PEARCY: DISTRIBUTION AND ABUNDANCE OF SMALL FLATFISHES 



Table l. — Average sediment texture, percent organic carbon,' 

 and median particle size^ at the seven stations off Oregon (from 

 Bertrand 1971). Stations are arranged according to depth. 



'The percent organic carbon was estimated by the difference In weight 

 between total carbon and calcium carbonate carbon Total carbon was deter- 

 mined by dry combustion In a Leco induction furnace and measurement of the 

 evolved CO2 in a Leco gas analyzer. Calcium carbonate was measured by 

 acidifying ground, dried sediment with 1 N HCI and measuring the CO2 

 evolved (Bertrand 1971). (Reference to trade names does not imply endorse- 

 ment by the National Fisheries Service. NOAA.) 



^Mdd) = rf)50' where * = -logjD and D = diameter in millimeters. See 

 Inman (1952). 



station at the center of the triangle. The upper 2 

 cm of the cores were analyzed. Sediment particle 

 size was measured by standard procedures 

 (Krumbein and Pettijohn 1938). The coarse sand 

 fractions were analyzed by the settling tube 

 method (Emery 1938*. Particle size of sediments in 

 the vicinity of each station was similar (Bertrand 

 1971). Sediments were also sampled at each sta- 

 tion during each cruise. According to Gunther 

 (1972), seasonal variations of sediment grain size 

 parameters within stations were not significant, 

 but significantly different sediment types were 

 found among stations at about the same depths, 

 and fairly similar sediments occurred at different 

 depths. 



Three station-pairs were identified that had 

 rather similar sediment characteristics but were 

 located at different depths (Table 1): 1) Stations 6 

 and 8 (148- and 195-m depth, respectively) had 

 highest percentages of clay and silt, lowest per- 

 centages of sand, and the highest organic carbon of 

 all stations; 2) Stations 22 and 15 (74 and 102 m) 

 had sandy sediments with low percentages of clay, 

 silt, and organic carbon; Station 22, however, was 

 almost entirely (99%) well-sorted beach sand; 3) 

 Stations 7 and 2 ( 100 and 190 m) had 60-70% sand 

 and intermediate percentages of clay and silt (12- 

 229c ) and organic carbon (0.6 and 1.0% ). Station 2 

 had a thin overlying layer of silt that was absent at 

 Station 7 (Roush 1970); 4) Station 23 located at 

 102-m depth, about the same as Stations 7 and 15, 

 was intermediate in sediment texture and organic 

 carbon between stations 7 and 2 and 6 and 8. Thus, 

 stations were recognized with three different 

 types of sediment at about 100 m and two different 

 types at 190-195 m. These sediment types agree 

 with three types recognized by Kulm et al. ( 1975) 



for the continental shelf off Oregon: 1) well-sorted 

 detrital sands (former beach sands) with a high 

 quartz content mainly on the inner shelf; 2) patchy 

 mud facies largely at midshelf depths and concen- 

 trated near large rivers; and 3) mixed sand and 

 mud between the sandy facies and the outer edge 

 of the shelf. Glauconite, the principal authigenic 

 constituent of shelf sands, occurs around the rocky 

 outcrops such as Heceta Bank and along the outer 

 edge of the continental shelf. 



Fishes were collected in beam trawls 3 m or 2.7 

 m wide and 76 cm high at the same seven stations 

 on the central Oregon continental shelf (Figure 1). 

 This net has a small mesh size ( 13-mm stretch 

 measure) and mouth opening and therefore 

 caught mainly small species and juveniles of most 

 commerical species. A total of 115 tows were made 

 on nine cruises between August 1968 and August 

 1970. Trawls were made during daylight hours. 

 Each station was sampled during the four seasons 

 of each year. The trawl was streamed at a ship 

 speed of 3.7 km/h (2 kn), and descended at 30 m 

 wire/min until a scope of 1:4 was achieved, towed 

 for about 15 min (mean, 16 min, SD 5.3), and then 

 retrieved at 30 m wire/min. Two beam trawl tows 

 were made at each station during each cruise with 

 standardized trawling procedures by the same 

 personnel. 



An odometer wheel was mounted outside of each 

 skid to provide estimates of the distance trawled 

 over the bottom. Area sampled was calculated 

 from the circumference of the odometer wheels, 

 the number of revolutions recorded on odometer 

 counters, and the distance between the skids (see 

 Carey and Heyamoto 1972). 



The two odometer readings for a tow were usu- 

 ally similar. Where they differed, I used the high- 

 est reading and assumed that slippage of the 

 wheel in sediments or jamming by sea pens, etc. 

 caused the low reading. Rigid stops were mounted 

 on the skid frame to prevent turning of the wheels 

 until they contacted the bottom. 



The effectiveness of odometer wheels to esti- 

 mate distance traversed by the beam trawl on the 

 bottom has been assessed by Carney and Carey. ^ 

 They recognized slippage of the wheels in the sed- 

 iment and failure of the footrope to effectively tend 

 the bottom at all times as possible errors in 

 measuring actual areas sampled. For these 



^Carney, R. S., and A. G. Carey, Jr. A report on the effective- 

 ness of metering wheels for measurement of the area sampled by 

 beam trawls. Unpubl. manuscr., 17 p. 



631 



