Queen Conch

The Convention on International Trade in Endangered Species (CITES) Authority issued injunctions in 2003 and 2004 to halt export trade of Caribbean queen conch (Strombus gigas) from several countries and initiated reviews of a number of other conch-producing countries. The current regula- tory framework for regional conch fisheries has obviously failed to protect stocks. I present a case study of the Belize conch fishery to examine fishing impacts, effectiveness of existing regulations, and potential for population recovery. Fishery-independent data from a no-take marine reserve indicated that unfished density and biomass were nearly an order of magnitude greater than in comparable fished areas. Size structure of the protected population showed that an average of 38% of the legal catch may consist of juvenile conch. The spawning potential ratio indicated that the fished stock is severely over- exploited, and furthermore, the protected population has not compensated to make the local fishery sustainable. Under these conditions, a moratorium under CITES may be warranted. Until stock assessment models are refined, action should be taken to reduce juvenile fishing mortality, extend closed seasons, and enforce a network of functional no-take reserves in essential habitat. 

For marine reserves to function as effective harvest refuges for exploited species, the reserve must protect a substantial proportion of the population for an indefinite period of time. Because most marine reserves are space-limited, the buildup and equilibrium population sizes of mobile species will be influenced by the size and boundary conditions of the refuge. A logistic rate model was used to predict equilibrium population sizes in a marine harvest refuge, based on species-specific dispersal dynamics and the spatial configuration of the refuge. The model parameters were derived for Caribbean spiny lobsters and queen conch in an isolated marine reserve at Glover’s Reef, Belize, and were compared to observed population change over a 5-yr period. Spiny lobsters and queen conch, the two most heavily exploited species in the Caribbean, differ in larval recruitment rates (immigration) and mobility of adults (emigration). The expected increase in the population size of spiny lobsters in this refuge was 250% and queen conch was 420% over that of the initial fished population. The observed densities of lobsters and conch in the refuge approached the predicted estimates within three years. To further explore the impact of alternative spatial configurations on refuge populations, the model was run on the same populations in two hypothetical refuges. In a refuge of the same area but 50% less absorbing boundary (adjacent to intensively fished areas), the spiny lobster population was expected to be 30% larger than the equilibrium population size in the original refuge, whereas the queen conch population was not expected to change from that in the original refuge. In a refuge that was 50% larger and with 50% less absorbing boundary, the spiny lobster population was expected to increase 110% and the queen conch population was expected to increase 50% over the equilibrium population size in the original refuge. Relatively minor changes in refuge area and boundary conditions may thus result in major population-level responses by exploited species, depending on dispersal dynamics and habitat availability. This simple model may be applicable for rapid assessment of the potential efficacy of proposed harvest refuges. 

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.  

Abstract:

The queen conch (Lobatus gigas) is under pressure and has decreased in distribution and abundance as a result of fisheries in the Caribbean region. To ensure sustainable fishery, knowledge on the population dynamics of this species is required. Therefore, this research focused on the status and the reproductive behaviour of the conch population around St Eustatius and provides information about the possibilities for a sustainable fishery. Conch distribution and abundance, population structure, reproductive activity and fishing pressure were determined in the coastal waters around the island of St Eustatius by dive surveys, towed video surveys, reproduction surveys and fishery catch surveys. The study covered the entire Statia National Marine Park waters and covered different habitats and depths up to 40m.

The study shows that the queen conch is abundant around St Eustatius, with mean densities of 57 (dive surveys) and 115 (video surveys) adults per ha. The total adult queen conch stock was estimated to be 184,100 (95% C.I.: 77,586-390,000) in 2,700 ha Marine Park. Further, a higher conch abundance was found on rubble habitats and at greater depths (17-31 m). Mainly mature conchs were detected, indicating a shortage of recruitment of young conch, or a difficulty in observing young conch. Further, reproductive activity started in March and declined after October, with peak reproductive activity during June and July. Minimum lip thickness reported for reproductive behaviour was 9 mm. However, this study also indicated that more research is necessary to qualify the exact spawning season and size at maturity of conch around St Eustatius.

