FISHERY BULLETIN: VOL. 86, NO. 2 



45° 

 00' 



-1 1 1 r- 



440 

 50' 



90 



80 



70 



60 



50 40 



30 



15 5 

 • • • •) 



20 10 It 



YAQUINA 

 BAY 



125° 

 00' 



124° 

 30' 



124° 

 00' 



Figure 1. — Location of stations along the transect off Newport, 

 OR. The numbers indicate distance offshore in kilometers. 



weeks of strong upwelling, during which very few 

 larvae were collected close to the coast, the sam- 

 pling scheme was modified for the two July 

 cruises by eliminating some of the inshore sta- 

 tions and extending the transect as far offshore as 

 90 km. Only night samples were collected during 

 July. 



One of the primary considerations of the survey 

 was to collect samples while minimizing net 

 avoidance by the target organisms. Reduction of 

 vessel-induced disturbance was accomplished by 

 deploying the collecting gear from the ends of 12 

 m-long outriggers on the FV Cumberland Trail, 

 a chartered 23 m commercial scallop-fishing ves- 

 sel. 



Two different nets were used to collect the sam- 

 ples. Larval fish and zooplankton were collected 

 with a Manta neuston net (Brown and Cheng 

 1981), modified to have a mouth 1.0 m wide x 0.7 

 m deep. The Manta frame was equipped with a 

 green-colored 0.333 mm mesh net, PVC cod end 

 bucket, and General Oceanics model 2030 digital 

 flowmeter'^. A two-point bridle was attached to 

 the upper corners of the frame. Drag on the net 

 while towing kept the entire bridle and towing 

 wire assembly out of the water. 



The second net was designed to collect the 

 larger juvenile fishes that were assumed to avoid 

 the smaller Manta net. The neuston trawl was 

 constructed with a mouth 3.50 m wide x 1.05 m 

 deep (Fig. 2a). The frame consisted of 43 mm (out- 



3References to trade names do not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



side diameter) heavy-duty galvanized pipe, with 

 towing points welded at the four corners. Flota- 

 tion for the frame was provided by three inflat- 

 able spar buoy floats. These 40 cm diameter floats 

 had hollow tubes running through their centers 

 and were fitted onto the upper bar of the frame. 

 The 8.5 m-long net was made of 4.8 mm green- 

 colored woven mesh, with a 15 cm-wide cloth 

 collar around the mouth, PVC cod end bucket and 

 General Oceanics model 2030 flowmeter. The net 

 had a mouth slightly larger than the frame 

 (3.70 m X 1.20 m) so the net could be laced around 

 the outside of the frame and flotation buoys. The 

 ends of six 12 mm polypropylene rope riblines 

 running the length of the net were shackeled to 

 the frame for additional support. A 4-point bridle 

 of 6.4 mm wire was attached to the corners of the 

 neuston trawl (Fig. 2b). Drag forces kept the en- 

 tire bridle and towing wire (except for the two 

 short segments attached to the bottom of the 

 frame) out of the water. A length of 5 cm 

 polypropylene rope was attached between the 

 upper towing points on the frame, as a bridle for 

 use in deploying and retrieving the net. A line 

 attached to the retrieval bridle was passed to a 

 hydraulic capstan through a block tied in the rig- 

 ging over the deck. During a tow, this retrieval 

 line was slackened, but remained attached to the 

 vessel, and floated in a broad arc behind the net 

 mouth. 



At each station, the neuston trawl and Manta 

 net were towed simultaneously from the port and 

 starboard outriggers, at approximately 1-1.5 m/ 

 second. Tows were generally made either against 

 or with the direction of the prevailing swells. The 

 Manta net was usually fished for approximately 

 8-9 minutes/tow and filtered about 300-400 m^. 

 The neuston trawl generally filtered 2,000-3,000 

 m'^ during a 10-11 minute tow. Additional tows 

 with the neuston trawl were frequently made at 

 a station to assess small-scale patchiness and 

 to sample visible "structures" in the surface 

 layer, such as convergence zones marked by foam 

 lines and rafts of the pleustonic hydroid Velella 

 uelella. 



On several cruises, onset of high winds and 

 rough sea conditions prevented use of the Manta 

 net during the daj^ime sampling of the transect 

 as we returned toward shore. However, we were 

 able to fish the neuston trawl in winds up to an 

 estimated 40—45 km/hour, and in white-capped 

 seas of 2-3 m. Neuston trawl samples were col- 

 lected at alternate stations during the periods of 

 adverse weather. 



300 



