Debrot, A.O.

Key Elements Towards a Joint Invasive Alien Species Strategy for the Dutch Caribbean

Summary:

Recent inventories have documented no less than 211 exotic alien species in the wild for the Dutch Caribbean. These amount to no less than 27 introduced marine species, 65 introduced terrestrial plants, 72 introduced terrestrial and freshwater animals and 47 introduced agricultural pests and diseases. A list of these species, pests and diseases are found in resp. Debrot et al. (2011), Van der Burg et al. 2012, and Van Buurt and Debrot (2012, 2011). The rate of introductions and establishment of invasive alien species (IAS) worldwide has grown rapidly as a result of increasing globalisation. Invasive species cause major ecological effects (decimating native flora or fauna populations) as well as economic losses to these islands, across sectors such as agriculture (diseases, weeds and vectors), fisheries (fish diseases and the lionfish), industry (rodents and termites), tourism (roadside weedy species) and public health (mosquitos). Recently in Curaçao the kissing bug Triatoma infestans was found; this is a vector for Chagas disease. It almost certainly came in with palm leaves imported from South America to be used as roof covering for recreational beach “palapa’s”.

Several countries in the Caribbean have developed a strategy to address the invasive species problem already, such as Jamaica (Townsend 2009), the Bahamas (BEST Commission 2003) and St. Lucia (Andrew and John 2010, Chase 2011). Islands are particularly at risk because of a number of factors: their small size, resulting in small vulnerable plant and animal populations, a relatively large border which is difficult to control, a small human population lacking the necessary expertise and resources to take adequate measures. For islands, the sea acts as a strong natural barrier for natural transport of terrestrial flora and fauna, however human activities helped in overcoming this barrier. The issue of feral animals, especially roaming cattle, donkeys, goats create similar problems everywhere: they have a devastating effect on tree and shrub regeneration, which greatly degrades the natural vegetation, with severe soil degradation as a result. This shifts the competitive advantage to hardy exotics and creates runoff of nutrients and silt into the sea, where algal growth and silt deposition are damaging the coral. The new nature policy plan for the Caribbean Netherlands assigns a high priority to the invasive species problem (MinEZ 2013), which worldwide is considered second only to habitat destruction as a long-term threat to biodiversity (Kaiser 1999, Mooney 2001).

While acknowledging a focus on the Caribbean Netherlands in specific (Bonaire, Saba, St. Eustatius) this report sets the first key steps in developing a common frame of reference for the whole of the Dutch Caribbean (i.e. including the islands of Aruba, Curacao and St. Maarten). These islands share historical and cultural ties, partly similar climates, scarce expertise, and experience most IAS as a common problem. The magnitude and severity of the problem is evident and necessitates a joint strategy into which action at insular level can be embedded for maximum efficiency and synergy: a common Invasive Alien Species Strategy (IASS).

Management Recommendations:

The main action points for implementation are:

1. Develop and adopt guiding legal lists for action: Black lists, Alert lists and Watch lists, enumerating the species for which border control is essential or for which control and management actions would be required. A special task group should be made responsible for keeping these lists up to date.

2. Install effective border controls. To prevent is better than to cure: the costs of controlling or eliminating invasives once established can be very costly. For this reason and because of the earlier indicated special vulnerability of the island ecosystems, it is strongly recommended to prevent the entrance of (more) invasives.

3. Establish Invasive Species Management Teams. For the coordination of data collection, evaluation and the initiation of actions, a special team is required. This ISMT team shall have its own facilities and budget.

4. Define responsibilities and mandates. Ultimate responsibility for IAS control lies with the island governments. This means that policies regarding IAS will be determined by the government. However, to be effective and efficient the ISMT (see 9.) needs full mandate to act within the limits of their own budget.

5. Require quarantine documents. Phytosanitary certificates and animal health certificates will be required for all imports.

6. Enforcement. Staff must be trained and instructed how to perform border controls. They must obtain sufficient mandate and means to confiscate and dispose of prohibited goods.

