Eulachon: A New Look at Fecundity

Ichthyoplankton sampling is the preferred method for the prediction/monitoring of eulachon Spawning Stock Biomass (SSB). The ichthyoplankton samples are expanded by the water discharge for the sampling period, and that number converted to pounds of adult spawners, using gender ratios, average weights, and relative fecundity. To re-examine historical fecundity averages, the fecundity of eulachon was examined during a 2 year study, using 350 fish that had been gathered in 3 different zones of the lower mainstem Columbia River, and also in the Cowlitz River.  One percent, 5%, 10%, 20%, and full egg counts were performed on six fish, in order to ascertain the most reasonable approach to counting large numbers of gonad samples for fecundity estimations.  A spawning scale was established in order to assure that the fish used for fecundity estimates were fully gravid.  Observed foreign bodies were examined with regards to pathogenic potential.  Fecundity and GSI values were examined relative to fish size and age.  Age compositions of the runs were obtained through examination of otoliths and other hard parts. Comparing the recent age composition to historical age composition estimates can help researchers understand the implications of changing ocean conditions on the eulachon.