Shell Lip Research Articles

Empirical support of predicted larval connectivity patterns demand conservation action for queen conch (Aliger gigas) in The Bahamas

AbstractThe conservation and spatial management of marine species with limited adult mobility, such as queen conch, is dictated by larval connectivity. Effectively placed reserves provide larval spillover to harvested areas while replenishing their own population. In past studies proximate to the Exuma Cays Land and Sea Park (ECLSP), surveys and probabilistic larval transport modeling demonstrated a spillover effect from the ECLSP to surrounding fished areas, while suggesting that incoming larval sources are lacking. Previous work was expanded in both upstream and downstream directions, enabling the statistical examination of (1) how queen conch abundance was linked to predicted larval transport from breeding populations in the ECLSP and (2) how age and size changed throughout the island chain as divided by management and connectivity. Biophysical modeling predictions of larval transport from breeding within the ECLSP were significantly associated with the relative abundance of juvenile conch observed across a nearly 200‐km span. Further, the abundance and shell lip thickness (relative age) of adults and the size of juveniles were significantly larger in ECLSP than unprotected areas. This empirical support for an effective, well‐enforced marine reserve and for using biophysical larval transport modeling as a spatial planning tool should be strongly considered in conch conservation and management.

Growth performance of juvenile snail (Archachatina marginata) fed different plant leaves

To assess the growth performance of juvenile snail (Archachatina marginata) fed different plant leaves, 180 juvenile snails of one month old were divided into 4 treatments (T1, T2, T3 and T4), of 15 snails and 3 replicates in pens equipped with feeders and drinkers. T1 received pawpaw leaves, T2 received cassava leaves, T3 received sweet potato leaves and T4 received blood root leaves. Feed and fresh leaves were measured and served daily, and the leftover also quantified, using an electronic weighing scale (0.01 g precision) to evaluate the feed intake. The results showed that the highest value of feed intake was recorded in animals that received blood root leaves, while the lowest value is registered in the treatment receiving pawpaw leaves. The highest value of leave intake was recorded in the treatment that received pawpaw leaves. The highest values for weight shell length, shell diameter, shell lip width, shell lip height and carcass characteristics of Archachatina marginata fed with different plant leaves were recorded for snails fed with blood root leaves. The lowest value of triglycerides (1.44±0.5) and total cholesterol (4.11±2.66) in the hemolymph was registered in animals receiving blood root leaves compared to other treatments. The lowest value of total protein (26.44±3.28) in the hemolymph was registered in the treatment receiving blood root leaves compared to the treatment that received pawpaw, cassava, and sweet potatoes leaves. In conclusion, blood root leaves can be used as staple diet to improve the productivity of Archachatina marginata.

CONCH FRITTERS THROUGH TIME: HUMAN PREDATION AND POPULATION DEMOGRAPHICS OF LOBATUS GIGAS ON SAN SALVADOR ISLAND, THE BAHAMAS

ABSTRACTLobatus gigas, the queen conch, is a central component of Caribbean cuisine but over-fishing of juveniles has threatened the stability of wild populations. Strombid gastropods, upon reaching sexual maturity, cease growing along the shell length axis and continue growing in width via a flared and thickened shell lip. This morphology serves as a useful indicator of an individual's sexual maturity. Here we examine temporal trends in population demographics, size, and morphology of harvested L. gigas individuals over the last ∼1 ky from San Salvador Island, the Bahamas to quantify the dynamics of human-induced stress on the local queen conch fishery. We collected 284 human-harvested individuals from shell middens at seven localities, measured seven morphological variables, and classified the specimens as either adult or juvenile. We randomly selected 64 of these shells for rapid AMS radiocarbon dating in order to establish three geochronological bins: Lucayan (Pre-European invasion, 1492 CE), Modern (∼102 y), and Global (∼101 y). The proportion of juveniles harvested increased significantly from 47% (Lucayan) to 61% (Modern) to 68% (Global) suggesting increasing pressure on the fishery through time. Patterns in body size and morphology diverge between adults and juveniles and are likely the result of an increase in the proportion of harvested juveniles, the selection of smaller juveniles through time, and possibly changes in fishing methods. This size selective predation did not result in the suppression of adult body size as found in other studies. Geohistorical data, such as these, are vital for providing long term ecological context for addressing anthropogenic ecological degradation and are central to the conservation paleobiology approach.

