Kuramae, A.

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 size-structure. 

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 fisheries-independent research will be needed to answer several critical questions regarding stock status and 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.

The recent status and trends in the Saba Bank fisheries up to and including 2015 port sampling data have been previously reported by de Graaf et al. (2017) and a policy brief has also been written based on those results (Debrot and de Graaf (2018). The purpose of this report is to update recent catch trends in the Saba Bank fisheries with the data from 2016 and 2017.

For the lobster fishery (Panulirus argus), the number of fishing trips (and number of traps set) gradually grew from 2012 to 2015 but has since leveled off. The resulting landings of lobster have shown a similar pattern of increase up to 2015 but have now leveled off at around 70 tons annually. Increasing landings per unit effort indicate that the formerly reduced lobster abundance, which had been declining since 2000 and which had reached its lowest level in 2011, has subsequently increased relatively steadily all through 2017, and now has increased back to levels close to those of 2007. The average size of lobsters taken, continues to be large, which is favourable to gradual stock recovery.

Mixed landings of reef fish in the lobster fishery have fluctuated between 10 and 20 tons annually. The LPUE abundance index in bycatch species also shows a decrease of about 35% from high levels in 2000 and 2007 to lowest levels in 2011, followed by an increase up to 2013, after which landings have levelled off.

In the redfish trap fishery (Lutjanus spp.), the number of trips in the redfish trap fisheries had grown significantly during the period 2012 to 2015. In 2016 effort increased again to 625 trips. In 2017 the exerted fishing effort dropped down to about 350 trips, a level seen last in 2012. The landings of redfish have fluctuated over this period, with lower values in 2012 and 2017 and higher values in 2014 and 2016. The LPUE abundance index shows a decrease by 50% between 2007 and 2011, followed by an increase to slightly higher and constant values between 2012 and 2016, while in 2017 the LPUE abundance index continued increasing. The only snapper for which sufficient data was available, was the silk snapper, Lutjanus vivanus. Average size of the silk snappers landed continued its increasing trend, indicative of gradual stock recovery. The drop in snapper landings, despite the higher LPUE in 2017, can especially be ascribed to the 6-month closed season implemented that year (Graaf et al. 2017).

The overall conclusion is that for both the lobster and redfish stocks, stock status, based on the LPUE index and size-structure trends have continued in developing favorably. Bottom drop longline, pelagic and bycatch landings have remained much less important and have shown no significant new developments.

There are two matters of concern that require follow up. Firstly, the positive prognosis for the snapper “stock” status may partly be based on targeting geographically different stocks as well as different species. Hence the data as collected and analyzed may actually be presenting a too optimistic assessment. To evaluate whether this is actually the case will require more detailed analysis based on individual species, as well as more accurate geographical recording of catches than as currently practiced. The second matter of concern regards the fate of the traps that were in the water on the Bank when the hurricanes Irma and Maria struck the area in September 2017. If trap loss was large, this may lead to higher detrimental impacts of ghost fishing in the coming years.

In this research benthic habitats of the Saba Marine Park were mapped. There were several reasons for an updated benthic habitat map: (1) to compare the current situation to the baseline study carried out in 1992 and identify habitat changes in the past 21 years; (2) to review the zoning plan of the Saba Marine Park for which an accurate habitat map is required to identify suitable zones for marine reserves, anchoring, diving and fishing; (3) to support stratification in fisheries research such as lobster, conch and fish population studies; and (4) to produce value maps as part of the economic valuation study currently taking place on Saba and Sint Eustatius (What’s Saba and Sint Eustatius Nature Worth?) for which habitat maps are necessary to assign monetary value at a spatial scale.
The research questions answered in this study were: (1) which benthic habitats are located where; (2) what are the rough species compositions in these habitats; and (3) what is the structural complexity in these habitats.
Data were collected from video images made with a HD camera, which was dropped from the marine park boat at 276 sample sites. A 150x150m grid was used to select sample sites at regular distances from the shore to the outer boundaries of the marine park. During data analysis three substrate types (sand, rubble and rock) and six benthic species groups (macro algae, sargassum, sea grass, corals, gorgonians and sponges) were identified and percentage coverage of these substrates and benthos were estimated. These percentage coverage were used to classify the samples into ten habitat types according to a pre-defined quantitative classification scheme based on the classification scheme of Caribbean coral reefs by Mumby PJ and Harborne AR (1999)
The resulting habitat map shows that of these ten habitat types only 7 occurred on Saba: bare sand, bare rock, diffuse patch reef, dense patch reef, coral reef, sea grass beds and algae fields. Sargassum fields did not occur, as this species of algae was not found on Saba. Gorgonian reef did not occur, although gorgonians were commonly present at other habitat types, i.e. patch and coral reefs. Bare rubble habitats did also not occur.
Besides the benthic habitat map, two other habitat maps were produced. A reef habitat map including the current zoning plan was produced to compare the zoning system of the Marine Park with the reefs identified in the study. A sand habitat map was produced to further specify the large number of sand habitats in two: bare sand and sand covered with algal and/or cyanobacteria mats. The sand habitat map revealed that sand habitats covered with algal and/or cyanobacteria mats were present around the entire island further ashore, of which the majority was at 30-50 meter depth

Marine habitat map of Saba (GIS)
 

See this report for more info.