Kangaroo Rat Population Response to Seismic Surveys for Hydrocarbon Reserves

Abstract

Seismic surveys are a method used to locate commercially producible deposits of crude oil and natural gas. These surveys entail generating energy waves that reflect off of subterranean strata and return to the surface where they are recorded and interpreted. In the southern San Joaquin Valley of California, a region rich in hydrocarbon deposits, the two common methods of creating these energy waves include detonating buried explosive charges (“shot-hole” method) and generating strong ground-penetrating vibrations (“vibroseis” method). However, this region also supports many species of conservation concern, including several endemic species of kangaroo rats (Dipodomys spp.). We investigated the effects of a seismic survey on kangaroo rats, including two rare species, the giant kangaroo rat Dipodomys ingens and the short-nosed kangaroo rat Dipodomys nitratoides brevinasus, to determine whether seismic survey activities reduced kangaroo rat abundance, survival, or condition. In 2011, we established 18 study plots: eight subjected to shot-holes, six subjected to vibroseis, and eight controls with no energy source activities. A live-trap grid consisting of 30 traps was established on each plot, and kangaroo rats were captured and marked for four consecutive nights during trapping sessions 1–2 wk before the seismic survey (presurvey), 1–2 wk after the survey (postsurvey), and 5 mo after the survey (long term). Based on capture rates of unique individuals, abundance was similar among shot-hole, vibroseis, and control plots in each of the trapping sessions. Based on recaptures of marked individuals from previous sessions, survival was similar among treatments. Based on mass measurements, condition was similar among treatments. We did not detect adverse impacts to kangaroo rats from a seismic survey; in part, the lack of impacts detected may have been attributable to mitigation measures implemented to avoid or reduce adverse effects. These measures included restricting vibroseis trucks to existing roads, limiting off-road vehicle activity to small tractor-mounted drilling rigs with balloon tires, and attempting to avoid all kangaroo rat burrows by at least 10 m. Similar measures are recommended for any future seismic surveys in this region and elsewhere when burrowing species of conservation concern may be present.

Land Use as a Driver of Patterns of Rodenticide Exposure in Modeled Kit Fox Populations

“…Pesticides are known to negatively impact non-target species, and SGAR residues have been found in many non-target species [ 14 , 15 , 17 , 20 , 49 ], including the kit fox [ 41 , 42 ]. Our study is one of the first to examine how rodenticides affect an entire wildlife population across its range, and where, in a complex landscape, those effects might be most severe (but [ 49 ] also considers spatial impacts across a limited population).…”

“…To assess the potential effects of rodenticides on kit fox populations we mapped areas of likely exposure to SGARs, applied a range of estimated SGAR-induced mortality rates to individuals that encountered rodenticides, and measured changes in kit fox population size and distribution. To map exposure we used a state agricultural database [ 11 ], surveys of residents [ 13 ], and liver tests of 68 opportunistically found kit foxes in and around Bakersfield [ 41 , 42 ] to identify land-use types in which SGARs are used. We assigned scores that described the relative likelihood of rodenticide exposure within different land-cover types.…”