Adolphe O. Debrot

Case study of a Rapid Response Removal Campaign for the invasive alien green iguana, Iguana iguana

Abstract

The Invasive Alien Green Iguana (IAGI), Iguana iguana, has spread worldwide via the pet trade, as stowaways and via other means and has become a pest species of global concern. It also represents a major threat to the endemic Lesser Antillean Iguana, Iguana delicatissima, on St. Eustatius. Following the capture of an adult female IAGI on St. Eustatius in early 2016, we conducted a Rapid Response Removal Campaign (RC) from April 2016 to January 2017. Three sets of directed visual surveys totaling 409.5 observer hours and covering a combined trajectory of 114.2 km realized only a single detection of a hybrid that was later removed. During the remainder of the campaign period, an additional four IAGI hybrids were opportunistically detected and removed thanks to park staff or community involvement. Since the end of the campaign, eight additional detections and removals have been realized, three of which were IAGIs caught while offloading freight in the harbour and five of which were hybrids caught in surrounding suburban areas. We suggest that at least four distinct IAGI introductions to St. Eustatius occurred between 2013 and 2020. Our results show the value of motivating and mobilizing stakeholders and the public at an early stage of an invasion. Since the program’s initiation, eight of the 13 iguanas detected for culling were thanks to public and key stakeholder support and involvement. Four years after our campaign, the number of IAGIs and their hybrids still appear to be limited and concentrated in and around inhabited areas. Additional removal campaigns should be initiated as soon as possible, firmly based in public outreach, motivation and engagement. New legislation is needed to prohibit the importation, possession and harbouring of IAGIs or hybrids and to provide a framework for long-term structural funding required for effective control and removal. Routine fumigation and rigorous inspection of arriving cargo to eliminate the risk of stowaway IAGIs are also recommended. Culling of IAGIs is recommended for the port of St. Maarten, which serves as a major point of dispersal of IAGIs to St. Eustatius and likely also other islands in the region.

Date
2022
Data type
Scientific article
Geographic location
St. Eustatius

High peak settlement of Diadema antillarum on different artificial collectors in the Eastern Caribbean

The massive die-off of the herbivorous sea urchin Diadema antillarum in 1983 and 1984 resulted in phase shifts on Caribbean coral reefs, where macroalgae replaced coral as the most dominant benthic group. Since then, D. antillarum recovery has been slow to non-existent on most reefs. Studying settlement rates can provide insight into the mechanisms constraining the recovery of D. antillarum, while efficient settlement collectors can be used to identify locations with high settlement rates and to collect settlers for restoration practices. The aim of this study was to compare pre and post die-off settlement rates and to determine possible settlement peaks in the Eastern Caribbean island of St. Eustatius. Additionally, we aimed to determine the effectiveness and reproducibility of five different settlement collectors for D. antillarum. D. antillarum settlement around St. Eustatius was highest in May, June and August and low during the rest of the study. Before the die-off, settlement recorded for Curaçao was high throughout the year and was characterized by multiple settlement peaks. Even though peak settlement rates in this study were in the same order of magnitude as in Curaçao before the die-off, overall yearly settlement rates around St. Eustatius were still lower. As no juvenile or adult D. antillarum were observed on the reefs around the settlement collectors, it is likely that other factors are hindering the recovery of the island's D. antillarum populations. Of all five materials tested, bio ball collectors were the most effective and reproducible method to monitor D. antillarum settlement. Panels yielded the least numbers of settlers, which can partly be explained by their position close to the seabed. Settler collection was higher in mid-water layers compared to close to the bottom and maximized when strings of bio balls were used instead of clumps. We recommend research into the feasibility of aiding D. antillarum recovery by providing suitable settlement substrate during the peak of the settlement season and adequate shelter to increase post-settlement survival of settlers. The bio ball collectors could serve as a suitable settlement substrate for this new approach of assisted natural recovery.

Date
2022
Data type
Scientific article
Theme
Education and outreach
Research and monitoring
Geographic location
St. Eustatius

Establishment of two nonnative parthenogenetic reptiles on Saba, Dutch Caribbean: Gymnophthalmus underwoodi and Indotyphlops braminus

The native herpetofauna of the Lesser Antillean island of Saba (13 km2; 17.63°N, -63.24°W) includes one snake, Alsophis rufiventris, and four species of lizards, Anolis sabanus, Iguana melanoderma, Sphaerodactylus sabanus, and Thecadatylus rapicauda (Powell et al. 2015). Here, we report the establishment of both Gymnophthalmus underwoo-di Grant, 1958 and Indotyphlops braminus (Daudin, 1803) on the island.