7. Develop action plans. A plan of action needs to be ready, describing the successive steps and decisions that have to be made for key threat species at all stages of the invasion process.

8. Arrange access to properties. When an alien species is invasive and needs to be eliminated, it is important that regulations allow the exterminators access to all properties, private and public alike.

9. Assure public support. Large scale programs for extermination and control, especially of animals, needs extensive public support. Volunteers may prove essential to assure enough ‘eyes’ and manpower.

10. Make rapid surveys. In order to decide whether a complete eradication is needed or that monitoring and restricting the distribution (mitigation) is the best or only option, a survey of the extent of the problem must be assessed by experts.

11. Rapid response. Usually a rapid action can localise the problem to a restricted area or eliminate the first individuals effectively so that no further costs have to be made.

12. Make risk assessments before introducing natural enemies. In case species are already present in vast numbers, biological control is often a last resort. This usually means introducing a natural enemy from the area of origin of the species. This means introducing another alien species, which may become a pest in itself. Expert consultation and small-scale experimenting is usually needed before the potential natural enemies can be safely released.

13. Create an information system. A team of experts managing a computer database is needed. This ISMT team needs to develop a system for easy reporting of new discoveries of alien species, for maintaining and updating information on key threats. The information system supports policy, action and research at all levels of the invasion process.

14. Create a platform for cooperation. In order to develop the system further, a national as well as an island platform is needed for participation of all relevant stakeholders. These platforms will develop recommendations for the ISMT and the island governments, and may also act as support group for the ISMT. 

Date
2014
Data type
Research report
Theme
Governance
Education and outreach
Legislation
Research and monitoring
Report number
C020/14
Geographic location
Aruba
Bonaire
Curacao
Saba
Saba bank
St. Eustatius
St. Maarten

Shark protection plan for the Dutch Caribbean EEZ

Summary:

Shark populations have steeply declined worldwide due to unsustainable overexploitation and in this the Caribbean region is no exception. Since the 1990s many initiatives have been developed to protect the most threatened species. Sharks play an important ecological role in tropical marine ecosystems and represent an important economic potential in the context of ecotourism. As the Netherlands has traditionally shown strong international leadership and commitment in biodiversity protection, a key ambition of the new Dutch Caribbean Nature Policy Plan 2013-2017, developed jointly with the Dutch Caribbean islands, is the effective implementation of shark protection.

This report provides the necessary review and background on which to base such an endeavour. In 2012 27 species of sharks and rays were documented to be present in a deskstudy by IMARES, and six other species were listed to be tentatively present according to the IUCN Shark Specialist Group. In 2013 three new species were documented in field surveys carried out by IMARES. For these species this report provides an overview of available scientific knowledge on life history characteristics, distribution, abundance and population status in the Caribbean. The life history characteristics of slow growth, late maturity and low fecundity make sharks very vulnerable to overfishing and reduce their ability to recover from past overfishing. Because of their life history characteristics and their coastal habitat use for specific life stages, destruction of their main habitats and nursery grounds also has a relatively large impact on shark populations.

The main threats to address in a shark protection plan are fishing mortality and habitat quality. Although directed shark fisheries are not occurring in the Dutch Caribbean, there are additional concerns to global shark populations, which are mixed-species fisheries, bycatch and Illegal, Unreported and Unregulated (IUU) fishing. Sharks do occur as bycatch in artisanal fisheries in the Dutch Caribbean and illegal fishing by foreign vessels also occurs occasionally.

Public environmental awareness and support for management measures are a key determinant for the successful implementation of a shark protection plan. As part of this research a questionnaire was distributed amongst three key coastal resource user groups: fishermen, sport divers and local residents. It appeared there was no consensus on the perception of the change in biodiversity and abundance of sharks and rays. However, a decisive majority of the respondents was in favour of shark protection and half of the fishers was in favour to manage bycatch. Respondents were asked to rank specific measures in order of importance. The most appreciated measure for fishermen was enforcement including meaningful penalties and the most appreciated measures for the other respondents were a ban on shark finning and landing of sharks, followed by enforcement and immediate release of bycatch. However, in the opinion of some fishermen sharks are considered a pest, which are not specifically targeted, but when caught are consumed or sold like any other fish. Awareness raising of especially fishermen and children was added by several divers and residents as an important additional protection measure.

