Target life cycle stage: Veligers
Sampling gear: Standard plankton net (either Student or Wisconsin)
Recommended habitat(s): Flowing or nonflowing water
Type of data collected: Either quantitative or qualitative
Deployment protocol: Using a labeled dropline (length marked), lower the net into water and allow it to sink below the photic zone (if possible). It will be necessary to attach weights to the net line to keep the net below the surface. Tow the net from a boat and retrieve. If quantitative data are desired, the distance that the net travels or the time the net collects must be calculated. When the net is retrieved, the sample is rinsed down into the collection vessel, drained, and stored for later analysis. Replicate samples of equal duration are recommended. At least 1000 L of water should be sampled in each replicate in waters where veligers have not previously been found.
Advantages: Excellent technique for sampling large quantities of water to determine presence or absence of veligers (qualitative data) or in areas with very low numbers of veligers.
Disadvantages: Calculating the amount of water filtered by the net can be difficult if quantitative data are desired. Tows may either be timed (if the speed of the boat or water current is known) or calibrated to known distances on shore.
Oblique plankton tow
For information on calculating data retrieved from plankton nets, see Analyzing Plankton Tows, Pumped Samples, and Shallow -Water Samples.