The Alewife provides cover for other fish
is  host for  freshwater mussel Anodonta implicata, the alewife floater. The alewives are also host to the alewife floater, a freshwater mussel that is species specific to the alewife. this mussel is another source of food in the ecosystem  that disappeared with the alewife.

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Alewife floater (Anodonta implicata)

The alewife floater is often abundant in Atlantic coastal
rivers and lakes, and its distribution is closely tied to, and
dependent upon, the alewife. If a dam blocks alewives from
reaching historical spawning grounds, then the alewife floater
will go extinct in upstream areas. Some evidence suggests
that the alewife floater was extirpated in several coastal
watersheds in the last four centuries. For example, it is
noticeably absent in rivers and lakes of southern coastal
Maine, where dams were built as early as 1634. Anadromous
fish migrations were halted decades and even centuries before
scientists could document fish or mussel populations in some watersheds. A quotation from the 1867 Fish Commissioner’s Report, referring to salmon in the Saco River, is particularly telling:
“We could obtain no estimate of their numbers in former times, as they had ceased to be plenty beyond the
recollection in the present generation.”

Freshwater mussels are large bivalved molluscs,
superficially resembling a marine quahog, which inhabit large
permanent waterbodies throughout North America. They
are one of the most endangered groups of animals on Earth.
In North America alone, nearly 75 percent of the 297 native
species are listed officially as Special Concern, Threatened
or Endangered in all or parts of their range, including eight
of the thirteen species native to coastal New England and
the Canadian Maritime provinces. The larvae of freshwater
mussels are obligate fish parasites. Female mussels release

larvae into the water, where they must find a suitable host
fish and attach to its fins or gills. Mussels are often specific
about the fish they canparasitize, and if environmental factors
change the abundance or availability of the host fish,
then mussel reproduction is compromised. The alewife is the
only known vertebrate host for the freshwater mussel
Anodonta implicata (alewife floater), though the blueback herring
and American shad, Alosa sapidissima, are also suspected hosts.

Alewife by Ethan Nedeau