Article

Reproduction, Laboratory Culture, and Growth of Strombus Gigas, S. Costatus and S. Pugilus in Los Roques, Venezuela

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Abstract

Egg masses of Strombus gigas, S. costatus, and S. pugilus were gathered from depths of 3 to 18 m in the western part of the Los Roques Archipelago, Venezuela. S. gigas spawns from early July through mid-November. S. costatus begins spawning in November, and continues until May. S. pugilus egg masses were first discovered on March 29. Eggs were hatched in the laboratory and veligers fed enriched natural cultures of phytoplankton. Juveniles were fed various species of algae which grew naturally on the sides of the tanks, plus algae growing on rocks, which were introduced into the tanks. Preliminary growth data show S. gigas reaching a length of 31.7 mm in 171 days after hatching. After 175 days, S. costatus reached 42.7 mm. S. pugilus attained a mean length of 20.9 mm after 121 days. Mariculture potential and some aspects of the ecology of the three species, especially the juveniles, are discussed.

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... Given the nature of gregarious mating in the Strombidae, and that males will seek out virgin females irrespective of body size, it is unlikely that females influence male mate choice as males are not inhibited in copulation by this open mating system (Brownell 1977;Catterall and Poiner 1983;Tewfik et al. 1998). Furthermore, there is no evidence of internal female sperm selectivity (Simone 2005). ...
... While intra-specific competition appears to limit the benefits of small male size through ease of displacement, the smaller size does correspond to faster development and increasing mating potential for smaller males prior to the maturation of larger males, particularity as spawning in the Strombidae, while seasonally variable, occurs throughout the year. This means that smaller males are likely to fertilise initial spawning events prior to the maturation of larger males (Brownell 1977;Cardenas et al. 2005;Irie and Morimoto 2008). Therefore, in general, there are two intraspecific forces acting on the size of males relevant to the modelling of sexual size dimorphism: one force driving an increase in size through intra-sexual competition, and a second opposing selective force for smaller males, driven by the benefits of rapid maturity and consequential maximisation of reproductive potential. ...
... 7. males seek out larger females as primary targets for mating. However, the impact of this selectional pressure is reduced as males also prefer virgin females (Brownell 1977;Tewfik et al. 1998;Zahradnik et al. 2008); ...
Thesis
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This dissertation presents a classical revision of Strombus urceus Linné, 1758 post Abbott 1960 (Mollusca, Neostromboidae, Strombidae) and has resolved this monospecific group into twelve species. This involved a review and the presentation of novel theories in the areas of speciation, hybridisation and clade recognition. The species concept was reviewed and a new theory for species conception was generated, essentialistc pluralism, which frees the taxonomist from the rigidity of a species conceptuality and enables the taxonomist to define a taxon based on the taxonomist’s perceived necessity. The novel idea of species and subspecies was reconceptualised such that subspecies is a rank that is restricted to those organisms where differences in genetic sequence data are the only way to distinguish organisms. If organisms can be differentiated without the use of genetics, then these are to be considered full species. The novel theory of how hybridisation leads to recognisable speciation, in particular when a set of organisms become identifiable as distinct species in real time, is identified. At the supraspecies level, the principles for clade recognition is presented. These principles are applied to circumscribe and define the clades that contain the target species below the level of superfamily using phylogenetic nomenclature. This is the first work to demonstrate that morphologically generated clades are acceptable in the diagnostic process required under the PhyloCode, demonstrated by their accepted registration by that body. This study is also the first to use phylogenetic nomenclature in the Mollusca. In order to achieve this recognition, the internal clades within Stromboidae were recognised and defined, something all workers on the complex have failed to do. These are supported by morphological differences and fall into discrete biogeographical regions. This thesis also presents a novel model that seeks to explain the spatiotemporal expression of sexual size dimorphism in stromboidians. Females show significant differences in the shape of the shell, which is reflected in the shape of the body whorls and width of the anterior aperture. Historically, the presence of a black aperture in what is now considered different species was an argument for the synonymisation of them. Using morphometric data and DArTseq data, I demonstrate that this phenotype does not define a species, and is considered a historical phylotypic remnant of a speciation or hybridisation event. The phylogeography of the species complex is presented with reference to interglacial periodicity, current dispersal potential, ecological barriers, and DArTseq data and morphometrics. At the species and intraspecies taxonomic levels, the type of Strombus urceus was identified and the species taxonomically stabilised after 200 years of instability. The synonymy of Strombus urceus was found to contain four valid species, one of which required recircumscription. Two subspecies were recognised prior to this study, both of which have now been recircumscribed as species. A total of six new taxa were recognised, resulting in the deconstructing of the once monotypic complex into twelve species. This thesis demonstrates that Abbott (1960) greatly underestimated stromboidean diversity and that, with biogeography and classical morphological analyses, species can be robustly described and radiation patterns postulated.
... To ensure that known spawning sites, including putative deep-water spawning locations, were included in the habitat layer, we ground-truthed our habitat map with spawning sites reported in the literature (Randall, 1964;D'Asaro, 1965;Brownell, 1977;Davis et al., 1984;Weil and Laughlin, 1984;Coulston et al., 1987;Wilkins et al., 1987;Wicklund et al., 1991;Berg Jr. et al., 1992;Garcıá-Escobar et al., 1992;Stoner and Sandt, 1992;Maŕquez-Pretel et al., 1994;Lagos-Bayona et al., 1996;Peŕez-Peŕez and Aldana-Aranda, 2003;Garcia-Sais et al., 2012;Cala et al., 2013;de Graaf et al., 2014;Meijer zu Schlochtern, 2014;Wynne et al., 2016;Truelove et al., 2017). Following this review, we incorporated 13 shallow-water polygons not initially present in our habitat layer in St. Eustatius, USVI, Colombia, Florida, Mexico, Jamaica, Saba, Bonaire, and The Bahamas (Randall, 1964;Coulston et al., 1987;Garcıá-Escobar et al., 1992;Maŕquez-Pretel et al., 1994;Meijer zu Schlochtern, 2014;Truelove et al, 2017). ...
... Following this review, we incorporated 13 shallow-water polygons not initially present in our habitat layer in St. Eustatius, USVI, Colombia, Florida, Mexico, Jamaica, Saba, Bonaire, and The Bahamas (Randall, 1964;Coulston et al., 1987;Garcıá-Escobar et al., 1992;Maŕquez-Pretel et al., 1994;Meijer zu Schlochtern, 2014;Truelove et al, 2017). We also included an additional 14 putative deep spawning sites, located outside of our polygons, as spawning sources exclusively for Venezuela, Cuba, The Bahamas, USVI, Turks and Caicos Islands (TCI), Saba, Colombia, Belize, Honduras, Puerto Rico and Jamaica (i.e., Pedro Bank) (Randall, 1964;Brownell, 1977;Davis et al., 1984;Weil and Laughlin, 1984;Wicklund et al., 1991;Stoner and Sandt, 1992;Lagos-Bayona et al., 1996;Aiken et al., 2006;Garcia-Sais et al., 2012;Cala et al., 2013;de Graaf et al., 2014; (Spalding et al., 2001;IMaRS-USF 2005;IMaRS-USF and IRD 2005;Andrefouët, 2008;. Individual habitats are buffered to facilitate visualization and are not represented to scale. ...
... The Weibull curve was the best fit overall, and the best-fit Weibull curve parameters were then averaged to create a single curve that could be applied to all jurisdictions, representing that the ramping up of spawning occurs at a slightly higher rate than the ramping down of spawning after the peak (SI Figure 1). We compiled the month of spawning peak and onset for each jurisdiction from published visual surveys of reproductive output and gonadal histological studies (Randall, 1964;D'Asaro, 1965;Hesse, 1976;Brownell, 1977;Davis et al., 1984;Appeldoorn, 1985;Cruz, 1986;Salley, 1986;Corral and Ogawa, 1987;Coulston et al., 1987;Berg et al., 1992;Stoner et al., 1992, Appeldoorn, 1993. Márquez-Pretel et al., 1994Aldana-Aranda et al., 2003;Avila-Poveda and Baqueiro-Caŕdenas, 2009;Bissada, 2012;Appeldoorn and Baker, 2013;Cala et al., 2013;Aldana-Aranda et al., 2014;Meijer, 2014;de Graaf et al., 2015;Wynee, 2016;Boman et al. 2018;Tiley et al. 2018;Delgado and Glazer, 2020). ...
Article
Full-text available
The queen conch, Aliger gigas, is an endemic and iconic marine gastropod of the Wider Caribbean region that has been harvested for thousands of years. Conch are slow-moving and require contact to mate; overfishing has reduced populations in many areas compromising its rates of reproduction. Long-range dispersal and mixing between distinct populations occur in the queen conch’s early life history stages, when pelagic larvae are transported by oceanic currents. Genetic studies suggest that gene flow between populations decreases as the distance between populations increases. Here, we assessed how the population connectivity of conch changes with spatially variable patterns of fishing exploitation by simulating larval dispersal and comparing the potential connectivity under an unexploited and a contemporary exploited reproductive scenario. Results demonstrate that reduced egg production, due to heterogeneous fishing pressure and localized depletion, significantly alters population connectivity patterns as well as the structuring of populations and metapopulations across the species’ range. This strongly suggests that estimates of contemporary demographic rates, together with estimates of reproductive output need to be included in population connectivity studies. The existence of self-sustained metapopulations of queen conch throughout the Wider Caribbean suggests that replenishment through larval dispersal occurs primarily within sub-regional spatial scales, emphasizing the need for regional and local conservation and management measures to build and protect reproductively active populations and nursery habitat across multiple jurisdictions.
... Given the nature of gregarious mating in the Strombidae, and that males will seek out virgin females irrespective of body size, it is unlikely that females influence male mate choice as males are not inhibited in copulation by this open mating system (Brownell 1977;Catterall and Poiner 1983;Tewfik et al. 1998). Furthermore, there is no evidence of internal female sperm selectivity (Simone 2005). ...
... While intra-specific competition appears to limit the benefits of small male size through ease of displacement, smaller size does correspond to faster development and increasing mating potential for smaller males prior to maturation of larger males, particularity as spawning in the Strombidae, while seasonally variable, occurs throughout the year. This means that smaller males are likely to fertilise initial spawning events prior to the maturation of larger males (Brownell 1977;Cardenas et al. 2005;Irie and Morimoto 2008). Therefore, in general, there are two intra-specific forces acting on the size of males relevant to the modelling of sexual size dimorphism: one force driving an increase in size through intra-sexual competition, and a second opposing selective force for smaller males, driven by the benefits of rapid maturity and consequential maximisation of reproductive potential. ...
