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Status and Distribution of Brook Trout in the Vicinity of the Appalachian National Scenic Trail

Appalachian National Scenic Trail showing HUC10 shell.
Figure 1. Historic Brook Trout range in the eastern United States and in proximity to the Appalachian National Scenic Trail. Background of map obtained from ESRI ArcGIS Online and data partners including USGS and © 2007 National Geographic Society.
The following review is based on information freely available from the Eastern Brook Trout Joint Venture (EBTJV). For more information about the EBTJV, visit that program at: http://www.easternbrooktrout.org/.

Introduction

Brook trout (Salvelinus fontinalis), the only trout native to the eastern United States, is an iconic species that many people associate with pollution-free cold-water streams found in the mountainous Appalachian region. The historic range of brook trout throughout the eastern United States is identified in figure 1 by the blue "hash-marked" zone that extends from Georgia to Maine. Figure 1 also shows the HUC10 shell, a zone surrounding the Appalachian National Scenic Trail (APPA) that we use to characterize natural resources that typify the APPA region.

Recent investigations by Hudy et al. (2008) and Thieling (2006) explore the status of brook trout throughout their historic range and attempt to assess the current status of brook trout for the same region. The work by Hudy and Thieling combines existing brook trout and water quality data with subwatershed delineations available from the Natural Resource Conservation Service (except for New York where only watershed level data were available). The result was a quilt-like map that identifies areas where the species is present, where it is declining, and where it is no longer present. In 2012, Hudy began building upon his earlier work by acquiring catchment level delineations for the southern portion of the range (Georgia through New Jersey). Though the 2012 work is preliminary, using finer scale delineations appears to improve the accuracy of their assessments.

The efforts of Hudy and Thieling are based on a combination of historic presence data as well as a series of models that predict the status of brook trout for areas where actual data are not available. The information presented on this web page regarding the status of brook trout in the vicinity of the APPA is based entirely on the work done by these researchers.

Methods

We began by downloading geographic information system (GIS) and tabular data from the EBTJV website (http://easternbrooktrout.org/). This includes data from Hudy's 2008 report as well as unofficial preliminary data from 2012 (also available from EBTJV). These data were subsequently clipped to the HUC10 shell to establish a geographic scope for the APPA project. HUC10 units (watersheds) are defined at the fifth level of the Hydrologic Unit Code system, with each being given a discrete 10-digit code. The HUC10 shell, or the general frame of reference used to establish an area of interest around the APPA, is the ‘outer’ boundary of all HUC10 hydrologic units that are within 5 miles of the APPA land base. The hydrologic unit system was developed by the USGS and subsequently modified by the Natural Resource Conservation Service (NRCS). There are 177 individual HUC10 hydrologic units within this shell. Though they are termed watersheds, Omernik (2003) explains that hydrologic units are not always true watersheds and that some hydrologic elements contained within the HUC10 shell may not include all upstream components of a true watershed. We use the HUC10 because it incorporates all areas of immediate interest to APPA resource managers as well as areas that are more distant but potentially of great ecological similarity. While the HUC10 shell does not guarantee that projects or data within it will be of interest, or that data and activities beyond it are not of interest, it does provide a starting point and some degree of guidance when attempting to determine if data or activities are worthy of further consideration.

We then combined the 2012 preliminary data (Georgia through New Jersey) with earlier data for the New York to Maine region to produce a hybrid map for the APPA region. We decided on this approach because it uses the most accurate information for the entire region even though the variation in resolution for the two regions (GA-NJ vs. NY-Me.) complicates the analysis. We also simplified the presentation by using only 3 status categories, intact, declining, and extirpated. Figures 2 and 3 show the percent of the respective region (south or north) that each status occupies based on total area (ha).

Brook Trout Status

Figure 4.
Figure 2. Brook Trout status in the vicinity of the Appalachian National Scenic Trail land area between New York and Maine.
Figure 3. Brook Trout status in the vicinity of the Appalachian National Scenic Trail land area between Georgia and New Jersey.
 

Brook Trout status along the Appalachian National Scenic Trail:

Discussion

Brook trout status' in figures 2 and 3 are identified as intact (green), reduced (yellow), or extirpated (red). Because the northern portion of the APPA region relies on data at the subwatershed scale while the southern portion of the APPA utilizes finer resolution catchment scale data, the status charts are not directly comparable. The spatial distribution of each status category is shown in figure 4.

The finer scale presentation from the southern portion of the APPA is thought to be the more accurate representation of actual brook trout status because each catchment, the element to which status is associated, is more closely aligned with individual stream segments. The coarser subwatershed presentation for the northern states aggregates multiple stream segments into each subwatershed element. Consequently, segments in the north where brook trout are identified as extirpated are under-represented, while segments in the north where brook trout are identified as intact are over-represented. The portion of extirpated brook trout habitat in the north will likely increase after catchment scale analyses are conducted, and intact brook trout habitat in the north will likely decrease.

Full brook trout range versus APPA HUC10 comparison

Hudy (2008) reports that brook trout are intact in 31% of its historic range, are reduced in 35%, and are extirpated or missing from 33%. These values fall between the values for the northern and southern parts of the APPA region, but because the Hudy (2008) values are based on subwatersheds, they are directly comparable to the northern APPA results. Comparing the full range to the northern APPA region, slightly more than twice as much area is intact along APPA, the amount of reduced habitat is less, and the amount of potentially suitable habitat from which brook trout are extirpated is about 15% of the range-wide estimation. Even though the amount of intact habitat for the northern APPA region is thought to be an over-estimate and the amount of extirpated habitat is thought to be an under-estimate, the contrast between the range-wide assessment and the northern APPA region suggests that suitable brook trout conditions are more common within the APPA HUC10 shell than the species' range as a whole.

Sources Cited

Hudy, M., T.M. Thieling, N. Gillespie and E.P. Smith. 2008. Distribution, status, and land use characteristics of subwatersheds within the native range of brook trout in the eastern United States. North American Journal of Fisheries Management 28: 1069-1085. American Fisheries Society.

Omernik, J.M. 2003. The Misuse of Hydrologic Unit Maps for Extrapolation, Reporting, and Ecosystem management. Journal of the American Water Resources Association. (JAWRA) 39(3):563-573.

Thieling, T. M. 2006. Assessment and predictive model for brook trout (Salvelinus fontinalis) population status in the eastern United States. Master’s thesis. James Madison University, Harrisonburg, Virginia.

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