Debrot, A.O.

We studied the bird communities of five contrasting semi-natural habitats of Lac Bay, Bonaire, South- eastern Caribbean, during the fall of 2011. A total of 420 point counts were conducted in five different habitats and 63 species were detected. Of these, 31 (49%) were migrants, 24 (38%) were residents, 6 (10%) occurred both as residents and migrants and 2 (3%) were migrants that possibly or irregularly breed. Most migratory species were shorebirds and waders (76%). The bird communities of the ve habitats studied showed signi cant differences in species composition and associated community parameters. Mangrove thicket and salt at habitats had roughly a two-fold higher total species richness and a four-fold higher migratory species richness compared to woodland habitats. In woodland habitats, breeding residents dominated, whereas migratory shore and waterbirds dominated in salt at habitat. The Northern Waterthrush, Parkesia noveboracensis, and Barn Swallow, Hirundo rustica, were the numerically most important migratory passerines. The Reddish Egret, Egretta rufescens, a globally Near-Threatened species, ranked among the top 10 most abundant species of the Lac Bay salt at habitat. Our results suggest that the relatively expansive hypersaline wetlands of Bonaire (of which Lac is only a small part) may be of special signi cance to migratory shore and waterbirds. In contrast to other areas of the Caribbean, invasive exotic birds so far play a minor role in the communities studied. 

From Bonaire, we here provide the first documented case of the green turtle feeding on the invasive seagrass, Halophila stipulacea, in the Caribbean. The seagrass is rapidly invading existing seagrass meadows and altering key foraging habitat of this endangered marine reptile throughout the eastern Caribbean. We expect that more records of green turtles feeding on this invasive species will gradually follow from throughout the region and that the green turtle might alter its foraging behavior in response to the changing species composition of its foraging habitat. 

Event: BirdsCaribbean 21st International Conference, Topes de Collantes, Cuba, 13-17 July, 2017

Abstract in scientific journal or proceedings

Five species of terns are reported breeding in Bonaire from April to August. For three years, the species Sternula antillarum, Sterna hirundo, Thalasseus maximus, Thalasseus eurygnatha and in 2017 Sterna dougalli were monitored in southern Bonaire during the breeding season, with the objective of suggesting management actions and increasing reproductive success. Monitoring results showed that the main threat is the presence of feral cats. The hatching success for Thallasseus species and Sterna species was relatively similar over the years. However, there are indications that hatching success for Sternula antillarum colonies on roads has increased from 17% (2014) to 36% (2016) after a pilot program for management of invasive predators began in 2015. On the other hand, native predators on artificial islands have had negative effects, suggesting that the creation of spaced islands is important to avoid large concentrations in small areas that favor predation.

The Saba Bank is a 2200 km2 shallow bank area that lies fully within the Dutch Kingdom’s Caribbean exclusive economic zone (EEZ) waters. In recent years it has gained international recognition as an area of exceptional biodiversity value and been accorded increasingly higher and more extensive conservation status. For instance, in 2012 it was accorded “Particularly Sensitive Sea Area (PSSA)” status by the International Maritime Organization (IMO) which forbids tanker traffic and in 2015 it became part of the “Yarari Marine Mammal and Shark Sanctuary” emphasizing its value to both endangered cetaceans and sharks.

The nineteen seventies, eighties and early nineties saw extensive overfishing of the bank by foreign vessels with major depletion of its stocks of large groupers and conch. Once the exclusive fishing zone (EFZ) had been claimed in 1993 for the Netherlands Antilles fisheries regulation was enacted and the Coast Guard was established in 1995, foreign illegal, undocumented and unmanaged (IUU) fishing was quickly brought to an end. This allowed renewed local interest in fishing on the bank and has given the bank new ecological perspective.

