Introduction

Two of the greatest threats to the sustainability of the ichthyofauna of aquatic systems are the spread of non-native species [1] and the extirpation of native ones [2]. To sustain health and persistence of fishes in aquatic systems it is necessary to prevent the introduction of invasive species and to restore native fishes that have been extirpated. The tools used to assess the quality and sustainability of ecosystems have evolved over time. The use of species-area curves used by Gleason [3] morphed into the use of diversity indices [4-7], autotrophic-heterotrophic ratios [8], saprobian designations [9, 10], and biotic indices [11].

The concentration of calcium content [12], distribution of fauna [13, 14], water zones [15], gradient [16], and stream order [17] have been used to classify streams. Cairns and Dickson [18] used inertia and elasticity to predict the sustainability of a system when subjected to a stress and its ability to recover once a structural or functional change in the biota occurred [19]. The biotic resistance or ability to impede invasive species of aquatic systems is dependent in part on a highly diverse native fauna [20-23]. Recently, to increase and maintain biodiversity and sustainability in aquatic systems, attempts have been made to reintroduce extirpated fauna to their native ranges and to enhance corridors among populations to increase stability of these native populations [2]. Certainly, the ability to identify suitable habitats within the native ranges of aquatic species in which such reintroductions will be successful, is difficult. The purpose of this paper is to propose the use of NetWeaver^TM to evaluate potential reintroduction sites within the Delaware River Basin, Pennsylvania.

NetWeaver is a knowledge-based development system used to interpret and evaluate data. NetWeaver is a graphical tool used by engineers that design knowledge-based natural resource management software. Because of NetWeaver’s graphical interface, overall ease of operation, and real-time interface, it was chosen as a fundamental technology and component of the Ecosystem Management Decision Support (EMDS) system [23-25]. The EMDS system is a Decision Support System (DSS) that integrates multi-taxa inventory data sets for analysis to help researchers and resource managers make sound management decisions more efficiently [23]. The EMDS system with its NetWeaver modeling tool component has also been successfully used in a variety of applications including natural resource condition assessment [26], wetlands management [27], and forest ecosystem sustainability [28]. NetWeaver modeling has also been used to study and classify lake water chemistry [29], to assess natural resources and watershed conditions at the Delaware Water Gap National Recreation Area and Upper Delaware Scenic and Recreational River [30], and to analyze U.S. Forest Service projects in various locations [23].

Over the years, NetWeaver has evolved, and its versatility has increased. The NetWeaver2 Knowledge-Base Model is the most recent version of NetWeaver. This modeling tool can be used to compare, contrast, and evaluate any ecosystem and produce scores by altering habitat character information. NetWeaver is a characterization mechanism; it compares the inventory of characters of a reference site to the inventory of characters from other research sites. Concurrently, NetWeaver can be used to study and document ecosystem integrity [24].

The modularity of NetWeaver allows the evolution of complex knowledge bases from small, incremental steps [24]. Key features of NetWeaver include object-based networks of logical propositions and fuzzy logic that provides a complete calculus for knowledge representation and can easily be used by resource managers [23, 24]. NetWeaver was selected as the modeling tool for this study because NetWeaver can examine and discern various characters of a variety of ecosystems [23, 24]. For this study, the NetWeaver modeling tool focused on the Bridle Shiner, Notropis bifrenatus (Cope) and Ironcolor Shiner, Notropis chalybaeus (Cope) in various habitats on the Atlantic seaboard.

These cyprinids historically were widespread throughout the Atlantic seaboard. Now both species exist in isolated pockets along the Atlantic seaboard with very limited, if any, gene flow among populations. Marshalls Creek may be the only isolated pocket where both shiner species currently occur sympatrically and syntopically [31, 32]. Marshalls Creek (Delaware River drainage, Monroe County, Pennsylvania) is approximately 42 km long. Marshalls Creek’s headwaters flow from the Pocono escarpment, and the entire drainage area is 69.4 km². Marshalls Creek water quality is designated as a high-quality cold-water fishery by the Pennsylvania Code water quality standards [31]. The Bridle and Ironcolor shiners inhabit a 3.7 km reach of Marshalls Creek.

