Queen Conch

Historical Data

A study conducted in 1969 by Hummelinck and Roosgave the first qualitative data forqueen conch general distribution throughout Lac Bay. In 2000, a study by Lottpresented the first quantitative data within the same study area. This was followed by asecond survey in 2007. From 2010 onwards (Conch Stock Restoration Project)assessment of queen conch population has been done at irregular intervals (2010,2013, 2015, 2016, 2020).

Results
A total of 43,200 m2 was surveyed and 85 live conchs were found and measured. This resulted in a population density of 19.27 conchs / Ha. To use the Allee effect, only sexually mature conchs should be considered. Over the course of this study, no sexually mature conchs were found , the oldest conch had a lip thickness which measured 6 mm.

Below, Table 1 has been included to summarize the results of the last 5 surveys (2010, 2013, 2015, 2016, 2020). It is interesting to note the dramatic increase between conch populations in 2010 and 2013, and then the rapid decrease in follow on surveys. The results of the 2020 survey highlight a significant issue with only 85 conchs found, none of which having reached sexual maturity. Figure 4 shows a map with the total number of live conchs found per location. There was also a significant number of poached conchs (Table 2/Figure 5) found within the bay. In fact, there were more poached conch shells (100) found than live conch (85), demonstrating that poaching is still an issue which needs to be addressed before the conch population can rebound. 

Each quadrant (quantity 49) equates to 0.09 ha. Using this value, the following densities per year were calculated: 2010 (6.35 conchs/ha), 2013 (51.70 conchs/ha), 2015 (46.49 conchs/ha), 2016 (21.54 conchs/ha), 2020 (19.27 conchs /ha) 

Dutch below

Queen conch are facing immense pressure leading to a dramatic decrease in their populations.  Luckily, a new project, started at the Curacao Sea Aquarium in 2020, will explore ways to reduce mortality rates and develop new methods for effective restocking of natural populations with hatchery-reared conch. 

Photo credit: Julia Ehrenheim

The large marine gastropod queen conch (Strombus gigas) is a charismatic and iconic symbol of nature and one of the most important demersal fishery resources in the Caribbean region. Trade of the species (largely for consumption) is regulated by the CITES treaty, to which the Kingdom of the Netherlands is party. 

The Problem

Today, these iconic marine snails are threatened by over-exploitation and loss of shallow water habitats, throughout the Caribbean as well as in the ABC islands.  Human activities have led to degradation of nearshore conch habitats causing breeding failure, decreased growth and survival of juvenile conch. Excessively low densities mean that animals of breeding age fail to find mates and therefore also fail to breed (the so-called Allee Effect). Queen conch are also particularly vulnerable to overfishing due to their unique life history (pelagic phase, density-dependent survival and reproduction). The exploitation of queen conch throughout large parts of its natural range has led to population collapses and decrease in population densities to levels where mating success is diminished.

Photo credit: Julia Ehrenheim

Hope on the Horizon

In 2020 the Queen Conch Hatchery Project was started at the Curacao Sea Aquarium with Julia Ehrenheim as the key scientist. The science of hatchery production has been well established for many years but rewilding to bolster natural populations has consistently failed. Therefore, the main goal of this project is to find ways to reduce and/or eliminate high mortality rates that occur in early life stages and develop methods for effective restocking of natural populations with hatchery-reared juvenile conch. In order to find answers to various elusive questions, Julia has started the research that she will use for her PhD degree at the University of Wageningen under Professors Tinka Murk and Dolfi Debrot.

The Experiments

Her first experiments aim to address the movement behavior of juvenile conch. For this she and her students tracked the activity of juvenile conch in a controlled hatchery environment. The results show that juvenile conch are more active at sunset than in the early morning or during midday. They also appear to preferentially move towards the current. Such experiments need to be done in the field but already suggest ways to facilitate the relocation of released hatchery conch and that juvenile conch will be most vulnerable to predators at sunset.

