A. Kuramae

Update on the 2016-2017 catch trends in the Saba Bank fisheries

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 levelled off. The resulting landings of lobster have shown a similar pattern of increase up to 2015 but have now levelled off at around 70 tonnes 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 tonnes 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 favourably. 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 analysed 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.

Date
2018
Data type
Research report
Theme
Research and monitoring
Geographic location
Saba
Saba bank

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.

Lobster fishery

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

Overall conclusion

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.

Date
2021
Data type
Research report
Theme
Research and monitoring
Report number
Wageningen University & Research report C062/21
Geographic location
Saba bank