Study

Experimental study of dune vegetation impact and control on leatherback sea turtle Dermochelys coriacea nests

  • Published source details Conrad J.R., Wyneken J., Garner J.A. & Garner S.A. (2011) Experimental study of dune vegetation impact and control on leatherback sea turtle Dermochelys coriacea nests. Endangered Species Research, 15, 13-27.

Actions

This study is summarised as evidence for the following.

Action Category

Manage vegetation using herbicides

Action Link
Reptile Conservation

Manage vegetation by hand (selective weeding)

Action Link
Reptile Conservation
  1. Manage vegetation using herbicides

    A randomized, controlled study in 2007 on coastal sand dunes in St Croix, US Virgin Islands (Conrad et al. 2011) found that using herbicide to remove the native plant ‘beach morning glory’ Ipomoea pes-caprae did not increase leatherback turtle Dermochelys coriacea nest productivity compared to plots with untreated vegetation, but fewer hatchlings became entangled in plant roots in herbicide treated plots compared to in untreated, vegetated plots. Herbicide treated plots had similar hatching success (24% hatched/total yolked eggs) and emergence success (21% hatched/total yolked eggs) compared to untreated vegetated plots (hatching: 20%; emergence: 15%), but lower hatching and emergence success compared to naturally unvegetated plots (hatching: 50%; emergence: 38%). However, the number of hatchlings that became entangled in plant roots was lower in herbicide-treated plots (17 of 393, 4% of hatchlings trapped) compared to untreated vegetated plots (36 of 314, 12% of hatchlings trapped). Ten herbicide-treated plots and 10 untreated vegetation plots (5 x 5 m) were randomly allocated across two experimental blocks. Ten unvegetated plots were established seaward of the experimental blocks. Herbicide (3% Roundup Pro ConcentrateTM) was applied once, 72 days before the nesting season. In April–May 2007, nests laid in areas of the beach liable to flooding were relocated to either herbicide-treated plots, untreated vegetated plots or naturally unvegetated plots (2 nests/plot; 16–20 nests/treatment). Nylon mesh nets were placed over nests before hatching. All nests were excavated 1–3 days after the main period of hatchling emergence and the number of hatched and unhatched eggs was counted.

    (Summarised by: Katie Sainsbury)

  2. Manage vegetation by hand (selective weeding)

    A replicated, randomized, controlled study in 2007 on coastal sand dunes in St Croix, US Virgin Islands (Conrad et al. 2011) found that manually removing the native plant ‘beach morning glory’ Ipomoea pes-caprae did not increase leatherback turtle Dermochelys coriacea nest productivity compared to plots with unmanaged vegetation, but fewer hatchlings became entangled in plant roots in removal plots compared to in untreated, vegetated plots. Manually-removed vegetation plots had similar hatching success (24% hatched/total yolked eggs) and emergence success (emergence success: 20% hatched/total yolked eggs) compared to unmanaged vegetated plots (hatching success: 20%; emergence success: 14% hatched/total yolked eggs), but lower hatching and emergence success compared to naturally non-vegetated plots (hatching success: 50%; emergence success: 38% hatched/total yolked eggs). However, the number of hatchlings that became entangled in plant roots was lower in plots with vegetation removed (19 of 397, 5% hatchlings trapped) compared to unmanaged vegetated plots (36 of 314, 11% hatchlings trapped). Vegetation removal was carried out using machetes and weeding by hand until no vines remained above ground in April before the start of the nesting season. Ten manually-removed and 10 unmanaged vegetation plots (5 x 5 m) were randomly allocated across two experimental blocks. Ten unvegetated plots were established seaward of the experimental blocks. In April–May 2007, nests laid in areas of the beach liable to flooding were relocated to either plots with manually-removed vegetation, untreated vegetated plots or naturally unvegetated plots (2 nests/plot; 16–20 nests/treatment). Nylon mesh nets were placed over nests before hatching. All nests were excavated 1–3 days after the main period of hatchling emergence and the number of hatched and unhatched eggs was counted.

    (Summarised by: Katie Sainsbury)

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