The Fingers, Heceta Bank, and 

 Cape Blanco grounds (Fig. 1, Table 5) using echo 

 integration (Thomas et al. fn. 5). The searchlight- 

 beam sonar available on the Chapman was inade- 

 quate to identify school types or provide estimates 

 of school density. This is because it employed only 

 a single transducer programmed to sweep back and 

 forth and did not provide continuous coverage of the 

 area within its range Therefore, all density and 

 biomass figures for this survey refer to total nekton 

 rather than widow rockfish. 



Table 5.— The mean fish and nekton density (g/m 2 ) and biomass (metric tons) by location, date, and 

 transect estimated by a conventional echo integration survey performed aboard the NOAA RV Chap- 

 man, 21-26 April 1981 . 1 



1 Thomas, G. L, C. Rose, and D. R. Gunderson. 1981. Rockfish investigations off the Oregon coast, annual 

 report. Unpubl. manuscr, 20 p. Univ. Wash., Fish. Res. Inst. FRI-UW-8119. 



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