The Ironcolor Shiner is listed as endangered in Maryland and both shiners are listed as endangered in Pennsylvania [33, 34]. The Bridle Shiner is listed as a special concern species in Massachusetts [35]. Ironcolor Shiners are not listed as an Endangered, Threatened, or Candidate species in Delaware [36]. Neither shiner is listed federally as an Endangered, Threatened, or Candidate species [37].

The native range of the Ironcolor Shiner is highly fragmented and includes the lowlands of the Atlantic Coast, Gulf Coast, and Mississippi River drainages from New York to Florida to Texas mostly south of Pennsylvania [32]. Their native range also includes sporadic areas of the southern Great Lakes region in Wisconsin, Illinois, and Indiana [38]. Except in the Southeast, most populations are disjointed [39]. The Ironcolor Shiner has disappeared from some areas of New Jersey. Populations in Iowa have been reported as extirpated. Ironcolor Shiners historically were widespread throughout the Delaware River drainage, however, their populations in Pennsylvania have significantly decreased [31]. The only known population in Pennsylvania is in Marshalls Creek.

The Bridle Shiner historically inhabited the Susquehanna River drainage and the Delaware River drainage. Populations have significantly decreased and are recently found in one (i.e., Marshalls Creek) of 31 other historical locations in Pennsylvania [40-43]. The Bridle Shiner was once widespread in Maryland. After extensive collection efforts in areas of historical occurrence since 1984 resulted in no Bridle Shiners. The extirpation of the Bridle Shiner in Maryland has now been reported [44].

Several factors including habitat alteration, losses of stream vegetation, urbanization, industrialization, water diversion, industrial and sewage plant discharges, and increased turbidity and sedimentation have all been implicated for these population declines [31,43]. The exact cause of the extirpation was unknown but declines in other regions have been attributed to increased sedimentation, the constant loss of native aquatic vegetation, the increase in non-native plants including Hydrilla verticillata (Hydrilla) and Myriophyllum spicatum (Eurasian Watermilfoil), and the increase of non-native predators including Micropterus nigricans (Largemouth Bass) and Ictalurus punctatus (Channel Catfish) [44]. Populations of Bridle Shiners in Virginia have been localized (i.e., the James River drainage) and some populations have been extirpated or nearly so (e.g., the Potomac River drainage and the Rappahannock River drainage) [39, 45]. Habitat alteration (i.e., light reduction that impairs growth of submerged aquatic plants and food-sighting ability of the fish) seems to be the general cause of the localization and population decline [39]. Our purposes included: (1) documentation of the aquatic habitat characters (i.e., the combination and interaction of biological, chemical, and physical habitat characters) that are coincident with these shiners in Marshalls Creek; (2) determination if these aquatic habitat characters are commonly found at other historical sites for these shiners; and (3) analysis of why these shiners are syntopic only in Marshalls Creek.

Materials and Methods

The modularity of NetWeaver (Fig. 1) allows the evolution of complex knowledge bases from small, incremental steps [24]. Key features of NetWeaver include object-based networks of logical propositions and fuzzy logic that provides a complete calculus for knowledge representation and can easily be used by resource managers [23, 24]. NetWeaver was selected as the modeling tool for this study because NetWeaver can examine and discern various characters of a variety of ecosystems [23, 24].

Figure 1: Aquatic Habitat Characters Dependency Network for the aquatic habitat scores in the NetWeaver Model [24]

The Bridle and Ironcolor shiners inhabit a 3.7 km reach of Marshalls Creek. Six Marshalls Creek sites (Sites 0–5) were sampled (Fig. 2) and seven sites in Massachusetts, two in Maryland, and four in Delaware (Fig. 3).

Figure 2: Research Sites 0-5 (a 3.7 km reach) and Road Bypass Construction at Marshalls Creek, Monroe County, Pennsylvania. Illustration Delorme 2013.