Vortex method for separation of forage fish eggs from beach sediment: Addendum to the 2006 revision of Field Manual for Sampling Forage Fish Spawn in Intertidal Shore Regions

Washington Department of Fish and Wildlife (WDFW) biologists have assessed marine shorelines for evidence of forage fish spawning (presence of eggs) since the 1970's. During this time, the biologists have continued to develop effective and efficient protocols for collecting and identifying forage fish eggs from beaches. The purpose of this document is to describe an alternative method for extracting forage fish eggs from beach sediment samples that increases lab efficiency and egg count accuracy.

The sampling protocols developed prior to 2015 are documented in Moulton and Penttila (2006 revision; https://wdfw.wa.gov/publications/01209/wdfw01209.pdf), which described the process from beach site selection and sediment sample collection through condensing bulk sediment samples to laboratory analysis. As described on pages 24 and 25 of the 2006 field manual, the first step in treating the bulk sample is to sieve the sample through progressively finer sieves (4 mm, 2 mm, and 0.5 mm mesh). Only the material collected in the 0.5 mm sieve is retained for further processing. During the winnowing process, the condensed sample material is transferred to a square washbasin where it is covered with a thin layer of water and agitated to suspend and concentrate the lighter material, including eggs above the heavier material. This top layer of lighter material is collected and retained for laboratory analysis (examination of material by microscope) to identify and count the eggs.

An alternative to the winnow method, the vortex method, was developed for condensing bulk samples to concentrate eggs. The vortex method, like winnowing, also follows sieving. The condensed material collected in the 0.5 mm sieve is added to a hydrocyclone device consisting of a circular bowl and a recirculating electric water pump to create a vortex that concentrates the light material. Thus, this step replaces the agitation process described in the 2006 field manual. The vortex method resulted in less material to be sorted through in the lab for egg identification. We intend the vortex method to be used in place of the winnowing method.

We compared the two condensing methods, winnow and vortex, and found the vortex method has a higher egg recovery rate than the winnow method (average smelt egg recovery rates, winnow method: 59%, vortex method: 90%) and results in a smaller volume of material to process in the lab. In light of these improvements in efficiency, we recommend the vortex method for condensing bulk samples after sieving. However, before any modifications are made to your sampling program, be advised that careful consideration should be given to potential impacts to results and whether results from the two methods are directly comparable. Please consult with WDFW staff if you would like to discuss compatibility with WDFW data standards.

This document contains a description of the process and system that we have designed and tested. Modifications to the process or system we describe below may alter the efficiency of the system and consequently lead to results that are not comparable with our results. Those who intend to utilize the vortex method should obtain training prior to implementation. Biologists using these methods for regulatory surveys must complete the WDFW training. Additional information and resources for training are provided on page 11 of this document.