Photo credit: Julia Ehrenheim

A second experiment showed that juvenile conch often aggregate together in the wild. Therefore, she studied if there was a beneficial density for growth. The first finding showed that juvenile conch grew the most in shell length with a density of 200 conch per m2. Lower and higher population densities gave lower growth rates and lower total shell length, even though all were grown under the same conditions of food availability.

Correlations between weight and growth (in total length) indicate that there are distinct phases of growth. It seems that growth alternates between predominant growth in the thickness of the shell and in total shell length. Both do not occur simultaneously. The significance of this phenomenon to juvenile survival is not understood.

Implications

These findings for hatchery-reared conch will be further investigated and verified in wild grown juvenile conch. Taken together the results of this PhD project will help clarify why juvenile hatchery-released conch are so vulnerable and what needs to be done to enhance their survival so that they can be effectively used to restore natural populations.

Photo credit: Julia Ehrenheim

DCNA  

The Dutch Caribbean Nature Alliance (DCNA) supports science communication and outreach in the Dutch Caribbean region by making nature related scientific information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article. 

Kroonslakken staan onder enorme druk, wat leidt tot een dramatische afname van hun populaties. Gelukkig is er in 2020 een nieuw project gestart in het Curaçao Sea Aquarium, waarin manieren worden onderzocht om de sterftecijfers te verlagen en nieuwe methoden te ontwikkelen voor het effectief uitzetten van natuurlijke populaties met in kwekerij gekweekte kroonslakken.

Foto: Julia Ehrenheim

De kroonslak (Strombus gigas) is een charismatisch en iconisch symbool van de natuur en een van de belangrijkste demersale visbestanden in het Caribisch gebied. De handel in de soort (grotendeels voor consumptie) wordt gereguleerd door het CITES-verdrag, waarbij het Koninkrijk der Nederlanden partij is.

Het probleem

Tegenwoordig worden deze iconische zeeslakken bedreigd door overexploitatie en verlies van ondiepe leefgebieden, zowel in het Caribisch gebied als op de ABC-eilanden. Menselijke activiteiten hebben geleid tot achteruitgang van leefgebieden van kroonslakken aan de kust, waardoor het voortplanten mislukt en de groei en overlevingskans van jonge kroonslakken afneemt. Te lage dichtheden zorgen ervoor dat dieren op geslachtsrijpe leeftijd geen partner vinden en dus ook niet voortplanten (het zogenaamde Allee-effect). Kroonslakken zijn ook bijzonder kwetsbaar voor overbevissing vanwege hun unieke levensloop (pelagische fase, dichtheidsafhankelijke overleving en voortplanting). De exploitatie van de kroonslak in grote delen van zijn natuurlijke verspreidingsgebied heeft geleid tot het instorten van de populatie en het afnemen van de populatiedichtheden tot niveaus waarop het paringssucces is verminderd.

Foto: Julia Ehrenheim

Hoop aan de horizon

In 2020 werd het Queen Conch Hatchery Project gestart in het Curaçao Sea Aquarium met Julia Ehrenheim als belangrijkste wetenschapper. De wetenschap van de productie van kweekerijen is al vele jaren goed ingeburgerd, maar het opnieuw verwilderen om natuurlijke populaties te versterken, is consequent mislukt. Daarom is het belangrijkste doel van dit project om manieren te vinden om de hoge sterftecijfers die zich in de vroege levensfasen voordoen te verminderen en/of uit te bannen, en om methoden te ontwikkelen voor het effectief uitzetten van natuurlijke populaties met in kwekerij gekweekte jonge kroonslakken. Om antwoorden te vinden op verschillende moeilijke vragen, is Julia het onderzoek gestart dat ze zal gebruiken voor haar promotieonderzoek aan de Universiteit van Wageningen onder professoren Tinka Murk en Dolfi Debrot.

De experimenten

Foto: Julia Ehrenheim

Haar eerste experimenten zijn gericht op het bewegingsgedrag van jonge kroonslakken. Hiervoor volgden zij en haar studenten de activiteit van jonge kroonslakken in een gecontroleerde kwekerij omgeving. De resultaten laten zien dat jonge kroonslakken actiever zijn bij zonsondergang dan in de vroege ochtend of middag. Ze lijken ook bij voorkeur naar de stroming toe te bewegen. Dergelijke experimenten moeten in de natuur worden gedaan, maar suggereren al manieren om de verplaatsing van uitgezette kroonslakken te vergemakkelijken en dat jonge kroonslak het meest kwetsbaar zijn voor roofdieren bij zonsondergang.