Throughout the world, sharks are playing an increasingly important role in island economies as an important natural attraction for eco-based recreation and tourism. A recent study has shown that a single shark can represent an average touristic resource value of US$ 2.64 million. Consequently, shark protection is taking flight around the world, including the Caribbean. In the last 3 years the region has seen the implementation of shark National Plan Of Action (NPOA) in the Bahamas, Honduras and Venezuela. Because the most destructive industrial-scale fishery practices (directed shark fisheries, shark finning, long-lining and gillnetting) have never been important in the Dutch Caribbean, the development and effective implementation of a shark NPOA is much simpler than in most situations. The overall feasibility for successful shark conservation are high due to a number of other factors listed in this report. 

Worldwide the use of sanctuaries is the main conservation tool. We therefore propose the establishment of a shark sanctuary as the main cornerstone to a Dutch Caribbean shark NPOA. This report outlines the ecological arguments for the establishment of a shark NPOA and sanctuary(ies), as well as the typical issues that need to be addressed. Legal designation of a shark sanctuary would form the first and most important step which provides the framework for all broader (international cooperation) and in depth (knowledge and conservation development) initiatives. Once a sanctuary is established, the fuller implementation of a shark NPOA should be seen as a gradual process, involving development of knowledge, policy, rules and regulations, public and stakeholder participation. In this, the Netherlands would follow and importantly reinforce the efforts of other nations who have already established NPOAs based on shark sanctuaries within the region.

The most promising area for establishment of a shark sanctuary is the little-fished Saba Bank as this area of unique biodiversity has the best shark population status, has recently already acquired national protected status and an active management structure, as well as international status as an EBSA and PSSA including IMO anchoring prohibition. Furthermore, a shark sanctuary for this area could importantly reinforce government plans to locate the first (part) of a Dutch Caribbean Marine Mammals Sanctuary at the Saba Bank. The shark population present presents unique research opportunities that could also generate considerable economic spin-off for the islands in terms of scientific research and knowledge development.

 

Management Recommendations:

  • Develop a simple and holistic shark NPOA based importantly on the use of one (or more) shark sanctuaries
  • Set up a shark research program combining on the one hand low tech opportunistic approaches (allowing participation of stakeholder groups for awareness and community support) and on the other hand using high tech approaches (genetic, telemetry, video-monitoring) to allow thorough insights even though abundance may be low
  • Start actively participating in regional shark conservation and ecosystem initiatives and seek active collaboration with sister sanctuaries of the region (Venezuela, Honduras, Bahamas) 
Date
2014
Data type
Research report
Theme
Governance
Education and outreach
Legislation
Research and monitoring
Report number
C209/13
Geographic location
Aruba
Bonaire
Curacao
Saba
Saba bank
St. Eustatius
St. Maarten

Diversity and spatial heterogeneity of mangrove associated sponges of Curaçao and Aruba

Abstract:

Sponges are major epibionts of mangrove roots in the Caribbean. Mangrove sponge communities in the Caribbean mainly consist of species that are typical to this habitat and community compositions often differ from those found on coral reefs nearby. Heterogeneity in species distributions between locations and within locations between roots is often reported. This study quantifies the diversity and abundance of mangrove associated sponges in the inner bays of Curaçao and Aruba and correlates variability of regional sponge diversity with environmental variables measured along the surveyed sites. Tannin concentrations vary between mangrove roots, and were correlated to sponge cover as a possible cause for habitat heterogeneity on a smaller scale. A total of 22 species was observed. Heterogeneity in species richness and abundance was apparent, and several sponge species were restricted in their depth of occurrence. Statistical data reduction suggests that sponge diversity may be partly explained by the distance towards adjacent reefs and to the degree of eutrophication, in which the latter is comprised of rate of planktonic respiration, total carbon and turbidity. Tannin concentrations did not determine within locality species heterogeneity as a priori postulated, but were positively related to sponge cover for reasons not yet elucidated. 