Today the bank supports two important long-time fisheries operating from Saba. These are a directed fishery for the West-Indian spiny lobster (Panulirus argus) and a “redfish” fishery for deep-water snappers (redfish). Both fisheries are principally based on the use of traps. Pelagic fishing for wahoo and dolphin fish is currently almost negligible, representing only about 2% of total landings by weight. About 60% of the annual commercial effort (in terms of fishing trips) is directed towards the lobster and 40% towards redfish. The total value of the fishery ten years ago amounted to about US$ 1.3 million per year ex-vessel value (Toller & Lundvall, 2008), involved roughly 10 fishing boats and provided direct employment for about 30 persons. In the period 2012-2015 the total fishery landings grew from 78.4 tons to 135.2 tons and still involved 10 boats. This is a major contribution to the local economy of this small island to which by comparison the main economic pillar for future development (nature tourism) contributes US$ 7.6 million annually (Van de Kerkhof et al., 2014).

Recent sightings by fishermen and Saba Bank Management Unit (SBMU) of fishing activities by foreign fishing vessels without commercial or recreational fishing license, (even inside the seasonal closed area during the Red Hind spawning aggregation season) suggest that IUU may again on the rise due to the lack of regular Coast Guard patrols and enforcement.

We here assess the current status of these two main fisheries and report on the monitoring results as funded by the Netherlands Ministry of Economic Affairs and as collected by the SMBU hosted by the Saba Conservation Foundation (SCF ) in collaboration with Wageningen Marine Research (WMR) during the period spanning 2012-2015. In addition, we discuss issues such as reef fish and shark bycatch and the status of the Queen conch stocks of the bank (Lobatus gigas).

Lobster trap fishery: This fishery only began during the 1980s with the advent of tourism on St. Maarten. Lobsters are fished with lobster traps (principally traditional Caribbean arrowhead traps with a modified entrance) up to depths of 45 m. This means that about 84 % of the bank is potentially suitable for this fishery, but only a part of the bank is usually fished. The fishery is strongly seasonal. Highest catches were realized in the months August through January while the lowest catches were made April to July. Egg-bearing (berried) females can be found all year long but there seemed to be a peak in berried females February to May. Recent years (2012-2015) has seen the annual number of traps set from about 48 000 traps set/y to about 73 000/y. The average soak time is 11.6 days and almost all the catch was exported to St. Maarten. Total annual catches in 1999, 2007 and 2012 respectively were estimated to be 62 tons, 92 tons and 36.8 tons. Since 2012 annual catches have steadily increased to about 76.5 tons in 2015. The information and data collected over the 5 years covered by the present study indicate a 50% increase in the effort (in terms of trap drops) of the lobster fishery, with a corresponding doubling in the lobster landings. Standardized catch per unit effort (CPUE) development shows that lobster abundance dropped from higher levels in 2000 to lower levels in 2011, with a progressive increase towards the level of 2007 since then. The observed pattern of catches for the Saba Bank since 2000 appears to mirror regional catch patterns (which are driven by regional recruitment patterns) but not local fishing pressure on the bank.

The average size of landed lobsters appears to have fluctuated between 108 and 118 mm carapace length (CL) since 2000, with no signs of significant decrease in average lobster size landed (which might have suggested overfishing). In fact, the average size of lobsters landed remains consistently high compared to other fisheries of the region. Average size at landing (113 -117 mm) is larger than size at maturity (females = 88 mm; males = 92.2 mm). Additional good news is that the landing of sublegal lobsters (<95 mm CL) has steadily decreased from about 28% in 2012 to about 4% in 2015.

We conclude that overall, based on our current analysis, there appears to be no strong sign of overfishing. We recommend the development of a spiny lobster fishery management plan which defines harvest goals and enforcement strategies that are simple, robust and cost-effective. Options to consider would be limits to the number of fishing licences, the number of traps per fishermen/licence (currently about 300 per fisherman), a total limit to traps deployed in the fishery, registry and visible marking of all traps and trap sets. Effective marking of gear for identification can also help prevent gear loss, and gear theft. The use of escape slots and biodegradable panels is an easy way to help limit negative impacts of gear without major costs. Finally a total quota for the combined catch can serve to cap the total harvest.

It is highly recommended that the management of spiny lobster is aligned with the principles outlined in the lobster conservation and management declaration of the 17 island state Caribbean Regional Fisheries Mechanism (CRFM, Annex 5). The Netherlands could become a member of CRFM for full participation in this regional management mechanism.

