Satellite image-based mapping of tropical forests is vital to conservation planning. Standard methods for automated image classification, however, limit classification detail in complex tropical landscapes. In this study, we test an approach to Landsat image interpretation on four islands of the Lesser Antilles, including Grenada and St. Kitts, Nevis and St. Eustatius, testing a more detailed classification than earlier work in the latter three islands. Secondly, we estimate the extents of land cover and protected forest by formation for five islands and ask how land cover has changed over the second half of the 20th century. The image interpretation approach combines image mosaics and ancillary geographic data, classifying the resulting set of raster data with decision tree software. Cloud-free image mosaics for one or two seasons were created by applying regression tree normalization to scene dates that could fill cloudy areas in a base scene. Such mosaics are also known as cloud-filled, cloud-minimized or cloud-cleared imagery, mosaics, or composites. The approach accurately distinguished several classes that more standard methods would confuse; the seamless mosaics aided reference data collection; and the multiseason imagery allowed us to separate drought deciduous forests and woodlands from semi-deciduous ones. Cultivated land areas declined 60 to 100 percent from about 1945 to 2000 on several islands. Meanwhile, forest cover has increased 50 to 950%. This trend will likely continue where sugar cane cultivation has dominated. Like the island of Puerto Rico, most higher-elevation forest formations are protected in formal or informal reserves. Also similarly, lowland forests, which are drier forest types on these islands, are not well represented in reserves. Former cultivated lands in lowland areas could provide lands for new reserves of drier forest types. The land-use history of these islands may provide insight for planners in countries currently considering lowland forest clearing for agriculture.
The endangered Lesser Antillean Iguana, Iguana delicatissima, is an emblematic species for the island of St. Eustatius and in Caribbean Netherlands it is only found on St. Eustatius. In this study we conducted an extensive population survey for the iguana and compared densities in different areas to densities documented most recently in 2004. We conducted 39 field surveys and spent a total of 80 hours and 21 minutes searching for iguanas. We covered 63,672 m of trails and tracks and found only 22 iguanas. An overall average of 3.70 hours were searched for each iguana found. Due to the low encounter rates, detailed estimation and comparison of population densities remain problematic. Overall population density was 0.35 iguanas per hectare which represents 0.5-1% of densities documented elsewhere in healthy populations. Current population densities have declined across all habitats since the 2004 survey. Iguana encounter rates and densities in natural habitat were highest for the region where the northern hills abut onto the central plain. Island-wide, those areas provide the best combination of sun, shelter, food and potential for nesting sites. The population of the Lower Town sector, indicated in 2004 as the most dense and promising subpopulation, has all but disappeared. Island-wide, the residential estate subdivisions remains the second-most important area for the iguana.
We conclude that even though several valuable conservation measures are in place (e.g. establishment of legally protected parks, designation as a legally protected species and a successfully-run awareness campaign), the status of the iguana has not improved significantly in the last 8 years. Our results show that compared to 2004 when the population was estimated to number 425 (275-650) animals, current population size certainly lies on the low side of this range. This is far below the required minimum viable population size of 5000 animals and means that the iguana is critically endangered on St. Eustatius. It is readily vulnerable to extirpation on the island. Human hunting is likely a minor problem, shelter and food availability on the island are abundant, and invasive predator densities in the wild are relatively low. Of the 28 documented instances of death or endangerment of iguanas during the study period, most were attributable to anthropogenic causes. Suitable nesting sites for the iguana appear very limited, especially due to a combination of geology and vegetation. Therefore, lack of nesting sites and high iguana mortalities due to anthropogenic causes are suggested as the two core factors limiting recovery of the iguana on St. Eustatius .
The following management measures are proposed:
1. Protect current populations by:
- Prevention of introduction of invasive species
(Train and equip border officials to prevent potential entry of the mongoose and the Green Iguana from neighbouring islands),
- Enforcement and upgrading of legal protection
(Implement enforcement and upgrade protective legislation),
- Development and protection of additional nesting sites
(Develop and maintain new additional nesting habitat, a measure that is both easy and inexpensive),
- Establishment of an “iguana-friendly yard” programme
(Establish a programme to promote “iguana-friendly” gardens, as the main means of reducing cumulative mortality).
