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Example spectrograms of various unknown sounds, likely produced by various fish species. Most frequently recorded call types are shown in panels (b) and (c). Sample rate down-sampled: 2 kHz (a,b,e); full recording sample rate: 16 kHz (c,d); FFT size: 256 pt (a,b,e), 512 pt (c), 1024 pt (d); overlap: 95 % (a,c,d,e), 99 % (b).
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The Antillean Island chain is a known breeding and calving ground for North Atlantic humpback whales (Megaptera novaeangliae). However, while most research efforts for this species have focused on the largest aggregation of whales, located on Silver Bank, off the northern coast of the Dominican Republic, there are still significant knowledge gaps w...
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The minke whale is one of the most abundant species of baleen whales worldwide, yet is rarely sighted in subtropical waters. In the North Pacific, they produce a distinctive sound known as the “boing,” which can be used to acoustically localize individuals. A vessel-based survey using both visual and passive acoustic monitoring was conducted during...
Citations
... De eerste resultaten zijn veelbelovend. Deze hebben geleid tot de ontdekking van andere bedreigde soorten die ook in het gebied voorkomen (e.g.Geelhoed et al., 2014) en geven relatief goedkoop kwantitatief inzicht in de soortensamenstelling en relatieve temporele abundantie van soorten over een groot gebied(Risch et al., 2014;Risch & de Haan, 2016).BronnenDebrot, A.O., 1998. New cetacean records for Curaçao, Netherlands Antilles. ...
In this assignment no less than 33 nature experts, researchers and managers contributed to report on the current "State of Nature" for 13 habitats, 9 species, 4 species groups and 3 key threats to nature in the Caribbean Netherlands. The approach outlined in the Habitat Directive of the European Union was closely followed. Key determinants for the documented status assessments are discussed and approaches towards management solutions are recommended. Because of the structural arrears in biodiversity knowledge and monitoring in the Caribbean Netherlands, a quantitative assessment for the majority of species and species groups proved impossible.
Based on our assessments we conclude that without exception, the current State of Nature in the Caribbean Netherlands should be considered to be "unfavorable-inadequate" or "unfavorable-bad". This is not only the case for habitats but also for the species and species groups dependent on those habitats. This is in stark contrast to the situation in the European Union and in the European Netherlands where governments have structurally invested in nature management already for many decades.
... The windward sector may form part of its former (or current) calving grounds (Debrot et al. 2011a). A recent study using passive acoustics (Risch & de Haan 2016) has confirmed the seasonal occurrence of humpback whales in the region around Saba Bank. ...
... Although the common minke whale (Balaenoptera acutorostrata) is listed in Table 2 as "possible occurring, no sightings confirmed", this species is probably common in the windward Dutch Caribbean, as indicated by acoustic detections at Saba Bank (Risch et al. 2014;Risch and de Haan 2016). ...
... From February to April humpback whale song was recorded on more than 89 % of all recording days. Minke whale click trains were detected less frequently (Risch and de Haan, 2016) and ...
The Yarari Marine Mammal Sanctuary (hereafter simply referred to as the Yarari Sanctuary, or Yarari) was formally established on September 2, 2015. It is currently composed of two sectors: one surrounding Saba and the Saba Bank and one covering the EEZ waters of Bonaire. In order to help establish an effective cetacean conservation management plan for the Saba and Saba Bank sector of the sanctuary we here review the main marine mammal threats, help identify main management goals and make both governance and management recommendations based both on stakeholder interviews and a management review of functioning marine mammal sanctuaries in the Western Atlantic.
There are 8 species of marine mammals known to occur in the windward Dutch Caribbean Yarari Sanctuary. The sanctuary has relatively low levels of human activity. Based on our review, cumulative contaminant impacts – such as oil contamination originating from St. Eustatius – are potentially highest, followed by collision impacts due to the relatively high level of shipping traffic. Other factors such as, fishery entanglement, bycatch-impacts and marine debris impacts are likely low compared to many areas directly outside the sanctuary. While whale & dolphin watching impacts are still probably negligible, the impacts of anthropogenic noise, climate-change impacts and cumulative impacts still remain unknown but are potentially high.
