284 PLANKTON STUDIES IN EELATION TO 



the other would fish hghtly. The same fisherman, moreover, stated 

 that he considered the shoals to lie parallel with the shore line. 



\_Note. — Amongst the fishing community at Plymouth and Newlyn a 

 considerable diversity of opinion at one time existed in regard to the 

 form and construction of the mackerel trawl. It may, therefore, be 

 desirable to state that the writer was informed by Mr. Chant, the 

 owner of the Condor, that the following details of construction, present 

 in the net which was lost, constitute the essential points in which the 

 mackerel trawl differs from an ordinary otter trawl. 



Not being in a position to show the actual specifications of the trawl 

 in question, Mr. Chant stated that the otter boards were heavier, 

 the length of the foot rope was 92 feet (less than that of an ordinary 

 otter trawl, which is usually 120 to 130 feet), and that the cod end was 

 longer and bred of a finer mesh, viz. one inch. These points alone, he 

 explained, constituted the difference in construction. The main point 

 of the successful manipulation of the trawl, he stated, appeared to lie 

 in the fact that, when trawling is proceeding at the pace of three miles 

 an hour, the length of hawser employed should be five times the depth 

 of the water. 



With this length of hawser, he explained, together with the extra 

 weight of the otter boards, there is no chance of the trawl leaving the 

 ground, although it does not work so heavily as an ordinary trawl would, 

 at the usual pace of two miles an hour. 



Mr. Chant further stated that the mackerel taken by the Condor 

 were caught in an ordinary otter trawl, the cod end of which had been 

 backed with netting of a finer mesh.] 



II. THE PHYSICAL AND BIOLOGICAL CONDITIONS OBSEKVED ON THE 

 START MACKEREL GROUND. 



As a result of a series of observations taken from the Oithona 

 at two positions on the mackerel trawling ground on March 27th, 

 1907, the following is a summary of the chief physical and biological 

 conditions then observed within the area : — 



First Position. — 15 miles S.W. from Start Point. 

 Depth, 38 fathoms. 

 Condition of bottom, fine sand. 



Temperatures : surface, 9"25°. 

 11 fathoms, 8-35°. 

 22 fathoms, 8-26°. 

 P)Ottom, 38 fathoms, 8"3°. 