Mixed reef fishes: The lobster fishery results in a certain degree of bycatch. Reef fish caught in lobster traps are in part landed for sale, for own consumption, or to serve as food for the spiny lobsters in their holding traps in the harbor. This bycatch is composed of a broad range of reef fish species. The three main reef fish species landed were the queen triggerfish, Balistes vetula, white grunt, Haemulon plumierii and the red hind, Epinephelus guttatus, representing upwards of 50% of the weight of landings. About 33% of the mixed reef fish (by weight) is discarded and mostly consists of nurse sharks, Ginglymostoma cirratum, honeycomb cowfish, Acanthostracion polygonius, cottonwick grunts, Haemulon melanurum and white grunt, H. plumieri. The catches of mixed reef fish have increased from 6.6t to 13.6t between 2012 and 2015, representing on average just under 20% of the overall total catch (all species combined) on Saba Bank. Overall, reef fish yields on Saba Bank appeared to be low compared to other areas. Based on the results from this study, a rough estimate of the yield is between 0.025 and 0.10 t/km2/year. These low yields can in part be due to the low reef fish densities on Saba Bank as estimated in fisheries-independent studies. Lower fish catchability of traps designed for lobsters likely also contributes to lower catches compared to studies using fish traps. The low fish density is unlikely to be caused by current overexploitation but to one or a combination of factors such as a naturally lower biomass of reef fish and losses of habitat for reef fishes due to bleaching-induced coral mortalities.

Redfish fishery: The “redfish” fishery is also largely conducted using traps. These are typically deployed at depths of between 50 en 250 m and catch mainly silk snapper, Lutjanus vivanus (69% by weight), blackfin snapper Lutjanus buccanella (10%), vermillion snapper, Rhomboplites aurorubens (7%), and “others” (14%). In 2000, redfish was exclusively still caught by line. However, by 2007 most snapper was being caught using fish traps and by 2012 there was practically no more line fishing for snapper. These shifts in gear use coincided with a change in fish size, (and species composition) from large adult snapper to smaller sub-adult snapper of about 30 cm fork length. In 2007 the average total trap haul was 28 traps/day while in 2012 it was about 33 traps/day and in 2015 about 25 traps/day. As fishing pressure increased from 2007 to 2012, annual landings seemed to decline from 41.3 tons in 2007 to 34.6 tons in 2012. Since then total landings increased (to 50.5 tons in 2014), but now may have started declining again (39.1 tons in 2015). When looking at CPUE which is an index of population size, it is evident that CPUE (landings) has fluctuated between roughly 2.5-5 kg of snapper per trap, with no appreciable trend. Therefore, the recent changes in total annual catch appear to be largely driven by changes in effort. This peaked in 2014 (at 537 total trips) but was less in 2015 (481 trips). These most recent data hence suggest no worrisome developments for this fishery, other than that the current fish stock is significantly (75%) lower than in the early 1970s “virgin” state. There is currently a small but growing fishery using deep-water long lines to target redfish in deeper waters (average depth: 260 m) where catches are dominated by the wenchman snapper (Pristipomoides aquilonaris) and the queen snapper (Etelis oculatus, sabonechi).

The status of the trap fishery is perceived by the fishers as undesirable with a CPUE 75% lower compared with underexploited conditions. On the 1st April 2017 a six month closed season was implemented through an agreement between fishermen. It is recommended to develop a harvest strategy for the deep-water snapper fishery and ensure that sufficient (on-board) samples are collected.

