Efficiency of Large-Volume Plankton Pumps, and Evaluation of a Design Suitable for Deployment from Small Boats

Abstract

A critical review of previously published studies, and evaluation of a newly developed pump system, showed the often stated shortcomings of large-volume pumps as instruments for sampling plankton communities (e.g. damage to organisms sampled, volumes too small to estimate plankton density accurately, and systems too cumbersome to handle) to be invalid. Previously published estimates of the comparative efficiency of large-volume pump samplers and tow nets should; however, be viewed with caution because the techniques used to estimate pumped volume are error prone. In-line flow meters are essential for accurate volume estimation. Comparative efficiency tests of a newly developed large-volume pumping system deployed simultaneously with 80- and 153-μm mesh standard plankton nets revealed that the pump, while sampling only 8% of the volume sampled by the nets, was equally effective in capturing capelin (Mallotus villosus) larvae (5-mm length), herring (Clupea harengus) larvae (9-mm length), large copepods (> 750 μm), small jellyfish, and hyperiid amphipods. The pump was superior to nets in sampling crab zoea and megalops larvae and becomes more efficient at capturing euphausiids and chaetognaths as their natural densities increase. Nets were superior in the capture of fish eggs (primarily cunner, Tautogolabrus adspersus), possibly due to the vertical distribution of eggs in the water column. The average length of capelin larvae captured by pumping was consistently 0.2 mm longer than that of larvae taken in nets, but the length–frequency distribution of larvae sampled was similar to that of larvae entering the pelagic environment. Attaching the pump intake to the cod-end of a rigid tow net is suggested as a method of surmounting potential errors when sampling organisms at densities below 1–5/m3.