Eulachon Embryonic Egg and Larval Outdrift Sampling Manual for Ocean and River Surveys

The anadromous eulachon (Thaleichthys pacificus) spawns in the lower reaches of coastal rivers and streams from northern California to Alaska. Although the distribution and timing in some rivers is well known, the occurrence in other rivers is uncertain or unknown. The presence of larval eulachon in estuaries and marine waters adjacent to rivers is a strong indication that a river is used by eulachon for spawning. Ichthyoplankton surveys designed to detect the presence or absence of eulachon larvae in coastal estuaries and inlets are easily conducted with minimal expense. Survey timing is the most important consideration. Eulachon spawning stock biomass (SSB) estimations based on in-river, egg and larval density measurements, however, require intensive replicate sampling to insure adequate spatial and temporal coverage. A swept volume (n/m 3), bongo net technique and daily river discharge measurements (m 3 /s) are used to estimate egg and larval production. Accurate fecundity determinations of spawning adults are also required in the calculation. In this manual, we describe and discuss the equipment and techniques that have been applied to estimate eulachon spawning stock biomass in the lower Fraser River and eulachon larval distribution and dispersion in central British Columbia mainland inlets and estuaries.