Een tweede experiment toonde aan dat jonge kroonslakken in het wild vaak bij elkaar komen. Daarom onderzocht ze of er een gunstige dichtheid voor groei was. De eerste bevinding toonde aan dat jonge kroonslakken het meest groeiden in schelplengte met een dichtheid van 200 kroonslakken per m2. Lagere en hogere dichtheden zorgden voor lagere groeisnelheden en een lagere totale schaallengte, ook al werden ze allemaal gekweekt onder dezelfde omstandigheden van voedselbeschikbaarheid.

Correlaties tussen gewicht en groei (in totale lengte) geven aan dat er verschillende groeifasen zijn. Het lijkt erop dat de groei afwisselt tussen overheersende groei in de dikte van de schaal en in de totale lengte van de schaal. Beide komen niet gelijktijdig voor. De betekenis van dit fenomeen voor de overleving van jonge kroonslakken wordt nog niet begrepen.

Implicaties

Deze bevindingen voor in kwekerij gekweekte kroonslakken zullen verder worden onderzocht en geverifieerd bij in het wild geboren jonge kroonslakken. De resultaten van dit doctoraatsproject zullen helpen verduidelijken waarom jonge kroonslakken die in kwekerijen zijn uitgezet zo kwetsbaar zijn en wat er moet worden gedaan om hun overlevingskans te vergroten, zodat ze effectief kunnen worden gebruikt om natuurlijke populaties te herstellen.

Foto: Julia Ehrenheim

DCNA

De Dutch Caribbean Nature Alliance (DCNA) ondersteunt wetenschapscommunicatie en outreach in de Nederlandse Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en de pers. Dit artikel bevat de resultaten van verschillende wetenschappelijke onderzoeken, maar de onderzoeken zelf zijn geen DCNA-onderzoeken. Aan de inhoud kunnen geen rechten worden ontleend. DCNA is niet aansprakelijk voor de inhoud en de indirecte gevolgen die voortvloeien uit het publiceren van dit artikel.

Published in BioNews 64

Dutch below

The Caribbean Netherlands Science Institute, partnering with the Queen Conch Lab at the Florida Atlantic University is exploring the impacts of shifting seagrass species composition on local queen conch populations.  Queen conch depend heavily on native seagrass throughout their lifecycle, so the decline of native meadows could threaten conchs not only on St. Eustatius, but throughout the Caribbean region.

Queen conch are an iconic species for the Caribbean. In addition to their beautiful shell, queen conch play an important part in local cuisine as well as a role in seagrass grazing, keeping algae growth under control.  Queen conch are dependent on native seagrasses throughout their life cycles.  In fact, conch start off as microscopic free-floating larvae, found throughout the water column.   After about 21 days of swimming around, cues from their environment, namely native seagrass beds, tell them it’s time to settle and morph to a sand dwelling grazer.

The problem

Unfortunately, native seagrass around St. Eustatius and other (Dutch) Caribbean islands are being threatened by an invasive species from the Red Sea- Halophila stipulacea.  This new seagrass creates a completely different habitat, which affects how the ecosystem functions which could lead to changes in the composition and abundance of associated species (such as the queen conch). It is unclear if these invasive species offer the same cues to the conch larvae as their native counterparts.  To better understand this impact, a new project funded by World Wildlife Fund INNO-fonds and SPAW Regional Activity Center, led by the Caribbean Netherlands Science Institute partnering with Megan Davis from the Harbor Branch Oceanographic Institute at the Florida Atlantic University, is exploring these impacts.

