Effect of net size on estimates of abundance, size, age and sex ratio of Mysis diluviana

We compared catches of Mysis diluviana in 80 vertical tows with large (1.0 m diameter) and small (0.5 m diameter) plankton nets to determine if the small net could be used in long-term monitoring historically conducted with the large net. Both nets were constructed of 500-μm aperture mesh and were towed simultaneously at 0.4 m/s. Comparisons were made at each of 10 stations on three occasions during July-September, 2014 at Dillon Reservoir, Colorado. Estimates of abundance and sex ratio were not different between the two nets but the larger net sampled a slightly broader range of sizes than the smaller net. We conclude that for most population monitoring purposes, the two nets can be used interchangeably; the smaller net is more useful for studies with gear size and weight constraints, but the larger net provides a four times larger sample size and thus may be better for detecting rare individuals.