The MOCNESS, referred to as M1 and M2 in the CalCOFI database, 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 meter² frame with 10 nets. M2 is a 10 meter² frame with six nets. The frame is rectangular and made of anodized aluminum. The nets are made of nylon, nominally .333 mm or .505 mm square mesh with 333µ used for the rigid cod ends. A motor/toggle release assembly is mounted on the top portion of the frame and stainless steel cables with swaged fittings are used to attach the net bars to the toggle release. A stepping motor is used to sequentially control the opening and closing of the nets.
The MOCNESS uses underwater and shipboard electronics for controlling the device. The nets are opened and closed sequentially by commands through conducting cable from an onboard computer. The computer system continuously monitors real-time (updates 2 times per second) the functioning of the nets, frame angle, horizontal velocity, vertical velocity, volume filtered and selected environmental parameters - salinity and temperature.