Toller, W.

Recent investigations of Saba Bank, Netherlands Antilles, have sought to develop inventories of marine biodiversity from this large, submerged coral reef atoll. Previous fish species inventories were compiled from underwater visual surveys and poison-based collections (RAP Survey Report, 2006), generating a list of more than 200 taxa (J. Williams, pers. com.). In June of 2007, a six-month port sampling study was initiated to examine landings of the Saba Bank commercial fishery. Port samples of finfish catch and bycatch produced novel fish species records for Saba Bank. These observations make a much needed addition to previous species inventories because they include records for fishes of commercial significance. The purpose of this note is to give a brief written and photographic account of new fish records from the Saba Bank commercial fishery. New species records from underwater surveys and observations from experimental trap fishing of Saba Bank are included as well.

The commercial fishery of Saba Bank, Netherlands Antilles, was assessed for six months from June 1 through November 30, 2007, by conducting port sampling interviews with Saban commercial fishermen to obtain information on fishing effort, gear usage, landings and species composition of catches. Results from our survey are compared to previous studies to provide an updated assessment of the Saba Bank commercial fishery.
 
The fishery can be summarized as follows. A small fishing fleet of approximately ten vessels operates from Fort Bay, Saba Island, and conducts small-scale commercial fishing on Saba Bank. Saban commercial fishermen may participate in either or both of two distinct types of fisheries: a lobster trap fishery and a “redfish” trap fishery. The two trap fisheries account for almost all commercial landings while other fishing methods (e.g. hook & line) make only a minor contribution to total landings from Saba Bank. Specific patterns of effort, landings and catch composition are identified within each trap fishery.
 
Lobster trap fishing is the more prevalent and economically significant Saba Bank fishery. Lobster catch rate is 0.84 lobster per trap-haul and 184 pounds per trip. Catch rates vary significantly with season. Projected annual lobster landings are 184,000 lbs (83.6 mt) with an exvessel value of US $1.3 million per year. The lobster trap fishery also harvests a diversity of “mixed fish” (shallow water reef fishes). Average catch rate of mixed fish is 0.5 pounds per traphaul and 37.8 pounds per trip, with projected annual mixed fish landings of 37,700 pounds (17.1 mt) at an ex-vessel value of US $68,700 per year.
 
The fish trap fishery targets “redfish” - an assortment of deepwater snapper species that is dominated by silk snapper, blackfin snapper, and vermilion snapper. These three lutjanid species comprise > 91 % of fish trap catch. Average catch rate of redfish in fish traps is 10 pounds per trap-haul, and 291 pounds per trip. Projected annual fish trap landings of redfish are 90,800 pounds (41.3 mt) with an ex-vessel value of US $289,000 per year. Fish trap landings also include a small quantity of mixed fish (< 9 % by weight of finfish in fish trap landings) comprised of a diversity of species but dominated by red hind and lane snapper. Catch rate of mixed fish in fish traps is 1 pound per trap haul and 27 pounds per trip.
 
Viewed as a whole, 2007 landings from Saba Bank by Saban commercial fishermen are projected to exceed 145 metric tons in 2007 with an ex-vessel value greater than US $1.6 million. Comparison to previous fisheries studies indicates that the Saba Bank commercial fishery is relatively stable in terms of total fishing effort, total landings, economic value, and fishing methods. The following trends were identified. Compared to 1999-2000, lobster catch rate in 2007 was approximately 33 % lower in terms of weight per trap-day, but there was only a small (6.3 %) reduction in total landings of lobster. A shift to smaller lobster size was not indicated by length frequencies: average carapace length was larger in 2007 (11.2 cm) than in 1999-2000 (10.7 cm). However, lobster fishing effort as measured by trap haul rate was 31 % greater in 2007 (80.9 trap-hauls per trip) than in 1999-2000 (62.0 trap-hauls per trip). We estimate that the total number of lobster traps in use on Saba Bank increased from 1,426 traps in 1999-2000 to 1,862 traps in 2007. Collectively, these findings indicate that Saba Bank fishermen of 2007 exert a greater fishing effort in order to maintain lobster landings at year 2000 levels. An increase in fishing effort coupled with a decrease in observed catch rate could suggest that lobster harvests are now at or exceed the maximum sustainable yield for Saba Bank stocks. However, more definitive conclusions about trends in lobster stock abundance are not possible owing to the limited time frame of available fisheries data sets.
 
