Double nets for mesh aperture selection and sampling in ichthyoplankton studies

A double-net sampler, composed of an inner conical net enclosed completely within a similar net of finer mesh, was constructed to determine per cent retention and lower size threshold of larval fish during actual field tows. Tests during 1985–1987 with 3 samplers, each of 1.0-, 0.48- and 0.25-mm aperture inner mesh and 0.14-mm aperture outer mesh, indicated that passage of larval fish (mainly clupeids) through mesh apertures of the inner net was 26% and 13% of the total catch, for 1.0-mm and 0.48-mm aperture mesh, respectively. A net with 0.25-mm aperture mesh was impervious to passage of larvae. Respective mean sizes of larvae that passed through 1.0- and 0.48-mm aperture mesh were 5.0 ± 0.8 mm and 3.4 ± 0.7 mm.