CalCOFI Net Descriptions

CalCOFI Nets

Two circles, 0.71 m in diameter, with a central yoke which connects to the towing cable. The nets are 3 m in length, a 1.5 m cylindrical portion joined to 1.5 m conical portion tapering to a detachable cod end. At least one (starboard net), the principal ichthyoplankton sample net, is made from 0.505 mm square mesh nylon. The sample from the port side net is used for other purposes; the mesh size is either 0.505 mm or 0.333 mm depending on requirements. The cod end of each net is constructed of 0.333 mm mesh. The ratio of mesh aperture area to mouth area is 4.8:1 for the 0.505 mesh net. Plankton samples are obtained by retrieving the sampler at an oblique angle. A 22 kg weight is attached to the bottom of yoke frame. While the survey ship is 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 is adjusted to maintain the towing cable at a constant angle to the vertical ( 45 degrees +/- 3 degrees). During each plankton tow 300 m of towing cable is paid out; thus the vertical depth sampled is approximately 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.

Pairovet or CalVET

0.25 m in diameter pair; the nets are 1.5 m in length, a 0.8 m cylindrical portion joined to 0.6 m conical portion tapering to a 0.1 m cod end. The ratio of mesh aperture area to mouth area is about 8:1. Egg samples are obtained by vertically retrieving the net. A 45 kg weight is attached to the end of the towing cable, a few meters below the sampler. With the survey ship holding a stationary position, 70 m of towing cable was paid out, the net was held at depth for 10 seconds and then retrieved vertically at a rate of 70 m/min. The angle of stray from the vertical was not allowed to exceed 15 degrees

1980 - 1982: net was 0.333 mm square mesh nylon.
1983 - 1985: net was 0.150 mm square mesh nylon.

MANTA

The twin winged continuous-flow surface tow, is used for samples on the ocean surface minimizing wake disturbance from the ship. The MANTA Net is an improved design from the Neuston Net and is capable of continuous-flow collection of organisms at the ocean surface. The frame is supported at the ocean surface by a pair of aquaplanes projecting at right angles from the paravanes. The net is towed by a wire yoke with one short bridle and one long bridle in order to angle the net from the ship. The net is nylon, nominally .505 mm square mesh with a 333 codend.

Other Nets

CAL1MOBL - standard CALCOFI plankton sampler from 1951 through 1978. 1-meter in diameter, net (approximately 4 m) was attached.
MOCNESS - is used for specialized tows for zooplankton. The MOCNESS or Multiple Opening/Closing Net and Environmental Sensing System is based on the Tucker Trawl principle and is manufactured by Biological Environmental Sampling Systems (B.E.S.S.). M1 is a 1 meter frame with 10 nets. M2 is a 10 meter frame with six nets.