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Monitoring Amphibians and Reptiles in the Maryland Biological Stream Survey

Mark T. Southerland, Paul Kazyak and Janis C. Chaillou

Versar, Inc.

Maryland Department of Natural Resources

[ Abstract ]

The purpose of this paper is to describe the component of the Maryland Biological Stream Survey (MBSS) that monitors amphibians and reptiles. While the MBSS is a comprehensive, statewide program for characterizing stream resources, assessing the condition of their biological communities, and identifying possible factors leading to their degradation, it focuses primarily on fish, benthic macroinvertebrates, physical habitat, and water chemistry. Monitoring of amphibians and reptiles is a secondary component of the Survey along with crayfish, mussels, and macrophytes. Nonetheless, we hope to make the maximum use of the information obtained on amphibians and reptiles, and perhaps improve our monitoring efforts relative to this component of Maryland's fauna as the MBSS evolves. To this end, we solicit the advice of conference participants on how to better evaluate the amphibians and reptiles component of the MBSS.

Background on the MBSS
The Maryland Department of Natural Resources (DNR) is charged with managing the natural resources of the state. Although site-specific studies have revealed adverse effects on non-tidal streams from acidic deposition and other anthropogenic stresses, no information is available on the condition of stream resources in Maryland at a statewide or watershed level. To address the lack of comprehensive information on the biological resources affected by acidic deposition and other stressors, DNR is implementing the Maryland Biological Stream Survey (MBSS). The MBSS will provide a comprehensive and technically defensible assessment of the extent to which certain anthropogenic stresses may have affected or may be affecting biological resources in the state. The survey will help decision-makers identify the geographic distribution of biological resources, establish priorities for environmental issues of concern in Maryland's non-tidal streams, and identify regions that require protection or mitigation.

MBSS Study Design
The MBSS has been designed explicitly to provide area-wide estimates of biological condition. This includes a probability-based sampling design in which sites are selected from a comprehensive list of stream reaches in Maryland such that all sampling sites have a known, non-zero probability of being sampled. This sampling design enables investigators to use data from the MBSS to estimate the condition of non-tidal streams on the basis of stream size (Strahler order), large watersheds, and statewide. Specifically, the survey incorporates a lattice design that ensures each of Maryland's 18 major river basins are sampled within a three-year period. This approach supports statistically valid population estimates of variables such as densities of particular species of fish or the number of miles of streams with degraded habitat. The MBSS sampling design also permits rigorous characterization of the sources of variability in the data.

Parameters Sampled in the MBSS
The MBSS field studies involve collecting biological, physical, and water chemistry data during the spring (March 1 to May 1) and summer (June 1 to September 30) index periods. Benthic macroinvertebrates and water chemistry parameters are sampled during the spring; fish, herpetofauna, crayfish, mussels, and macrophytes are sampled, and the physical habitat is evaluated during the summer. Biological variables are used to evaluate the ecological condition of streams within a region or watershed. Habitat indicators are used to evaluate the condition of the physical environment and determine how habitat condition contributes to ecological condition. Information about water chemistry, land use, and other anthropogenic stressors are used to describe and identify potential causes of degraded ecological condition.

Current MBSS Field Sampling Methods For Amphibians and Reptiles
To date, amphibians and reptiles are sampled qualitatively during the summer index period. A 15-minute search is conducted of the riparian area within 5 meters on both sides of the 75-m stream segment. Voucher specimens and individuals not positively identifiable in the field are retained for examination and verification in the laboratory. Periodically, specimens are submitted to taxonomic experts at the Smithsonian Institution for verification or identification.

Any amphibians or reptiles collected during the electrofishing of the stream segment for fish are also included in the tally. Double-pass electrofishing is conducted throughout the 75-m stream segment. Block nets are placed at each end of the segment and direct current backpack electrofishing units are used. A consistent effort is applied over the two passes, sampling all available cover and habitat structures throughout the segment. Fish population estimates are corrected for the double-pass method by species and geographic area, but field crews do not report the number of amphibian and reptile species sampled. Therefore, no population estimates for amphibians and reptiles are possible.

