Sharks

Over the last century anthropogenic activities have rapidly increased the influx of metals and metalloids entering the marine environment, which can bioaccumulate and biomagnify in marine top consumers. This may elicit sublethal effects on target organisms, having broad implications for human seafood consumers. We provide the first assessment of metal (Cd, Pb, Cr, Mn, Co, Cu, Zn, As, Ag, and THg) and metalloid (As) concentrations in the muscle tissue of coastal sharks from The Bahamas. A total of 36 individual sharks from six species were evaluated, spanning two regions/study areas, with a focus on the Caribbean reef shark (Carcharhinus perezi), and to a lesser extent the tiger shark (Galeocerdo cuvier). This is due their high relative abundance and ecological significance throughout coastal Bahamian and regional ecosystems. Caribbean reef sharks exhibited some of the highest metal concentrations compared to five other species, and peaks in the concentrations of Pb, Cr, Cu were observed as individuals reached sexual maturity. Observations were attributed to foraging on larger, more piscivorous prey, high longevity, as well a potential slowing rate of growth. We observed correlations between some metals, which are challenging to interpret but may be attributed to trophic level and ambient metal conditions. Our results provide the first account of metal concentrations in Bahamian sharks, suggesting individuals exhibit high concentrations which may potentially cause sublethal effects. Finally, these findings underscore the potential toxicity of shark meat and have significant implications for human consumers.

Referenced in BioNews Article https://dcnanature.org/sharks-toxins/

List of pelagic fishes found around Bonaire and Curacao, including scientific, English, Spanish and Papiamento names. Published by the Agriculure, Husbandry and Fisheries Service of Curacao, as Agrinoticia, Piská – No.1

Facts About Tiger Sharks

We are going to present before you some interesting facts about tiger sharks. It is one of the most feared sharks in the ocean. People are afraid of it. The name "tiger" also adds to that reputation of its being a dangerous animal. Let us learn some interesting info about it.

Alterations in predation pressure can have large e ects on trophically-structured systems. Modi cation of predator behaviour via ocean warming has been assessed by laboratory experimentation and metabolic theory. However, the in uence of ocean acidi cation with ocean warming remains largely unexplored for mesopredators, including experimental assessments that incorporate key components of the assemblages in which animals naturally live. We employ a combination of long-term laboratory and mesocosm experiments containing natural prey and habitat to assess how warming and acidi cation a ect the development, growth, and hunting behaviour in sharks. Although embryonic development was faster due to temperature, elevated temperature and CO2 had detrimental e ects on sharks by not only increasing energetic demands, but also by decreasing metabolic e ciency and reducing their ability to locate food through olfaction. The combination of these e ects led to considerable reductions in growth rates of sharks held in natural mesocosms with elevated CO2, either alone or in combination with higher temperature. Our results suggest a more complex reality for predators, where ocean acidi cation reduces their ability to e ectively hunt and exert strong top-down control over food webs. 

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 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.  

Data collection with stereo Baited Remote Underwater Videos (sBRUV) deployed throughout the islands of the Dutch Caribbean over the past few years is almost completed, with only parts of Bonaire left as final sampling locations. The collected data already gives great insight into the status of shark populations in the waters around Saba, St. Eustatius, St. Maarten, Bonaire, Curaçao and on the Saba Bank (Figure 1). Since 2012 researchers from Wageningen Marine Research with project leader Dr. Martin de Graaf, in partnership with local partners, have used simple, non-invasive stereo Baited Remote Underwater Videos (sBRUV) to gather important information on the size, diversity, species composition and abundance and of shark populations across different management zones in the Dutch Caribbean. To this date, over 800 sBRUV videos have been deployed across the Dutch Caribbean, including 103 around Bonaire (and continuing), 164 around Curacao, 108 around Saba, 164 on the Saba Bank, 104 around St. Eustatius and 214 around St. Maarten.

This news-item was published in BioNews 5-2017.

A dedicated Saba Bank Symposium was organised by the University of Wageningen in December 2016. The Symposium was held in Den Helder and brought together researchers and conservationists from throughout the Kingdom to share their knowledge and to provide an overview of the current state of scientific knowledge about the Netherland’s largest and most remote National Park.

Among others, presentations were given on the following topics:

• Where does our interest in Saba Bank come from? by Paul Hoetjes
• State of the reefs: 3 expeditions to Saba Bank by Erik Meesters
• Fish and fisheries at Saba Bank by Martin de Graaf
• Importance of Saba Bank for local communities, by Kai Wulf
• Research by NIOZ on the Saba Bank, by Fleur van Duyl
• Coral diversity and historical collections of Saba Bank, by Bert Hoeksema
• Shark habitat use, by Erwin Winter
• Listening to the Bank: whales and dolphins, by Dick de Haan

The Symposium ended with a panel discussion on the sustainable use of the Saba Bank and what is needed to protect the Saba Bank for the future.

We have done our best to capture the wealth of information presented at the symposium for you in our BioNews letter and hope, that like us, you are impressed by the depth and diversity of the work that has been done to explore and document our largest National Park: The Saba Bank.

To read this interactive Pdf, please make sure to have Adobe Acrobat Reader installed on your computer. We recommend you to open BioNews in full screen.  In case you do not have this program, please click here to download. Feel free to email research@DCNAnature.org in case you experience any issues downloading the program so we can assist you.

BioNews is produced by the Dutch Caribbean Nature Alliance and funded by the Ministry of Economic Affairs.

Raw data of shark observations by St.Eustatius Scubaqua dive school.

Please contact Wageningen Marine Research for more information.

Raw data of shark observations by the Nature Foundation and St.Maarten dive schools (Dive Adventures, Dive Safaris, Scuba Fun, Ocean Explorers).

Please contact Nature Foundation St.Maarten for more information.

Observations by SeaSaba dive instructors which include turtles, sharks, rays, snappers, groupers and marine mammals. Observations are made during every dive (and at surface). Dive instructors are at minimum level 3 REEF fish identifiers.   

Please contact SeaSaba for more information.

The handtyped observations (no species picklist) is interpreted into a Comma Separated Values file by a java program which is included in the download.