Juvenile Herring Assessment in Prince William Sound

Hydroacoustic surveys have been successfully conducted on adult Pacific herring in Prince William Sound (PWS), Alaska, for nearly two decades.  In 2006, attempts were initiated to apply similar techniques to juvenile herring assessment.  The objective was to improve understanding of the factors that governed herring recruitment.  A major hypothesis is that the critical mortality occurs over the first winter of the herring life history, so the hydroacoustic assessment was focused on age 0 herring and combined with energetics, disease and predation research.  A key to successful hydroacoustic surveys is species identification, or in this case, identification of age 0 herring.  Adult herring (3+) during winter are characterized by large, high-density schools that are virtually monospecific, thus readily detected and identified.  Age 0 herring are more dispersed, although usually distributed near the heads of protected bays during winter.  We are in our 5^th year of both fall and late winter surveys.  In some circumstances we have been able to identify and quantify age 0 abundances.  In other cases, species and sizes appear mixed and are difficult to quantify.  The major challenges to improved quantification are the species identification, the widespread dispersal and uncertainties in the degree of over-winter movements among locations.