... The time taken to mature affects the reproductive potential, and larger males take longer to achieve sexual maturity (Irie and Morimoto 2008); (7) males seek out larger females as primary targets for mating. However, the impact of this selection pressure is reduced as males also prefer virgin females (Brownell 1977;Tewfik et al. 1998;Zahradnik et al. 2008); (8) predation occurs primarily during the veliger life-stage and is not considered a major selection factor for inter-population or sex-specific size differences in the Strombidae (Wiedemeyer 1998;Stoner et al. 1998;McIntyre et al. 2006;Preston and Roberts 2007); (9) no intra-population resource access pressures generate sexual dimorphism within a population in Strombidae. The animals are phytophagous raspers living in gregarious populations (Abbott 1960;Catterall and Poiner 1983); (10) sexually dimorphic differences in soft-part morphology are a consequence of allometric physiological differences among sexes or, in rare cases where there appears to be no physiological explanation, a consequence of fluctuating asymmetry (Colton 1905;Mutlu 2004;Simone 2005); (11) in gastropods, larger females, have higher reproductive success (Shawl and Davies 2004;Cardenas et al. 2005); and (12) Cope's Rule in terms of small animals, which states that taxa evolve larger body sizes through time to maximise reproductive potential and heighten the exploitation of resources where carrying capacity is not a signifcant regulator of population size, or where is there no other constraining limiations on size (Blanckenhorn 2000). ...
Article
Full-text available
Modelling sexual dimorphism has important implications for understanding the evolution of size relationships among and within organisms. We present a composite model for the regulation and evolution of sex-specific inter-population shell size in a family of herbivorous marine molluscs, the Strombidae. In particular, this model postulates that gene flow acts as a size regulator that limits inter-population divergence by not allowing the mean size of each sex to deviate significantly between disparate populations. The mean shell size of individuals within populations is affected by the ecological setting in which the animal is growing. The model considers niche divergence as inconsequential in the regulation of sexual dimorphism, whereas environmental regulation for the mean size of a population is considered a significant driving factor. Sexual competition, where males may dislodge other males during copulation, is also considered a non-significant driver of male body size because of the open mating system. In such a system, smaller males can simply mate before larger males have matured. Selection for earlier mating in males so as to maximise lifetime fecundity favours male maturation at small body sizes. Conversely, greater fecundity at larger body size in females argues for larger females. The postulated composite model presented here fills a knowledge gap by graphically illustrating the factors affecting inter-and intra-specific variation. These differences include the modelling of mean inter-population shell size, as well as the regulation of intra-population sex size ratios. The components of this new model can be applied to a wider range of sexually dimorphic organisms to explain the evolutionary factors involved in regulating the observed sexual dimorphism.
... There appears to be no uniform pattern of migration directly related to reproduction other than availability of high-quality foods for the non-reproductive season coupled with adjacent sandy habitat for best possible mate-finding and egg-laying during the reproductive period. Egg masses have been found in water depths from 2 to 45 m (Robertson 1959;Brownell 1977;Iversen et al. 1987;García-Sais et al. 2012). ...
... Queen conch females store sperm in the receptaculum seminus (see Sec. 2.1) and eggs are fertilized as they are laid. In dense populations of adults more than 1 male is frequently observed near a female, particularly when eggs are being laid (Brownell 1977;Weil and Laughlin 1984), mating is frequent, and it is known that multiple males can fertilize the same egg mass (Reed 1995b;Medley 2008). Furthermore, female queen conch are known to copulate and lay eggs at the same time (Randall 1964;Buckland 1989) (Figure 6), and Weil and Laughlin (1984) concluded that egg-laying females were more attractive to males than mating females, suggesting that the egg-laying process might produce pheromones. ...
... The consensus is that most intensive reproductive behavior begins with the rise of ambient water temperature or some threshold of temperature often observed in April or May. Subsequently, reproduction continues through the warmest summer months, and declines in parallel with temperature in the fall (e.g., Brownell 1977;Weil and Laughlin 1984;Buckland 1989). Shawl and Davis (2004) reported that egg-laying in captive strombid species was directly related to water temperature. ...
Article
Full-text available
The queen conch (Aliger gigas) is a culturally and economically important molluskan fishery resource in the Caribbean region showing increasing signs of over harvest. Shallow-water distribution and large size facilitate capture, and internal fertilization and density-dependent reproduction make managing for reproductive biology critical to stock rehabilitation. In fact, the natural lifetime fecundity of conch is very high but most fisheries in the region harvest conch before even a small fraction of that reproductive potential can be attained. The goal of this review is to provide an up-to-date synthesis of the vast research literature on queen conch biology (spanning >60 years) and to discuss how knowledge of reproduction in conch can help to guide field surveys, fishery management decisions, and stock recovery projects. The review covers the subjects of anatomy, maturation and fecundity as they relate to conch age and size, reproductive behavior including migrations, seasonality, mating, and egg-laying, and the influences of both environmental and demographic variables on reproductive potential. Successes and failures under different forms of management practice are discussed as they relate to reproductive biology and recommendations are made for future research and fishery management alternatives. Successful management will require multiple regulatory approaches.
... A combination of aquaculture and stock enhancement using hatchery-produced juveniles of L. turturella has been proposed for their conservation and sustainable use (Cob et al. 2009a;Supratman and Syamsudin 2016). Commercial aquaculture and restocking programs have been conducted with other Strombus such as Aliger gigas, Macrostrombus costatus, and S. pugilis (Appeldoorn 1985;Brownell 1977;Aldana-Aranda and Suarez 1998). However, the success rate of restocking into the natural population highly varies and still needs further improvement (Stoner 2019). ...
... Under the conditions of abundant food and in the absence of predators in laboratory culture, they actively feed during the day and night. According to Brownell (1977), in a natural environment, feeding during daylight is probably minimal owing to the presence of predators. However, they are very selective during feeding, as indicated by active probing before consumption. ...
... Other Strombus juveniles are extensively reported living as infauna during the early development stage (Brownell 1977;Sandt and Stoner 1993). In the present study, newly metamorphosed and small juveniles from field (0 + year and < 1 cm shell length) never completely burrowed into the sediment. ...
Article
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The dog conch, Laevistrombus turturella, is an important marine resource of ecological and economic importance in the Southeast Asian region. Natural populations of L. turturella are under threat due to development and overexploitation, so efforts should be taken in culturing this species for commercial and conservation purposes. This study aimed to fill the knowledge gap in the life-history characteristics of L. turturella by investigating the growth and behavior of early juvenile L. turturella under laboratory conditions. Egg masses of L. turturella were collected from conch natural-spawning habitat. Upon reaching the late veliger stage (stage IV), L. turturella larvae was chemically induced, and newly metamorphosed juveniles were reared in small-scale laboratory microcosms. The microcosms were placed in an incubator at 28 °C and under 12:12 h light-dark condition, with very minimal aeration. Specific behavioral characteristics were observed at the onset and during the metamorphosis, and these characteristics resulted in highly camouflaged juveniles covered by surrounding sediment and debris. Burrowing behavior was first observed at day 56 post settlement, but they were only partially buried. Generally, juvenile conch showed fast and continuous growth, which were best modelled by fitting linear equations. Thus, a minimum size of 10 mm-shell-length juveniles is recommended for restocking. All these results indicated the technical viability of producing hatchery-reared juveniles for commercial purposes and for enhancing natural-stock populations.
... After sexual maturity (around four years old), the rate of tissue growth decreases, and switches from primarily thickening of the meat, to increasing the weight of the gonads. Once the conch is around ten years of age, the shell volume starts to decrease, as layers of the mantle are laid down from the inside (Randall 1964 (Appeldoorn 1985), while juveniles in hatcheries grew 0.3mm/day (Brownell 1977;Ballantine and Appeldoorn 1983). Conch in Exuma grew an average of 0.12mm/day (Wicklund et al. 1991) and 0.3mm/day in Barbados (Phillips et al. 2011). ...
... During this planktonic stage, the conch larvae feed on phytoplankton. If the larvae do not receive the right amount of nutrition during this period, development can be delayed (Brownell 1977). ...
... Export Reference 1943 2619 Lockhart et al. 2007Lockhart et al. 1969 16. 4 Lockhart et al. 20071970-1980100-200,000/year Brownell and Stevely 1981 1.9 million conch Brownell andStevely 1981 1978 400 Illegal poaching is known to be an issue in TCI, and steps are being made to control it by introducing a new satellite monitoring program to detect foreign vessels which is functioning as of August 2012 (Wood 2012;. Personnel shortages and lack of funding are also contributing to this problem of IUU fishing, and and recruitment for enforcement personnel is happening. ...
... The first four communities develop within the benthic realm that is much more diverse in comparison to the pelagic, and clusters more mature and complex communities due to its lesser exposure to random environmental fluctuations [35]. The marine resources of these islands, highly coveted by man, are turtles [38][39][40][41][42][43], lobsters [44,45], reef fishes [46][47][48], and Strombus gigas [39,[49][50][51]. Los Roques and, to a lesser extent, Las Aves de Sotavento Archipelago, sustain large populations of Strombus gigas. ...
... All five species of Strombidae are present in Los Roques Archipelago [96,97], although Strombus gigas is, by far, the most abundant [49,96,97]. In this archipielago, large areas of sea grass beds, mainly Thalassia testudinum and Syringodium filiforme, cover an area of about 5400 km 2 with a depth between 0.5 to 1 m [50]. ...
... The area that surrounds Dos Mosquises Island is one of the best-studied habitats of Strombus gigas in the Caribbean [29,39,49,51,94,98]. On the east of the island to a depth of one meter, a 50-m wide strip of Thalassia testudinum covers an area of approximately 3400 m 2 . ...
Article
Full-text available
This paper examines the pre-Hispanic assemblage of queen conch (Strombus gigas) remains recovered during systematic archaeological excavations at the Los Roques Archipelago, 135 kilometers off the coast of Venezuela. Amerindian sailors belonging to different cultures from mainland north-central Venezuela, occupied these islands periodically between A.D. 1200 and 1500. The data indicate that the pre-Hispanic exploitation of marine animals in this group of islands was focused on the queen conch, which is absent or rare on the mainland coast. This mollusk has been highly coveted by the Amerindian mainland groups as food and as a raw material. The shell was coveted as well as an exotic good and social status marker used in the production of personal ornaments and funerary offerings. The data discussed here are useful for archaeological reconstruction of eco-nomic, social and ideological aspects of queen conch exploitation. These data can be compared to those of modern fishery statistics through interdisciplinary research and will also provide valuable information for the reconstruction of the history of queen conch populations at the Los Roques Archipelago. Finally, it could help determine long-range fishery management strategies and policies of this endangered species.
