226 



SCIENCE, 



[Vol. IV., No. 84. 



by a long beam, generally of wood, supported 

 upon iron runners ; and there are one or more 

 inner, funnel-shaped traps, to prevent the 

 escape of fish after they have entered. The 

 nets are sometimes very large, and the beams 

 often measure forty-five or fifty feet in length. 

 The lower side of the mouth of the net, which 

 is leaded, hangs loose, so as to drag over the 

 ground in a deep backward curve. It does 

 not dig into the bottom, but simply scoops into 

 its capacious mouth every loose object lying in 

 its course. Large quantities of soft sand and 

 mud are, however, often taken up. 



In adapting the fishermen's trawl for zoolo- 

 gical work, a few modifications have been 

 made, mainly as regards size and the materials 

 used in its construction. For small trawls a 

 beam of iron gas-pipe is now preferred hy the 

 fish-commission to wood, as being more dur- 

 able, less bulk} T , and less liable to injury from 

 pressure in deep water ; the defect of wooden 

 beams, in the latter respect, having seriously 



a depth of 2,650 fathoms in nearly the same 

 locality, but in the Pacific Ocean made several 

 successful casts in more than 3,000 fathoms, 

 the trawl they had having been of about the 

 same size and pattern as the American. 



The method of attaching the bridle in the 

 Challenger trawl was similar to that afterwards 

 adopted for the Blake trawl, the bridle ropes 

 being made very long, and extending along 

 the sides of the net to its extremity, with 

 lashings to the runners on each side, and to 

 the hinder end of the bag. The object of this 

 arrangement of the bridle was not stated by 

 Sir Wyville Thomson ; but it was presumably 

 to allow the forward fastenings to break, in 

 case of fouling, and permit of the net being 

 hauled up hind-end first. 



The Blake trawl. 



The objection above raised to the use of the 

 ordinary beam-trawl in deep water suggested 



Fig. 2. — The Blake trawl ok double beam-trawl. In use (or in position for dragging on the bottom). 



inconvenienced the deep-sea trawling opera- 

 tions of the Challenger. 



The different sizes of trawls employed vary, 

 in the length of beam, from seven and a half 

 to eighteen feet, a wooden beam being used 

 for the latter size only. With an eleven-foot 

 beam, the runners measure twenty-eight inches 

 in height and four feet in length, the beam 

 having a diameter of two inches and a quarter, 

 and screwing into brass strap bands on the 

 tops of the runners. The openings through 

 the runners are closed b} T netting. In the 

 smaller trawls the net is about eighteen feet 

 long, with a single pocket, and, in the larger, 

 measure from twenty-five to forty feet in length, 

 with either one or two pockets. 



For the greater depths of water, the eleven 

 and fifteen feet beams are preferred. The 

 largest size is seldom used, except in moderate 

 depths ; and in shallow water, the Otter trawl, 

 another English pattern, is not unfrequently 

 emploj-ed. 



The common beam-trawl has been used suc- 

 cessful^ by the fish-commission in all depths 

 down to 2,949 fathoms, the latter indicating 

 the deepest trawling-station on record for the 

 Atlantic Ocean. The Challenger trawled to 



to the officers of the Blake dredging-party, in 

 the winter of 1877-78, the construction of a 

 reversible trawl, having in this respect all the 

 advantages of the naturalists' dredge. This 

 pattern, termed the ' Blake trawl,' or ' double 

 beam-trawl,' bears the same relation to the 

 fishermen's beam-trawl as does the naturalists' 

 dredge to the oyster-dredge ; the changes in 

 both cases being demanded by the necessity of 

 working wich greater precision in deep water, 

 where the loss of time occasioned by the use of 

 ill-suited appliances cannot well be afforded. 



The Blake trawl (fig. 2) was the joint 

 invention of Mr. Alexander Agassiz, Com- 

 mander Sigsbee, U.S.N. , and Lieut. Ackly, 

 U.S.N. , and was used with great success on 

 the several dredging-cruises of the steamer 

 Blake from 1878 to 1880, undergoing, during 

 this time, a few slight improvements to perfect 

 its working. In 1880 it was adopted by the 

 fish-commission for deep-water work, in con- 

 nection with the old pattern ; and in 1883 it was 

 also copied by the French exploring-steamer 

 Talisman. The following description is made 

 up from one of the trawls belonging to the 

 latter party, and differing but slightly from 

 that of the Blake. 



i 



