the ship's speed is reduced when the wire retrieval 

 begins, the trawl may sink and continue fishing 

 deeper than the calculated maximum depth re- 

 corded for the horizontal tow. The oblique tows 

 were made in two ways: (1) by letting out a 

 selected length of wire as fast as feasible and re- 

 trieving slowly or in stages (as, on a deep tow, 

 taking in 100 m. of wire during about 3 to 5 min- 

 utes and towing for 10 minutes before retrieving 

 more wire) and (2) by letting the wire out slowly 

 or in stages and retrieving as fast as possible. 



COLLAPSIBLE MIDWATER BEAM TRAWL 



On vessels such as the Black Douglas, inade- 

 quately equipped to operate (most) large nets, it 

 was necessary to have a collapsible net (fig. 3). 

 Views of operation of the net and certain details 

 of construction and the jury-rigged winch and H- 

 frame aboard the Bl-ack Douglas are shown in 

 figures 4 and 5. 



In devising the CMWBT, several features desir- 

 able in operating such a net were considered, and 

 attempts were made to incorporate these features 

 into the design and function. 



Mouth opening. — This should be large to sample 

 a relatively large area and to reduce escapement. 



The horizontal opening was fixed at 10 feet by the 

 top and bottom beams. The vertical, nonrigid 

 opening was hung at 14 feet. In towing, the 

 vertical opening was reduced to about 12 feet at 2 

 knots and to about 10 feet at 4 knots; the latter 

 still left a sampling area of about 100 square feet. 



Towing speed. — The CMWBT was strongly 

 constructed. The maximum speed at which it 

 was towed was about 5 knots, but faster speeds 

 could have been used. 



Mouth opening obstruction. — There was no ob- 

 struction from the top beam bridle, and that from 

 the bottom beam bridle was not great ; this could 

 be eliminated by a spreader bar. 



Specimen damage. — This was reduced by a 

 specially constructed cod end (figs. 3 and 5D). 



The bullet-shaped device attached to the top 

 beam in figure 4 is a bathykymograph. This 

 model functioned sporadically and unsatisfactor- 

 ily in our experiments. 



SUMMARY OF FISHES COLLECTED 



More than 189 species of fishes were taken in the 

 survey. The exact number cannot be determined 

 at. this time because of the uncertain identifica- 

 tion of more than 18 forms. At least one previous- 



\s" 



4' 3" LENGTH 



BOTTOM BRIDLES' 1 

 25' 9" LENGTH 



- BOTTOM BEAM 

 -DEPRESSORS 



-TWO IRON RINGS 

 -METER 0IAMETER 



CANVAS COD END 

 WITH 1/8" ACE 

 NYLON LINER 



. 2" BAR NYLON WITH 

 1/8" BAR ACE NYLON LINER 



Figure 3. — Diagram (lateral view) of 10- by 14-ft. collapsible mid water beam trawl (CMWBT). 

 PELAGIC FISHES, CALIFORNIA CURRENT AREA 



631 