Shark bycatch

Sharks are considered unwanted bycatch or nuisance in especially the lobster trap fishery. Nurse sharks, were caught in around 60% of the trips using lobster traps but most of the time in low numbers (less than 7 sharks per trips). However for 5% of the trips, large numbers (from 11 up to 71 individuals) were caught. The estimated annual number of discarded nurse sharks varied between 1712 and 2499 individuals, mainly coming from the lobster fishery. Almost all sharks are discarded (alive) and very few sharks were killed and landed. Of 319 trips sampled between 2011 and 2016, a total of 11 landed sharks were observed, most of them from the lobster fishery (7 sharks in 139 samples). Based on our port sampling interviews we estimate that 40 sharks per year (mainly nurse sharks) were landed in the whole Saba Bank fishery. Nevertheless, personal observations during onboard observation show that catches may also amount to tens or even up to 60 sharks per lobster fishing trip (A. Debrot, and J. Odinga, pers. comm.). Further on-board observation is clearly needed to obtain direct figures on shark catch rates. As the Saba Bank is a designated shark sanctuary since August 2015 it is important to work together with the fishermen to fully eliminate all shark taken and ensure that they are released unharmed. The development of nurse shark exclusion devices for the lobster traps would be highly recommended to protect the nurse sharks and to reduce the damage to fishing gear and catch.

Sustainable fish traps

Biodegradable panels: Biodegradable panels did not show any degradation during a 480 daylong experiment but tested panel attachment materials did. Biodegradable panels attached to traps by material with short breakage time (max. 20 days) as required in the current fishery regulations may not be accepted by fishers due to potential loss of catch and time associated with replacing the panels. If the regulations on biodegradable panels is to be maintained, it is recommended to adjust the breakage time to 3-12 months and to clearly describe in the regulations the type and diameter of the material that is to be used to attach the biodegradable panel.

Ghost fishing: In 2012-2015 Saban fishers lost on average 0.6 lobster traps per fishing trip, resulting in ca. 400-600 derelict lobster traps annually. Our experiments show that mortality of reef fish and lobster was low and most fish and lobster appeared to be able to enter and exit the ghost traps freely. Nevertheless, derelict traps kill 2.7 to 7 lobsters and 2.7 - 3.9 kg of reef fish per trap per year. As wire traps continue to ghost fish for roughly two years we estimate the total annual kill by ghost fishing amounts to $23000 - $51000 for reef fish and $46000-$176000 for lobster. Fortunately, simple modification to lobster traps such as correctly functioning escape panels will significantly reduce mortality from ghost fishing. Our studies show that the average deterioration time in days (including range between brackets) for escape panels attached with hemp and cotton is respectively, 105 (85-114), 150 (128-241). All other options such as wire or hog rings lasted more than twice as long and are not recommended.

Escape slots: We examined the effects of biodegradable panels with 2 trap design (5ft D-type traps and 4ft M-type traps) as well as the effect of 25 and 38 mm escape slots on reef fish bycatch and sub-adult snapper catches. Trap type did not affect the average number of lobsters or fish caught per trap. The only exception was for the white grunt for which the catch rates were markedly higher in the larger D-traps. However catch rates in terms of weight of bycatch were almost double for the type D-traps with 25mm escape vents compared with the control traps. This difference was mainly due to an increase in the catch rate of species of intermediate economic value. So the larger 5 ft D-traps catch no more lobster but do catch a lot more bycatch. Hence the larger D-type traps are not recommended.

Lobster traps: Our results indicate that both trap types with escape slot had higher catch rates for lobster than the control traps. There was a significant difference of 0.55 lobster per trap for the experiment with the 38 mm escape vent. The difference for the 25 mm escape slot was not significant (0.20 lobster per trap). The results suggest that crowding with fish reduces lobster entry into traps. It was different for reef fish bycatch. Escape slots of 25 mm greatly increased the catch rate of bycatch species like grunts. In contrast, the 38 mm escape vent reduced the catch rates of bycatch substantially; by about 60% for the D-type traps, and 80% for the M-type traps.

The most important result of these experiment is the observation that both 25mm and 38 mm escape slots and trap size (4ft M-trap or 5ft-D traps) appeared to have little negative effect on lobster catches. The traps with 38 mm escape slots even caught significantly more lobsters (ca. 0.5 lobsters per trap). Therefore, the bycatch of mixed reef fish in the lobster trap fishery could be limited by regulating trap size and the use of escape slots. Reducing trap size and/or implementing 38 mm escape slots will drastically reduce the amount of mixed reef fish without impacting (possibly even improving) the catch of lobster, the main target species.

