Status and trends in Saba Bank fisheries: Analysis of fisheries data collected over the period 2011-2020
This report is an update of earlier published reports on the status and trends in the of Saba Bank fisheries (Graaf et al. 2017, Brunel et al. 2018). The new analyses presented here are based on three additional years (2018-2020) of data collected by the Saba Bank Management Unit.
After a period of increase from 2012 to 2015, fishing effort in the lobster fishery (Panulirus argus), has gradually declined in subsequent years, with nearly a halving of the effort between 2015 and 2020. The resulting landings of lobster have shown a similar pattern with an increase up to 2015 when they amounted to 78t, and, after a period of relative stability in 2016-2017, showed a marked decline to 27t in 2018, before partial recovery in 2019 and 2020. Increasing landings per unit effort (number per trip) indicate that the formerly reduced lobster abundance, which had been declining since 2000 and which reached its lowest level in 2011, has subsequently increased relatively steadily all through 2020, back to levels close to those of 2007. Length based proxies for exploitation level with respect to MSY suggest that there has been overfishing of the stock (F/FMSY >1) for all the period covered by the data, and the mean size of the lobsters landed has been decreasing over the last 5 years.
Lobster fishery fish bycatch
Mixed landings of reef fish in the lobster fishery have fluctuated between 7 and 15t annually. The biomass index derived from the LPUE of these bycatch species also shows a decrease of about 35% from high levels in 2000 and 2007 to lowest levels in 2011. After a partial recovery from 2011 to 2013, the biomass declined slowly until 2018, and then rose sharply in 2019. Among the three main species landed, two - the Queen triggerfish, Balistes vetula, and the white grunt, Haemulon album,- are being overfished according to length-based indicators while the Red hind, Epinephelus guttatus, is being fully exploited (F/FMSY close to 1). Red fish trap fishery The figure below gives a summary of the trends in the red fish trap fishery, which principally targets a mix of deep water snappers such as the Silk snapper, Lutjanus vivanus, the Vermillion snapper, Rhomboplites aurorubens, the Blackfin snapper, Lutjanus buccanella and the Lane snapper, Lutjanus synagris. In the redfish trap fishery (Lutjanidae), the number of trips has grown from 335 to 566 (corresponding to 10 000 and 13 400 traps set respectively) during the period 2012 to 2016 but dropped considerably to 271 trips in 2017 (5 600 traps). In the last three years, the effort increased again to reach nearly 600 trips in 2020 (16 000 traps), the highest effort for the whole period considered. The landings of redfish (mainly silk snapper and in smaller proportions blackfin and vermillion snapper) broadly followed the variation of the effort, with the highest estimates (>50t) for the last two years, recovering from a low value in 2017 (25t). This drop in snapper landings and effort in 2017 is the consequence of a 6- month closed season voluntarily implemented by the fishermen that year (Graaf et al. 2017).
The biomass index derived from the LPUEs shows a decrease of 50% between 2007 and 2011, followed by a steady increase until 2019 and a sharp decrease in 2020. Length-based indicators for fishing mortality indicate that silk snapper and vermillion snapper have been heavily overfished, with a ratio F/FMSY higher than 1.3. For the other two snapper species (but also for the vermilion snapper in the most recent years), the length composition data is scarce which results in a large uncertainty. Nevertheless, the F/FMSY proxy also suggests that these two stocks are subject to overfishing although this is less pronounced than for the two principal species.
Other fishing métiers
Bottom drop longline, pelagic and bycatch landings have remained much less important and have shown no significant new developments
For both the targeted lobster and “redfish” stocks, the LPUE based indices indicate that stock size overall increased since the beginning of the current port sampling program (2011), when they were at a lower level. In this report, length-based indicators of fishing mortality levels are presented for the first time. This provides new insights on the exploitation status of the stocks. These indicators suggest that, despite the overall increase in stock size, the stocks are subject to overfishing, slightly for the lobsters, but more severely for the redfish. With the current declining trend in effort for the lobster fishery, it can be expected that the fishing mortality is declining. It is important to continue monitoring the fishery (and particularly length measurements of the landings) to see if the length-based indicator will reflect such a decline in fishing mortality in coming years. The situation is more worrying for the redfish fishery for which the recent trend is an increase in the fishing effort. This, combined with the indication that the fishing mortality of these stocks has been well above FMSY, suggest that management action is needed to bring the fishing mortality to lower levels. Again, continued monitoring of the fishery is essential, as well as improved biological sampling and reporting of the catches. The current ability to accurately estimate the status of individual redfish species is limited by the fact that the fisheries data is not reported by species. Being able to split the landings per species, either by encouraging the fishers to report landings per species, or by increasing the intensity of biological sampling, would, on the long term, provide a better basis to manage the “redfish” snapper stocks. The present study further suggests that three key finfish species, which are mainly landed as bycatch from the lobster fishery, are either being overfished (Queen triggerfish and White grunt) or are at the verge of being overfished (Red hind). The Queen triggerfish and Red hind formerly were common in the landings in the Dutch Caribbean but now still only have significant populations on the Saba Bank. Therefore, both of these species require a cautionary management approach as well.