Date
2008
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Aruba
Curacao

Effect of introduced species and habitat alteration on the occurrence and distribution of euryhaline fishes in fresh- and brackish-water habitats on Aruba, Bonaire and Curaçao (South Caribbean)

Abstract:

We conducted an ichthyological survey during the dry season of 2006 on the semi-arid islands of Aruba, Bonaire and Curaçao to provide information on species composition, richness and dis- tribution in natural and non-natural aquatic habitats. The dry season species assemblages (N = 9 species) comprised less species than the wet seasons, and these data refine our knowledge of the indigenous fish fauna and its refuge localities during phases of drought and ensuing high salinity. A hierarchical cluster analysis reveals that the three islands have different species compositions with Curaçao being the most diverse, probably due to its having the most habitats and freshwaters present throughout the year. Species richness was unrelated to salinity and species diversity was highest in canalised streams. In the dry season fewer amphidromous species are present than in the wet season. We found no significant effect of human-induced changes on the presence or absence of fish species in the Netherlands Antilles. The presence of exotic species (including Xiphophorus helleri on Aruba, a first record for this island, and Oreochromis mossambicus and Poecilia reticulata occurring on all three islands) did not have a clear effect on the presence of indigenous species, nor did human alteration of the habitats have an influence on the occurrence of fish species. 

Date
2008
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao

Marine mammals in the Wider Caribbean – Current research and priorities for future studies

Summary:

Information on the distribution, abundance and ecology of marine mammal in the Wider Caribbean Region is scarce. This report aims at collating the on-going research in the Wider Caribbean Region, at identifying the most critical knowledge gaps that need to be addressed to inform and facilitate conservation actions and assess the most suitable research techniques to fill these knowledge gaps.

Numerous research activities aiming at marine mammals have been commenced by individual organisations as well as regional or even international collaborations throughout the Wider Caribbean over the past years. These efforts, ranging from visual to acoustic surveys, satellite telemetry, stranding response, and many more, provide valuable insight into important aspects of the ecology of marine mammals and show that the motivation and need to conduct research on marine mammals in the Caribbean waters is high. Due to lack of funds and capacity most current and past cetacean research in the region can be characterised as small-scale, low in sophistication, opportunistic, temporary and local which is a great limitation to the understanding required for proper conservation of this increasingly important resource in this tourism-oriented region. Consequently, if continued with the current level of capacity and expertise, the results will continue to remain limited. There is an urgent need to combine forces, work on a larger geographic scale and use new and innovative techniques if we want to move beyond the current patchwork in activities and understanding. Ideally, all on-going and suggested future research efforts should become integral parts of a joint international research strategy for the wider Caribbean.

The choice of research methods to be used, however, depends in large part on the questions to be answered. Knowledge on temporal and spatial scale of marine mammal occurrence in the Caribbean waters is essential for any effective management and conservation and should have first priority, followed by studies on the effect of anthropogenic activities on marine mammals. In the absence of adequate data on marine mammals in this region, but with cautious extrapolation of knowledge and experience gained in other parts of the world we suggest to concentrate research efforts on visual and acoustic surveys and monitoring, stranding networks and necropsy of stranded animals, along with photo ID and tissue sampling for genetic analysis. All these methods differ in terms of the aims for which they will be suitable. Therefore, the aims must be clear before choosing the method. Research on the diverse groups of marine mammals has to modular and collaborative such that it can be synergistic, provided that there is sufficient collaboration and communication between all parties involved.

Public outreach by involvement of local institutions, marine parks, tour operators as well as communication of any research plan and results to local, regional and international regulators, policy makers and public representatives, plays an equally important role in achieving management and conservation goals.