... D' Asaro (1965) had cultured queen conch through larval stages and provided detailed descriptions of the veligers (see also Davis et al. 1993), but Berg was the first to culture conch through metamorphosis to benthic juvenile stages. Interest in culturing queen conch toward the goals of stock restoration and direct grow-out for food increased rapidly after that (see Siddall 1983Siddall , 1984, and by the early-1980s cultures of queen conch to juvenile stages had been successfully accomplished in Venezuela (Brownell 1977;Laughlin and Weil 1983), Puerto Rico Ballantine and Appeldoon 1983), the Turks and Caicos Islands (Davis and Hesse 1983;Davis et al. 1987;Davis and Dalton 1991), The Bahamas (Heyman et al. 1989), Florida, Mexico, Bonaire and the Virgin Islands (Jory and Iversen 1985). While it took dedicated efforts in several laboratories to advance cultures from beakers to hatchery scale, and many of the research programs listed above ended for lack of funding, it is now possible, with a supply of field-collected egg masses, clean seawater, algal cultures for food and meticulous husbandry, to reliably produce thousands (or millions) of larvae ready for metamorphosis in 2 and 3 weeks in relatively small land-based systems. ...
... Predicting locations for good growth Unlike some mariculture species, queen conch do not grow rapidly. Brownell's early studies in Venezuela showed that average growth rate for early post-settlement conch is $0.2 mm/day (Brownell 1977), which results in growth from 2 mm shell length at settlement to $75 mm in 12 months after metamorphosis depending upon temperature. Early enthusiasm for queen conch culture in the 1980s hinged in part upon Berg's (1976) suggestion that market size could be achieved in 2.5 years. ...
Article
Full-text available
Rehabilitating overfished species through releases of cultured juveniles depends upon growth and survival of those animals in the field. Releasing cultured queen conch (Strombus gigas) was proposed 40 years ago to rebuild over-harvested populations. Hatchery culture has been perfected and thousands of juveniles can be produced with meticulous husbandry. Many field experiments have been conducted with hatchery-raised queen conch since the early 1980s, but the results cast doubt regarding stock enhancement. Queen conch demonstrates high natural mortality rates, and cultured conch can have morphological and behavioral deficiencies that diminish survival. Deficiencies can be reduced with perfect culture conditions and prerelease field conditioning; and survival can be improved by releasing large juveniles, but all of these measures add to cost of seed stock. Also, release requirements are problematic. Habitat selection, release timing, and release patterns are all critical for reducing predation losses. While all of these challenges have been considered , no field release has resulted in survival rates that are encouraging. The cost of stock restoration through release of cultured queen conch will be enormously expensive, if successful at all, and every effort should be made to conserve wild populations. Hatchery production for stock restoration should be considered a last resort.
... Se han establecido varias alternativas para superar esta situación y recuperar las poblaciones sobreexplotadas de L. gigas, como la creación de áreas marinas protegidas (AMP) (Appeldoorn, 1994;Stoner, 1996;Anon, 1999) que permitan preservar la alta densidad del stock de desove y el mantenimiento de un refugio para los adultos con mayor capacidad de reproducción (Anon, 1999). Otra alternativa es la acuicultura con técnicas dirigidas a la producción de juveniles (Brownell, 1977;Creswell, 1994). ...
... In order to overcome this situation and to recover the overexploited populations of L. gigas, several alternatives have been established, such as the creation of marine protected areas (MPA's) (Appeldoorn, 1994 ;Stoner, 1996;Anon, 1999) which allow the preservation of spawning stock at high densities and maintain a haven for adults with higher reproducibility (Anon, 1999). Another alternative is aquaculture with techniques directed to produce juveniles (Brownell, 1977;Creswell, 1994). ...
Article
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Bacterial community structure in different tissues of the wild Lobatus gigas (Linnaeus, 1758) from the Caribbean Seaflower Biosphera Reserve Mónica Marcela Higuita-Valencia, Olga Inés Montoya Campuzano, Edna Judith Márquez Fernández, Claudia Ximena Moreno Herrera
... Se han establecido varias alternativas para superar esta situación y recuperar las poblaciones sobreexplotadas de L. gigas, como la creación de áreas marinas protegidas (AMP) (Appeldoorn, 1994;Stoner, 1996;Anon, 1999) que permitan preservar la alta densidad del stock de desove y el mantenimiento de un refugio para los adultos con mayor capacidad de reproducción (Anon, 1999). Otra alternativa es la acuicultura con técnicas dirigidas a la producción de juveniles (Brownell, 1977;Creswell, 1994). ...
... In order to overcome this situation and to recover the overexploited populations of L. gigas, several alternatives have been established, such as the creation of marine protected areas (MPA's) (Appeldoorn, 1994 ;Stoner, 1996;Anon, 1999) which allow the preservation of spawning stock at high densities and maintain a haven for adults with higher reproducibility (Anon, 1999). Another alternative is aquaculture with techniques directed to produce juveniles (Brownell, 1977;Creswell, 1994). ...
Article
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The microbial diversity of Lobatus gigas has not been thoroughly studied despite of them is a specie endangered. Knowledge of microbiota may help to improve the conservation and cultivation of this species. The objective of this study was to evaluate the bacterial populationsassociated with the gonad and the gut compartments of the wild endangered L. gigas from the Caribbean Seaflower Biosphere Reserve, using microbiological methods and culture-independent molecular tools. The genetic profiles of the bacterial populations were generated and Temporal Temperature Gradient Electrophoresis (TTGE) was used to compare them with total DNA. A genetic and statistical analysis of the bacterial communities revealed a low level of diversity in gonad tissue based on the number of bands detected using TTGE. In addition, statistical differences in bacterial community structure were found between the foregut and hindgut tissue of L. gigas. The dominant phylogenetic affiliations of the gonad bacteria, as determined using 16S rRNA gene sequencing, belong to Ralstonia (50%). The possible involvement of this genus in the reproduction and development of the conch is discussed. On the other hand, the bacterial phylotypes from foregut and hindgut included members of Alphaproteobactera (12.5%), Betaproteobacteria (12.5%), Gammaproteobacteria (12.5%), Bacilli (31.25%), Clostridia (6.25%), Actinobacteria (6.25%), Mollicutes (6.25%) and Deinococci (6.25%) classes. Knowing the composition of the gonad and foregut and hindgut bacteria of L. gigas is the first step toward exploring the proper management of this species, as well as provides useful information to future researches that allow a better understanding of the role of these bacterial populations in the health and reproductive rate of L. gigas.
... Several herbivores that use Thalassia leaves as a primary source of food are in turn fished commercially: the green turtle (Chelonia mydas) (22,24), the manatee (Trichechus manatus) (40), fishes (40,41), the queen conch (Strombus gigas) (7,39,40), and the sea urchins (Tripneustes esculentus and Lytechinus uariegatus) (1,31) (table 1). Further, these herbivores are also eaten by natural predators in the ecosystem, forming an array of food chains which, if simplified, could be divided into the following five proposed categories (figs. ...
... [1][2][3][4][5]: the large herbivore food chain, the fish herbivore food chain, the gastropod herbivore food chain, the urchin herbivore food chain, and the detrital food chain. These five food chain types are based on personal observations and communications, and on data published (6,7,9,18,21,22,24,25,26,28,30,31,32,33,34,38,39,40,41,46) . ...
Article
The chemical composition of Thalassia leaves is described. Of the leaf-dry matter, 40.6% consists of soluble nutrients: crude protein, lipids, soluble carbohydrates and ash. Crude protein content was 17% (R = 15.8-18.1%). Essential nutritive minerals were found in considerable quantities: calcium, 1.32% (R = 1.21-1.47%); phosphorus, .21% (R = .19-.23%); potassium, 3.0% (R = 2.47%-3.30%) and magnesium, 1.26% (R = 1.09%-1.38%). The cell wall or neutral-detergent fiber fraction was 59.4% (R = 46.1-64.6%), of which 19.1% consisted of hemicellulose. The lignin content varied from 22.9% (KMnO4) to 9.1% (H2SO4) depending on whether KMnO4 or H2SO4 was used as an oxidizing agent. The importance of Thalassia leaves as a food source for the seagrass community is described by five major food chains hereby proposed: the large herbivore, the fish herbivore, the gastropod herbivore, the urchin herbivore and the detrital food chains. The potential value of Thalassia as a food source for domestic animals is evaluated on the basis of comparison with forage crops.
... Declining populations of queen conch (Strornbus gigas L.), usually attributed to overfishing, have been reported for numerous areas in the Caribbean region (Brownell and Stevely, 1981;Appeldoorn et al., 1987;Berg and Olsen, 1989). Hatchery production and field release of juvenile conch have been suggested as a means of restoring depleted stocks (Berg, 1976;Brownell, 1977;Davis and Hesse, 1983;Iversen et al., 19861 but release methods have not been perfected (Stoner, unpubl. data). ...
... data). Similar mention of epifaunal habits in early juveniles was made by Brownell (1977). It seems likely, therefore, that queen conch have different strategies of defense depending upon habitat. ...
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In the southern Exuma Cays, Bahamas, during winter 1988-1989, early juveniles (35-54 mm siphonal shell length) primarily inhabit shallow unvegetated zones where they burrow in the sediment during the day and surface at night. The burrowing rhythm was endogenous. Highest densities of 1- and 2-yr-old juveniles (80-140 mm) conch were observed in adjacent, deeper seagrass beds, suggesting that queen conch make an ontogenetic shift in habitat. Growth rates of early juvenile conch were higher in seagrass (0.11 mm/day) and in rubble (0.09 mm/day) than in bare sand (0.01 mm/day) where they were initially found. Observations suggest that emergence of juvenile conch and movement to vegetated habitats at 35-54 mm shell length is associated with changes in nutritional requirements. Changing habitat association with age may also be related to predator avoidance and burrowing capabilities. -from Authors
... Aliger gigas es una especie dioica, y la proporción sexual es aproximadamente 1:1 (Alcolado 1976, Botero 1984, Márquez 1993. La reproducción generalmente ocurre en los meses cálidos; sin embargo, en algunas regiones se reproduce durante todo el año (Brownell 1977). La hembra pone una masa de huevos gelatinosa que contiene cerca de 400.000 huevos. ...
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Anteriormente aceptada con el nombre Farfantepenaeus notialis, pero a partir del trabajo de Ma et al. (2011) quedó clara la monofilia del género Penaeus sensu lato, que incluye los géneros Penaeus, Fenneropenaeus, Litopenaeus y Farfantepenaeus.
... Aliger gigas es una especie dioica, y la proporción sexual es aproximadamente 1:1 (Alcolado 1976, Botero 1984, Márquez 1993. La reproducción generalmente ocurre en los meses cálidos; sin embargo, en algunas regiones se reproduce durante todo el año (Brownell 1977). La hembra pone una masa de huevos gelatinosa que contiene cerca de 400.000 huevos. ...