Five main clusters of interrelated goals and objectives were identified based on expert and management stakeholder interviews. The most essential proximate goal for management should be to establish a minimum structural level of institutional capacity. Under the reigning conditions of resource limitation, the next key goal should be to establish effective collaboration towards jointly achieving the higher management goals and objectives.
Based on our review of species, threats, operations of other sanctuaries and expert and stakeholder input we list 23 priority recommendations and action points towards implementation of cetacean conservation for the Saba and Saba Bank Yarari sector.
Governance
• Use the Saba Bank Management Unit (SMBU) governance model for Yarari management implementation.
• Consider merging Yarari tasks into the SMBU to effectuate resource pooling and prevent management fragmentation.
Legal resources
• Design and implement a simple legal mandate for Yarari management.
• Copy and implement international legal guidelines for whale watching.
• Revise the Fishery Framework Act BES (Vissery Visserijwet besluit BES) or draft a Decree (Regeling) under the Nature Conservation Framework Act BES (Wet Grondslagen Natuurbeheer en-bescherming, WGN) to forbid all forms of pelagic (not benthic) longline and purse seine fishing in Yarari waters.
• Devise and implement legal measures and guidelines to safeguard Yarari from anthropogenic noise pollution.
Finances
• Based on the review of functioning sanctuaries, and current stressor levels, a basic annual budget of US$ 150 K will be sufficient to implement satisfactory marine mammal conservation.
• Focus expenditures on management development, outreach and international cooperation.
• Limit expenditures on costly enforcement and research. Participation in these activities should principally be limited to essential monitoring and practical support of collaborating parties.
Personnel and logistics
• Based on the review of functioning sanctuaries, two (additional) personnel members are sufficient to effectuate adequate Yarari cetacean conservation.
• The combined personnel should include both technical and boat handling skills as well as management development skills for effective local and international policy development support and cooperation.
• Saba island is the logical choice for basing Yarari headquarters.
• A larger vessel (than the current Queen Beatrix) is needed for safer and more effective operation in Yarari waters.
Management priorities
• Aim for sanctuary expansion to include St. Maarten and St. Eustatius marine waters (and ultimately also Curaçao and Aruba EEZ waters).
• Establish and expand cooperation with local enforcement and research partners.
• Develop close ties with local stakeholders and encourage their active involvement.
• Actively represent Yarari interests in regional marine mammal policy development and research initiatives.
Research priorities
• Use remote methods (AIS) and current port fishery sampling to monitor fishery activity, and ship traffic inside Yarari.
• Use passive acoustic monitoring and sighting records to monitor cetacean distribution and abundance.
• Use passive acoustic monitoring to measure and follow background noise levels.
• Record and collect data on and specimens from stranding incidents using published guidelines and protocols.
• Subsample stranding fatalities to determine contaminant loads of the cetaceans inside Yarari and their prey species.
• Document the abundance and source of marine debris found in the sanctuary.
... Of the 13 whale sightings for which species was identified, 12 were identified as humpback whales. A second large whale that may be represented amongst the 29 unidentified whale sightings is the minke whale which has in any case been documented for the bank (Risch & de Haan 2016). The main occurrence of whale sightings was in the months January to March, which fits with current knowledge on humpback and minke whale migration patterns in the area (e.g. ...
The Saba Bank is a 2200 km2 shallow bank area that lies fully within the Dutch Kingdom’s Caribbean exclusive economic zone (EEZ) waters. In recent years it has gained international recognition as an area of exceptional biodiversity value and been accorded increasingly higher and more extensive conservation status. For instance, in 2012 it was accorded “Particularly Sensitive Sea Area (PSSA)” status by the International Maritime Organization (IMO) which forbids tanker traffic and in 2015 it became part of the “Yarari Marine Mammal and Shark Sanctuary” emphasizing its value to both endangered cetaceans and sharks.
