Pennsylvania Angler & Boater - September/October 2013 - 52

State Wildlife
Action Plan:

Identifying
Threats to
Pennsylvania’s
At-Risk
Aquatic Species
photo-PFBC archives

by Diana Day and Chris Urban
In the November/December 2012 issue of the Pennsylvania
Angler & Boater magazine, an overview of the State Wildlife
Action Plan highlighted the importance of the plan for
guiding the protection, recovery and management of some
of the Commonwealth’s most vulnerable species and their
habitats. As part of the revision process, and as required by
Congress, identifying threats to species and habitats is one
of the eight elements to be addressed in the State Wildlife
Action Plan. Therefore, in this issue, we would like to further
explore this important component of the State Wildlife
Action Plan and identify some prominent threats facing
species at-risk and the challenges for addressing these threats.
First, it is important to define or characterize a threat.
Essentially, a threat is any factor that affects the survival of a
species. A threat could be a disease, competition for food or
habitat, predation, changes in environmental conditions such
as hydrology or temperature, reduced quantity or quality of
habitat, physical or chemical features that interrupt the lifehistory of a species or other factors. In this article, we briefly
investigate some of these threats.
A common, prominent threat to a species is a change
in habitat (i.e., loss or modification), which can impede its
survival. Habitat alteration or modification is the number one
threat to most species and is the primary culprit to species
becoming listed as threatened or endangered. Historically, for
example in the late 19th and early 20th centuries, demand for
coal and forest products in Pennsylvania led to the loss of, or
changes in, aquatic habitats. These changes included loss or
diminished quality of water and habitats leading to incredible

Pennsylvania Angler & Boater • September/October 2013

Holtwood Dam on the Susquehanna River

burdens on the Commonwealth’s aquatic life. Specifically, loss
of aquatic habitats resulted from flooding wetlands, dams,
deforestation, mining, urban development, and associated
industrial pollution and sedimentation. Although in the
intervening years, conditions have improved, and some of the
Commonwealth’s habitats have recovered. “Legacy” problems
remain from these historical activities. Sediment in streams,
acid mine drainage and dams continues to negatively impact
aquatic life. Current day expansion of urban areas further
stresses natural resources.
For aquatic habitat, dams continue to present a
particularly important threat. Thousands of dams remain in
Pennsylvania. Despite concerted efforts to remove dams and
include enhancements (e.g., fish passage) on larger dams,
migratory and local fish movement is still often impeded.
Dams not only pose a physical threat to movement, but they
can also modify water quality (e.g., temperature and dissolved
oxygen) in the impounded area and disrupt the natural
sediment transport functions of streams. Two Pennsylvania
fishes specifically influenced by dams are the American
shad and American eel. In addition to direct impacts on
these species, the loss of some fishes in a river can alter other
biological components of these systems. For example, the
American eel is a host fish species for a freshwater mussel,
the eastern elliptio (Elliptio complanata), found in the
Susquehanna River Basin. However, dams on this river have
greatly inhibited upstream movement of eels and may be
contributing to the reduction of eastern elliptio populations
in this river system.
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Pennsylvania Angler & Boater - September/October 2013

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