Bemmelen, R.S.A. van

Summary:

In November 2013 aerial surveys were conducted for the first time in the Exclusive Economic Zone of Aruba, Curaçao and Bonaire to evaluate aerial surveys as a tool for marine mammal surveys in these waters, and to assess the distribution and abundance of marine mammals. A secondary aim of these surveys was to collect data on the occurrence of other megafauna (e.g. sharks, rays, turtles) and seabirds. Marine mammals were assessed using distance sampling methods; for other species a strip transect method was applied.

Four marine mammal species were sighted, all of them cetaceans: Humpback Whale, Atlantic/Pantropical Spotted Dolphin, Bottlenose Dolphin and Rough-toothed Dolphin. The total number of individuals seen was 107. Numbers of sightings were too low to calculate densities and abundance estimates for any of the species recorded.

In addition to the marine mammals, sharks, rays, turtles and seabirds were recorded. Noteworthy observations include the first record of a (living) Basking shark and records of seabirds that are scarcely documented in these waters: Red-billed Tropicbird and either Great Skua or South Polar Skua. The number of sightings for these groups were too low to calculate densities and abundance estimates for any of the species recorded.

This survey was commissioned by the Dutch Ministry of Economic Affairs (EZ), and World Wildlife Fund The Netherlands. 

Findings:

Species richness

Species richness is highest in Lac’s mangrove thickets and salt flats. They have a two-fold higher total species richness and a fourfold higher migrant species richness compared to woodland habitats.

The coastal barrens habitats have the lowest number of species.

Composition of bird communities

63 species were recorded. 38% were resident species; 10% had resident populations but also potentially occurred as migrants, 49% were migrants and 3% were migrants that are known to possibly or irregularly breed on Bonaire.

Significant differences were found in the bird communities of the five habitats studied.

• Migrant species are significantly more abundant among the waterbirds (herons, flamingo, waders).
• The highest concentration of migrant birds is in the mangrove thickets and salt flat habitats
• Migratory shorebirds and waders dominate the bird communities of Lac’s salt flat habitat.
• The bird communities of Lac’s woodland habitats are dominated by breeding resident species.
• Migratory passerines are not a major component of Lac’s bird fauna.

Significance of Lac

Lac Bay may be of local significance as a breeding and foraging site to the globally Near-Threatened Reddish Egret, Egretta rufescens.

Lac Bay’s mangroves seem to be of local significance as a nesting and roosting habitat for the Scaly-naped Pigeon, Patagioenas squamosa.

The Yellow-shouldered Amazon no longer uses Lac’s mangrove thickets as a roosting area. Probable causes are decrease in persecution and increase in the quality of the woodlands in many areas of Bonaire.

The Caribbean Coot is not present in Lac’s salt flat habitat. It prefers a number of freshwater locations around the island.

Lac’s number of West Indian flamingo, Phoenicopterus ruber, has grown significantly. This suggests a wider ecological shift taking place within the bay (growth of stagnant backwaters and salt flats behind the mangroves) which threatens Lac’s premier values as a mangrove and seagrass nursery area.

Management Recommendations:

Further observations to document potential egret breeding activity at Lac.