Relative Effectiveness of Two Ichthyoplankton Sampling Techniques

Abstract

Two common ichthyoplankton sampling devices, a pump and a conical plankton net, were evaluated for their relative effectiveness in collecting various sizes of clupeid larvae in the headwaters of Watts Bar Reservoir in eastern Tennessee. Triplicate surface pump and towed-net samples were taken during both day and night on three dates in June 1979 to detect any diel differences in sampler effectiveness. Clupeid larvae, 4–10 mm long, were collected in numbers large enough to make meaningful statistical comparisons of the two techniques. The differences in the mean densities of most length groups between nighttime pump and tow samples were not statistically significant. During the day, however, the pump collected significantly more 4-mm larvae and the towed net collected more 5- to 10-mm larvae. Our results indicate that under conditions by which these samplers are commonly deployed in open waters, most sizes of young shad larvae exhibited a greater ability to avoid the pump sampler than the towed net during the daytime.Key words: ichthyoplankton, pump, nets, fish larvae, avoidance