 

Date
2021
Data type
Scientific article
Theme
Education and outreach
Research and monitoring
Geographic location
Saba

Assessing effectiveness of the seasonal closure of the Moonfish Bank of the Saba Bank for two species of concern, the Red Hind and the Queen Triggerfish: the first five years

Summary

Based on traditional knowledge of the Saban fishermen, a spawning aggregation area (SPAG) for the Red Hind (Epinephelus guttatus) and the Queen Triggerfish (Balistes vetula) has long been known at the northeast end of the Saba Bank, locally known as the Moonfish Bank. SPAG’s are very vulnerable to overfishing because these fish aggregations are predictable in space and time. Both are species of special concern throughout the wider Caribbean, due to overfishing. In 2013 a 5-year seasonal closure was arranged that prohibited fishing the Moonfish Bank from the 1st of December to 28th of February, within which, according to local knowledge, mass spawning takes place. The closure ended in February 2018. In this report we provide a preliminary evaluation of the effect of this 5-year seasonal closure on Red Hind and Queen Triggerfish populations of the Saba Bank based on the monitoring of fishes landed in the Saba Port in those 5 years, throughout the year. For both focal species we examined annual differences in the length-frequency distributions and Landings Per Trip (LPT; number of fish landed per fishing trip) from bycatches in both shallow (~30 m) lobster traps and deep (~100 m) snapper trap fisheries, using port landing data from 2011, which is prior to implementation of the closure measure in 2013, until September 2018.

Our preliminary assessment by means of Generalized Linear Model (GLM) analysis gives no indication of any improvement in LPT or mean size caught for either of the two species examined since the seasonal closure was initiated in 2013. Results even suggest a small but significant decrease in the size of Red Hinds caught as by catch in the lobster pot fishery. This means that, based on the port sampling method used, no significant positive effect on the Red Hind and Queen Triggerfish populations of the 5-year closure can yet be demonstrated. There are many possible explanations for this result, which are presented in the discussion. In particular, there is reason to believe that the current closure area may not be large enough to properly protect the Moonfish Bank SPAG and that there likely are other SPAG’s on the Saba Bank that may also need protection. Therefore, further fisheries-independent research on these and other matters is needed on which basis it may be possible to improve protection so that positive evidence of the effectiveness of the closure may be documented in the future.

Based on fisheries-independent visual diver surveys in the shallow (~ 20m depth) coral reef zone of the Saba Bank edges in 2011, 2013 and 2015, the current population status of our focal species (in that limited habitat zone of the Bank) is as follows: Red Hinds averaged 118.7 ± 53.5 (ind. ha-1 ) with a mean size of about 24 cm, while Queen Triggerfish averaged 56.0 ± 37.6 (ind. ha-1 ) with a median size of about 29 cm (data of 2011, 2013 and 2015 combined). For both focal species, the median size landed in the fishery (Red Hind: about 31 or 33 cm depending on the type of fishery pots; Queen Triggerfish: 34 cm) was considerably larger than the mean size of the population on the reef based on surveys along the available coral reef transects. This is generally to be expected as fishing gears and fisheries typically select for larger individuals. We cautiously suggest that compared to many other areas in the Caribbean (e.g. Bonaire and Curaçao) where the Red Hind and the Queen Triggerfish once were common but now have disappeared, the populations of both these species living in the shallow coral reefs of the Saba Bank still seem relatively healthy in terms of both population density and sizestructure. Based on experiences elsewhere in the region, there is no question that protection of spawning aggregations is a basic need for sustainable management and fishery production in mass-spawning species. Therefore, our main management recommendation is that the closure should continue. However, to reliably asses the effect of seasonal closure and to further improve protection of the spawning grounds for these species, more intensive and consistent data is needed from port sampling which should also (minimally) include data on sex and maturity of the landed fish, even though such data fall outside the typical scope of routine fisheries port sampling. Most critically, directed fisheriesindependent research will be needed to answer several critical questions regarding stock status and Wageningen Marine Research report C040/20 | 5 of 40 when and where spawning aggregations are actually taking place, to improve the effectiveness of seasonal closures of spawning areas of Red Hind and Queen Triggerfish on the Saba Bank.

 

 

Referenced in BioNews 38 Article "Protecting Saba Bank’s Red Hind and Queen Triggerfish Populations"

Date
2020
Data type
Research report
Theme
Education and outreach
Research and monitoring
Report number
Wageningen University & Research report C040/20
Geographic location
Saba bank