This report is part of the Wageningen University BO research program (BO-11-011.05-005) and has been financed by the Ministry of Economic Affairs (EZ) under project number 4308701020. 

Date
2014
Data type
Research report
Theme
Research and monitoring
Report number
C007/14
Geographic location
Aruba
Bonaire
Curacao
Saba
Saba bank
St. Eustatius
St. Maarten

Predation threats to the Red- billed Tropicbird breeding colony of Saba: focus on cats

Summary:

Feral domestic cats (Felis catus) are recognized as one of the most devastating alien predator species in the world and are a major threat to nesting colonies of the Red-billed Tropicbird (Phaethon aethereus), on Saba island, Dutch Caribbean. Cats and rats are both known to impact nesting seabirds and hence are both potential threats to the tropicbird on Saba. However, whereas the tropicbird has coexisted with rats for centuries, cats have only recently become a problem (since about 2000). Several studies from the region suggest that the tropicbird may be less-vulnerable to rats but cats have been unequivocally implicated in the depredation of tropicbird nests on Saba (unpublished data, Michiel Boeken). In this study we collected baseline data on cat and rat distribution, and cat diet and health. We also conducted 83 questionnaire interviews with Saba residents to assess their views on cats, rats, tropicbirds and the acceptability of different management options.

Two methods were used to assess cat density distribution. We used baited camera traps (73 successful 2-night deployments divided among 4 habitat categories) as an index of relative density. We also used scat densities (collected from 15,474 meters of transect from eleven trails) from which to extrapolate and compare relative cat densities in different habitats. For the study of diet we collected and analysed a total of 94 cat scats and studied the intestinal contents of 13 sacrificed feral cats.

Both scat densities and camera trap recordings showed large and statistically significant differences in cat density on trails between habitat zones. Cat densities were lowest in the lush forest habitat found at higher elevations (mean: 4 cats/km2) on the island and highest at lower coastal elevations. Densities were particularly high (mean: 286 cats/km2) in the small area surrounding the island landfill where food, consisting of human refuse and garbage was abundant. These densities are for areas along hiking- and goat-trails. These are actively selected by cats. Therefore, densities along trails cannot be simply extrapolated to the rest of the island.

While at the landfill daily incineration of garbage takes place, un-incinerated garbage is left open overnight almost every day. This provides feral cats with an ample food source. Construction of a vermin- proof, concrete overnight storage pen could greatly reduce food availability to cats and rats. Dry woodland and coastal scrub trail habitat had intermediate cat densities (respectively, 107 and 166, cat/km2). Rat density as documented using camera traps was highest in the forest habitat where food, water and shelter for rats was particularly abundant. Rat and cat density were markedly inversely related. Cats were concentrated at lower elevations and in more open areas where tropicbirds principally nest.

Diet analysis showed the feral cats on Saba are an opportunistic predator-scavenger consuming various categories of prey (mammals, birds, reptiles, and insects) as well as anthropogenic waste. Food composition of the feral cats of Saba differed significantly between habitats. Overall, rats were the most important food species of the cat, followed by reptiles and birds. However at the landfill where cat population densities were highest, birds and rats were strongly reduced in the diet, while garbage and reptiles were of greatly increased importance. Scats collected in the forest zone suggested a lower importance of rats in the diet of cats than at lower arid elevations. The cat scats collected in the urban environment had no prey species represented and were apparently all from well-fed house cats. The opportunistic and flexible food habits documented for cats in this study allows them to easily switch to seasonally abundant prey (for instance during the seabird breeding seasons).

Preliminary veterinary assessments on cats removed from the landfill showed the animals to be in overall poor health. This suggest that releasing neutered cats back into the wild without any further supporting care may be much less humane than typically assumed. Based on these results and taking into account the welfare concerns of the tropicbirds preyed upon by cats, the Saba Foundation for Prevention of Cruelty to Animals (SFPCA) has decided to discontinue its practice of releasing neutered unwanted cats into the wild (Trap-Neuter-Release, or TNR).

