The effect of urban land use on juvenile river herring growth

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Tyler Pina and Matthew Devine, Environmental Conservation, University of Massachusetts Amherst, Amherst, MA

Background/Question/Methods
River herring (collectively alewife Alosa pseudoharengus and blueback herring A.aestivalis) are anadromous fish that migrate between freshwater and marine ecosystems throughout the east coast of North America from Canada to Florida. They have experienced substantial population declines across their range over the past five decades. A potential factor responsible for these reductions may be habitat degradation and water quality impairment from urbanization discharge into nursery ponds. The objective of this study is to investigate the relationship between land use, water quality, and juvenile river herring growth rates at five coastal Massachusetts lakes. Lakes were sampled monthly from June-August of 2019. Juveniles were sampled at night by purse seine, and preserved in 95% ethanol. Water quality (e.g. phosphorus, nitrogen, chlorophyll-a, dissolved organic carbon) was also collected during fish sampling. In the lab, total fish length was measured and otoliths from 50 fish per month for each lake were extracted, mounted in resin, and double-aged. Length-based growth rates were calculated for individuals and averaged across lakes and months. Land use data was extracted from the National Land Cover Database and re-classified in ArcMap using 100m buffers around each lake.
Results/Conclusions
Lakes varied significantly in their land cover, water quality, and herring growth rates. Percent urbanization ranged from 27.2% to 95.6%, while percent agriculture, percent forest, and percent wetlands ranged from 0% to 2.1%, 3.2% to 51.1%, and 0% to 23%, respectively. Total phosphorus ranged from 3.6 to 75.9 (µg/L) and total nitrogen ranged from 0.22 to 1.06 (mg/L). Juvenile herring sizes used for this study ranged from 15 to 93 mm and individual growth rates varied wildly (0.74–1.41 mm/d) among lakes. Analysis of Variance models were used to test for differences among lakes and multiple regression models were used to examine relationships between land cover, water quality, and juvenile herring growth. Current management objectives include restoring river herring to historic spawning habitats, yet favorable conditions are not well described. Literature suggests growth rates as changing due to delay in timing of spawning events, and how temperature and flow affect recruitment, although they rarely dive into how conditions on land may be influencing these phenomena as well. Without understanding what constitutes ideal conditions for growth and survival, restoration strategies and locations are limited.