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

摘要

A natural gas pipeline expansion within the range of the federally threatened "western popula-tion" of the gopher tortoise (Gopherus polyphemus) resulted in a US Fish and Wildlife Service andFederal Energy Regulatory Commission requirement that the long-term impact of operation andmaintenance on the tortoise population within the right-of-way be assessed. In many areas, util-ity rights-of-way may provide the only suitable habitat for the gopher tortoise. Tortoises excavateburrows in sandy and clayey soils. The study focused on the potential impacts of right-of-waymowing. Machinery used may cause burrows to collapse and lead to tortoise entombment. Dur-ing the inactive season, 33 occupied burrows in sandy and clayey soils were collapsed in a "worsecase" manner with a suitably sized tractor. All but one of the tortoises excavated themselves. Ra-dio telemetry monitoring and observations following tortoise emergence suggest no subsequentmortality, injury, or ill effects. Assuming no burrow protection measures, the observed mortalityrate was used to estimate a per mowing event mortality rate of 0.14%. Biannual mowing couldresult in one mortality every nine years. If current burrow protection measures continue, the cur-rent population was estimated to double in 200 years. If burrow protection measures are notimplemented, biannual mowing would reduce the estimated, 200-year population size by 12.4%.