Queen conch. Photo credit: Marion Haarsma

The Project

The first step of the project is to collect eggs from wild queen conch.  The female Queen conch lays her eggs in a thin sticky thread-like casing. This thread bundles together into an egg mass, often covered in sand so it can be very difficult to find. Each thread contains millions of eggs, so only a small portion of this egg mass (size of a 25 cent coin) is needed for the experiment. Once collected the eggs are transported to a lab where they can be placed in a tank to be monitored daily. After 4-5 days the eggs will hatch, releasing many microscopic conch larvae into the tank.

Time to Hatch

Once the eggs hatched, they are moved in small batches to individual beakers so they can be easily fed and monitored. Once they reach about 1 mm in length they are almost ready for their metamorphosis, about 21 days. The final stage of the project is to introduce various cues to the larvae to see how they respond.  In total four different cues will be used, in various combinations.  These cues include two native seagrasses, the invasive seagrass as well as that of bare sand.  After introduction, the conch larvae will be checked throughout the following week to see how they develop.

Want to know more about this project? Follow along with lead scientist, Dr. Kimani Kitson-Walters and check out the following vlog.

Updates to this project will also be featured in future BioNews articles.

DCNA

The Dutch Caribbean Nature Alliance (DCNA) supports science communication and outreach in the Dutch Caribbean region by making nature related scientific information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and through the press. This article contains the results of one of those scientific studies but the study itself is not a DCNA study. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article.

Het Caribbean Netherlands Science Institute dat samenwerkt met het Queen Conch Lab van de Florida Atlantic University, onderzoekt de gevolgen van een veranderende samenstelling van zeegrassoorten op lokale kroonslakpopulaties. Kroonslakken zijn gedurende hun hele levenscyclus sterk afhankelijk van inheems zeegras, dus de achteruitgang van inheemse velden kan een bedreiging vormen voor de kroonslak, niet alleen op Sint Eustatius, maar in het hele Caribische gebied.

De kroonslak is een iconische soort voor het Caribisch gebied. Naast hun prachtige schelp spelen kroonslakken een belangrijke rol in de lokale keuken, evenals een rol bij het grazen van zeegras, waardoor de algengroei onder controle wordt gehouden. Kroonslakken zijn gedurende hun hele levenscyclus afhankelijk van inheems zeegras. In feite beginnen kroonslakken als microscopisch kleine, vrij zwevende larven, die overal in de waterkolom te vinden zijn. Na ongeveer 21 dagen rondzwemmen, vertellen signalen uit hun omgeving, voornamelijk inheemse zeegrasvelden, hen dat het tijd is om zich te vestigen en te veranderen in een grazer die in het zand leeft.

Het probleem

Helaas wordt het inheemse zeegras rond Sint Eustatius vervangen door een invasieve soort uit de Rode Zee. Dit nieuwe zeegras creëert een compleet ander leefgebied, wat invloed heeft op het functioneren van het ecosysteem en kan leiden tot veranderingen in de samenstelling en overvloed van verwante soorten (zoals de kroonslak). Het is onduidelijk of deze invasieve soorten dezelfde aanwijzingen geven aan de kroonslak als hun inheemse tegenhangers. Om deze impact beter te begrijpen, onderzoekt een nieuw project, gefinancierd door het INNO-fonds van het Wereld Natuur Fonds en het SPAW Regional Activity Centre, geleid door het Caribbean Netherlands Science Institute in samenwerking met Megan Davis van het Harbor Branch Oceanographic Institute van de Florida Atlantic University, deze impact .

Kroonslak. Photo credit: Marion Haarsma

Het project

De eerste stap van het project is het verzamelen van eieren van wilde kroonslakken. De vrouwelijke kroonslak legt haar eieren in een dunne kleverige draadachtige omhulling. Deze draad bundelt zich tot een eimassa, vaak bedekt met zand, dus het kan erg moeilijk te vinden zijn. Elke draad bevat miljoenen eieren, dus slechts een klein deel van deze eimassa (ter grootte van een euro munt) is nodig voor het experiment. Eenmaal verzameld, worden de eieren naar een laboratorium vervoerd waar ze in een tank kunnen worden geplaatst om dagelijks te worden gecontroleerd. Na 4-5 dagen komen de eieren uit, waardoor veel microscopisch kleine larven in het aquarium terechtkomen.

