Time series assessment of anadromous Atlantic salmon smolt production in the Narraguagus River, Maine USA

NOAA’s National Marine Fisheries Service initiated modern smolt assessments in 1996 with a feasibility study of rotary screw traps (RST) in Maine rivers.  Since then, RSTs have been used to estimate smolt production, describe the biological characteristics and age structure of the migrating population, as well as serve as a platform for estuary and marine studies.  An RST array in the lower Narraguagus River has been operated since 1997 to enumerate the population of naturally reared (product of wild spawning or fry stocking) Atlantic salmon smolts. Using these data, we have explored the biological and ecological variability which exists within the population. Smolts collected at RST sites have a mean fork length of 167 mm (± 15 S.D) and a mean weight of 48 g (± 14 S.D.), which are within species norms.  The median run date differs between years, but generally occurs during the second week in May.  Since 2000, we have documented an average   population size of 1,500 individuals, which is 20% of expected productivity based on available rearing habitat and estimated capacity.  We summarize these and other data collected from RST operations in Maine, and highlight research results and implications vital for Atlantic salmon recovery.