The nineteen seventies, eighties and early nineties saw extensive overfishing of the bank by foreign vessels with major depletion of its stocks of large groupers and conch. Once the exclusive fishing zone (EFZ) had been claimed in 1993 for the Netherlands Antilles fisheries regulation was enacted and the Coast Guard was established in 1995, foreign illegal, undocumented and unmanaged (IUU) fishing was quickly brought to an end. This allowed renewed local interest in fishing on the bank and has given the bank new ecological perspective. Today the bank supports two important long-time fisheries operating from Saba. These are a directed fishery for the West-Indian spiny lobster (Panulirus argus) and a “redfish” fishery for deep-water snappers (redfish). Both fisheries are principally based on the use of traps. Pelagic fishing for wahoo and dolphin fish is currently almost negligible, representing only about 2% of total landings by weight. About 60% of the annual commercial effort (in terms of fishing trips) is directed towards the lobster and 40% towards redfish. The total value of the fishery ten years ago amounted to about US$ 1.3 million per year ex-vessel value (Toller & Lundvall, 2008), involved roughly 10 fishing boats and provided direct employment for about 30 persons. In the period 2012-2015 the total fishery landings grew from 78.4 tons to 135.2 tons and still involved 10 boats. This is a major contribution to the local economy of this small island to which by comparison the main economic pillar for future development (nature tourism) contributes US$ 7.6 million annually (Van de Kerkhof et al., 2014). Recent sightings by fishermen and Saba Bank Management Unit (SBMU) of fishing activities by foreign fishing vessels without commercial or recreational fishing license, (even inside the seasonal closed area during the Red Hind spawning aggregation season) suggest that IUU may again on the rise due to the lack of regular Coast Guard patrols and enforcement. We here assess the current status of these two main fisheries and report on the monitoring results as funded by the Netherlands Ministry of Economic Affairs and as collected by the SMBU hosted by the Saba Conservation Foundation (SCF ) in collaboration with Wageningen Marine Research (WMR) during the period spanning 2012-2015. In addition, we discuss issues such as reef fish and shark bycatch and the status of the Queen conch stocks of the bank (Lobatus gigas).
Lobster trap fishery: This fishery only began during the 1980s with the advent of tourism on St. Maarten. Lobsters are fished with lobster traps (principally traditional Caribbean arrowhead traps with a modified entrance) up to depths of 45 m. This means that about 84 % of the bank is potentially suitable for this fishery, but only a part of the bank is usually fished. The fishery is strongly seasonal. Highest catches were realized in the months August through January while the lowest catches were made April to July. Egg-bearing (berried) females can be found all year long but there seemed to be a peak in berried females February to May. Recent years (2012-2015) has seen the annual number of traps set from about 48 000 traps set/y to about 73 000/y. The average soak time is 11.6 days and almost all the catch was exported to St. Maarten. Total annual catches in 1999, 2007 and 2012 respectively were estimated to be 62 tons, 92 tons and 36.8 tons. Since 2012 annual catches have steadily increased to about 76.5 tons in 2015. The information and data collected over the 5 years covered by the present study indicate a 50% increase in the effort (in terms of trap drops) of the lobster fishery, with a corresponding doubling in the lobster landings. Standardized catch per unit 6 of 124 | Wageningen Marine Research report C077/17 effort (CPUE) development shows that lobster abundance dropped from higher levels in 2000 to lower levels in 2011, with a progressive increase towards the level of 2007 since then. The observed pattern of catches for the Saba Bank since 2000 appears to mirror regional catch patterns (which are driven by regional recruitment patterns) but not local fishing pressure on the bank.
The average size of landed lobsters appears to have fluctuated between 108 and 118 mm carapace length (CL) since 2000, with no signs of significant decrease in average lobster size landed (which might have suggested overfishing). In fact, the average size of lobsters landed remains consistently high compared to other fisheries of the region. Average size at landing (113 -117 mm) is larger than size at maturity (females = 88 mm; males = 92.2 mm). Additional good news is that the landing of sublegal lobsters (<95 mm CL) has steadily decreased from about 28% in 2012 to about 4% in 2015.
We conclude that overall, based on our current analysis, there appears to be no strong sign of overfishing. We recommend the development of a spiny lobster fishery management plan which defines harvest goals and enforcement strategies that are simple, robust and cost-effective. Options to consider would be limits to the number of fishing licences, the number of traps per fishermen/licence (currently about 300 per fisherman), a total limit to traps deployed in the fishery, registry and visible marking of all traps and trap sets. Effective marking of gear for identification can also help prevent
gear loss, and gear theft. The use of escape slots and biodegradable panels is an easy way to help limit negative impacts of gear without major costs. Finally a total quota for the combined catch can serve to cap the total harvest.