Book
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Este libro presenta los resultados de la segunda evaluación del riesgo de extinción de invertebrados marinos en Colombia, un esfuerzo coordinado por INVEMAR y MINAMBIENTE, que involucró a 53 investigadores nacionales y contó con la asesoría del personal de la UICN.
... There is often a level of non-significant sex ratio bias in stromboidean samples (Maxwell et al. 2020a). The determination and expression of sex ratio bias in stromboidean populations is affected by the type of clustering that the sample is drawn from (Brownell 1977;Catterall & Poiner 1983;Maxwell 2017). While there were no juveniles in the sample, the lack of information on mating pairs makes the type of adult cluster impossible to discern. ...
Article
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The Molluscan family Strombidae Rafinesque, 1815 is taxonomically diverse, with a widespread global distribution. However, the population structure of many of these taxa remains enigmatic. There is a growing interest in exploring population structures within species across their distributions to understand factors affecting morphological diversity. In particular, there is an inherent focus on sexual-size dimorphism between females and males in both physiology and shell morphometrics, as well as sexual bias (Mutlu 2004; Maxwell et al. 2017, 2020a, 2021), in order to provide a basis from which models of sexual dimorphism in general might be generated. Furthermore, the expression of pseudohermaphroditism in stromboideans, which is linked to the environmental causal agent tributyltin (TBT), a marine pollutant, has also been the focus of recent studies, with varying findings in expression ranging from absent to 36 % within populations (Multu 2004; Maxwell et al. 2020a; Reed 1993a, 1993b; Ruaza 2019). In addition, another population dynamic that has received recent attention is the expression of colour phenotypes within and between populations (Maxwell et al. 2020a, 2021). Despite these recent studies and the development of a general model for sexual dimorphism (Maxwell et al. 2022), many stromboideans still remain unstudied in terms of morphological variability, sex-ratio bias and pseudohermaphroditism, particularly at the population level.
... One of the major problems in determining whether an underlying sex-bias in stromboidean populations is present is not knowing the nature of the population clustering from which the sample is derived. Within congregations of the same taxon, four distinct categories for clustering can be discerned: mixed age; juvenile; mating; and non-mating clusters (Brownell, 1977;Catterall & Poiner, 1983). While female bias is more common (Laevistrombus vanikorensis (Quoy & Gaimard, 1834) -Maxwell et al., 2017; Canarium labiatum (Röding, 1798) -Maxwell et al., 2020aGibberulus dekkersi Maxwell, Hernandez Duran, et al., 2021c(not Gibberulus gibbosus Röding, 1798) -Maxwell, Rymer, et al., 2021b, and seen here in C. (C.) esculentum, studies where males are more frequent, such as with C. (C.) incisum in the present study, may F I G U R E 2 Boxplot of median and quartile of the axial lengths of each sex of Canarium (Canarium) incisum (Wood, 1828) from Corong Corong Beach, El Nido, Philippines and Canarium (Canarium) esculentum Maxwell, Rymer, Congdon and Dekkers, 2020b from Cebu, Philippines be evidence of a spawning event, such as is seen in previous studies in the related Conomurex luhuanus (Linné, 1758), which showed a similar female to male ratio of 1 female to 1.42 males (Catterall & Poiner, 1983). ...
Article
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Canarium (Canarium) incisum and Canarium (Canarium) esculentum are small members of the molluscan Strombidae family. Little is known of their population structure. Therefore, we explored this using samples from a population of each. The first sample from Corong Corong Beach, El Nido, Philippines, consisted of 81 adult C. incisum, of which 33 were female and 48 were male. The second sample from Olango Island, Philippines consisted of 73 adult C. esculentum, of which 40 were female and 33 were male. Bias in sex ratio between species was not significant. However, there was bias in sex ratio within species, where males from both species were smaller in axial length than females. We found no evidence of pseudohermaphroditism. The black colouration of the aperture is a phenotype shared by many stromboidians, and 7.4% of C. incisum population exhibited this trait, while the C. esculentum population contained 50.1% black apertures specimens. Preliminary DArTseq analysis indicates that organisms with the black aperture colouration are nested within the populations. Our study fills a knowledge gap on C. incisum and C. esculentum population structure, and gives greater insights to size dynamics of stromboidian taxa in general.
... The type of clustering may affect the distribution of sex ratios between males and females. Within congregations of the same taxon, four distinct categories for clustering can be discerned: mixed age; juvenile; mating; and non-mating clusters (Brownell, 1977;Catterall & Poiner, 1983). Therefore, it is important to note the clustering nature of the sample on collection, particularly the age demographic and presence of sexual activity, as this may affect whether a sexratio bias is observed or not. ...
Article
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Canarium labiatum is a small gastropod of the Strombidae family that is commonly encountered in the inter-tidal zones of tropical Queensland, Australia, yet little is known of its population structure. A targeted survey of the Canarium labiatum population on Green Island, located near Cairns, Queensland, was conducted on 12 August 2015. Ninety adult specimens were collected, of which 49 were female and 41 were male. The sample demonstrated significant sexual axial-length size dimorphism, with a bias towards larger females. While we collected more females than males, this did not represent a statistically significant bias, and rather may reflect the clustering nature of the sample. In addition, there was no evidence of pseudohermaphroditism in females within the population under consideration. Interestingly, 11.1% of the sample did not show banding and brown/grey-blue maculations on a light grey shell, the typical colour pattern associated with Canarium labiatum. This paper fills a knowledge gap in Queensland's Canarium labiatum population structure and provides a basis for a wider study into the size dynamics of Strombidae in general, but Canarium in particular.
... All conch encountered were counted and lip thickness was measured (nearest 0.1 mm) with a caliper by placing it as far as possible onto the middle of the shell lip. Adults were defined as individuals with flared lips ≥5 mm thick (Brownell, 1977). This criterion was adopted since 2003 although more recently higher values have been proposed (e.g., ≥13 mm; Avila-Poveda and Baqueiro-Cardenas, 2006). ...
Article
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https://www.frontiersin.org/articles/10.3389/fmars.2020.00646/full .... Queen conch Aliger gigas (Linnaeus, 1758), formerly known as Strombus gigas, constitute a valuable commercial and cultural resource for native communities since pre-Hispanic times (Baisre 2010). Populations of this marine gastropod are registered for 36 countries in the Caribbean, extending from Florida to the northern coast of South America and live mainly on sandy bottoms, in clear waters down to a depth of 100 m (CITES, 2003). Mating and spawning usually take place during the warmer months of the year, although in some areas, mainly in the western Caribbean, the breeding activity is continuous at low reproduction levels throughout the year (Avila-Poveda and Baqueiro-Cardenas 2009, Aldana-Aranda et al. 2014, Boman et al. 2018). Moreover, some populations migrate seasonally from open waters to shallower waters for spawning (Appeldoorn 1993). Over the past decades, intensive overfishing has led to population decline, collapse of stocks, and temporary closure of fisheries in different locations at Bermuda, Cuba, Colombia, Florida, Mexico, Netherlands Antilles, Virgin Islands and Venezuela (Stoner and Schwarte, 1994; Stoner et al., 2018). Studies indicate that most populations of A. gigas continue their decline despite having been listed in the CITES appendices for being threatened by local fisheries in countries like Belize, Colombia, Dominican Republic, Haiti, Honduras, Panama, Puerto Rico and the Virgin Islands, as well as the support by regional fisheries management agencies (Stoner et al. 2012, Prada et al. 2017, Tewfik et al. 2019). In the Colombian Caribbean, A. gigas has been one of the most significant fishery resources for many years, being therefore subject to large-scale exploitation. Specifically, for the Seaflower Biosphere Reserve, which included the archipelago of San Andrés, Providencia and Santa Catalina, the landings reached a maximum of 813 tons in 1988, decreasing to 465 tons in 1993 and 81 tons in 2003 (Prada et al., 2009). Restricted access to this resource was enforced in this region between 2005-2007 and 2011-2013. The fishery was reopened between 2008 and 2010 in the areas of Serrana and Roncador banks, and in 2013 only for Serrana bank (Castro et al., 2011; Prada et al., 2009). In terms of conservation activities, following the guidelines of FAO and CITES, efforts for the responsible management of the queen conch have been implemented in Colombia, which enforced fishing management and regulations since 1977 (Castro et al., 2011). In recent years, studies have estimated densities and abundances of the queen conch throughout habitat and depth strata on different banks of the Seaflower Biosphere Reserve at least once every three years (Castro et al., 2011). With the new ecosystem-based management approach, the 8% control rule proposed by Medley (2008) was incorporated as a criterion of sustainability to regulate the intensity of fishing activity. This increased the restriction for fishing in small banks, taking into account the recruitment of juveniles, the zoning of the Marine Protected Areas (MPA’s), and illegal fishing. With this model, it was possible to define the fishery closing and reopening cycles, which have shown positive effects on species recovery (Castro et al., 2011). The combination of overfishing and the loss and disturbance of habitats are the main factors influencing the population decrease of the queen conch. The current study presents a multi-temporal analysis of A. gigas populations on Serrana bank, which is an atoll in the western Caribbean that is included into the Seaflower Biosphere Reserve. This reserve was declared a Marine Protected Area since 2005. The main objective was to release raw data from these valuable observations and assess whether the management tools in the MPA are having positive effects on the recovery and conservation of juvenile and adult populations of A. gigas.
... The Strombus gigas in Los Roques is, by far, the most abundant of five species of Strombidae (Rehder 1962;Work 1969;Brownell 1977), widely distributed from Bermuda to the Gulf of Mexico and from the West Indies to Brazil (Warmke and Abott 1969;Abott 1974;Acosta 1994). In Los Roques, large extensions of seagrass beds, mainly Thalassia testudinum and Syringodium filiforme, at depths between 0.5 and 1.0 m, cover an area of about 5400 km 2 Weil 1983, 1985). ...