Preliminary Findings on the Amphibians and Reptiles Component of the MBSS
A total of 22 amphibian and 20 reptile species have been collected during the 1994, 1995, and 1996 MBSS sampling programs. The amphibian checklist includes 10 species of frogs and 12 species of salamanders; the reptile checklist includes 8 species of turtles; 2 species of lizards, and 10 species of snakes (see Table 1). Of the 22 amphibian species sampled, 18 species were found all three years. Maryland DNR currently reports that 42 species of amphibians and 52 species of reptiles are known from the state. Therefore, the MBSS has sampled 45% of the state's herpetofauna and 52% of the state's amphibian species. The listing of amphibians observed does not include any state-listed endangered, threatened, or species of special concern (see Table 2).

In 1995, six of the 18 river basins in Maryland were sampled: Youghiogheny, Upper Potomac, Lower Potomac, Patapsco, Chester, Choptank, and Nanticoke. The Lower Potomac Basin had the highest species richness of amphibians and reptiles (a mean of 4.1 species observed per site), with approximately twice the number of species found in other basins. As expected from their aquatic affinity, amphibian species (frogs, toads, and salamanders) were the most commonly observed groups, occurring at more than 50% of the sites. Reptiles (turtles, snakes, and lizards) were present at only 16%, 14%, and 3% of sites, respectively. The only discernable pattern of herpetofaunal species richness among stream orders was the fact that salamanders were more common in first-order streams, occurring at 63% of first-order sites and only at 47% of larger order sites. The species richness of salamanders in first-order streams may make them effective indicators of biological integrity in small streams with few or no fish. Variation in geographic distributions was greater for amphibians than reptiles. Specifically, frog species were observed at a greater percentage of sites in the central and eastern portions of the state than in western Maryland. In contrast, salamanders were most common in the western part of the state but nearly absent on the eastern shore.

Future Plans for the Amphibians and Reptiles Component of the MBSS
Maryland DNR and the MBSS recognize the importance of amphibians and reptiles to the native fauna of the state. DNR has recently conducted research aimed at developing a statewide atlas of amphibian and reptile distributions. We believe that the MBSS has potential as a component of this Maryland atlas program or as a source of independent monitoring information on amphibians and reptiles. The MBSS differs from most atlas programs in that it is planned, though not yet funded, as a continuing effort. Because of this, the MBSS has the potential to provide valuable trends information on amphibian populations that may shed light on the conundrum of amphibian decline throughout the region and the globe.

With the goal of improving the information on amphibians and reptiles provided by the MBSS, DNR is considering the following modifications to its sampling methods (within projected time and budget constraints):

  1. Conduct sampling for amphibians and reptiles during both the spring and summer index periods. Many species are more active (e.g., breeding) during the spring than the summer (when certain species go underground in response to high temperatures and lack of precipitation). Expanding the sampling to include the spring index period would provide a better picture of the entire Maryland herpetofauna.
  2. Quantify the sampling. Obtain actual counts for each species instead of simply recording presence or absence. At present, the electroshocking of a known stream area and the timed search of the riparian area provide means to quantify the abundance of amphibians and reptiles. To this end, collections from the stream segment (electroshocking) versus the riparian area (timed search) should be recorded separately. Currently, species collected from each area are included in a single list for the stream sampling location.
  3. Increase the timed search of the riparian area to 30 minutes or 1 hour. The current time limit of 15 minutes allows only a cursory search of the approximately 750 square meters of riparian habitat (5-m on each side of the 75-m stream segment). The amphibian and reptile search should precede other activities in the riparian area that might cause animals to disperse or hide. Research by the Maryland Amphibians and Reptiles Atlas program has shown that systematic hour-long searches produce results comparable to drift fence collections.
  4. Increase the resolution of the search by including larval amphibians and egg masses. Larval salamanders, in particular, represent a large component of the fauna of smaller streams. Using closer examination and finer mesh nets in these streams could effectively characterize this component; the quantitative results could then be incorporated in population estimates based on the stream length calculations already developed for fish.

We welcome your comments and suggestions for improving the utility of the amphibians and reptiles component of the MBSS. Certain modifications may be incorporated in time for implementation during the 1997 sampling program, scheduled to start March 1. Major changes to the MBSS sampling program will likely be deferred until after the three-year MBSS implementation period is completed in 1997; such changes could be incorporated into a repeat of the baseline MBSS (e.g., in 2000) or in special studies to begin in 1998.

Please provide your comments in the format provided by the conference organizers, or contact us directly at:

U.S. Department of the Interior
U.S. Geological Survey
Patuxent Wildlife Research Center
Laurel, MD, USA 20708-4038
Contact: Sam Droege, email:
Last Modified: June 2002