It is highly recommended that the management of spiny lobster is aligned with the principles outlined in the lobster conservation and management declaration of the 17 island state Caribbean Regional Fisheries Mechanism (CRFM, Annex 5). The Netherlands could become a member of CRFM for full participation in this regional management mechanism.
Mixed reef fishes: The lobster fishery results in a certain degree of bycatch. Reef fish caught in lobster traps are in part landed for sale, for own consumption, or to serve as food for the spiny lobsters in their holding traps in the harbor. This bycatch is composed of a broad range of reef fish species. The three main reef fish species landed were the queen triggerfish, Balistes vetula, white grunt, Haemulon plumierii and the red hind, Epinephelus guttatus, representing upwards of 50% of the weight of landings. About 33% of the mixed reef fish (by weight) is discarded and mostly consists of nurse sharks, Ginglymostoma cirratum, honeycomb cowfish, Acanthostracion polygonius, cottonwick grunts, Haemulon melanurum and white grunt, H. plumieri. The catches of mixed reef fish
have increased from 6.6t to 13.6t between 2012 and 2015, representing on average just under 20% of the overall total catch (all species combined) on Saba Bank. Overall, reef fish yields on Saba Bank appeared to be low compared to other areas. Based on the results from this study, a rough estimate of the yield is between 0.025 and 0.10 t/km2/year. These low yields can in part be due to the low reef fish densities on Saba Bank as estimated in fisheries-independent studies. Lower fish catchability of traps designed for lobsters likely also contributes to lower catches compared to studies using fish traps. The low fish density is unlikely to be caused by current overexploitation but to one or a combination of factors such as a naturally lower biomass of reef fish and losses of habitat for reef fishes due to bleaching-induced coral mortalities.
Redfish fishery: The “redfish” fishery is also largely conducted using traps. These are typically deployed at depths of between 50 en 250 m and catch mainly silk snapper, Lutjanus vivanus (69% by weight), blackfin snapper Lutjanus buccanella (10%), vermillion snapper, Rhomboplites aurorubens (7%), and “others” (14%). In 2000, redfish was exclusively still caught by line. However, by 2007 most snapper was being caught using fish traps and by 2012 there was practically no more line fishing for snapper. These shifts in gear use coincided with a change in fish size, (and species composition) from large adult snapper to smaller sub-adult snapper of about 30 cm fork length. In 2007 the average total trap haul was 28 traps/day while in 2012 it was about 33 traps/day and in 2015 about 25 traps/day. As fishing pressure increased from 2007 to 2012, annual landings seemed to decline from 41.3 tons in 2007 to 34.6 tons in 2012. Since then total landings increased (to 50.5 tons in 2014), but now may have started declining again (39.1 tons in 2015).
When looking at CPUE which is an index of population size, it is evident that CPUE (landings) has fluctuated between roughly 2.5-5 kg of snapper per trap, with no appreciable trend. Therefore, the recent changes in total annual catch appear to be largely driven by changes in effort. This peaked in 2014 (at 537 total trips) but was less in 2015 (481 trips). These most recent data hence suggest no worrisome developments for this
fishery, other than that the current fish stock is significantly (75%) lower than in the early 1970s “virgin” state. There is currently a small but growing fishery using deep-water long lines to target redfish in deeper waters (average depth: 260 m) where catches are dominated by the wenchman snapper (Pristipomoides aquilonaris) and the queen snapper (Etelis oculatus, sabonechi). The status of the trap fishery is perceived by the fishers as undesirable with a CPUE 75% lower compared with underexploited conditions. On the 1st April 2017 a six month closed season was implemented through an agreement between fishermen. It is recommended to develop a harvest strategy for the deep-water snapper fishery and ensure that sufficient (on-board) samples are collected.