Article
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The human impact on marine molluscs on the Caribbean coast of Venezuela can be traced back to the end of the Pleistocene, between 15,000 and 12,000 B.C. However, the most important molluscan resource in the country, the Queen Conch (Strombus gigas) populations located on the offshore islands of the Los Roques Archipelago, had not been discovered until the beginning of the second millennium A.D. In Los Roques, the large-scale exploitation began ca. A.D. 1200, and the shellfish was preserved for delayed consumption and further redistribution on the mainland. Interdisciplinary research has indicated that at least 5,500,000 queen conchs were extracted and processed for food between ca. A.D. 1200 and 1500, and the production oscillated between 3 and 5 tons of shellfish yearly. Pre-Hispanic middens are largely composed of adult shells (between 81 and 94%) with a mean body size at maturity between 22.0 and 23.0 cm in length. During the contemporary fishery regime that began in 1950, between 8,000,000 and 11,500,000 conchs were extracted and deposited in 173 middens. The annual production between 1950 and 1964 fluctuated between 10 and 20 tons of shellfish and between 1970 and 1985 it attained its climax with 50 to 75 tons. Since 1985 the production diminished to ca. 10 tons yearly. In modern shellmiddens we have observed the remarkable rise of premature individuals from 39 to 73%, accompanied by the reduction of mean size at sexual maturity from 22.1 to 20.2 cm. The presence of less valuable specimens in terms of age and body size in these middens has been considered as a result of heavy pressure, whilst the pre-Hispanic fishery has been considered as less harmful to local Queen Conch populations.
... Los Roques formerly supported a large population of this species (Fernández 2002). Brownell (1977) and Weil & Laughlin (1984) studied reproduction and growth in various Lobatus species of Los Roques. At the regional level, there are various governmental agreements for the extraction and marketing of this mollusk in the Caribbean. ...
Article
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The Los Roques and Las Aves oceanic coral reef archipelagos of Venezuela lie in a biogeographically unique and biologically diverse area of the Caribbean and possess extensive coral reefs, seagrass beds, mangroves and shallow macroalgae meadows. The geographic location of these archipelagos safeguards them from most Western Atlantic hurricane damage as well as the most severe Caribbean coral bleaching episodes. While the Aves islands remain uninhabited and are an area of low accessibility, Los Roques has been a managed national park since 1972. We here present an updated synthesis of recent research for these archipelagos as an aid to scientists and conservationists interested in these island groups for which no recent ecological reviews are available. Los Roques has been much better documented than Las Aves and is the largest coral reef marine protected area of Venezuela. It has about 1,500 inhabitants living principally from tourism and fisheries. Studies show that Los Roques possesses fish populations that suffer comparatively less fishing pressure and may serve as a rare benchmark for pristine fish communities elsewhere in the Caribbean. It has also successfully maintained its importance to seabird colonies for the last five decades, notwithstanding serious marine park funding and staffing shortages. A new baseline biological inventory for Las Aves is particulary critical considering the fragmentary information available for this archipelago. The relatively intact and resilient oceanic coral reef systems of Los Roques and Las Aves are of regionally significant conservation value and deserve much more conservation and biodiversity attention than so far accorded.
... Los Roques formerly supported a large population of this species (Fernández 2002). Brownell (1977) and Weil & Laughlin (1984) studied reproduction and growth in various Lobatus species of Los Roques. At the regional level, there are various governmental agreements for the extraction and marketing of this mollusk in the Caribbean. ...
Article
Full-text available
The Los Roques and Las Aves oceanic coral reef archipelagos of Venezuela lie in a biogeographically unique and biologically diverse area of the Caribbean and possess extensive coral reefs, seagrass beds, mangroves and shallow macroalgae meadows. The geographic location of these archipelagos safeguards them from most Western Atlantic hurricane damage as well as the most severe Caribbean coral bleaching episodes. While the Aves islands remain uninhabited and are an area of low accessibility, Los Roques has been a managed national park since 1972. We here present an updated synthesis of recent research for these archipelagos as an aid to scientists and conservationists interested in these island groups for which no recent ecological reviews are available. Los Roques has been much better documented than Las Aves and is the largest coral reef marine protected area of Venezuela. It has about 1,500 inhabitants living principally from tourism and fisheries. Studies show that Los Roques possesses fish populations that suffer comparatively less fishing pressure and may serve as a rare benchmark for pristine fish communities elsewhere in the Caribbean. It has also successfully maintained its importance to seabird colonies for the last five decades, notwithstanding serious marine park funding and staffing shortages. A new baseline biological inventory for Las Aves is particulary critical considering the fragmentary information available for this archipelago. The relatively intact and resilient oceanic coral reef systems of Los Roques and Las Aves are of regionally significant conservation value and deserve much more conservation and biodiversity attention than so far accorded.
... Recently, no study of management of captive breeding in L. gigas has been realized (Shawl and Davis 2004). Also culturing conch in captivity can reduce the harvest pressure in the fishery (Berg 1975;Brownell 1977;Shawl and Davis 2004). Total quantity of abalone produced on farms worldwide has increased significantly while abalone from fisheries has declined (Cook 2016). ...
Article
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Profiles were generated of the sex hormones estrogen, progesterone, and testosterone in the marine snail Lobatus gigas every 2 months for 1 year. A non-invasive technique involving feces collection was used. Hormones were extracted from the feces with 80% methanol. After filtering, hormone concentrations were measured by high-performance liquid chromatography and a UV detector. All three sex hormones were present in L. gigas feces, and their concentrations increased contemporaneously with the conch reproductive period. Males and females showed the highest concentration of testosterone in May (1.8 ± 0.3 and 2.1 ± 0.8 ng/ml, respectively). Both sexes presented a maximum estrogen concentration in May (1.2 ± 0.7 and 1.0 ± 0.3 ng/ml). Progesterone in females remained constant from March to July. Pearson correlation between estrogen and spawning activity were r = 0.66 (p = 0.03) and for testosterone (r = 0.5216) and progesterone (r = 0.437). This study constitutes the first use of this technique in this species. Results show that sex hormones may be controlling this species’ reproductive events, as occurs in other gastropods. The understanding of the L. gigas reproductive process, this is one of several steps that will allow in the future improve aquaculture systems and supporting conservation of wild populations.
... Shell contributors to Tarawa sand have not been identified before (Smith and Biribo, 1995). The identified mollusc genus Strombus ( Figure 5A) lives on sandy areas of patch reefs, commonly found near coastlines in depths ranging from 3 to 30 m (Brownell, 1977;Tewfik and Guzman, 2003), and gastropods such as Strombus are common in nearshore lagoon waters on Tarawa (Thomas, 2001). These habitat preferences may explain the significantly higher mollusc shell composition on lagoon beaches relative to reef-facing beaches. ...
Article
Sandy beaches are critical resources for low-lying Pacific atoll communities, providing protection during storms, and land area for many coastal villages. Information on the nature of atoll beach sediment, its geochemistry and composition, can help to establish priorities to effectively protect the sources of Pacific island beach sediment. To understand sand sources, this study evaluated its physical characteristics including grain-size, geochemistry and composition, from windward and leeward beach profiles around Abaiang Atoll, Kiribati. Beach sand was >99% carbonate, averaging 37% coral fragments, 30% mollusc shells, 12% foraminifera, and 20% calcareous algae. Significant differences were found between reef and lagoonal sites in proportions of coral and mollusc fragments and foraminifera tests, with lagoon beaches having higher mollusc and coral proportions and lower foraminifera relative to reef beaches. This is attributed to high foraminiferal productivity offshore of reef beaches, and taphonomic durability of coral fragments in longshore drift into the lagoon. Mean sediment diameter increased from the upper to lower beaches at all sites, but fine sediment was lacking, attributed to its dissolution by rainfall and groundwater outflow. Geochemical analysis showed a mean of 84% Ca-Mg carbonates, of which 80% was calcium carbonate. There was no significant difference in the mean calcium percentage or calcium carbonate composition of the sediment between lagoon and reef beach sediment sources. Magnesium and magnesium carbonate content were significantly higher at reef sites relative to lagoon sites, attributed to higher proportions of foraminifera. Sediment-producing near shore habitats are critical to village protection through provision of beach sand, and this study shows the need to better conserve and manage coral reefs and habitats such as lagoon seagrass beds, to ensure continued atoll beach sand supply.
... After 24 h, the percentage of living conch that had metamorphosed in each container was recorded. A veliger was categorized as having undergone metamorphosis when it had lost its velar lobes, crawled on its propodium, and searched the substratum or container wall for food with its proboscis (Brownell, 1977). Dead or missing conch were excluded from the totals on which percentages were based. ...
Article
Laboratory experiments were conducted to test the adaptive significance of settlement and metamorphosis responses in competent veligers of Strombus gigas Linnaeus (queen conch). When competent veligers were tested for metamorphic response to 15 substrata collected from nursery grounds in seagrass beds of the Florida Keys, 0-38% underwent metamorphosis. Substrata with complex physical and biotic structures such as the calcareous red alga Neogoniolithon strictum (Foslie) Setchell and Mason, the green alga Dasycladus vermicularis (Scopoli) Krasser, and the matrix of algae and sediment attached to rock substrata elicited highest responses. No larvae responded to live blades of the seagrasses Thalussia testudinum Koenig and Syringodium jilifome Kuetzing, indicating that these plants are not the primary inducement for recruitment of conch to seagrass meadows. When newly-settled conch were grown for 16 days on the same substrata used to test for metamorphic responses, growth rates ranged from 7-62 pm/day and were weakly correlated (r = 0.71) with frequency of metamorphosis. High growth rates were associated with substrata that elicited high, low, or no metamorphic responses (e.g.. on Thalassia testudinum), but low growth was always associated with low metamorphosis. High metamorphosis occurred with substrata that were preferred as habitat by postlarval conch and yielded high growth rates. Settlement decisions by queen conch larvae appear to have important adaptive significance for newly metamorphosed recruits.
... Several egg masses, each containing -400,000 eggs, are laid by females on clean sand during the summer season (Robertson, 1959;Stoner and Sandt, 1992). Larvae hatch in 3-5 d and live in the upper 5-10 m of the water column for 16-28 d, feeding on phytoplankton (Brownell, 1977;Davis et al., 1993;Stoner and Davis, in press, a). Vertical migration appears to be slight (Barile et al., 19941, and the larvae drift passively on near-surface currents (Stoner and Davis, in press, b). ...
