The many scales of Alosa sapidissima success on the Potomac River

The American shad was once one of the Potomac River’s most important and abundant fish.   By the mid-1970s, water pollution, over-harvest and loss of spawning habitat caused a severe decline and a harvest moratorium since 1982.  In 1995, the Interstate Commission on the Potomac River Basin, working with the U.S. Fish and Wildlife Services’ (USFWS) Harrison Lake National Fish Hatchery, initiated a stocking program. Over 20 million American shad fry have been stocked.  The shad population is showing good signs of recovery, Age 0 shad have become substantially more numerous and returning adults have increased twenty-fold.   However, as with many trends in the natural world, the reasons for this rebound are multiple.  Attributing success to one factor is a mistake.   Significant water quality improvements helped reset the Potomac's ecological functioning.   The return of submerged aquatic grasses, one of those resets, strengthened chain reactions of water quality and habitat improvements.  Shad harvest moratoriums, in both rivers and ocean, were very necessary.  A new fishway at Little Falls re-opened roughly ten miles of important spawning habitat.  The ICPRB/USFWS's shad stocking program entered on cue and provided a needed shove to a remarkably productive river.