Brook Trout: Past, Present, and Future

Once widely distributed throughout the state, results from the 1995-97 MBSS indicate that brook trout are restricted to only a few watersheds in Maryland. Further, between 200,000 and 400,000 brook trout now live in Maryland. To get an idea of what the pre-European settlement population may have been like, brook trout densities at MBSS sites were reviewed and a subset of the better streams was used to approximate densities which may have existed historically. These densities were extrapolated to a geographic area which approximates the historical distribution of brook trout.

Based on our conservative calculations, the population of brook trout today is at least 10 times smaller than it was historically. The remaining populations in basins such as the Patapsco (approximately 2300 individuals) may be at risk because of low abundance and increasing development pressure. In western Maryland, populations of brook trout that are perceived to be healthy are also at risk from acid deposition and competition from brown trout. In 1996, a near-total failure of brook trout reproduction occurred in the Savage River watershed, probably due to a major influx of acid during a January snowmelt/rain event (the chemistry of this event was captured at Big Run, a Savage trib, by Dr. Keith Eschelman at the UMCES Appalachian Laboratory).

Recently, MBSS crew leader Matt Kline observed evidence of successful brown trout reproduction throughout Blue Lick, one of the highest quality tributaries in the Savage River watershed. Although adult brown trout have been sporadically collected by the MBSS in Savage streams in previous years, the presence of young-of-year browns may signal the beginning of a brown trout takeover not unlike the apparent displacement of brook trout by brown trout in the lower Savage River. Although the reasons for the decrease in brook trout compared to historical levels are many, one of the most important factors may be water temperature. As trees were cleared for agriculture and housing, previously forested streams were exposed to direct sunlight as well as hot water runoff from impervious surfaces like roads and rooftops. Today, fewer and fewer streams have temperature

Data from the MBSS confirms that brook trout are extremely sensitive to the amount of roads, rooftops and other hand surfaces in a watershed.

regimes suitable for brook trout, particularly in the eastern half of the state. In addition to impervious surfaces, other major threats to the continued existence of brook trout in Maryland include: silt from new construction and agriculture, competition from non-native brown trout, habitat loss from logging, loss of forests along streams, acid rain, and global warming.

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