Migratory fish and urbanization
Of the two watersheds in the study, the urbanized stream was unused by spawning River Herring, ocean-going fish that return to natal streams each spring to spawn. Research biologists have quantified the correlation between urbanization and loss of migratory fish. 
This research likely explains the absence of River Herring in the more urbanized stream. It may also explain the decline in River Herring eggs in the Mattawoman main stem as one approaches Billingsley Road compared to 1971 DNR studies.
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