Declining size of adults and juvenile harvest threatens sustainability of a tropical gastropod, Lobatus gigas, fishery

Abstract Queen conch (Lobatus gigas) is a large herbivorous gastropod, found across the Caribbean, which forms the basis of important dive fisheries. Conch have a two‐phase shell growth pattern, first in shell length (SL), which ceases well before maturity, followed by growth in shell lip thickness (LT) into maturity. This growth pattern must be considered in determining the ideal size and associated maturity for sustainable harvest. Shell morphology, sex organ development and soft tissue masses indicated that mature adult conchs at Glover's Atoll, Belize, were those with thick shell lips (≥10 mm), eroded shells and heavier soft tissue masses. Therefore, SL‐based regulations cannot serve as a proxy for maturity and harvest. The use of inappropriate minimum size limits (SL = 178 mm, 85 g market clean meat mass) has allowed significant juvenile harvest and the fishery appears to have truncated the SL size distribution of conchs with a flared shell lip (i.e. adults) over the last 15 years. The reduced SL observed in lipped conchs may lead to a significant impact on the reproductive success of the population as well as diminished economic yield from the fishery, as smaller adult conchs of the same age have lower gonad and meat weight. We believe this to be the first documentation of a decline in the SL of adult queen conchs, and that the SL‐based size limits have contributed to this decline. Refinement of the individual size‐based regulations for conch in Belize to LT will probably facilitate local recovery as well as regional harmonization of regulations. Future research in Belize should include movement dynamics of conch in relation to replenishment zone size and spillover as well as the importance of deep‐water conch to shallow‐water recruitment, which is thought to be limited.

Barnacles, their molluscan hosts, and comparative ecology in the St. Mary’s Formation (late Miocene) of Maryland, USA

AbstractFossils can inform the study of modern ecosystems by showing how species interactions in ancient communities compare with those today and how extinction is selective not only with respect to species but also with respect to entire modes of life. We studied the life habits and pattern of occurrence of the barnacleChesaconcavus chesapeakensisZullo, 1992 on the shells of the gastropodConradconfusus parilis(Conrad) and the bivalveChesapecten santamaria(Tucker) from Chancellor’s Point in the Windmill Point Member of the St. Mary’s Formation (late Miocene, Tortonian) of Maryland. Using several criteria, we show that the barnacle occupied living hosts only. The 59% incidence of the barnacle onConradconfusus parilisis high compared to known living associations between barnacles and gastropods. AlthoughConradconfusus pariliswith and without barnacles do not differ in size, suggesting that the barnacle had little effect on this gastropod, there is some indication thatChesapecten santamariawith barnacles are somewhat smaller than those without and may therefore have been adversely affected by the presence of barnacles. On the basis of morphology and the low (15%) incidence of repaired scars,Conradconfusus pariliswas a predator that did not use its shell lip to subdue prey. No ecological equivalents ofConradconfususandChesaconcavushave existed in the temperate northwestern Atlantic between Cape Cod and Cape Hatteras for the past three million years.

Shell Lip Thickness Is the Most Reliable Proxy to Sexual Maturity in Queen Conch (Lobatus gigas) of Port Honduras Marine Reserve, Belize; Informing Management to Reduce the Risk of Growth Overfishing