Article
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Marine fishery reserves (MFRs) have been set aside in coastal areas throughout the world with the hope of reversing population decreases commonly observed in many marine resources. In this study, a comparison of population structure of the commercially important gastropod Strombus gigas, queen conch, was made between a fished area and an MFR in the Exuma Cays, central Bahamas. There were 31 times more adult conch on the shallow (<5 m) Great Bahama Bank i n the MFR, and in a survey at 7 depth intervals (to 30 m) on the island shelf in the Exuma Sound, mean adult density was always higher in the MFR, by as much as 15 times. Shell length and lip-thick-n e w measurements indicated t h a t adults in the MFR migrate with age from bank nursery sites into deeper sound water, whereas those on the bank in the fished area were harvested before reaching water sufficiently deep to protect them from free-diving fisher-men. Although sparsely distributed juveniles in shallow-water (<15 m) habitats of the sound were the primary source of adults in the fished area, large juvenile aggregations on the bank also contributed to the deep-water adult stock in the MFR. Total larval densities in the MFR were frequently a n order of magnitude higher than those found in the fished area, and densities of late-stage larvae were 4 to 17 times higher. Because the surface current along the Exuma Cays shelf flows to the northwest, late-stage larvae found inside the reserve must have been spawned outside the reserve; thus the high densities of juvenile and adult conch are the result of natural accumulation of larvae in the area, as well as the result of protection from fishing. Although the fate of larvae dispersed from the reserve is uncertain, it is likely that high numbers of reproductive stock and larvae in the reserve have a significant positive effect on 3 4 * I populations in the northern Exuma Sound. Designs of reserves that consider ontogenetic requirements of the target species and strategic locations for larval production, import, export, and metapopulation dynamics will optimize fishery benefits for the many marine vertebrate and invertebrate species that possess pelagic larvae. I i)
... If they settled on sand at the 2 study sites, small animals would probably be able to derive sufficient nutrition by feeding only on the benthic diatoms and cyanobacteria that were abundant there. Even our medium and large conch grew well on sand (0.2 to 0.5 mm d -l ) , within and above the range reported for cultured animals (0.1 to 0.4 mm d-'; Brownell 1977, Ballantine & Appeldoorn 1983, Davis & Dalton 1991 even though rates were significantly lower than in seagrass. Consumption of foods with higher biomass such as detritus, macroalgae, and epiphytes (Stoner & Waite 1991, Stoner et al. 199513) apparently becomes more important with size. ...
Article
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Growth, survivorship, and habitat choice in a newly settled seagrass gastropod, Strombus gigas ABSTRACT: The roles of nutrition, predation, and habitat choice were tested as mechanisms for shaping natural distribution of newly settled queen conch in seagrass Thalassia testudinurn meadows in the central Bahamas. Small animals from 3 size classes were enclosed at 2 sites in 3 different habitats across a seagrass gradient (bare sand, low-density seagrass, medium-density seagrass) for 3 wk. Medium (11 mm shell length) and large (22 mm) newly settled conch grew faster in both seagrass habitats than on bare sand, but differences were not significant for small (5 mm) conch. Small and medium conch grown on sand, however, weighed more than those of the same length grown in seagrass, In laboratory habitat-choice experiments, newly settled conch preferred living seagrass and seagrass detritus over bare sand. Medium conch tethered in the 3 habitats at both sites suffered very high mortality (50 to 96% killed in 11 d), with those tethered in medium-density seagrass showing an advantage, Juvenile conch over 1 yr old are primarily associated with medium-density seagrass, but younger animals have been observed on sand, Results from this study show that nutrition is adequate on sand for newly settled conch, but an ontogenetic shift from sand into seagrass is unlikely because predation occurs before food becomes limiting or a habitat choice can he made. Nevertheless, post-settlement mortality is high regardless of where conch settle in the seagrass gradient, and predation is the most important mechanism influencing distribution.
... If they settled on sand at the 2 study sites, small animals would probably be able to derive sufficient nutrition by feeding only on the benthic diatoms and cyanobacteria that were abundant there. Even our medium and large conch grew well on sand (0.2 to 0.5 mm d-l), within and above the range reported for cultured animals (0.1 to 0.4 mm d-'; Brownell 1977, Ballantine & Appeldoorn 1983, Davis & Dalton 1991 Strombus gigas. Preferences shown by newly settled conch (5 to 10 mm) during 4 habitat choice comparisons. ...
Article
Growth, survivorship, and habitat choice in a newly settled seagrass gastropod, Strombus gigas ABSTRACT: The roles of nutrition, predation, and habitat choice were tested as mechanisms for shaping natural distribution of newly settled queen conch in seagrass Thalassia testudinurn meadows in the central Bahamas. Small animals from 3 size classes were enclosed at 2 sites in 3 different habitats across a seagrass gradient (bare sand, low-density seagrass, medium-density seagrass) for 3 wk. Medium (11 mm shell length) and large (22 mm) newly settled conch grew faster in both seagrass habitats than on bare sand, but differences were not significant for small (5 mm) conch. Small and medium conch grown on sand, however, weighed more than those of the same length grown in seagrass, In laboratory habitat-choice experiments, newly settled conch preferred living seagrass and seagrass detritus over bare sand. Medium conch tethered in the 3 habitats at both sites suffered very high mortality (50 to 96% killed in 11 d), with those tethered in medium-density seagrass showing an advantage, Juvenile conch over 1 yr old are primarily associated with medium-density seagrass, but younger animals have been observed on sand, Results from this study show that nutrition is adequate on sand for newly settled conch, but an ontogenetic shift from sand into seagrass is unlikely because predation occurs before food becomes limiting or a habitat choice can he made. Nevertheless, post-settlement mortality is high regardless of where conch settle in the seagrass gradient, and predation is the most important mechanism influencing distribution.
... Nevertheless the On the other hand, it is important to note in the mollusk group, the presence of the queen conch or pink conch (Lobatus gigas) which is the largest gastropod mollusk in the Caribbean region (Appeldoorn, 1997;Chakalall andCochrane, 1997, cited by Shapira 2007), and it is considered that there is a significant population in archipelago Los Roques (Fernández 2002). Brownell (1977) and Weil and Laughlin (1984) studied reproduction and growth in various Lobatus species of Los Roques. At the regional level, there are various governmental agreements for the extraction and marketing of this mollusk in the Caribbean. ...
... Lip thickness instead of minimum shell length is the appropriate indicator for maturity in conch and is advised to be used in queen conch fisheries management regulations. Brownell (1977), Weil & Laughlin (1984) If a queen conch fishery is re-opened it is recommended to protect the breeding population by introducing: ...
Technical Report
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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.
... Variation in annual ocean temperatures was found to have a significant negative effect on the duration of the reproductive season and appears to be a more important factor than mean annual temperature. Indications of this have previously been seen as fluctuations in sea temperature have been reported to initiate and stop reproductive behavior in queen conch (Brownell, 1977;. However, did indicate that photoperiod is also important and might be even more important than temperature in regulating the duration of the reproductive season in queen conch. ...
Article
Queen conch (Lobatus gigas), is an economically and culturally important marine gastropod. The species is subject to extensive exploitation throughout large parts of the Caribbean which has led to a decrease in population densities across much of the species’ distribution range. Hence, there is a need for protective measures to safeguard the reproductive stock. This requires a better estimation of its size at maturity, which is best quantified as the thickness of the lip that the shell develops after reaching its maximum length. The lip thickness at 50% maturity (LT50) was determined using a logistic and an accumulation model, from seven representative location of distribution of this species in the Wider Caribbean Region. LT50 of both females (7–14 mm) and males (4–11.5 mm) varied between different locations in the Caribbean, although it did not correspond with variation in water temperature. In most cases females had a larger LT50 than males indicating sexual dimorphism. LT50 values estimated with the logistic model were smaller (7–14 mm for females, 4–11.5 mm for males) than values estimated with the accumulation model (13–26 mm for females, 16–24 mm for males), showing an overestimation of LT50 in queen conch in previous studies which used the accumulation model to estimate LT50. Locations with a relatively high variation in water temperature had a significantly shorter reproductive season. The implementation of adequate minimum size regulation based on lip thickness (ca. 15 mm) and a Caribbean wide seasonal closure (May–September) using the most recent biological information from this study, taking into consideration the local differences in LT50 and reproductive season, will assist in developing a long term sustainable queen conch fishery in the Caribbean.
... Elemental analysis was determined using energy-dispersive X-ray analysis (EDX) with a highresolution scanning electron microscopy (HR-SEM) and X-ray photoelectron spectroscopy (XPS) Table 3. Average and SD of elemental content analysis established by scanning the shell length axis along a line, of 30-day-old larvae of Strombus gigas (n = 5 larvae) at pH 8.1, 28 and 30°C, using a high-resolution scanning electron microscopy (HR-SEM) and X-ray photoelectron spectroscopy (XPS) Brownell (1977) observed metamorphosis between 28 and 33 days, Sidall (1983) and Hensen (1983) from 20 to 28 days, while Ray and Davis (1989) observed this characteristic between 21 and 40 days. In this study, metamorphosis took from 27 to 29 days, recorded in 49 and 20% of the larvae reared at 30 and 28°C, respectively. ...
Article
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The queen conch, Strombus (Lobatus) gigas, is one of six species of conch distributed throughout the Caribbean of significant commercial importance. The Caribbean region is adversely impacted by climate change, which affects the marine ecosystems and the calcification process of organisms with calcareous structures, such as mollusks. We tested the influence of global warming predicted in 2100 on queen conch, Strombus gigas larval development, growth, survival rate, and calcification by exposing egg masses and larvae to increased temperatures (28, 28.5, 29, 29.5, and 30 °C) for 30 days. For analysis of calcification, imaging and chemical mapping (proportion, wt) were performed on 30-day-old larvae using a high-resolution scanning electron microscopy (HR-SEM) and X-ray photoelectron spectroscopy (XPS). A temperature of 30 °C resulted in the highest larval growth rate (mean ± SD 27.33 ± 2.96 μm day−1), significantly among treatments (p ≤ 0.05). Development was fastest at 30 °C, where the first larvae settled by day 27 (49%) and the mortality rate was 76%. At 28 °C, day 29 was the first day where settlement was observed for 20% of the larvae. There are significant differences among treatments on larval growth and development. The calcification process of S. gigas larvae was not affected by the experimental temperatures tested. Percent Ca content of shelled larvae showed no significant differences among treatments (mean ± SD 25.44 ± 4.74 and 24.99 ± 0.74% w for larvae grown at 30 and 28 °C, respectively).
... Many of these studies dealt with the taxonomy, biology, ecology, larval culture, and fisheries of important economic reef and sea grass invertebrate and vertebrate species (i.e. Work 1969;Cobo de Barany 1970;Cobo de Barany et al. 1975;Provenzano and Brownell 1976;Brownell 1977Buitriago 1980Buitriago , 1981Buitriago , 1987Cervigón 1980Cervigón , 1985aGrajal 1981;Laughlin and Weil 1982a,b;Laughlin et al. 1982Laughlin et al. , 1983Laughlin et al. , 1984Laughlin 1984, 1985;Alvarez et al. 1985;Díaz et al. 1985Díaz et al. , 1987Alcala 1987), and the interactions of different organisms with scleractinian corals (Grajal 1981;Grajal and Laughlin 1984;Pulido 1983;Villamizar 1985;Villamizar and Laughlin 1991). Coral reefs around the Dos Mosquises Marine Station on the southwest end of the archipelago were quantitatively characterized by Hung (1985), and the population dynamics of Acropora cervicornis in the western end of the Park was studied by Sandia and Medina (1987). ...