2. Increase the biological knowledge about the iguana by conducting studies for a better knowledge of the critical biological parameters,
3. Create public awareness for the plight of the species,
4. Establish a small, local husbandry project.
(Development of an in situ husbandry and breeding project could serve a pivotal role in bolstering the other core program themes and especially offers a relaxed setting in which islanders can experience the iguana as the gentle and beautiful animal that it is).
This report is part of the Wageningen University BO research program (BO-11-011.05-004) and was financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308701004.
The paleotsunami debris deposits of Aruba, Curaçao and Bonaire are investigated with regard to their geomorphologic characteristics, spatial distribution and their depositional history during the Younger Holocene. Differences between three distinctive formations – ridges, ramparts and boulder assemblages are highlighted and related to their origin within the coastal environment. Relative and absolute age determinations proved evidence for the occurrence of three paleotsunami events at 400-500 BP, 1500 BP and 3500 BP. The tsunamis approached the islands from a northeasterly direction leaving the most impressive geomorphic traces on Bonaire and due to shadowing effects reduced sedimentary effects on Curaçao and Aruba
The Dutch Windward Islands (St. Eustatius, Saba, St. Maarten) support a collective herpetofauna consisting of two frogs (both introduced), six turtles (one introduced, one of uncertain origin, and four sea turtles, of which three are known to nest in the islands), 15 or 16 lizards (depending on whether the iguanas of Saba are a species distinct from Iguana iguana), and three snakes (one introduced). Although politically united, the islands are distinct biogeographic entities and binary similarity indices for the herpetofauna are 0.38 for St. Eustatius/Saba, 0.35 for St. Eustatius/St. Maarten, and 0.20 for Saba/St. Maarten (with values varying only little when the introduced species are included). Only three species, Eleutherodactylus johnstonei, Hemidactylus mabouia, and Thecadactylus rapicauda, are found on all three islands. Species given formal recognition as being in need of protection include the sea turtles (listed in CITES appendices and the IUCN Redlist), Geochelone carbonaria (CITES), Iguana delicatissima (CITES and IUCN), Iguana iguana (CITES), and two species of Alsophis (IUCN). Other species of conservation concern include two species of Ameiva, both of which are restricted to areas of considerable human activity on islands where mongooses (Herpestes javanicus) are established, and Mabuya sp., which may be extirpated on St. Maarten. Three factors largely responsible for the status of these species are: (1) large size and economic value (turtles and iguanas), (2) persecution by people who fear them (snakes), and (3) diurnally active, terrestrial, and vulnerable to predation by mongooses (snakes, Ameiva, Mabuya). Non-governmental organizations on each island are largely responsible for conservation and related educational efforts. Specific recommendations for each island are listed.
With the transition of the islands of Bonaire, St. Eustatius and Saba (BES) from the former Netherlands Antilles to special municipalities of the Netherlands on the 10th of October 2010, the Netherlands gained a significant amount of biodiversity. The Ministry of Economic Affairs, Agriculture and Innovation (EL&I) has gained an important new area of responsibility in terms of nature policy and management. Ecological monitoring can assist in directing management action and conservation of natural areas. It is essential that biodiversity on the BES-islands is monitored, particularly as it is threatened by a large array of natural and human factors. Aside from the national responsibilities that the Kingdom of the Netherlands holds for monitoring nature and biodiversity in these special municipalities, the Netherlands also has international obligations stemming from their participation and membership in global and regional environmental treaties.
This report aims to establish a foundation and define several priority action points for setting up a structural biodiversity monitoring system on the BES-islands, by investigating and contrasting the development, character and organization of biodiversity monitoring in the Netherlands with that of the BES-islands. This research was conducted using purely qualitative research methods; a literature review was conducted, various interviews were conducted in the Netherlands, surveys were distributed amongst actors involved in monitoring on the BES-islands, web-based research was used, and personal communication with a former representative of the Netherlands Antilles Central Government Department of Nature and the Environment as well as advice from two experts from Wageningen Institute for Marine Resources and Ecosystem Studies complemented the research.
