Figure 2a. A standard 1/2-m diameter two net, with a No. 6 nylon mesh (0.239 mm aperture), equipped with a T. S. flow-meter.
Figure 2b. A Miller sampler with a No. 12 mesh net (0.199 mm aperture).
On August 24 and 25, 1967, five series of six tows were taken at 1341 to 1555 hours, 1824 to 2000 hours, 2408 to 230 hours, 0655 to 0855 hours, and 11 31 to 1321 hours. The depths sampled were in 25 m intervals from the surface to 125 m. A sample from 125 m was lost from the second series of tows.
In 1968, a sampling device designed by Miller (1961), a modified small Hardy plankton sampler with a No. 12 mesh net (0. 199 mm aperture), was used in place of the standard tow net (Figure 2b). Its small size, light weight, and increased efficiency made it very effective for sampling the depth strata simultaneously at high towing speeds.
Unlike the standard tow nets, the Miller samplers did not have flow meters. All horizontal tows taken with the Miller sampler were towed exactly 10 minutes in order to standardize the volume of water sampled. The only exception was the first series of tows on July 24, 1968, which were towed for 15 minutes.
During a sampling series four Miller samplers were simultaneously towed horizontally at 12.5 m depth intervals from 25 to 62.5 m and 75 to 125 m (omitting a sample from 112.5 m). Two samplers were simultaneously towed at 1 and 12.5 m. A cable angle of 70 degrees was maintained after a sufficient cable length was attained to reach the desired depth. The length of cable needed to reach the desired depth was calculated from the following relationship:
Six series of horizontal tows were made during July 24 and 25, 1968, at 1340 to 1415 hours, 1700 to 1728 hours, and 2013 to 2100 hours, 2408 to 2457 hours, 0536 to 0639 hours, and 0928 to 1013 hours. No samples were taken from 1 and 12. 5 m during the first two series because previous results showed that few if any organisms were to be found at those depths during periods of high illumination. One sample each was lost on the fifth series at 125 m and on the sixth from 12.5 m.
On August 28 and 29, 1968, six additional series of horizontal tows were made at 1200 to I245 hours, 1617 to 1659 hours, 2115 to 2158 hours, 0205 to 0245 hours, 0739 to 0817 hours, and 1118 to 1159 hours. No samples were lost during this series.
Contamination
Since none of the sampling equipment employed in 1967 or 1968 had a closing apparatus, attempts were made to estimate the extent of contamination of the samples by zooplankton encountered while towing back through depths above 125 m. Immediately after sampling the vertical distribution on August 25, 1967, two vertical tows using the No. 6 mesh standard tow net were made from 125 m to the surface to estimate the contamination from depths above 125 m.
After sampling the vertical distribution on August 29, 1968, a Miller sampler was lowered to 125 m to duplicate the upward path of samples taken at this depth, the cable length was increased and cable angle brought to 70 degrees before the Miller sampler was hauled to the surface.
