Fish monitoring in Shenandoah National Park: 2010 summary report

Wofford, John; Demarest, E.

Shenandoah National Park (SHEN) monitors fish communities as part of the National Park Service (NPS) Vital Signs Program. Vital signs are a subset of physical, chemical, and biological elements and processes of park ecosystems that are selected to represent the overall health or condition of park resources (Fancy et al. 2009). Within Shenandoah National Park, fish are monitored to help characterize the status and trends of park aquatic ecosystems.During 2010, a total of 66 sites along 38 park streams were sampled. Of the 66 sites that were monitored, 41 of these sites are ―primary‖ sites that were visited every year until 2004 and then every other year thereafter. In contrast, the other 25 sites were ―secondary‖ sites that included inventories of new streams or revisits to sites that had not been assessed in more than 8 years. A total of 32,360 individual fish representing 26 species were captured from all monitoring sites. No new species were detected during monitoring efforts. Data were ultimately summarized by sites according to watershed underlying bedrock geology and associated acid neutralizing capacity (ANC) groups as defined in Cosby et al. (2006).Within primary sites across the park, recruitment of juvenile brook trout (Salvelinus fontinalis) in 2010 was essentially non-existent and age 0 (i.e. ―juvenile‖ or ―young-of-the-year‖) trout densities were near record lows. Age 0 trout density averaged 3.2 trout per 100 m2, approximately 6 times lower than long-term averages (19.1 per 100 m2) and representing a year class failure for brook trout populations in SHEN. This year-class failure was likely the result of large winter flows during January and March of 2010 – developing brook trout eggs are very sensitive to disturbance during winter months. Age 1+ (i.e. ―adult‖) brook trout densities in 2009 were above long-term averages, but likely declined during late summer and early fall as a result of extremely low base flows in most park streams. An analysis of data from 1996-2010, indicates a significant decreasing trend in age 0 trout densities in high ANC streams. In contrast, a significant increase in age 1+ trout densities in low ANC streams was documented.Acid deposition continues to influence fish species richness as well as brook trout production in SHEN. Streams with less capability to buffer acid rain events generally have fewer fish species, have poorer brook trout reproduction, and support smaller populations of adult brook trout. Nevertheless, as noted above, other large scale environmental phenomena such as droughts, floods, and other weather related events, continue to play a large role in determining trout abundance. It should also be noted that data are highly variable and longer-term monitoring is required to accurately assess trends.

Fish monitoring in Shenandoah National Park: 2010 summary report

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