Snapper traps: Escape vents of 25 mm seem to increase snapper catch rate by about 20% (though not statistically significant). In contrast, escape vents of 38 mm greatly reduced snapper catches. A 25 mm escape vent also increased the proportion of vermillion snapper in the catch. Based on studies elsewhere, Johnson (2010) reported an increase in average size of (reef) fish in traps fitted with 25 mm escape vents. Our experiments indicated that the 25 mm escape slot did function as intended and did not reduce the proportion of sub adult silk snappers.

So as for the effect of escape slots on fish catch the results are consistent: the 25 mm vent increases fish catch while the 38 mm slot lets almost all fish escape and yields low catches. We suggest that this might mean that when traps become too crowded, less fish will enter. By using 25 mm escape vents, small, non-target species easily escape thereby creating more room in the trap for target species.

Whales and dolphins

The cetacean sighting frequency for Saba bank fishing trips amounted to an average of one sighting for every 13.2 trips. Between 2012 and 2016 a total of 142 sightings were generated. Only 25% of whale sightings and 8% of dolphin sightings allowed reliable species identification. Of the 25% of confirmed whale sightings 23% concerned the humpback whale and 2% the sperm whale. While the collected data provide some indication of the presence of cetaceans on and around the bank, clearly, there is much room for improvement of baseline data collection.

Queen conch

After the de facto (but not formal) closure of the conch fishery on the Saba Bank in the mid-1990s, the queen conch population has recovered. Out of the 131 transects conducted during our video survey, adult conch were found in 91 transects, ranging from 16 conch/ha to 882 conch/ha (mean 130.8 conch/ha, 99.7–161.8 95% CI). In 52 transects (40 % of all transects) more than 100 conch/ha were found. So maybe 800 km2 or more of the Saba Bank have conch densities that could justify a limited fishery. Adult queen conch were found at depths of 17 to 58 m, with highest densities documented at 22m. Mating success in queen conch is density dependent and studies recommended that a mean density of 100 adult conch/ha should be the minimum to avoid the risk that recruitment might be impaired. This means that at present a controlled limited fishery should well be possible, if judiciously controlled and regulated. Based on our data, an estimated 14 million adult queen conch are currently present on the Saba Bank in the 20-40 depth zone.

A sustainable annual quota could be set ca. 1 million adult queen conch (ca. 8 % of the adult population). If a fishery is re-opened, it is recommended to: 1) introduce a minimum legal size at 10mm lip thickness and an annual closed season during May-September, 2) ensure that queen conch are landed with shell, 3) regular stock assessment are conducted to adjust the quota and avoid recruitment impairment, 4) identify and open only those areas to the fishery where densities are high enough, 5) set strict regulations on harvesting methods to prevent development of dangerous ‘hookah’ fishing practices. Any development of a conch fishery will take time as both bringing the species in from the sea to land and export will require permits.

Lionfish

Based on observations, it appears that the invasive lionfish first arrived on the Saba Bank between 2008 and 2011. Since then it has spread and is a frequent bycatch species in redfish and lobster traps. Our data show that it had much higher catch rates in the deeper waters during fishing for redfish. Average catches in the last three years amount to about 1 lionfish for every one or two snapper traps hauled. The availability of lionfish bycatch has led to a local market arising. Based on this, several fishermen have expressed interest in testing special traps which concentrate and trap lionfish and may allow the development of a directed deep-water lionfish fishery.  

The avifauna of the Dutch Caribbean island of St. Eustatius has been little studied. We document 22 new bird species for the island and update the status of several important species based on our recent observations. The documented avifauna of the island amounts to 75 published species records. We conclude by pointing out several positive developments in the avifauna and ascribe these to the combined effects of reduced hunting, the legal establishment of protected park areas, and a growing environmental awareness among the island’s inhabitants.