Tijd om uit te komen

Zodra de eieren zijn uitgekomen, worden ze in kleine hoeveelheden naar individuele bekers verplaatst, zodat ze gemakkelijk kunnen worden gevoerd en gecontroleerd. Zodra ze ongeveer 1 mm lang zijn, zijn ze bijna klaar voor hun metamorfose, ongeveer 21 dagen. De laatste fase van het project is om verschillende signalen aan de larven te geven om te zien hoe ze reageren. In totaal worden vier verschillende signalen in verschillende combinaties gebruikt. Deze signalen omvatten twee inheemse zeegrassen, het invasieve zeegras en dat van kaal zand. De hierop volgende week worden de larven gecontroleerd op ontwikkeling.

Meer weten over dit project? Volg mee met hoofdwetenschapper Dr. Kimani Kitson-Walters en bekijk de volgende vlog: https://youtu.be/ioXYjohQCeg

Updates van dit project zullen ook worden vermeld in toekomstige BioNews-artikelen.

DCNA

De Dutch Caribbean Nature Alliance (DCNA) ondersteunt wetenschaps communicatie en bereik in de Nederlandse Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en via de pers. Dit artikel bevat de resultaten van een van die wetenschappelijke onderzoeken, maar het onderzoek zelf is geen DCNA-onderzoek. Aan de inhoud kunnen geen rechten worden ontleend. DCNA is niet aansprakelijk voor de inhoud en de indirecte gevolgen die voortvloeien uit het publiceren van dit artikel.

Published in BioNews 61

A new survey technique provides insight into Queen Conch populations off the islands of Anguilla, St. Eustatius and within the Saba Bank. This research offers new information concerning Queen conch population distribution, useful for management authorities. Queen conch population in the Caribbean in general  have been decimated by intense fishing pressure so improving surveying techniques will aid in their overall management in the region. 

Queen conch. Photo source: Mark Vermeij

Queen conchs (Aliger gigas) are an iconic species of the Caribbean, representing both economic and cultural importance. Unfortunately, these species are heavily exploited, as their meat is popular in local cuisine and their shells are popular decorative pieces. Historically population data for Queen conch were gathered using dive surveys, however, these can be logistically demanding and expensive and limited to depths accessible to divers. Luckily, a new collaborative study by Wageningen University and Research, Chicago’s Shedd Aquarium, Van Hall Larenstein University of Applied Sciences and the Royal Netherlands Institute for Sea Research worked to improve these population estimates by implementing a novel towed video system.   

New Techniques 

Through combining traditional dive surveys with the towed video system, researchers can now explore species abundance to a depth of 60 m. In addition, this method allows new relationships between environmental variables and conch abundance through this range which had previously been poorly studied. It is understood that Queen conch move to deeper waters as they mature, so being able to document these deeper depths will give researchers and managers a more complete view of conch populations.   

The Results 

Surveys were conducted throughout three different locations: Anguilla, St. Eustatius and within the Saba Bank. Saba Bank was found to have the highest overall mean conch density, with an average of 126 conch per hectare, and ranged from depths of 16 m to 50 m. St. Eustatius was found to have a mean density of 62 conch per hectare, ranging from depths of 11 m to 45 m. For all three locations the highest densities of conch were found in water deeper than 25 m, with densities of 393 conch/ha at depths greater than 40 m on Saba Bank and 285 conch/ha at depths greater than 30 m on St. Eustatius. 

In general, this study found patchy distribution patterns of adult conch, likely due to aggregating behavior during spawning events. Other environmental factors, such as algal cover, distance to the open ocean and depth were also shown to impact conch abundance. Depths between 17 and 45 m were shown to have the greatest number of reproductive conch, highlighting the importance of safeguarding these areas to protect the reproductive capacity for these populations in the future. 

