Comparison of Three Forms of a Juvenile Index for River Herring

River herring are typical of many anadromous species in that the data describing their juvenile abundance are collected during surveys designed for other species.  In Maryland the data are collected during the striped bass juvenile seine survey in the summer and early fall.  The data include number of fish caught per tow by species and  site environmental information.  Preliminary examination of the data showed patterns typical of schooling juvenile  alosids, in that more than 20% seining events caught no river herring and some events produced very high values.  Typically, the geometric mean is developed in Maryland and other states.  We used these same data to also develop the “Daily Mean Catch”, otherwise known as the area-under-the-curve method.  The associated environmental covariates were used in the “Delta” regression method to develop a third index.  Not surprisingly, salinity and temperature showed significant effects on presence of river herring in the catch.  These three indices are compared and their relative usefulness in management discussed.