The researched shows that if the Kingdom of the Netherlands wants to be able to provide complete national and international reporting on biodiversity and nature policy, additional monitoring is required on the BES-islands. Nature monitoring in the Netherlands has existed for more than 10 years for both the terrestrial and marine environment, is very well organised and steered by government demand. Though there are already biodiversity monitoring activities taking place on the islands and there have been several attempts to coordinate monitoring efforts on the BES-islands, monitoring activities are not organised and the necessary foundation for a structural monitoring system is still lacking. Thus, we are faced with a situation where there is quite a lot of data in existence but no infrastructure in place to organise structural terrestrial and marine biodiversity monitoring. Based on the conclusions it is recommendable to set up a monitoring network with all current parties involved in biodiversity monitoring in order to establish agreements on monitoring priorities and information sharing. In addition to this, a data storage and management system must be set up with someone responsible for data maintenance and reporting. A last vital action point is to define monitoring priorities based on the information available in this report and optimize monitoring methods.
- The boundaries of the WSNP should be expended to include all the salinas included in this survey. This expansion will not only benefit the waterbirds but every other native species of flora and fauna as well.
- Pursue the designation of Salina Frans as a Ramsar site for Bonaire, given its importance as a habitat for both terrestrial and waterbirds.
- Keep collecting data for long term monitoring programs. It is fundamental for the proper management of our natural resources.
- Provide more training for the staff involved in the counts.
- Install permanent depth gauges in all the salt flats being monitored.
- Conduct more scientific research for a better understanding of the ecological functions of the salinas as a habitat for water birds
- As resources or time become available, start a monitoring program for the nesting seasons of our resident waterbirds.
We here provide an overview of 72 invasive animals of the terrestrial and freshwater environments of the Dutch Caribbean, eleven of which are no longer present. All invasive animals that are principally agricultural pests and or animal and plant diseases (46 species) are excluded as these are discussed separately elsewhere. The 61 species documented and discussed here as presently living in the wild or semi-wild state on one or more of the Dutch Caribbean islands, amount to 12 exotic mammals, 16 birds, 13 reptiles, 5 amphibians, 2 freshwater fishes, 3 insects, 2 mollusks and 8 exotic earthworms. For most species, the ecology, distribution, status and current impact remains poorly known as few invasive species have been object of directed studies. Some of the most deleterious animal introductions have been mammals, particularly the grazers and the predators, most of which have been introduced in the historical past. Among these, the four key species are grazing goats, the mongoose the cat and the black rat. In most cases, such species cannot be eradicated because they are widespread and firmly established or even kept as livestock. Nevertheless, these species must urgently be controlled in sensitive areas where possible. Our review also shows that many introduced mammals and reptiles are still present in relatively small populations, making eradication still very feasible. Seven species have the status of being native in parts of the Dutch Caribbean but introduced to other parts where they are not native. The most threatening of this last category is the green iguana, as introduced to St. Maarten where it outcompetes and hybridizes with the weaker Lesser Antillean iguana.
The key priorities for successful action against invasive exotic animals are:
- the control of goats;
- control of introduced predators (rats and cats) near seabird breeding colonies;
- eradication of several small populations of exotic mammal predators and reptiles as long as this is possible before the get a strong foothold and spread;
- eradication of introduced species from small satellite islands which serve (or served) as seabird breeding habitat.
In addition to such on-island action against species already present, it is critical to prevent further introductions. The most important pathways to focus control on are the container transport of goods, the international trade in pets and the trade in ornamental plants. Two key action points are urgently needed: a) develop the existing legislation and b) invasive species management teams (ISMTs) empowered for action. It is essential that these initiatives be firmly imbedded in a policy framework. The first step ahead in these respects should be to outline an Invasive Species Strategy and Action Plan (ISSAP). However, in the interim, the lack of an ISSAP should not hinder directed critical action at the local level (eg. against goats in the national parks and cats at seabird breeding sites).
This research is part of the Wageningen University BO research program (BO-11-011.05-004) and has been financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308202004.