Shark bycatch: Sharks are considered unwanted bycatch or nuisance in especially the lobster trap fishery. Nurse sharks, were caught in around 60% of the trips using lobster traps but most of the time in low numbers (less than 7 sharks per trips). However for 5% of the trips, large numbers (from 11 up to 71 individuals) were caught. The estimated annual number of discarded nurse sharks varied between 1712 and 2499 individuals, mainly coming from the lobster fishery. Almost all sharks are discarded (alive) and very few sharks were killed and landed. Of 319 trips sampled between 2011 and 2016, a total of 11 landed sharks were observed, most of them from the lobster fishery (7 sharks in 139
samples). Based on our port sampling interviews we estimate that 40 sharks per year (mainly nurse sharks) were landed in the whole Saba Bank fishery. Nevertheless, personal observations during onboard observation show that catches may also amount to tens or even up to 60 sharks per lobster fishing trip (A. Debrot, and J. Odinga, pers. comm.). Further on-board observation is clearly needed to obtain direct figures on shark catch rates. As the Saba Bank is a designated shark sanctuary since August 2015 it is important to work together with the fishermen to fully eliminate all shark taken and
ensure that they are released unharmed. The development of nurse shark exclusion devices for the lobster traps would be highly recommended to protect the nurse sharks and to reduce the damage to fishing gear and catch.
Sustainable fish traps: Biodegradable panels: Biodegradable panels did not show any degradation during a 480 daylong experiment but tested panel attachment materials did. Biodegradable panels attached to traps by material with short breakage time (max. 20 days) as required in the current fishery regulations may not be accepted by fishers due to potential loss of catch and time associated with replacing the panels. If the regulations on biodegradable panels is to be maintained, it is recommended to adjust the breakage time to 3-12 months and to clearly describe in the regulations the type and diameter of the
material that is to be used to attach the biodegradable panel.
Ghost fishing: In 2012-2015 Saban fishers lost on average 0.6 lobster traps per fishing trip,
resulting in ca. 400-600 derelict lobster traps annually. Our experiments show that mortality of reef fish and lobster was low and most fish and lobster appeared to be able to enter and exit the ghost traps freely. Nevertheless, derelict traps kill 2.7 to 7 lobsters and 2.7 - 3.9 kg of reef fish per trap per year. As wire traps continue to ghost fish for roughly two years we estimate the total annual kill by ghost fishing amounts to $23000 - $51000 for reef fish and $46000-$176000 for lobster. Fortunately, simple modification to lobster traps such as correctly functioning escape panels will significantly reduce mortality from ghost fishing. Our studies show that the average deterioration time in days
(including range between brackets) for escape panels attached with hemp and cotton is respectively, 105 (85-114), 150 (128-241). All other options such as wire or hog rings lasted more than twice as long and are not recommended.
Escape slots: We examined the effects of biodegradable panels with 2 trap design (5ft D-type traps and 4ft M-type traps) as well as the effect of 25 and 38 mm escape slots on reef fish bycatch and sub-adult snapper catches. Trap type did not affect the average number of lobsters or fish caught per trap. The only exception was for the white grunt for which the catch rates were markedly higher in the larger D-traps. However catch rates in terms of weight of bycatch were almost double for the type D-traps with 25mm escape vents compared with the control traps. This difference was mainly due to an increase in the catch rate of species of intermediate economic value. So the larger 5 ft D-traps catch no more lobster but do catch a lot more bycatch. Hence the larger D-type traps are not
recommended.
Lobster traps: Our results indicate that both trap types with escape slot had higher catch rates for lobster than the control traps. There was a significant difference of 0.55 lobster per trap for the experiment with the 38 mm escape vent. The difference for the 25 mm escape slot was not significant (0.20 lobster per trap). The results suggest that crowding with fish reduces lobster entry into traps. It was different for reef fish bycatch. Escape slots of 25 mm greatly increased the catch rate of bycatch species like grunts. In contrast, the 38 mm escape vent reduced the catch rates of bycatch substantially; by about 60% for the D-type traps, and 80% for the M-type traps. The most important result of these experiment is the observation that both 25mm and 38 mm escape slots and trap size (4ft M-trap or 5ft-D traps) appeared to have little negative effect on lobster catches. The traps with 38 mm escape slots even caught significantly more lobsters (ca. 0.5 lobsters per trap). Therefore, the bycatch of mixed reef fish in the lobster trap fishery could be limited by regulating trap size and the use of escape slots. Reducing trap size and/or implementing 38 mm escape slots will drastically reduce the amount of mixed reef fish without impacting (possibly even improving) the catch of lobster, the main target species.