Source: Marion Haarsma

Recommendations 

With this new information, management authorities can now focus their attention to areas likely to host Queen conch populations. Researchers from this project recommend that future Queen conch surveys operate over a range of depths while sampling a variety of bottom conditions. These results can then be analyzed to better understand the connection between the conch distribution and local or regional factors. Although each island may require their own approach, this study highlights that many of these factors may be universal and should be considered when designing future campaigns. 

There is still much to be learned about Queen conch, such as the impact of algal cover or shifts in seagrass densities and species on their foraging behaviors. Gaining a holistic understanding of local conch populations will aid in the design and implementation of effective conservation projects moving forward. To learn more about this project, you can find the published article on the Dutch Caribbean Biodiversity Database by using the link below. 

Report your sightings  

Have you observed an Queen conchs? Report your nature sightings and photos on the website DutchCaribbean.Observation.org or download the free apps (iPhone (iObs) & Android (ObsMapp)). Species reports by local communities and tourists are invaluable for nature conservation efforts to help increase public awareness and overall species protection. Besides, DCNA, Observation International and Naturalis Biodiversity Center are working together to develop on automated species identification app for your phone. Your uploaded photos are of great value to make this possible. For questions, please contact research@DCNAnature.org  

Read more  

You can learn more about this research by reading the published article on the Dutch Caribbean Biodiversity Database using the button below. 

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 52

There has been a recent increase in public awareness of environmental issues as the effects of climate change have become ever more noticeable in our daily lives. As we enter a new decade, it becomes useful to review what conservation efforts have worked so far, and take inventory of what efforts will be required for the future. Starting with the constitutional referendum creating the Caribbean Netherlands (Bonaire, St. Eustatius and Saba (BES), the response to conservation challenges of all six Dutch Caribbean islands have varied. Since 2010, the BES islands have seen an overall increase in funding support and conservation actions, and therefore presumably also saw greater improvements when compared to Aruba, Curaçao and Sint Maarten, though clearly not enough (Sanders et al, 2019).

The goal of this Transboundary Species special edition of BioNews is to provide an update on the latest published research results and highlight the need for transboundary protection. These species know no boundaries, and thus move between the Dutch Caribbean islands and beyond. Their protection will require broadscale conservation efforts which cover the entire Caribbean, including the six Dutch Caribbean islands. Collaboration between all six islands is of the utmost importance. This is one of the Dutch Caribbean Nature Alliance’s (DCNA) main goals: working together and sharing skills, knowledge and resources to maintain a solid network and support nature conservation in the entire Dutch Caribbean.

The Queen conch Strombus gigas, a large marine gastropod, is found in the territorial waters of 36 countries and tettitories in the Caribbean region.  Over the past decades, intensive fishing has led to population declines resultin gin the total or temporal closure of the fishery in a number of locations.  Since November 1992, the species has been included in Appendix II of CITES.  In 2002, concerns about levels of illegal trade led to a "review of Significant Trade" in queen conch by TRAFFIC on behalf of the CITES.  For this review, data on commercial fisherisies landings, CITES trade data, stock status, and management measures were compiled with the assistance of CITES and fisheries authorities, and regional experts.

Large-scale distribution of a large, commercially significant gastropod, Strombus gigas (queen conch), was investigated in a II ,OOO-haregion of the Great Bahama Bank near Lee Stocking Island, Exuma Cays. Maps of depth and seagrass biomass, generated with Landsat thematic mapper data, and a 4-year survey of juvenile conch distribution showed that most of the juveniles were in aggregations located in 1.5-4.0-m water depth. Although general locations of juvenile conch aggregations remained the same between 1989 and 1992, their total surface area occupied only about 1.5% of the 8,300 ha of seagrass habitat available. Locations of only the most persistent long-term aggregations could be predicted on the basis of preferred seagrass biomass (30-80 g dry weight m-2); however, important conch nurseries were always located in tidal channels which brought clear, oligotrophic water from the Exuma Sound. Harmonic analysis of water temperature data from sites with and without juvenile aggregations showed that conch nurseries were subject to flushing with oceanic water on every tide, whereas non-conch sites reflected only diurnal heating and cooling of bank water. Relationships between circulation and juvenile conch distribution on the Great Bahama Bank may be related directly to larval recruitment, or indirectly to aspects of nutrient cycling and food production; evidence for both mechanisms exists. Although exact locations of conch aggregations shift from year to year, these shifts appear to occur within larger nursery habitats, the boundaries of which are set by a precise combination of physical and biological factors. Because most meadows are probably unsuitable for this severely ovcrfished species, critical nursery habitats should be identified and protected. 