Public views regarding cats, tropicbirds and management options as assessed using a simple questionnaire and 83 questionnaire returns were obtained. Around 30% of the participants owned cats of which only about 5% were not neutered. A significant majority of respondents (66%) believed feral cats on Saba are an environmental problem. In this there was no difference between natives and expat residents. Most (44%) believed that cats were principally a problem in being a threat to wildlife. Diseases and parasites was quoted as the second-most perceived problem with feral cats (30%). Feral cats and rats scored as the two most important perceived threats to the tropicbird (respectively, 65% and 70%). When asked “how many saved tropicbirds do you think justifies the death of one cat”, 38% of Sabans and 22% of expats did not answer the question. Of those that did answer, 36% of Sabans and 48% of expats, valued the life of a tropicbird more than that of a single cat. The remainder considered cats somewhat more important than one tropicbirds but only few (5% natives, 18% expats) considered feral cats more important than the combined sum of all their tropicbird prey. Between 70-80% of respondents thought registration, neutering and removal of cats from breeding colonies was a good idea. When asked if euthanization would be acceptable to them, a significant majority (80%) found it to be an acceptable method for use in cat control. Finally, 43% even thought that total eradication of all cats (domestic and feral) from the island would be a good idea. Of the participants upwards of 80% stated that rats were also an environmental problem and more measures to control rats are supported by 75% of those interviewed. Awareness and willingness of the Saban resident population towards measures against cats and rats are clearly high. This means that there exists a wide management scope to implement measures with which to address these problems.

For more than 15 years government rat control has used brodifacoum as the main rodenticide, but rats remain a widespread and unrelenting problem on Saba. This suggests that the rats might well have become partly resistant to this anticoagulant toxin and that the time has come to alternate to a different rodenticide. Alternating use of rodenticides is the internationally recommended practice for rat control. It is already being practiced on nearby St. Eustatius where rat problems are much less acute than on Saba (but where feral fruit trees are also less abundant and landfill practices are also less favourable to vermin).

Key management recommendations:

  • Upgrade the 2004 Saba “Island Ordinance on Identification and Registration of Livestock and Domestic Animals” to prohibit the importation and keeping of unneutered cats.
  • Capacitate the SFPCA to enforce the mandatory registration of domestic animals.
  • Construct a vermin-proof concrete overnight pen at the Saba landfill (for secure storage of the garbage that might not be incinerated the same day).
  • From now on euthanize all unwanted and uncared-for stray and feral nuisance cats.
  • Judiciously use humane euthanization to address the acute overpopulation of cats in particularly sensitive areas (such as the mapped seabird colonies) as this is quite acceptable to Saban residents.
  • Start use of a new alternative rodenticide, following the example from St. Eustatius.
  • Management measures need to be accompanied by an (inter)active and effective communication plan to keep public support levels high.

Key recommendations for research:

  • Investigate the role of rats as predators, not only with respect to seabirds but also in the forested zone where they are most abundant and may seriously impact native forest species.
  • Assess the effect of cat removal on tropicbird breeding success and on rat population density, as well as the broader predator-prey relationships on the island. 
Date
2014
Data type
Research report
Theme
Research and monitoring
Report number
C011/14
Geographic location
Saba

Use of satellite data for the monitoring of species on Saba and St. Eustatius.

Abstract:

On 10 October 2010 Bonaire, Saba and St. Eustatius became ‘special municipalities’ of the Netherlands, making the Dutch government responsible for the implementation and adherence to several international conventions that apply to these islands (e.g. Convention of Biological Diversity, Ramsar convention), including the protection of nature.