Snapper traps: Escape vents of 25 mm seem to increase snapper catch rate by about 20%
(though not statistically significant). In contrast, escape vents of 38 mm greatly reduced snapper catches. A 25 mm escape vent also increased the proportion of vermillion snapper in the catch. Based on studies elsewhere, Johnson (2010) reported an increase in average size of (reef) fish in traps fitted with 25 mm escape vents. Our experiments indicated that the 25 mm escape slot did function as intended and did not reduce the proportion of sub adult silk snappers. So as for the effect of escape slots on fish catch the results are consistent: the 25 mm vent increases fish catch while the 38 mm slot lets almost all fish escape and yields low catches. We suggest that this might mean that when traps become too crowded, less fish will enter. By using 25 mm escape vents, small, non-target species easily escape thereby creating more room in the trap for target species.
Whales and Dolphins: The cetacean sighting frequency for Saba bank fishing trips amounted to an average of one sighting for every 13.2 trips. Between 2012 and 2016 a total of 142 sightings were generated. Only 25% of whale sightings and 8% of dolphin sightings allowed reliable species identification. Of the 25% of confirmed whale sightings 23% concerned the humpback whale and 2% the sperm whale. While the collected data provide some indication of the presence of cetaceans on and around the bank, clearly,
there is much room for improvement of baseline data collection.
Queen conch: After the de facto (but not formal) closure of the conch fishery on the Saba Bank in the mid-1990s, the queen conch population has recovered. Out of the 131 transects conducted during our video survey, adult conch were found in 91 transects, ranging from 16 conch/ha to 882 conch/ha (mean 130.8 conch/ha, 99.7–161.8 95% CI). In 52 transects (40 % of all transects) more than 100 conch/ha were found. So maybe 800 km2 or more of the Saba Bank have conch densities that could justify a limited fishery. Adult queen conch were found at depths of 17 to 58 m, with highest densities
documented at 22m. Mating success in queen conch is density dependent and studies recommended that a mean density of 100 adult conch/ha should be the minimum to avoid the risk that recruitment might be impaired. This means that at present a controlled limited fishery should well be possible, if judiciously controlled and regulated. Based on our data, an estimated 14 million adult queen conch are currently present on the Saba Bank in the 20-40 depth zone. A sustainable annual quota could be set ca. 1 million adult queen conch (ca. 8 % of the adult population). If a fishery is re-opened, it is recommended to: 1) introduce a minimum legal size at 10mm lip thickness and an annual closed season during May-September, 2) ensure that queen conch are landed with shell, 3) regular stock assessment are conducted to adjust the quota and avoid recruitment impairment, 4) identify and open only those areas to the fishery where densities are high enough, 5) set strict regulations on harvesting methods to prevent development of dangerous ‘hookah’ fishing practices. Any development of a conch fishery will take time as both bringing the
species in from the sea to land and export will require permits.
Lionfish: Based on observations, it appears that the invasive lionfish first arrived on the Saba Bank between 2008 and 2011. Since then it has spread and is a frequent bycatch species in redfish and lobster traps. Our data show that it had much higher catch rates in the deeper waters during fishing for redfish. Average catches in the last three years amount to about 1 lionfish for every one or two snapper traps hauled. The availability of lionfish bycatch has led to a local market arising. Based on this, several fishermen have expressed interest in testing special traps which concentrate and trap lionfish and may
allow the development of a directed deep-water lionfish fishery.
That is the research question that, Stacey Mac Donald, a Ph.D. researcher from The Netherlands, is seeking to answer through the use of anthropological and social psychological research insights. Mac Donald also tackles a number of other questions within the fields of nature conservation and, preservation of cultural heritage on the islands of Bonaire, St. Eustatius and Saba, also known as the BES Islands.