In conclusion, the status of the queen conch could be qualified as good and does not seems to appear under direct pressure in the coastal waters of St Eustatius. With this population status, small- scale fishery may be possible without negative consequences for the queen conch population. However, to ensure long-term sustainable of a conch fishery, harvest restrictions as advised by the queen conch working group are recommended to be used; like a minimum of 15 mm lip thickness, closed areas and an annual harvest of maximal 6200 adult conch. Thus, non-detrimental fishing is possible for queen conch on St Eustatius, under the conditions that, proper management and harvest restriction regulations need to be developed, implemented and enforced in close co-operation with stakeholders. 

Abstract:

In 1999 a survey was carried out (Lott, 2000) to estimate the conch population and determine the status of the seagrass beds in Lac Bay, Bonaire. Since 1999 the recreational use of Lac has increased, new structures have been built around Lac and illegal conch fishing still goes on (conch fishing is forbidden by Marine Ordinance of 1991). In order to assess the effects of the moratorium and the impact of increased activity in and around Lac the 1999 survey has been repeated, applying the same methods. Fieldwork was carried out from the end of May 2007 through the beginning of October 2007.

Findings:

The main conclusion from this study is that the moratorium on conch fishing seems to be effective as Lac Bay’s conch population has increased; however, the cover of turtlegrass has diminished, which is most likely linked to an increase in anthropogenic disturbance of Lac.

• The conch population has increased: in the 51,000 m2 survey area, 223 live conch were found, against 111 in 1999.
• Adult conch were found (4% of the population) while in 1999 no adult conch were recorded.
• The cover of turtlegrass has diminished in most of the 17 grids (2,142 quadrats of 1 m2 ) studied; these grids were spread over Lac Bay. Grid Cai showed no reduction in cover.
• Trampling from windsurfers, snorkelers and other users of Lac Bay plays a major role in the reduction of turtlegrass.
• Cover by macro algae has changed but not necessarily diminished; in some grids the cover increased, in others it decreased.
• The number of most invertebrates has decreased.

Management Recommendations:

• Further study on Lac Bay’s species composition.
• Further study on Lac Bay’s water quality.

Abstract:

Queen Conch, Lobatus gigas, is a large, herbivorous, marine gastropod found primarily in the Western Atlantic Caribbean region. Adult conch range in length anywhere from 143-264 mm and are typically found in depths up to 25 meters, but are more often found between 10 – 18 meters. Due to its commercial importance and high market value, queen conch populations have dwindled to extremely low levels within its range. St. Eustatius Marine Park was established in 1996 and became actively managed in 1998 to conserve and protect the marine environment surrounding St. Eustatius up to and including the 30-meter (100 feet) depth contour and regulates the conch fishery on the island. Within the park, two no-take reserves are established on both the northern and southern ends of the island. The study revealed numerous sites that are ideal conch habitat from depths of 60-110 feet. Average density of conch was 0.043 conch/m2. A total of 86 individuals were included in the survey. The average length of conch was 22.1 cm with average lip thickness was 1.0cm. Individuals were on average 170.4 cm apart and were uniformly distributed. Density of Lobatus gigas in St. Eustatius is three times greater than densities reported for Turks and Caicos but drastically lower than densities reported for beds at similar depths in the Bahamas and Dominican Republic. The results of this survey suggest that Statia’s conch population may be very unique because the shallowest bed is located at 60 feet and conchs have been observed in depths up to 110 feet. Conch may be aggregating in certain areas for nutritional, reproductive or protective benefits. Typical locomotory and reproductive behaviour were observed during the study. Most conch surveyed met regulation size, which is encouraging because it means that juveniles are being left and allowed to reach sexual maturity thereby replenishing the population. Because catches are not reported it is not known if most conchs being collected are greater than 19cm (siphonal length) and have a fully-grown lip, which may mean immature individuals may be being removed prior to reproducing. There are numerous opportunities for further study on the L. gigas population in the St. Eustatius Marine Park including larval, behavioural and migration studies as well as collection of basic oceanographic data, which would have widespread applicability.