... Many of these studies dealt with the taxonomy, biology, ecology, larval culture, and fisheries of important economic reef and sea grass invertebrate and vertebrate species (i.e. Work 1969;Cobo de Barany 1970;Cobo de Barany et al. 1975;Provenzano and Brownell 1976;Brownell 1977Buitriago 1980Buitriago , 1981Buitriago , 1987Cervigón 1980Cervigón , 1985aGrajal 1981;Laughlin and Weil 1982a,b;Laughlin et al. 1982Laughlin et al. , 1983Laughlin et al. , 1984Laughlin 1984, 1985;Alvarez et al. 1985;Díaz et al. 1985Díaz et al. , 1987Alcala 1987), and the interactions of different organisms with scleractinian corals (Grajal 1981;Grajal and Laughlin 1984;Pulido 1983;Villamizar 1985;Villamizar and Laughlin 1991). Coral reefs around the Dos Mosquises Marine Station on the southwest end of the archipelago were quantitatively characterized by Hung (1985), and the population dynamics of Acropora cervicornis in the western end of the Park was studied by Sandia and Medina (1987). ...
Chapter
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Venezuela has some of the most diverse and well-developed coral reefs in the Caribbean, although they are limited in their distribution mainly by geomorphologic and environmental factors. The only extensive reef formations along the mainland of Venezuela are found in the west, in the Morrocoy and San Esteban National Parks. In the 1980's, live coral coverage in Morrocoy ranged between 20 and 50%. Today, the live coral coverage in the area is significantly lower due to natural and anthropogenic changes in the environment, such as high sedimentation rates and a mass-mortality event that occurred in 1996. Along the eastern mainland coast, coral reef development and coral diversity are limited by unfavorable conditions produced by seasonal upwelling, fiver outflow, and unstable substrate. Coral communities with low diversities of reef organisms and no reef accretion are common on eastern rocky shores along the mainland and around the near-shore islands. The best-developed and more diverse coral reefs of Venezuela are located offshore, away from continental influences and direct anthropogenic impact. Coastal reefs are threatened by uncontrolled land development, over-fishing and tourism, coastal refineries, petrochemical plants, deforestation, eutrophication, and ship tank wash and dumping, while island reefs north of Venezuela are mostly impacted by over-fishing, uncontrolled tourism, and the occasional oil slick or shipwreck.
... The report of the proboscis appearing between 17 and 20 d by Brito-Manzano et al. (1999) was a misunderstanding, due to confusion between the propodium and the proboscis. Brownell (1977) reported that the proboscis does not appear before day 25 of larval development and begins to function for grazing on algae within 2 d in L. gigas and L. costatus, while Cob et al. (2009a) observed this phenomenon 16 d after hatching in Laevistrombus canarium. The organs responsible for crawling behaviour of S. pugilis (the propodium and foot) became distinguishable 10 d after hatching. ...
Article
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http://mollus.oxfordjournals.org/cgi/content/abstract/eyv011? ijkey=wN63ugdccwM8mx4&keytype=ref
... The report of the proboscis appearing between 17 and 20 d by Brito-Manzano et al. (1999) was a misunderstanding, due to confusion between the propodium and the proboscis. Brownell (1977) reported that the proboscis does not appear before day 25 of larval development and begins to function for grazing on algae within 2 d in L. gigas and L. costatus, while Cob et al. (2009a) observed this phenomenon 16 d after hatching in Laevistrombus canarium. The organs responsible for crawling behaviour of S. pugilis (the propodium and foot) became distinguishable 10 d after hatching. ...
Article
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The organogenesis, histogenesis and growth of larvae of the fighting conch Strombus pugilis (Linné, 1758) were studied over a period of 30 d after hatching in laboratory culture. Early development of S. pugilis was examined by light and scanning electron microscopy. Rearing was conducted at 27 ± 1 °C. Veligers were reared at 200 larvae l−1 in 4-l containers. Larvae were fed with the microalgae Isochrysis galbana and Nanochloropsis oculata at a concentration of 1,000 cell l−1. The protoconch at hatching measured 212 ± 12.14 μm in length and the shell reached 1,100 ± 29.11 μm 29 d after hatching. Development characteristics are described from hatching to settlement. Newly hatched veligers possess two velar lobes, a larval shell consisting of 1.5 whorls, eyespots and a single right tentacle. Late veligers (5-d old larvae) have four velar lobes and two shell whorls and the left tentacle appears. Pediveligers show a functional adult heart at 11 d. Crawling behaviour and settlement were observed from 27 to 31 d. Plantigrades were observed after 29 d, when a functioning proboscis is observed and the velar lobes are lost. This study will facilitate the identification of gastropod larval shells in the plankton and of juveniles in the meiobenthos and will aid aquaculture of Strombus species.
... Typically it has 6 -8 month egg-laying season between March and October (Davis et al. 1984, Davis et al. 1994, Stoner et al. 1996a). During the reproductive season, large numbers of conch will migrate towards shallow waters (10m or less) and breed in coarse sandy habitats near reefs and Thalassia testudinum seagrass beds (Robertson 1959, Randall 1964, D'Asaro 1965, Brownell 1977, Weil and Laughlin1984, Stoner and Schwarte 1994, making them vulnerable to exploitation. ...
... As might be predicted, decimated conch stocks in Bermuda have not recovered despite 10 years ofprotection. Abbott and Jensen (1967) report cy clic disappearances of species in shell collections from Bermuda over the previous 110 years, including the con generic S. costatus, which has a larval period similar to that of S. gigas (Brownell, 1977;Ballantine and Appel doorn, 1983). Although Strombus alatus is the most common species of Strombus in northern areas and its planktonic larvae occur in the neritic waters off North Carolina (Thiriot-Quievreux 1983), it disappeared from Bermuda sometime since the Pleistocene, when glaciers forced the GulfStream to the south and into a more east west orientation, bringing it closer to Bermuda (Keffer et al., 1988). ...
Article
Genetic variation from 8 polymorphic enzyme loci among 17 population samples of queen conch, Strombus gigas, exhibits similarity of allelic frequencies throughout the species distribution. Analyses of standardized variances of allelic frequencies and of the frequencies of private alleles indicate that gene flow among populations in the Caribbean must be high. However, analyses of allelic frequencies clearly demonstrate that the populations are not panmictic. Bermuda is isolated from Caribbean populations, and there are numerous further examples of heterogeneity of allelic frequencies among populations within island groups. Limited data suggest that normal conch and samba, a slower growing, melanic form, are genetically differentiated.
... From routine laboratory and hatchery cultures of Strombus gigus and S. costalus larvae, growth rates and time to competence are known to vary with temperature, nutrition, and density of culture (BOIDRON-METAIRON, 1992;BROWNELL, 1977;DAVIS, 1992;GLAZER & BERG, 1992;M. Gongora, personal communication;L. ...
Article
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Development, growth rates, and shell morphology are compared for the larvae of the three most abundant Strombus species living in the Bahamas: S. gigas, S. costatus, and S. runinus. Illustrations are provided for positive identifications of the larval shells from field studies. Maximum shell dimensions of S. costatus, S. gzgas, and S. runinus differ significantly at hatching (388 +. 14 pm SL, 354 rt. 15 pm SL, and 197 +. 8 fim SL, respectively). T h e shell length (SL) for these species at competence was correlated with developmental time to competence in laboratory culture (6 = 0.95). Strombus runinus had the largest shell at competence (1450 +. 53 pm SL) and the longest larval cycle (40 days). Strombus costatus was 14% smaller (1277 +. 101 pm SL) and was competent at 32 days, while S. gigas had the smallest shell at competence (1170-t 58 Nm SL) and the shortest larval period (21 days). These differences in developmental rate suggest species-specific differences in potential larval dispersal and recruitment processes.
... fishery has been closed completely since 1986 (Berg and Olsen, 1989). Mariculture has been suggested as a way to rehabilitate queen conch populations (Berg, 1976;Siddall, 1984a;Davis et al., 1987), and research efforts during the past two decades have made it possible to culture large numbers of juvenile conch for stock enhancement (Brownell, 1977;Ballantine and Appeldoorn, 1983;Hensen, 1983;Laughlin and Wei& 1983;Cruz, 1986;Davis et al., 1987;Heyman et al., 1989;Creswell,l993;Davis, 1993). Unfortunately, field outplants of hatchery-reared stock have met with little success because of very high mortality (Appeldoorn and Ballantine, 1983;Laughlin and Weil, 1983;Appeldoorn, 1985;Marshall et al., 1993;Dalton, 1993). ...
Article
The investigation of sex bias and pseudohermaphroditism is a relatively unexplored area of research in the Neostromboidae. Here, we inform on these phenomena in a population of Gibberulus dekkersi Maxwell, Hernandez Duran, Rowell & Rymer, 2021 on Green Island, Great Barrier Reef. We collected 598 individuals, and noted the size of the cluster in which it occurred. Each individual was placed ventral side up and the body of the animal observed at the time of righting. Sex was determined by the presence or absence of a verge. During this sexing process, females were inspected for the presence of external male sexual organs to indicate the presence or absence of pseudohermaphroditism. We found that, overall, the population was not sexually biased towards one sex. However, we did find that individual clusters within the population showed significant sex bias, with different clusters favouring either males or females. Smaller clusters had a structural sex-ratio bias in favour of females. No evidence for pseudohermaphroditism was recorded, which indicates that the marine pollutant tributyltin (TBT) may not be present or at harmful levels in the surrounding environment. This study adds information from an unstudied Queensland taxon to the growing evidence on sex bias, clustering effects and pseudohermaphroditism within the Neostromboidae.
Chapter
Hydroponics is the growing of plants in nutrient solutions, with or without an inert medium to provide mechanical support. Vegetables normally raised in soil can be grown in a solution or moist inert material that contains the necessary nutrients. The hydroponic techniques used to raise such vegetables as cabbage, lettuce, and tomatoes can be integrated with fish farming: The plants take needed nutrients from wastewater from the fish-rearing facility, thereby often improving water quality. Tilapia have shown great improvements in feed conversion, and hence greater production of marketable fish, when their farming was integrated with hydroponics, due to the improved water quality in the integrated system.