The shallow marine habitats surrounding St. Eustatius fulfil critical ecosystem services in terms of fishery production, recreation, dive tourism and coastal protection. In this a key role is played by the fish communities. In this report we document the relative finfish community composition, density and distribution in the shallow coastal waters of the St. Eustatius Marine Park based on 104 baited video stations distributed among two management sectors and five habitat classes ranging in depths from 8-30 m. In doing so we introduced to the Dutch Caribbean the use of a technology-based method that provides more precise length data than common visual transects, is applicable to wide range of depths and sampling conditions, and is more sensitive for detecting and monitoring apex (top) predatory fish species such as shark.

Compared to earlier survey results our findings highlight the virtual disappearance of large grouper species from the reefs of St. Eustatius. The natural absence of mangrove nursery habitat is one key driver of fish community structure in St. Eustatius and the loss of former seagrass beds is a second key factor probably accounting for the lack of typical mangrove and seagrass-associated scarids (e.g. Scarus coeruleus and guacamaia), snappers (e.g. Lutjanus apodus and griseus) and grunts (e.g. Haemulon sciurus).

The most important local determinant of fish community structure was found to be habitat three- dimensional structure while the measured effect of designated fishing reserve zones was much less pronounced. Nevertheless, mean overall fish size was slightly higher in the fishing reserves. However, our community sampling was insufficient to meaningfully compare densities and size structure of main commercial target species. Community abundance of planktivores and herbivores were notably inversely related, with low-structured sandy habitat being dominated by planktivores and higher-structured hard- bottoms being dominated by herbivores. Low-structured habitat which offered little critical shelter to small fish had the highest mean fish size of all five habitats.

Our results indicate a relatively low quantifiable effect of the present fishing reserves. This may have to do with either or a combination of a) low finfish fishing effort and/or low fishing selectivity, b) problems in the enforcement of the fishing reserves or, c) geographic scale issues due to the movement of fish between defined zones which act to blur potential effects of stated management regimes, and finally our sampling design as a fish community baseline lacking focus on targeted commercial species. Further directed research is needed to properly evaluate and enhance the functioning of the marine park reserves which are accorded an important role in the future socio-economic development of St. Eustatius.

The reefs of St. Eustatius are characterised by very low levels of three-dimensional structure (Risk’s Index: 1-1.3, see Debrot et al. 2014), which was found to be the most important local determinant of fish abundance and distribution. The potential for habitat enhancement to jointly help achieve fishery and conservation goals seems evident. We recommend that measures to enhance such three- dimensional structure may be useful to help increase fish abundance to the benefit of both fishing and biodiversity stakeholders such as the conservation, dive and tourism sectors.

The relatively high presence of sharks (Caribbean reef sharks and nurse sharks) around St. Eustatius is encouraging in the context of conservation, valuable for dive tourism, and interesting for research. As top predators, these sharks play an important ecological role in healthy reefs and their higher abundance around St Eustatius compared to most other areas of the Caribbean may contribute to and be a useful indicator of overall coastal ecosystem health. Further studies of these important species are called for.

Report number C058/15 5 of 49

Our assessment of the use of the BRUV method for fish community assessment showed that, due to the deployment strategy used, our test power to detect changes in both numerical and species changes in the communities studies was relatively low. A combination of extensive BRUV surveys (once every 3 years) in combination with yearly fish surveys (i.e. protocol Global Coral Reef Monitoring Network) at a small number of permanent sites with high structural complexity is recommended to ensure the timely detection of trends in reef fish populations. 

In 2013, the invasive Giant African Land Snail, Achatina fulica was found in a small part of urban St. Eustatius. In collaboration with local government agencies and Dutch universities we conducted field and laboratory pilot trials of control methods from October 2015 to June 2016. From the initial two gardens in 2013, the species has since been confirmed in 37 gardens encompassing an epicentre of about 100 lots in the Bay Brow area. During the study period, application of eco-friendly iron-phosphate snail bait successfully prevented further spread into adjacent buffer-zone monitoring areas. Iron-phosphate snail bait was effective in greatly reducing snail population density. It was applied once a week at an average density of 0.7 g/m2 at garden level, but was concentrated in hotspot snail habitat areas. Nevertheless, hand picking, which is more labour intensive and gives more variable results, also appeared effective in reducing snail density. Finally, beached Sargassum seaweed, brought forth as a snail deterrent used on neighbouring islands, did not measurably kill snails above zero control levels, and we conclude that seaweed is unlikely to be effective in snail control. 

