METHODS 



A 0.9 -m. Isaacs -Kidd midwater trawl (Isaacs 

 and Kidd, 1953; Aron, 1962) was used to 

 sample the animal population. The body and 

 throat of the net were constructed from 

 64-mm. (stretched measure) cotton netting with 

 a liner of 13-mm. bait netting in the throat 

 (fig. 1). The cod end was a nylon plankton net 

 of 3-mm. mesh with a mouth 1/2 m. in diam- 

 eter. 



Collections were obtained from May 3 to 

 May 16 (79 samples) and from October 28 to 

 November 22 (60 samples) along lines per- 

 pendicular to the coast. Four lines of stations 

 were spaced about 111 km. apart during the 

 spring cruise (fig. 2), and nine lines of sta- 

 tions were spaced about 56 km. apart during 

 the fall cruise (fig. 3). Stations were located 

 near the 55-, 183-, 914-, 1,829-, and2,377-m. 

 depth contours on each line except line V, where 

 all stations were near the 183-m. depth con- 

 tour. An additional station at the 119-n-i. 

 depth contour was sampled during the fall 

 cruise on lines II, III, IV, VI, VII, and VUI. 



During the lowering, towing, and retrieval 

 of the net, the speed of the vessel was main- 

 tained at 3 to 4 knots. Depth of the trawl was 

 based on a 4: 1 ratio for wire length to depth, 

 established by repeated lowerings of the trawl 

 with a bathythermograph attached to the de- 

 pressor. Depths are believed to be accurate 

 within +20 m. at a depth of 150 m. and +8 m, 

 at 30 m. The average length of time for lower- 

 ing and retrieving the net from the sampling 

 depths was: 7 minutes for 150 m., 3 minutes 

 for 75 m., 1 minute for 30 m., and less than 1 

 minute for 20 m. or shallower. Additional in- 

 fornnation on the towing characteristics of 

 similar gear is given by Aron, Raxter, Noel, 

 and Andrews (1964). The catches probably in- 

 cluded animals from water above the sampling 

 depths, because the net was open throughout 

 the tows. 



Samples were obtained from shallow oblique 

 tows (30 m. to the surface) at each station during 

 both cruises (appendix tables 1 and 2). Inaddi- 



tion, samples from deep oblique tows (1 50-30 m.) 

 were taken at stations where the bottom depth 

 was 914, 1,829, or 2,377 m. during the spring 

 cruise (appendix table 1). All tows were made 

 between 1 hour after sunset and 1 hour before 

 sunrise. Tows were made in steps: for the 

 shallow tows, 8 m. of cable were retrieved 

 every 2 minutes for 15 steps; and for the deep 

 tows, 16 m. of cable were retrieved every 

 minute for 30 steps until 120 m. of cable re- 

 mained in the water. This remaining length of 

 cable was retrieved as rapidly as possible, 

 usually within 1 minute. Thus, the duration of 

 the tows was 30 minutes from the time the net 

 reached maximum depth until it was at the upper 

 limit (surface or 30 m.) of the depth interval. 



Horizontal tows were taken at two stations 

 during the spring cruise to provide informa- 

 tion on vertical movement of organisms in the 

 upper 150 m. (appendix table 3). At station 8, 

 samples were obtained at dusk, midnight, dawn, 

 and afternoon during a 24-hour period at the 

 surface and depths of 15, 30, 75, and 150 m. 

 (Because of equipment failure, samples were 

 collected at 4:00 p.m. instead of "noon.") At 

 station 17, samples were taken at dusk, mid- 

 night, dawn, and noon, at the surface and depths 

 of 10, 20, 30, 75, and 150 m. At both stations, 

 the net was at the specified depth for 10 

 minutes. 



At the laboratory, water was removed from 

 the samples by filtering through nylon cloth 

 having about 1.5-mm. mesh. Fishand medusae 

 larger than 1 cm. were removed, and the re- 

 mainder of the sample was weighed with an 

 accuracy of + 0.1 g. The volume of eachfiltered 

 sample was determined by displacement of 5- 

 percent Formalin in a graduated cylinder. The 

 values for weight and volume had a correlation 

 coefficient of 0.99. In this paper, weight is used 

 as the measure of biomass. Samples of more 

 than 30 g. were subdivided by a Folsom 

 plankton splitter (McEwen, Johnson, and Fol- 

 som, 1954) so that the subsamples contained 

 about 400 organisms. The organisms from 



SWIVEL 



BRIDLE 



DIAMETER -j METER 



\ COLLECTING BUCKET 



COD END 

 3-MM. NYLON NETTING 

 13-MM. MESH 



STRLTCHED MEASURE) 



DEPRESSOR 



64-MM. MESH (STRETCHED MEASURE 



Figure 1. — The 0.9-m. I.saacs-Kidd midwarer rrawl. 