ABSTRACT: Effectiveness of a marine protected area (MPA) in supporting fisheries productivity depends upon replenishment patterns, both in supplying recruits to surrounding fished areas and having a sustainable spawning stock in the MPA. Surveys for queen conch Strombus gigas were made in 2011 at 2 locations in the Exuma Cays, The Bahamas, for direct comparison with surveys conducted during the early 1990s at Warderick Wells (WW) near the center of the Exuma Cays Land and Sea Park (ECLSP) and at a fished site near Lee Stocking Island (LSI). There was no change in adult conch density and abundance in the shallow bank environment at LSI where numbers were already low in 1991, but numbers declined 91% in the deeper shelf waters. At WW, the adult population declined 69% on the bank and 6% on the island shelf. Unlike observations made in the 1990s, queen conch reproductive behavior near LSI is now rare. Average age of adult conch (indicated by shell thickness) at LSI decreased significantly during the 20 yr period between surveys, while average age increased at WW and juvenile abundance decreased. These results show that the LSI population is being overfished and the WW population is senescing because of low recruitment. In 2011, the ECLSP continued to be an important source of larvae for down- stream populations because of abundant spawners in the shelf environment. However, it is clear that the reserve is not self-sustaining for queen conch, and sustainable fishing in the Exuma Cays will depend upon a network of MPAs along with other management measures to reduce fishing mortality. 

ABSTRACT: There is increasing recognition that habitats should be managed as part of fisheries management. It is generally assumed that amount of suitable habitat is linked to production of de- mersal species and that maps of bottom type will provide the information needed to conserve essen- tial habitats. In this review, a synthesis of nursery habitat is made for Strombus gigas (queen conch), a large, economically important gastropod in the Caribbean region. Juveniles occur on a variety of bottom types over their geographic range. In the Bahamas, nurseries occur in specific locations within large, beds of seagrass, while obvious characteristics of the benthic environment such as seagrass density, depth and sediment type are not good predictors of suitable habitat. Rather, nurseries persist where competent larvae are concentrated by tidal circulation and where settlement occurs selec- tively. Nursery locations provide for high juvenile growth resulting from macroalgal production not evident in maps of algal biomass, and they provide for low mortality compared with seemingly simi- lar surroundings. Therefore, critical habitats for queen conch juveniles are determined by the inter- section of habitat features and ecological processes that combine to yield high rates of recruitment and survivorship. While maps of bottom type are a good beginning for habitat management, they can be traps without good knowledge of ecological processes. A demersal species can occupy different substrata over its geographic range, different life stages often depend upon different bottom types, and specific locations can be more important than particular habitat forms. Habitat management must be designed to conserve habitat function and not just form. Implicit in the concept of ‘essential habitat’ is the fact that expendable habitat exists, and we need to prevent losses of working habitat because of inadequate protection, restoration or mitigation. Key nurseries may represent distinctive or even anomalous conditions. 

An important scientific workshop on queen conch was held in Caracas, Ven­ ezuela, in July 1991. This workshop and the proceedings that emerged from it (Appeldoom and Rodriguez, 1994) pro­ vided a good background on the status of research on biology, fisheries, and mariculture of the queen conch. Be­ cause the general biology of the queen conch is already relatively well known, the purpose of this paper is to summa­ rize some of the important advances made in the study of queen conch since the 1991 workshop. Emphasis has been placed on topics related to the ecology of queen conch that are most relevant to fisheries management and stock re­ habilitation. In the following sections an attempt has been made to draw con­ clusions about habitat requirements for the species, mortality of juveniles as it relates to stock rehabilitation and en­ hancement, larval ecology and fisher­ ies oceanography of the species, and the conservation of reproductive stocks.