The importance of redfish, as a percentage of total annual landings, has increased by three-fold since 2000. Yet, the Saba Bank redfish fishery is characterized by a lack of information. Stock densities are either unknown, or may be based on very optimistic calculations. The commercial fishery now harvests redfish primarily with fish traps, in contrast to hook & line fishing methods that predominated in 2000. Given that stock size remains poorly known, the current practice of harvesting almost exclusively juvenile fishes is a risky fisheries strategy. If reproductive output by silk snapper stocks is sufficiently reduced by harvesting it may lead to abrupt population declines or even a stock crash.
 
We recommend that the following actions should be priorities for management of Saba Bank fisheries resources: establishment of a program for long-term commercial fisheries monitoring, elimination of anchoring by large vessels on Saba Bank, development of a framework for monitoring and regulating the harvest of deepwater snappers, implementation of conservation measures to protect a red hind spawning aggregation, and initiation of a study to evaluate ghost fishing by lost traps.

A small submersible remotely operated vehicle (ROV) was used to explore mid-depth habitats of Saba Bank – a submerged carbonate platform in the northeastern Caribbean Sea. The ROV enabled observation and specimen collection to greater depths (40 to > 150 m) than possible with conventional scuba methods. The topography, substrate, benthic communities and fish assemblages of a prominent front reef system at Overall Bank were examined in some detail. Observations made from ROV indicate that substrate and benthic communities show consistent zonation patterns along the depth gradient of the front reef slope. A transition in the reef fish assemblage was also evident, though less pronounced, along this same depth gradient. Fish diversity (number of species observed per survey) was greatest in the reef crest zone and declined with depth, however sightings of commercially important lutjanids species such as silk and blackfin snapper increased with depth. Significant cover by reef-building corals (i.e. constructional reef development) was only evident in the reef crest zone, and terminated at 38 to 42 m depth. Substrate of the transition slope zone, from 42 m to 75 m depth, was primarily a hard bottom consisting of consolidated reef structures and rubble with sand interspersed. Sponges, gorgonians and macro algae dominated the benthic community there. In the deep slope zone (> 75 m depth), a soft bottom substrate predominated that was composed of fine, readily resuspended sediments together with scattered rubble fragments. Benthic invertebrates were very sparse in the deep slope zone. In addition to the surveys at Overall Bank, four ROV surveys were made at two other Saba Bank areas: Poison Bank and Grapplers Bank. The substrate at Poison Bank was comprised of coralline algal nodules or “rhodoliths” which formed extensive rhodoliths beds. At Grapplers Bank, a steep rocky escarpment was explored. The near-vertical rocky scarp began at 120 m depth and extended down slope beyond the limits of the ROV survey (157 m depth). Observations made from ROV at Overall Bank suggested a continuous reef system that is relatively uniform and predictable at mid-depths in terms of its structure, substrate composition, and community zonation patterns. In contrast, the few observations made by ROV at Poison Bank and Grapplers Bank revealed habitats that were quite different from those at Overall Bank. This implies that future ROV explorations to new areas of Saba Bank are likely to reveal still greater diversity in mid-depth habitat types.

Saba Bank is a large and completely submerged carbonate platform in the northeastern Caribbean Sea located approximately 4 km southwest of Saba Island, Netherlands Antilles. Zonation patterns of reef-like bathymetric features, together with observations of significant shelf edge coral reef development, suggest that Saba Bank is an actively growing coral reef atoll. Little quantitative data exists to evaluate the composition and distribution of marine benthic communities or fish assemblages of Saba Bank. In the present study, habitat surveys were conducted to investigate the abiotic characteristics, benthic community composition, and fish assemblage structure of habitats from an eastern portion of Saba Bank known as Overall Bank. A random stratified sampling design was developed that utilized remote sensing data for bathymetry and ocean color superimposed on reef zones. Five sampling strata, which putatively delineated five distinct marine habitat types, were identified along a shelf edge-to-lagoon gradient. Survey results indicate that the proposed strata correspond to distinct marine habitat types in terms of substrate composition, benthic cover, and dominant macro algae. Significant coral cover was restricted to the outer reef edge in the fore reef habitat (11.5 %) and outer reef flat (2.4 %), declining to near absence in the lagoon habitats towards the bank center. Macro algae dominated benthic cover in all habitats (32.5 – 48.1 % cover) with the composition of dominant algal genera differing among habitats. Gorgonians reached their highest density and greatest average colony height in the fore reef zone. Gorgonian colony height was also pronounced in softbottom habitats of the lagoon. Fish assemblage structure showed patterns that were concurrent with observed habitat zonation. Highest fish densities were observed in the outer reef flat, fore reef, and inner reef flat zones. Fish abundance and diversity was low in the lagoon zone and lowest over softbottom habitats within the lagoon. The greatest diversity of fishes (average number of species per survey, cumulative number of species) occurred in the fore reef zone and outer reef flat zone. Fish biomass followed the same pattern of distribution, with the greatest weight occurring in the outermost zones and least in the lagoon. Queen conch were most frequently encountered in the softbottom lagoon zone and estimates of average conch density were between 42 and 60 individuals per hectare. Abundance of spiny lobster was not adequately surveyed by the methods employed in this study and recommendations are made for improved field assessment of lobster stocks. Collectively, the results of this study indicate that the benthic communities of Saba Bank follow predictable patterns of distribution, diversity, and abundance across a gradient from shelf edge to lagoon. Recommendations for future research are given. 