Queen conch (Lobatus gigas) is an important food source and export product for Belize, where extraction is regulated by shell length (SL) and market clean weight (MCW) limits. However, lip thickness (LT) limits are used to manage juvenile mortality and reduce risk of growth overfishing in other countries. Empirical studies suggest relationships between LT and sexual maturity vary spatially and need to be determined locally. This study was conducted to determine the most reliable, easily measurable proxy indicator(s) of maturity and associated target size limits in L. gigas that can effectively restrict harvest of juveniles. Morphological measures (SL, LT, lip width, unprocessed meat weight, MCW, operculum dimensions), gonadosomatic index (GSI) and histological evaluations were recorded from L. gigas collected in PHMR before, during, and after the L. gigas closed season. Upon determining Period 2 (during closed season) as the peak reproductive period, relationships between these variables in Period 2 were examined. No relationship was found in males between SL and maturity, and was weak in females, whereas there were significant curvilinear relationships between LT and GSI for both sexes, suggesting urgent need to base size limits on LT not SL. LT at which 50% of the population was mature (LT50) was 15.51mm for females and 12.33mm for males, therefore a 16mm LT limit is recommended. MCW of female L. gigas was also significantly related to GSI, indicating MCW may be an appropriate management tool in conjunction with LT as it can be measured at landing sites whereas shells are usually discarded at sea. However MCW at which 50% of females were mature (MCW50) was 199g and many individuals exceeding LT50 had MCW less than 199g, suggesting the current 85g MCW limit is too low to protect juveniles yet 199g MCW limit would be too high to substitute the recommended LT limit at landing sites. To minimize short-term impacts yet maximize long-term benefits to fishers’ livelihoods, multi-stage adaptive management is recommended that integrates initial catch reductions, followed by introduction of size limits of 16mm LT, and 150g MCW. Adjustable LT and MCW limits determined by fishery simulation could later be introduced.

Distribución, abundancia, densidad y morfometría de Strombus gigas (Mesogasteropoda: Strombidae) en el Arrecife Alacranes, Yucatán, México

A population of the conch Strombus gigas was sampled in 109 transects (100X10 m each) for an area of 109 000 m2 (eight surveys in 1998 and six in 1999) in Yucatan, Mexico; S. gigas was the most abundant conch species (97% of individuals)and ocurred at depths of 0.5-18 m. Mean density was 0.0084 individuals/m2 (Standard deviation SD=0.0138, n=1910). Maximum density (0.015 individuals/m2) was at 0.5-2 m and minimal (0.001 individuos/m2) at 16-18 m. Shell length was120-290 mm (mena=211.6, SD=26, n=1136). Shell lip thickness, measured only in adults, was 1-28 mm (mean=8.7, SD=7.5, n=1136).

The combined effects of reduced pH and elevated temperature on the shell density of two gastropod species measured using micro-CT imaging

The increased absorption of atmospheric CO2 by the ocean affects carbonate chemistry and calcification rates of marine organisms. The impacts of low pH and seawater warming were investigated for the intertidal gastropods Nassarius nitidus and Columbella rustica. The combined effect of reduced pH (7.6) and increased temperature (25 °C) was studied at intermediate time intervals for a total period of 3 months in order to investigate variability and fluctuations of the shell structure and density over time. The pH and temperature conditions used for the experiment were selected according to the predictions of the Intergovernmental Panel on Climate Change. Deterioration of the external surface structure and reduction of shell density of the gastropods were confirmed using an innovative imaging and analysis method based on micro-computed tomography. The effect of low pH at ambient temperature was detrimental for N. nitidus with a 38.1% reduction of density in the shell lip and a 47.7% decrease in the apex, which is the oldest shell region. C. rustica was also affected, although to a much lesser degree (the maximum reduction observed was 8% at the apex). The negative effects of reduced pH were further reinforced for C. rustica when the temperature was increased, while N. nitidus was not affected significantly by the combination of the two factors. Increased temperature at ambient pH had an inhibitory effect on the shell density of N. nitidus causing a reduction of about 40%, whereas the shell density of the widest and lip regions of the C. rustica were increased under the same conditions. Different species are characterised by different vulnerability and tolerance responses regarding ocean acidification and warming, and this variability may affect ecological interactions and marine biodiversity.

