Effects of urbanization of coastal watersheds on growth and condition of juvenile alewives in New England

Abstract

Alosa pseudoharengus (alewife) has declined throughout New England. A factor that may be responsible for such stock reductions is urbanization of watersheds discharging into alewife nursery ponds. We found that young-of-the-year (YOY) alewife length, weight, condition factor, and growth rate decreased in relation to increased urban land cover on watersheds of nine Massachusetts and Maine ponds. The watersheds ranged from 3% to 60% urbanized land cover. YOY δ15N increased significantly in proportion to urbanized land cover on watersheds, suggesting a concrete link between watershed land cover and YOY alewife metrics, which is in agreement with previous knowledge that N discharges from more urbanized watersheds bear higher δ15N. The New England results confirmed results across a wide latitudinal gradient that suggested that the size of YOY alewife decreased as urban land cover on watersheds increased. The dominant influence of urban land cover in the YOY is highlighted by the fact that YOY alewife from ponds with the highest percentage of urban cover reached δ15N as high as that of adult spawners migrating from the ocean, who feed at higher trophic levels.