Protection benefits desert tortoise (Gopherus agassizii) abundance: the influence of three management strategies on a threatened species
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Published source details
Berry K.H., Lyren L.M., Yee J.L. & Bailey T.Y. (2014) Protection benefits desert tortoise (Gopherus agassizii) abundance: the influence of three management strategies on a threatened species. Herpetological Monographs, 28, 66-92.
Published source details Berry K.H., Lyren L.M., Yee J.L. & Bailey T.Y. (2014) Protection benefits desert tortoise (Gopherus agassizii) abundance: the influence of three management strategies on a threatened species. Herpetological Monographs, 28, 66-92.
Actions
This study is summarised as evidence for the following.
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Limit or exclude off-road vehicle use Action Link |
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Protect habitat: All reptiles (excluding sea turtles) Action Link |
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Cease livestock grazing: Grassland & shrubland Action Link |
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Limit or exclude off-road vehicle use
A replicated, randomized, site comparison study in 2011 in desert shrub and grassland in California, USA (Berry 2014) found that Agassiz’s desert tortoises Gopherus agassizii were more abundant and had a lower mortality rate in a protected area fenced to exclude recreational vehicle use and livestock grazing. Desert tortoise densities were approximately six-times higher in the most protected area, the Tortoise Natural Area (15 tortoises/km2) than designated tortoise critical habitat with some vehicle restrictions (2 tortoises/km2) and four-times higher than on private lands with no vehicle restrictions (4 tortoises/km2). Tortoise annual death rates over the preceding four years were estimated as lowest in the Tortoise Natural Area (3% mortality/year) compared to private lands (6%) or in tortoise critical habitat (20%, results were not statistically tested). Tortoises were surveyed in 240 1 ha plots across three different management areas (80 plots/area): Tortoise Natural Area (1973: closed to recreational vehicles; 1980: fully enclosed and closed to mining and livestock grazing, 2010: 12 km of fencing extended to prevent tortoises leaving), tortoise critical habitat areas (1994: recreational vehicle use restricted but not enforced with some annual closures, 1990: closed to sheep grazing) and private lands (unregulated sheep grazing, intensive recreational vehicle use, hunting and trash dumping). In April–May 2011 plots were surveyed on foot twice in a day for live or dead tortoises and field signs.
(Summarised by: Katie Sainsbury)
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Protect habitat: All reptiles (excluding sea turtles)
A replicated, randomized, site comparison study in 2011 in desert shrub and grassland in the western Mojave Desert, California, USA (Berry et al. 2014) found that in an area with the most human restrictions Agassiz’s desert tortoises Gopherus agassizii were more abundant and had a lower mortality rate. Desert tortoise densities were approximately six-times higher in the most protected area, the Tortoise Natural Area (15 tortoises/km2) than in designated tortoise critical habitat (2 tortoises/km2) and four-times higher than on private lands (4 tortoises/km2). Tortoise annual death rates over the preceding four years were estimated as lowest in the Tortoise Natural Area (3% mortality/year) compared to private lands (6%) and in critical habitat (20%, results were not statistically tested). Tortoises were surveyed in 240 1 ha plots across three different management areas (80 plots/area): Tortoise Natural Area (1973: closed to recreational vehicles; 1980: fully enclosed and closed to mining and livestock grazing, 2010: 12 km of fencing extended to prevent tortoises leaving), critical habitat areas (1994: recreational vehicle use restricted but not enforced with some annual closures, 1990: closed to sheep grazing) and private lands (unregulated sheep grazing, intensive recreational vehicle use, hunting and rubbish dumping). In April–May 2011 plots were surveyed on foot twice/day for live or dead tortoises and field signs.
(Summarised by: Katie Sainsbury)
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Cease livestock grazing: Grassland & shrubland
A replicated, randomized, site comparison study in 2011 in desert shrub and grassland in the western Mojave Desert, California, USA (Berry et al. 2014) found that Agassiz’s desert tortoises Gopherus agassizii were more abundant and had a lower mortality rate in a protected area fenced to exclude livestock grazing and recreational vehicle use. Desert tortoise densities were approximately six-times higher in the most protected area, the Tortoise Natural Area (15 tortoises/km2) than in designated tortoise critical habitat (2 tortoises/km2) and four-times higher than on private lands (4 tortoises/km2). Tortoise annual death rates over the preceding four years were estimated as lowest in the Tortoise Natural Area (3%/year) compared to private lands (6%/year) or in critical habitat (20%/year, results not statistically compared). Tortoises were surveyed in 240 1 ha plots across three different management areas (80 plots/area): Tortoise Natural Area (1973: closed to recreational vehicles; 1980: fully enclosed and closed to mining and livestock grazing, 2010: 12 km of fencing extended to prevent tortoises leaving), tortoise critical habitat areas (1994: recreational vehicle use restricted but not enforced with some annual closures, 1990: closed to sheep grazing) and private lands (unregulated sheep grazing, intensive recreational vehicle use, hunting and rubbish dumping). In April–May 2011 plots were surveyed on foot twice in a day for live or dead tortoises and field signs.
(Summarised by: Katie Sainsbury)
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