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Lack of information about the biology, distribution and abundance of gastropods around the world has beenrecognized. These species represent the target of some fisheries, bycatch in many others and also are sold to conch collectorsor in the aquarium industry. Venezuela does not escape from this reality and for that reason, this study focus in generateinformation about length structure, abundance and distribution of gastropods captured in Cubagua Island. A total of 52 stationswere studied around the island during the year 2008, where four replicates of bands transect of 50m2 were carried out, for atotal of 200m2 of analyzed substrate in each sampling station. Nine gastropods species were analyzed, and the total length ofeach individual was measured. The most abundant species were Phyllonotus spp. (n=169; 0,016±0,06 org/m2) and Chicoreusbrevifrons (n=34; 0,003±0,006 org/m2), followed by less abundant species such as Voluta musica (n=17; 0,002±0,005 org/m2),Cyphoma gibbosum (n=20; 0,0018±0,009 org/m2), Fasciolaria tulipa (n=11; 0,0008±0,002 org/m2), Cyphoma signatum(n=4; 0,0004±0,002 org/m2) and Cassis madagascariensis (n=3; 0,0003±0,002 org/m2). Only three dead specimens of Tonnapennata and one of Charonia variegata were encountered, while no individuals of Cassis flamea, C. tuberosa or Tonna galeawere observed. The most aggregated species were Cyphoma gibbosum, Phyllonotus spp. and Voluta musica. Chicoreusbrevifrons showed preference for substrates of bivalve beds, whereas all the remaining species did not show any significantdifferences in the densities per substrate types. The administration and regulation of commercial gastropod catches aroundthis island and the performance of continuous studies about their populations is recommended.
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Gastropods of the family Strombidae are well-known and important constituents of modern tropical marine communities. The biology of several modern species has been thoroughly investigated due to their economic value as a human food resource. Unlike many gastropods, strombids undergo pseudo-determinate growth; they therefore present intriguing possibilities for investigation of size-related patterns of change. Unfortunately, they also display a wide degree of intraspecific morphologic variation, making reliable determination of species identity difficult. In this paper, we examine members of this family from the late Miocene and early Pliocene deposits of the Cibao Valley, located in the northwestern portion of the Dominican Republic on the Caribbean island of Hispaniola. After brief descriptions of the general geologic setting of the Cibao Valley and the biology of modern strombids, we delineate the observed geographic and stratigraphic ranges for species of Strombus and Lobatus in the Cibao Valley. At least 11 species of strombids have been reported from the Dominican Republic. Based on the high degree of intraspecific morphologic variation common in these genera and upon examination of individual specimens, we synonomize several older names and recognize only five species in two genera from the Cibao sequence: S. bifrons, S. proximus, L. haitensis, L. galliformis, and L. dominator. We describe some aspects of strombid paleoecology and summarize spatiotemporal patterns of distribution. Differences exist between modern strombid populations and our collections of Miocene Dominican ones; strombids of the Cibao Valley are in general smaller and appear to have occupied somewhat different habitats than those of their modern relatives.
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Resumo A detailed comparative morphology of the following 21 species is made: 1) Strombidae: Strombus pugilis (Brazil), S. alatus (Florida, USA), S. gracilior (form Panama, Pacific coast), Eustrombus goliath (Brazil), E. gigas (Caribbean), Aliger costatus, A. gallus (northeastern Brazil), Tricornis raninus (Caribbean); Conomurex luhuanus, Canarium urceus, Lambis lambis, Terebellum terebellum (all Australia), Tibia insulaechorab (Pakistan); 2) Struthiolariidae: Struthiolaria papulosa (New Zealand), Tylospira scutulata (Australia); 3) Aporrhaidae: Cuphosolenus serresianus new comb., Aporrhais occidentalis and A. pespelicani (North Atlantic and Europe); 4) Xenophoridae: Onustus caribaeus and Xenophora conchyliophora (West Atlantic) and O. indicus (Australia). The three former families are usually considered members of the superfamily Stromboidea, while the Xenophoridae are included in their own superfamily Xenophoroidea. A phylogenetic (cladistic) analysis is undertaken, based on 102 characters (255 states); with some basal Caenogastropoda as the main outgroup. A single most parsimonious tree was obtained (length: 209, CI: 74; RI: 86) as follows: ((T. scutulata - S. papulosa) (C. serresianus ((A. occidentalis - A. pespelicani)((O. caribaeus - O. indicus) - X. conchyliophora)(T. terebellum (C. urceus (C. luhuanus (T. raninus (L. lambis (S. pugilis - S. alatus - S. gracilior)((E. goliath - E. gigas) (A. costatus - A. gallus))))))))))). According to this analysis, Stromboidea (including Xenophoridae) is a monophyletic superfamily supported by 42 synapomorphies, Xenophoridae and Strombidae are monophyletic, as well as Strombus, Aliger and Eustrombus are monophyletic genera; whereas Aporrhaidae and Aporrhais are paraphyletic taxa; the Xenophoridae are the sister taxon of the Strombidae. Lambis lambis is represented in a branch within species currently included in Strombus, thus some genera were revalidated (Eustrombus and Aliger) and subgenera require elevation to genera (Strombus s.s., Tricornis, Conomurex, Canarium).
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RESUMEN Se presentan resultados de un estudio realizado entre 1995 y 1997 sobre diversos aspectos poblacionales del caracol rosado strombus gigas (distribución de tallas, densidad poblacional, tasa de crecimiento, relaciones morfométricas y crecimiento alométrico) y de las langostas espinosas Panulirus argus y P. guttatus (distribución de tallas, proporciones sexuales, densidad poblacional y aspectos reproductivos) en el Parque Chankanaab, Cozumel. Se hace especial énfasis en comparaciones de los aspectos poblacionales entre dos ambientes marinos del Parque: la Laguna de Chankanaab y la Zona Marina. La población de s. gigas en el interior de la Laguna es en gran parte resultado de la introducción artificial de individuos, mientras que en la Zona Marina hay una población abierta de s. gigas con densidades poblacionales y tasas de crecimiento relativamente elevadas. La presencia de juveniles de s. gigas en la Laguna, cuya densidad se incrementó después de una elevada mortalidad de adultos, sugiere que llegan a penetrar larvas o pequeños juveniles a través del túnel que comunica la Laguna con la Zona Marina. Dentro de la Laguna, se encontraron grandes concentraciones de individuos de P. argus, posiblemente por su alto valor como refugio para esta especie. En cambio, P. guttatus fue rara dentro de la Laguna pero presentó densidades medias similares a las de P. argus en la pared rocosa de la Zona Marina. Se comparan las densidades e intervalos de tallas de las tres especies registradas en los dos ambientes del Parque con valores registrados en diversas localidades de su ámbito de distribución.
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The present study of the rreproductive cycle of Strombus gigas at San Andres, Providence y Santa Catalina, Colombia revealed a problematic situation in this population. Samples were obtained by a cooperation program "Estrategias reproduc-tivas del Caracol pala Strombus gigas en el Caribe Insular colombiano" No. 003/abril, 2003, between Departamento Archipiélago de San Andrés, Providencia y Santa Catalina, Colombia and Laboratorio de Biología y Acuacultura de Moluscos, CINVESTAV IPN Mérida, Yucatán, Mexico. 311 organisms were analyzed from February 2003-to January 2004, with a shell length ≥ 230 mm. Samples from visceral mass and gonad were taken and processed for histological study. Gametogenesis was observed all year round but at a low percentage. Mature stage was observed only in August-September with percentages ≤ 10%. Such a detrimental situation may be related to an intense and generalized putative sporozoan infection detected in the sampled S. gigas population. The parasite, apparently a Coccidian was found in the digestive gland of every sampled organism throughout the year, infecting from 70% to 100% of the digestive gland alveoli, with a frequent total invasion of every alveolar cell. This infection may be responsible for the low intensity of maturity and scarce spawning stages registered at San Andres Archipelago. However, the actual knowledge of spatial and temporal variations of the reproductive cycle of S. gigas and of its parasitic status is not sufficient to propose an efficient management for its sustainable exploitation. Complementary studies appear necessary and urgent to understand its biological status throughout the reproductive cycle. Meanwhile, a mandatory minimal catch size could be a lip thickness > 7 mm in order to protect the endangered reproductive stock of S. gigas at San Andrés. The level of protection will depend on an efficient survey and protection of the populations and a high enforcement of regulations to control exploitation and reduce illegal fishing.
Article
Laboratory conditions under which the veligers of Strombus gigas were reared are defined. Spawning beds, egg mass formation, and the morphology of the egg capsule thread are described. The developmental description begins with the evagination of the shell gland and extends through 60 days of planktotrophic veliger development. Factors affecting metamorphosis of the swim-crawl stage are discussed and related to the early planktotrophic veliger. The difficulties in systematic separation of veliger species are discussed and compared to the morphologic stages of the veliger of Strombus.
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The biology of Storombus gigas Linnaeus is described on the basis of a study conducted at St. John, Virgin Islands, over a period of two and one-half years. The economic importance, systematic position, size, sexual differences, sex ratio, habitat, growth, movements, feeding habits, reproduction, development, predators and commensals of this abundant gastropod are discussed.
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The external appearance of Strombus gigas Linnaeus is described. Internal anatomy is described and illustrated, emphasis being placed on the structure of the stomach, the blood vascular system and the kidney; and a suggestion is made concerning the functioning of the latter and of the nephridial gland. The nervous system is shown in illustrations, and some of its details are discussed. The reproductive system is not described.
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One hundred and twenty-five species of mollusks of the Los Roques Archipelago are treated. The habitat and associated fauna of each molluscan assemblage are discussed. An attempt is made to establish accurate geographic ranges for each species. Notes concerning the feeding habits of ten species of gastropods are included, and the egg capsules of three species are illustrated.
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Data on the growth of the large marine snail Strombus gigas was obtained from specimens collected as veligers in the plankton and reared through metamorphosis, from larger individuals (5.5 cm) reared in a mariculture system, and from field tagrecapture experiments. Using the von Bertalanffy growth equation, I estimate that 1, 2, and 3 year-old juvenile snails are 10.8, 17, and 20.5 cm in maximum shell length, respectively. The snails reach the flaring-lip stage after 3 years and have a mean longevity of another 3 years. Approximately 12% of the total weight of a juvenile snail is marketable meat. Measurements of meat weight, shell length, and total weight are highly correlated with one another, thereby providing reliable means of assessing meat yields from living snails. The mariculture of S. gigas is feasible, but because of the snails' slow rate of growth it may not be economically practical at this time. Perhaps local fisheries in the Caribbean Sea could be reestablished and/or maintained by seeding subtidal algal flats with hatchery-reared juvenile snails.
Conch fishing industry of Union Island, Grenadines, West Indies
  • J E Adams
Adams, J. E. 1970. Conch fishing industry of Union Island, Grenadines, West Indies. J. Trop. Sci. 12: 279-288.
Notes on distribution and underwater observations on the Molluscan genus Strom bus as found in the waters of Trinidad and Tobago
  • P L Percharde
Percharde, P. L. 1968. Notes on distribution and underwater observations on the Molluscan genus Strom bus as found in the waters of Trinidad and Tobago. Carib. Jour. Sci. 8: 47-55.