Knowledge on the whereabouts of endangered and key species or habitats is essential to ensure their protection against the negative effects of activities such as uncontrolled socio-economic developments (e.g. construction works, harbour expansion, expansion of residential areas) and natural phenomena (e.g. hurricanes, Sea Level Rise). This necessitates early identification of risk locations where future expected activities may collide with species/habitat presence. To determine these whereabouts, monitoring is necessary. Monitoring in the field, however, is often costly and time-consuming. A more effective and quicker approach is desired to obtain a realistic overview of key habitat distributions and associated key species.

At the request of the Dutch Ministry of Economic Affairs the present study examines the possibility to identify the different land cover types (natural and artificial) on Very High Resolution1 satellite images of the Caribbean islands Bonaire, Saba and St. Eustatius, using remote sensing1 analysis. In addition, the possibility to link key species with specific land cover types was assessed by identifying the species’ habitat requirements. Linking species habitat requirements with associated land cover types allows for the identification of their potential occurrence on the islands. It was expected that with niche-modelling potential distribution maps could be developed for different species and habitats. Such maps are valuable to determine risk locations where species/habitat occurrence and planned activities may conflict in the future. This would allow for the proper and early implementation of protective measures.

Worldview-2 satellite images of Saba and St. Eustatius (acquired on 3 December 2010 and 18 February 2011, respectively) were analysed. Analysis of the satellite image of Bonaire was not possible, due to time constraints. From the results of Saba and St. Eustatius it can be concluded that identification of land cover types using satellite images is possible. At present, the results are limited due to a) heterogeneous land cover types and b) the lack of ecological knowledge (e.g. baseline studies).

The identification of artificial features1 (e.g. infrastructure) is not a problem. The challenges encountered are mainly related to the largely mixed heterogeneous vegetation found on Saba and St. Eustatius. Due to the high level of mixing, spectral overlap between different vegetation types is high. Consequently, separating the different vegetation types is difficult. Corrections can be made based on visual interpretation and expertise in the field. This requires time and expert knowledge of the different vegetation types. In addition, both Saba and St. Eustatius exhibit strong differences in altitude, resulting in numerous shadowed areas that impede the identification of the land cover types underneath. Such terrain effect can be corrected using a Digital Elevation Model (DEM). Unfortunately, a sufficiently good DEM (with a high spatial accuracy of around 1 meter) was not yet available2.

Analysis of satellite images resulted in land cover maps with good fit to the distribution of the different land cover types on Saba and St. Eustatius. The produced land cover maps (Figures 4 to 7) give a coarse representation of the distribution of Forest, Shrub, Pasture and Artificial surface on the islands. In addition, it was possible to identify the extent and location of invasive vegetation (e.g. Corallita and other species), although identification to species-level was not possible. At present, these maps provide insufficient detail for biodiversity monitoring, because of the lack of connection with species. They could, however, be used to monitor different land cover development (e.g. forestation, artificial surfaces, shrub and pastures) on the long term (e.g. in years) or to gain a quick overview on the location of invasive vegetation. A distinctive land cover classification based on the available satellite images during the present study, however, was only achieved for the coarser vegetation types.

Ecoprofiles were developed for various species and habitats, describing their habitat requirements. With sufficient detail, these requirements link the species to habitats and thereby allow for the creation of species specific maps. The level of available data on habitat requirements varies per species. Overall knowledge on habitat requirements is generally not sufficient, associating species with multiple habitat types, and making it difficult to pinpoint essential habitat types. The amount of knowledge on habitat requirements has direct influence on the success of niche modelling. This illustrates the necessity of detailed knowledge on species biology, ecology and life history characteristics even when using advanced techniques such as remote sensing.

The production of maps through niche-modelling meant to show the expected geographical distribution of species was not possible due to the limited level of detail within the identified land cover types, and the restricted data on the habitat requirements of the species occurring on Saba and St. Eustatius, in combination with time constraints. Before such maps can be developed several issues need to be solved first. These include specific knowledge on species biology, ecology and life history characteristics of the target species (baseline studies); the collection of more training samples (ground truthing data) in the field; a high quality DEM of Saba and St. Eustatius (and Bonaire as well). This will lead to further adaptation of the chosen classification scheme and aid in separating spectral overlap between the different vegetation types.