Abstract:

Biodiversity surveys were conducted on Saba Bank, Netherlands Antilles, to assess ichthyofaunal richness and to compare with published surveys of other Caribbean localities. The primary objective was to estimate the total species richness of the Saba Bank ichthyofauna. A variety of sampling techniques was utilized to survey the fish species of both the visually accessible megafauna and the camouflaged and small-sized species comprising the cryptic ichthyofauna. Based on results presented herein, the number of species known on Saba Bank is increased from 42 previously known species to 270 species. Expected species-accumulation curves demonstrate that the current estimate of species richness of fishes for Saba Bank under represents the actual richness, and our knowledge of the ichthyofauna has not plateaued. The total expected fish species richness may be somewhere between 320 and 411 species. The Saba Bank ichthyofaunal assemblage is compared to fish assemblages found elsewhere in the Caribbean. Despite the absence of shallow or emergent shore habitats like mangroves, Saba Bank ranks as having the eighth highest ichthyofaunal richness of surveyed localities in the Greater Caribbean. Some degree of habitat heterogeneity was evident. Fore-reef, patch-reef, and lagoonal habitats were sampled. Fish assemblages were significantly different between habitats. Species richness was highest on the fore reef, but 11 species were found only at lagoonal sites. A comprehensive, annotated list of the fishes currently known to occur on Saba Bank, Netherland Antilles, is provided and color photographs of freshly collected specimens are presented for 165 of the listed species of Saba Bank fishes to facilitate identification and taxonomic comparison with similar taxa at other localities. Coloration of some species is shown for the first time. Preliminary analysis indicates that at least six undescribed new species were collected during the survey and these are indicated in the annotated list. 

Saba Bank is a 2,200 km2 submerged carbonate platform in the northeastern Caribbean Sea off Saba Island, Netherlands Antilles. The presence of reef-like geomorphic features and significant shelf edge coral development on Saba Bank have led to the conclusion that it is an actively growing, though wholly submerged, coral reef atoll. However, little information exists on the composition of benthic communities or associated reef fish assemblages of Saba Bank. We selected a 40 km2 area of the bank for an exploratory study. Habitat and reef fish assemblages were investigated in five shallow-water benthic habitat types that form a gradient from Saba Bank shelf edge to lagoon. Significant coral cover was restricted to fore reef habitat (average cover 11.5%) and outer reef flat habitat (2.4%) and declined to near zero in habitats of the central lagoon zone. Macroalgae dominated benthic cover in all habitats (average cover: 32.5 – 48.1%) but dominant algal genera differed among habitats. A total of 97 fish species were recorded. The composition of Saba Bank fish assemblages differed among habitat types. Highest fish density and diversity occurred in the outer reef flat, fore reef and inner reef flat habitats. Biomass estimates for commercially valued species in the reef zone (fore reef and reef flat habitats) ranged between 52 and 83 g/m2 . The composition of Saba Bank fish assemblages reflects the absence of important nursery habitats, as well as the effects of past fishing. The relatively high abundance of large predatory fish (i.e. groupers and sharks), which is generally considered an indicator of good ecosystem health for tropical reef systems, shows that an intact trophic network is still present on Saba Bank