Calibration of the stable isotope composition and body size of the arid-dwelling land snail Sphincterochila candidissima, a climatic archive abundant in Mediterranean archaeological deposits

Land snails recovered from archeological deposits may be used to deduce climatic conditions during prehistoric occupation because their aragonitic skeletons are usually well-preserved and document valuable climatic information in the form of isotope codes. Since the snail Sphincterochila candidissima is common in archeological sites along the western Mediterranean but has been minimally investigated, the present work examines the relationship between the oxygen (δ18O) and carbon (δ13C) stable isotopes of modern specimens and relevant meteorological data. Individuals of Sphincterochila were regularly live-collected throughout 1 year (from September 2013 to October 2014) in Tarragona, NE Spain, and the δ18O and δ13C values were measured at the shell lip or aperture, which depicts the last growth episode closest to specimens’ collection date. Shell margin δ18O values varied from +3.1‰ in September to −0.8‰ in April. Average shell margin δ18O values per collection date positively correlated with monthly averaged rainwater δ18O, and negatively correlated with monthly averaged maximum relative humidity, while other variables (i.e. temperature and precipitation amount) did not explain monthly–submonthly isotopic variations in the shell lip. Shell margin δ13C values ranged from −11‰ in September to −4.8‰ in March, pointing to detectable variations in snails’ diet between seasons. Interestingly, snail body size positively correlated with shell margin δ18O and δ13C values, suggesting that larger snail size is reached under drier conditions. This work shows that S. candidissima from the western Mediterranean is a valid paleoprecipitation δ18O and/or paleohumidity proxy in the region at the monthly–submonthly scale. Although shell margin δ18O recorded fall and spring climate conditions only, limiting therefore their use to estimate the season of harvest, snails that grow year-round (e.g. at subtropical–tropical regions) may be used usefully for such analyses.

Dynamics and ecology of an Indo-Pacific conch, Conomurex persicus (Mollusca: Gastropoda) in southeastern Turkey

Conomurex persicus, one of the tropical conchs, has been introduced to one of the subtropical regions, the northeastern Mediterranean Sea, and invaded sandy bottoms between 1 and 10 m deep. Population dynamics were studied from specimens collected with a standard dredge (60 x 15 cm mouth opening, 0.5 x 0.5 cm eye opening of net). Samples of C persicus were collected monthly along the 5 and 10 m depth contours off Erdemli, Mersin, Turkey, in February and May 2000. Intra-annual density depended on salinity levels, while inter-annual density was correlated with bottom water temperature. Specimens underwent spring emergences and winter burial and sheltering (disappearance). Emergence took place in March when temperatures rose and the disappearance occurred in October-November when temperatures dropped. Adults live at 10 m, juveniles are recruited at a 5 m depth. Recruitment began in April and continued for the next 6 months. In contrast to shell width or shell lip thickness, shell length was not a convenient index for estimation of growth parameters. Annual production and mortality were calculated to be 7.86 g m(-2) and 3.80 g m(-2), respectively, in April-November.

Proxy Measures for Queen Conch (Strombus gigas linné, 1758) Age and Maturity: Relationships Between Shell Lip Thickness and Operculum Dimensions

Estimating age and maturity of the commercially harvested queen conch (Strombus gigas) offers fishery managers a unique challenge: How can these variables be determined if only the soft, edible parts of the marine gastropod are landed in port whereas the shells used for aging purposes are discarded at sea? Throughout the greater Caribbean region, including The Bahamas, the age and maturity of S. gigas are estimated by measuring the thickness of the flared lip of the shell. Given the traditional fishery practices for queen conch, including at-sea processing, developing proxy measures for S. gigas age and maturity would greatly benefit fishery managers. To this end, we used traditional morphometric analysis to find a significant inverse relationship between the ratio of operculum length to operculum width and shell lip thickness. A logistic regression model using the same operculum metric and a breakpoint of 15mmfor shell lip thickness as an indication of S. gigas maturity predicted correctly the maturity level for 86% of queen conch sampled in The Bahamas. This study provides the proof of principle for relationships between operculum measures and queen conch age and maturity that can be applied by fishery managers throughout the geographical range of the species.