A semi-detailed landscape-based vegetation map (scale: 1: 37,500) is presented for the 13 km2 Lesser Antillean steep volcanic island of Saba, Netherlands Caribbean. The map is based on a total of 49 vegetation plots that were sampled in 1999 using a stratified random sampling design and analysed using TWINSPAN cluster analysis. Three hundred and fourteen (314) plant species, representing 56% of the total known flora (565 species), were recorded in the sample plots. The principal lower sections of the island possess a tropical savannah climate whereas the upper slopes reaching a maximum altitude of 870 m can best be characterized as a tropical rainforest climate.
A total of two main and nine different sub-landscape types were distinguished based on geology, geomorphology and nine distinguished vegetation types. In Saba, sharp contrasts in soil, geomorphology and climatic factors are found on a small spatial scale and this meant that compared to the other islands of the Dutch Caribbean there is little mixing and merging of vegetation types at the landscape vegetation level. Consequently, vegetation type translates relatively directly into landscape vegetation units. Aside from important contrasts in vegetation that correspond to what is known about differences in soil and climate, our study also shows that large vegetation changes have taken place on the island since the survey by STOFFERS, five decades earlier. These largely appear to be due to three major forces: a) hurricane impacts; b) natural succession made possible due to diminished agricultural activity and; c) invasive plants and plant pest species.
The most recent hurricane, hurricane Georges, which struck the island one year before this study, clearly caused much damage to the vegetation, especially high on Mount Scenery. As a consequence, the elfin woodland vegetation has virtually disappeared, while remnant sections have been radically altered. Based on studies elsewhere in the region, the elfin woodland can be expected to take very long (if at all) to gradually recover. The impact of various hurricanes in the last 60 years has clearly caused major disturbance of the vegetation throwing it back into earlier stages of succession. The development of the “Tree fern brake” into “Pioneer forest” vegetation must be seen as a positive change where a secondary community had entered a higher stage in the sequence of succession. The virtual disappearance of the formerly prominent secondary shrub communities like Miconia thickets, Piper dilatatum thickets and Leucaena thickets can also be seen as likely evidence of natural successional forces thanks to diminished agriculture and woodcutting. Invasive species was the third major force of change that clearly appears to have been active on Saba in recent decades. The lasting impacts of insect invaders which have decimated formerly prominent Opuntia (cactus) and Tabebuia (tree) populations testify to the impact of invasive species as a major driver of recent vegetation changes on Saba.
Our field data show that most wilderness areas of Saba remain strongly affected by roaming grazing goats even though the contribution of goats to the local island economy is negligible. Goat dung or traces of grazing were recorded in or adjacent to 46% of the sample plots. Grazing by exotic mammals reduces the resilience of natural vegetation types and interferes with natural succession. Highest livestock densities and impacts seem to be in the more vulnerable coastal arid zones along the western and southern sections of the island with poor soil conditions and more open and shrubby vegetation. The development of ‘Dry evergreen woodland’ under similar conditions on the more remote, windy and salt spray-affected, but less-grazed, northern sectors of the island, suggest that those disturbed areas of the southern and western coastal zones should have potential for woodland recovery if and when goat grazing is reduced. Therefore, a key priority for terrestrial conservation in Saba should be to reduce feral grazer densities to allow vegetation recovery and reduce vulnerability to erosion. We suggest the use of pilot demonstration projects for grazer exclusion as a useful way to help build stronger arguments and public support for tackling the roaming goat problem in Saba.

Presentation summarizing results of MSc theses of various students

Abstract

We provide the first documentation of Southern Lapwing (Vanellus chilensis) breeding in the Dutch Caribbean and new island records for the Caribbean Martin (Progne dominicensis) and Killdeer (Charadrius vociferus).