Growth models and growing degree-days: assessment of young-of-year Alewife and Blueback Herring in Potomac River tributaries

Geography and nursery-specific dynamics guide environmental drivers of growth for young-of-year (YOY; larval and juvenile) Alewife (Alosa pseudoharengus) and Blueback Herring (Alosa aestivalis), two species collectively termed river herring; of these factors, temperature is considered one of the most influential. To better understand future YOY growth relative to climate change, this study was designed to determine the site-specific growth rates of YOY river herring in Potomac River tributaries, and determine if temperature was a driving factor of growth. Daily ages were ascertained from YOY otoliths and used to calculate growth rates using nine growth models. Weighted Akaike information criterion (AICw) determined the best-fit model for both species was the von Bertalanffy growth model. Von Bertalanffy growth parameters differed between species (p < 0.0001), between years for both species (p < 0.0001), and between locations for Blueback Herring (p = 0.0002), emphasizing the need for species-specific assessments. Standard length and cumulative growing degree-days were highly correlated within each year for both species, but significantly different between species and years for each species (Pearson’s r = 0.740–0.913, p < 0.0001). Estimating site-specific growth rates and drivers of growth can help managers determine the potential of Potomac River tributaries as viable nurseries in future climates.