C1...CAL1MOBL Net

The 1-meter net, referred to as C1 in the CalCOFI database, was the standard CALCOFI plankton sampler from 1951 through 1978. The construction consisted of a 1" galvanized pipe ring, 1-meter in diameter, to which an elongate cylindrical-conical shape net (approximately 4 m) was attached. A short 3-way towing bridle was connected to several meters of line which in turn was clamped to a towing table suspended from a survey ship.

Since 1951, there has been two different materials used in the the construction of the nets. From 1951 through 1968, nets constructed of silk, nominally 0.55 mm square mesh was used. The last 40 cm of the net, which included the cod end, used 25 mm square mesh. Beginning in 1969 the nets were constructed of nylon, nominally 0.505 mm square mesh throughout. The ratio of mesh aperture area to mouth area was 3.2:1 for the silk net and 4.8:1 for the nylon net.

Plankton samples were obtained by retrieving the sampler at an oblique angle. While the survey ship was making 1-2 knots, a fixed amount of towing cable is paid out, the net is held at depth for 30 seconds and then retrieved at a constant rate (20 m/min). Ship speed was adjusted to maintain the towing cable at a constant angle to the vertical (45 degrees +/- 3 degrees). From 1951 through 1968, 200 m of towing cable was paid out during each plankton tow; thus the vertical depth sampled was approximately 140 m. Beginning in 1969, 300 m of towing cable was paid out increasing the vertical depth sampled to an estimated 210 m. In shallow areas the amount of towing cable paid out is adjusted so that the net fished to approximately 15 m off the bottom.

photo of elongate cylindrical-conical shape plankton net

 

Last modified: 12/24/2014