This research is part of the Wageningen University BO research program (BO-11-011.05-019) and was financed by the Dutch Ministry of Economic Affairs (EZ) under project number 4308701012. 

Date
2013
Data type
Research report
Theme
Research and monitoring
Report number
C124/13
Geographic location
Saba
St. Eustatius

Continued expansion of the trans-Atlantic invasive marine angiosperm Halophila stipulacea in the Eastern Caribbean

Abstract:

Halophila stipulacea (Hydrocharitaceae) is reported for the first time from Aruba, Curaçao, Grenadines (Grenada), St. Eustatius, St. John (US Virgin Islands), St. Martin (France), and St. Vincent and the Grenadines, bringing the total number of known occurrences from eastern Caribbean islands to 19. Native to the Red Sea and western Indian Ocean, H. stipulacea spread to the Mediterranean Sea in the late 1800s and became established in the eastern Caribbean in 2002. The species has dispersed north and south of its first sighting in Grenada and now spans a latitudinal distance of 6° (>700 km), most likely facilitated by a combination of commercial and recreational boat traffic. The continuing range expansion of H. stipulacea indicates the species has successfully acclimated to surviving in the Caribbean environment, warranting further investigation into its ecological interactions with the indigenous seagrasses.

Date
2013
Data type
Scientific article
Theme
Research and monitoring
Document
Journal
Geographic location
Aruba
Curacao
St. Eustatius
St. Maarten

A Review of the Freshwater Fishes of Curaçao, with Comments on those of Aruba and Bonaire

Abstract:

Based on a field survey and review of published records, I report the occurrence of 13 species of fishes in fresh waters of Curaçao. Seven species are new or previously unpublished freshwater records for the island. New records are also provided for the adjacent islands of Aruba and Bonaire. Although the native freshwater fish fauna is dominated by predatory gobiid and eleotrid fishes, the most frequently encountered species was the endemic molly, Poecilia vandepolli. The next most frequent species was the native mountain mullet (Agonostomus monticola), followed by the exotic Mozambique tilapia (Oreochromis mossambicus) and the native emerald sleeper (Erotelis smaragdus). High dams block surface water flows in Curaçao and prevent migration of native amphidromous fish. The introduced tilapia has apparently reduced the abundance of native species. 

Date
2003
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao
Author

Geographic coupling of juvenile and adult habitat shapes spatial population dynamics of a coral reef fish

Abstract:

Marine spatial population dynamics are often addressed with a focus on larval dispersal, without taking into account movement behavior of individuals in later life stages. Processes occurring during demersal life stages may also drive spatial population dynamics if habitat quality is perceived differently by animals belonging to different life stages. In this study, we used a dual approach to understand how stage-structured habitat use and dispersal ability of adults shape the population of a marine fish species. Our study area and focal species provided us with the unique opportunity to study a closed island population. A spatial simulation model was used to estimate dispersal distances along a coral reef that surrounds the island, while contributions of different nursery bays were determined based on otolith stable isotope signatures of adult reef fish. The model showed that adult dispersal away from reef areas near nursery bays is limited. The results further show that different bays contributed unequally to the adult population on the coral reef, with productivity of juveniles in bay nursery habitat determining the degree of mixing among local populations on the reef and with one highly productive area contributing most to the island’s reef fish population. The contribution of the coral reef as a nursery habitat was minimal, even though it had a much larger surface area. These findings indicate that the geographic distribution of nursery areas and their productivity are important drivers for the spatial distribution patterns of adults on coral reefs. We suggest that limited dispersal of adults on reefs can lead to a source–sink structure in the adult stage, where reefs close to nurseries replenish more isolated reef areas. Understanding these spatial population dynamics of the demersal phase of marine animals is of major importance for the design and placement of marine reserves, as nursery areas contribute differently to maintain adult populations.

Date
2013
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao