80 



Part III. — Seventeenth Annual Report 



No. II., immediately above Otter Spit ; No. III., about one mile above 

 Minard Narrows ; No. IV., crossing the loch at Inveraray ; and No. V., 

 opposite Cairndow at the head of the loch, were judged to be fairly 

 representative of the Upper Loch. The distances between the stations 

 are — Between I. and II., 10 miles; II. and III., 8 miles; III. and IV., 

 9 miles ; and between IV. and V., 4 miles. In the selection of the 

 stations, Captain Campbell, late of the Garland, kindly assisted me. 



It was not always possible for me, with the appliances at my disposal, to 

 examine the water of the loch from the surface to the bottom, since it was 

 necessary on most occasions to employ fishing boats and a small local 

 steamer ; the stratum of water examined on each station was 15 fathoms 

 deep. While on Station V. bottom may be found at 15 fathoms, in the 

 middle of the other stations very much greater depths are found. 



In order to ascertain the numbers of eggs present on any one station, a 

 number of nets were fastened along a rope at such intervals as to cause 

 them when towed horizontally to fish at certain depths. These depths 

 were — Surface, 1 fathom, 2 fathoms, 4 fathoms, 6 fathoms, 10 fathoms, 

 15 fathoms. In order to offer as small a resistance as possible to the 

 passage of the water through the cloth of the net a fairly open canvas, 

 which has been much used on the Garland, was found suitable. The 

 meshes of this cloth when wet with sea-water have openings measuring on 

 an average *45 x '45mm. ; the thread of the cloth is # 4mm. in thickness. 

 The mouth of each net had a diameter of 2 feet. In addition to the 

 horizontal tow, a vertical haul was made on each station, The net used 

 for this purpose had a mouth of 3 feet diameter ; it was let down to a 

 depth of 15 fathoms, and then drawn vertically to the surface. By having 

 the cod-end weighted, the net was prevented from fishing as it descended. 

 In this way the forms floating in a vertical column of water were 

 captured. The material of which this net was made was silk grit gauze. 

 When wet with sea-water the meshes were '55 x '45 mm. ; the threads 

 were of two sizes — one '33mm. thick ; the other, at right angles to the 

 former, '27mm. thick. The nets thus had small enough meshes to retain 

 all pelagic fish eggs and the greater proportion of the Copepoda and 

 Zoese, but allowed all Diatoms and most of the Invertebrate larvse to 

 escape. Each visit to a station was timed to take place exactly 28 days 

 after the preceding examination. While in the case of certain stations 

 this was successfully accomplished, on some occasions a few days over the 

 allotted interval elapsed before an opportunity of carrying out the work 

 presented itself. Bad weather was the disturbing factor. 



In addition to the tow-net work, physical observations were made each 

 month on all the stations. The temperature and specific gravity of the 

 water were taken at the surface, 7 J fathoms, and 15 fathoms. For the 

 temperature observations, the reversing thermometers used on board the 

 Garland were employed ; in connection with the specific gravity determina- 

 tions Mill's self-locking water-bottle and the Kiel Hydrometers were 

 made use of. During May, when I was unable to have the Garland's 

 self-locking bottle, an attempt was made to get water from 7g and 15 

 fathoms with a zinc bottle, the cork of which was intended to be drawn 

 when the bottle sank to the desired depth. This bottle was, however, 

 unworkable. An improvement was made by replacing the cork with a 

 ground brass valve, which was found to be comparatively easily 

 drawn at a depth of 15 fathoms. Leakage occurred ; but it was very 

 slight. The improved bottle was used in June. In January and August 

 the work was carried on by means of the Garland ; during the intervening 

 months fishing boats were employed for Stations I. and II., and a small 

 local paddle-boat was hired for Stations III., IV., and V. 



The temperature of the air was noted, as also were the direction and 

 force of the wind, the state of tide, and weather. 



