Reintroduction when threats still exist 347


TABLE 1 A ranked list of the proposed areas for potential reintroduction of the St Croix ground lizard Pholidoscelis polops, based on com- bined scores of habitat suitability, mongoose presence, and mongoose control measures.


Protected area


Existing populations Ruth Cay Wildlife Sanctuary


Protestant Cay Wildlife Sanctuary Green Cay National Wildlife Refuge Buck Island Reef National Monument


Ranked reintroduction sites Sandy Point National Wildlife Refuge Altoona Lagoon Beach Recreation Area Southgate Coastal Preserve East End Marine Park


Salt River Bay National Historic Park & Ecological Preserve East Bay & Point Udall Estate Little Princess


U.S. Virgin Islands Wetlands


Derick O. Steinmann Memorial Beach Manning Bay Wetlands Long Point Bay Estate Great Pond


Jack & Isaacs Bays Preserve Total for reintroduction sites Entirety of St Croix


Area (km2)


0.097 0.026 0.043 0.695


1.555 0.068 0.419 0.551 1.623 0.535 0.194 0.350 0.008 0.299 0.078 0.129 1.208 7.017


217.500


Habitat (km2)


Suitable habitat (%)1


0.097 100.0 0.025 0.030 0.620


95.4 70.2 90.0


0.434


0.068 100.0 0.193 0.146 0.663 0.031 0.158 0.068 0.001 0.292 0.022 0.021 0.028 2.125


28.2 46.1


26.6 40.9 5.8


81.5 19.4 16.1 97.6 27.9 16.4 2.4


11.690


30.3 5.0


1Per cent of the total habitat in the categories: potentially suitable, suitable, most suitable. 2Carrying capacity was estimated from the model, and summed to obtain an estimate for the entire area.


could be supported in protected areas on St Croix, based on a mean of 8.2 ± SD 4.1 (range 0.0–24.0) lizards per 30m2 grid cell. Based on themodel results and ranking of potential sites, we prioritized reintroduction sites that contained suitable lizard habitat and reduced threat from mongooses (Fig. 3). Eight of the 30 protected areas with lizard habitat already have some mongoose control measures in place, specifically trapping to reduce mongoose density.Mongoose-proof bar- riers do not currently exist on St Croix, but could be con- structed at some sites with , 3 km of fencing. We included this information in the ranking should managers decide to build barriers. The three most suitable reintroduction sites are: (1) The


Sandy Point National Wildlife Refuge, which is located on the south-west end of St Croix and contains 43.4 ha of suit- able habitat. The mongoose population in the Refuge has been monitored and reduced through trapping. Lizard rein- troductions can occur without fencing, but a 2.9 km mon- goose exclusion fence proposed to benefit nesting marine turtles would also reduce mongoose predation on the St Croix ground lizard in this area. (2) Altoona Lagoon, which ismanaged by theGovernment of the Virgin Islands, with 6.8 ha of habitat. Our model showed the entire area as suitable habitat for the St Croix ground lizard. The site is protected and is equal in size to Protestant Cay and Green Cay com- bined, where the lizards persisted after extirpation from St Croix. A wetland adjacent to coastal forest and beach is an


important area for migratory birds. This would be a good site to study effects of mongoose control on St Croix ground lizard density. (3) The SouthgateCoastal Reserve, which con- tains 19.3 ha of suitable habitat and is managed by the St Croix Environmental Association. Southgate has a large salt pond supporting birds, and a beach used by nesting mar- ine turtles on the north shore of St Croix. A birding trail is used for environmental education, and outreach activities for the St Croix ground lizard could be included. The reserve is currently fenced with stainless steel chain link, which can potentially be modified to exclude mongooses if deemed necessary.


Discussion


Two successful conservation introductions showed the St Croix ground lizard can be established on small offshore cays where mongooses have been eradicated, such as on Buck Island. However, all four existing populations are vul- nerable.Continued recovery of this Endangered endemic spe- cies depends on reintroducing it to the main island of St Croix. The short-term risk of reintroduction to the survival of the extant populations is low, because the new population on Buck Island has .2,000 individuals and can serve as source of individuals for reintroductions. Two successful translocations of the St Croix ground lizard to Ruth Island


Oryx, 2021, 55(3), 344–351 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319001091


Predicted carrying capacity2


461 151 499


2,150 1,273 1,722


488


1,941 8,193 1,829 847


1,130 52


1,835 258 478


1,423 21,469 142,421 Priority


Extant Extant Extant Extant


Highest Highest Highest High High High High High Low Low Low Low Low


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