Impact of Natural Gas Pipeline Operation and Maintenance on Long-Term Population Viability of the Threatened Gopher Tortoise.

A natural gas pipeline expansion within the range of the federally threatened "western population" of the gopher tortoise (Gopherus polyphemus) resulted in a US Fish and Wildlife Service and Federal Energy Regulatory Commission requirement that the long-term impact of operation and maintenance on the tortoise population within the right-of-way be assessed. In many areas, utility rights-of-way may provide the only suitable habitat for the gopher tortoise. Tortoises excavate burrows in sandy and clayey soils. The study focused on the potential impacts of right-of-way mowing. Machinery used may cause burrows to collapse and lead to tortoise entombment. During the inactive season, 33 occupied burrows in sandy and clayey soils were collapsed in a "worse case" manner with a suitably sized tractor. All but one of the tortoises excavated themselves. Radio telemetry monitoring and observations following tortoise emergence suggest no subsequent mortality, injury, or ill effects. Assuming no burrow protection measures, the observed mortality rate was used to estimate a per mowing event mortality rate of 0.14%. Biannual mowing could result in one mortality every nine years. If current burrow protection measures continue, the current population was estimated to double in 200 years. If burrow protection measures are not implemented, biannual mowing would reduce the estimated, 200-year population size by 12.4%. [ABSTRACT FROM AUTHOR]