This is Part II of our Data User’s Guide. If you haven’t read Part I, you’d get a lot more out of this article if you did read it first.
The PAFBC, along with PASDA, which is the state GIS clearinghouse, provides some of best data available anywhere on trout streams, hydrography, and the other stuff we trout fishermen care about. So we can draw insights about interpreting stream data by comparing different sources, and infer how to make intelligent guesstimates in states where our data sources are more limited.
Let’s look at SE Pennsylvania. The “P” towards the right side of the image is center-city Philadelphia.
The brown basins are the “extirpated” basins. The open basin right below the “P” (lower Schuykill River) was never part of the brook trout range, and neither was any of the coastal plain you see on the other side of the Delaware in southern NJ. You can tell because these areas have a black border. The “red” bordered basins are the lowest grade of brook trout habitat in the EBTJV database.
The havoc wreaked on brook trout habitat by development of the greater-Philly megalopolis is pretty obvious. The big block of extirpated basins radiating outwards from Philly is apparent. Of the few, non-extirpated basins you see, most are “red”, the lowest grade possible. It’s over 60 miles to the nearest basin that presents better habitat.
But now let’s turn on the PAFBC data layer showing streams supporting reproducing Trout.
As you can see, there are actually more than a few streams near Philly that support wild trout. Note that once you’re far enough away from the inner city, and the inner suburbs, the there are several “extirpated” basins that support just as many wild trout streams as the red basins. “Yeah”, I hear you ask, “but are any of them any good?” In the photo below, we’ve reduced the transparency of the stream lines you see above, and overlaid the state’s “Class A Wild Trout Streams” designation, which are bright blue in the photo. What you see is that a few of them actually are pretty good. However, note here that the color coding isn’t completely irrelevant: a higher proportion of the streams in the colored basins are Class A than in the extirpated basins. Note, however, that there’s one Class A stream in particular that’s very close to Philly, marked with a V.
The “V” stream is no secret. It’s Valley Creek, that runs in part through Valley Forge National Park. Being the closest Class A stream to Philly, it is very well known. It’s also tough to fish, with very spooky brown trout, so gets less pressure than you might think. You can see a closer view of the area, with the extirpated basins turned off, below:
How could this stream survive so close to the megalopolis? Well the park helps, for sure, but it protects only a relatively small segment of the drainage. The full answer lies in the bedrock. Check out the view below. It’s hard to see the stream because of the coloration (but the V is in the same place). The dark blue band cutting across the image indicates a narrow strip of limestone baserock. Virtually the entire extent of Valley Creek is in this formation.
This case study underscores some of the key points we made earlier: good streams can be anywhere within the full extent of the EBTJV original range, including the extirpated basins. However, as we look at the worse habitat, we’ll need to examine candidate streams on a case by case. As we get into better habitat, a higher percentage of the streams should be pretty good.
For more information on how to sort through some of these variables, and the dynamics you’re looking at, click on to see Part III: Case Study – RI.