Plastic and Heritable Variation in Shell Thickness of the Intertidal Gastropod Nucella lapillus Associated with Risks of Crab Predation and Wave Action, and Sexual Maturation

The intertidal snail Nucella lapillus generally has thicker shells at sites sheltered from wave action, where crabs are abundant and pose a high risk of predation, than at exposed sites where crabs are rare. We studied two populations showing the opposite trend. We reciprocally transplanted snails between field sites and measured shell length, width and lip thickness of those recaptured 12 months later. Snails transplanted to the sheltered site grew larger than sheltered-site residents, which in turn grew larger than transplants to the exposed site. Relative shell-lip thickness was greater in residents at the exposed site than at the sheltered site. Transplants from shelter to exposure developed relatively thicker shells than their controls and relatively thinner shells from exposure to shelter. Progeny of the two populations were reared for 12 months in a common garden experiment presenting effluent from crabs feeding on broken conspecifics as the treatment and fresh sea-water as the control. The crab-effluent treatment decreased foraging activity, concomitantly reducing cumulative somatic growth and reproductive output. Juveniles receiving crab-effluent grew slower in shell length while developing relatively thicker shell lips than controls, the level of response being similar between lineages. F2 progeny of the exposed-site lineage showed similar trends to the F1s; sheltered-site F2s were too few for statistical analysis. At sexual maturity, shell-lip thickness was greater in snails receiving crab-effluent than in controls, indicating plasticity, but was also greater in the exposed-site than in the sheltered-site lineage, indicating heritable variation, probably in degree of sexual thickening of the shell lip. Results corroborate hypotheses that ‘defensive’ shell thickening is a passive consequence of starvation and that heritable and plastic control of defensive shell morphology act synergistically. Shell thickening of juveniles was similar between lineages, contrary to hypotheses predicting differential strengths of plasticity in populations from low- or high-risk habitats.

Maturation and age in queen conch (Strombus gigas): Urgent need for changes in harvest criteria

The queen conch (Strombus gigas) is a large economically important gastropod that has been severely depleted throughout much of the Caribbean region. The species has determinate growth and reaches maximum shell length before sexual maturation; thereafter the shell grows only in thickness. In this study, queen conch were collected in the Exuma Cays, Bahamas, to evaluate maturity with respect to shell length (SL) (170–255mm) and shell lip thickness (LT) (2–42mm). Soft tissue weight and gonad weight increased with SL, but these same variables, along with the gonadosomatic index (gonad weight/soft tissue weight), all had dome-shaped distributions with LT and decreased slightly with LT>22mm. This indicates some loss of fecundity with age; however, no loss of reproductive capability was evident in histological data. Gonad maturity lagged substantially behind first formation of the shell lip. Minimum LT for reproductive maturity was 12mm for females and 9mm for males, and 50% maturity for the population was achieved at 26mm LT for females and 24mm LT for males, higher than previous estimates. A review of fishing regulations indicates that immature queen conch are being harvested legally in most Caribbean nations, providing at least a partial explanation for widespread depletion. While relationships between shell lip thickness, age, and maturity vary geographically, sustainable management of queen conch will require a minimum shell lip thickness for harvest no less than 15mm, along with other urgently needed management measures.

一般講演(16):クロチョウガイPinctada margaritifera および アコヤガイPinctada fucata貝殻リップ部の干渉色とその垂直下の結晶層の厚さの関係についての考察

一般講演(16):クロチョウガイPinctada margaritifera および アコヤガイPinctada fucata貝殻リップ部の干渉色とその垂直下の結晶層の厚さの関係についての考察

Populations of <i>Cepaea Hortensis</i> (O. F. Müller, 1774) polymorphic for the colour of shell lip in north-western Poland and north-central Germany

Populations of <i>Cepaea Hortensis</i> (O. F. Müller, 1774) polymorphic for the colour of shell lip in north-western Poland and north-central Germany

Complex species interaction in tropical backreef communities

A complex interaction between the sea urchin, Tripneustes ventricosus, and snail, Cerithium litteratum, has emerged in lagoonal backreefs of Jamaica. These two species are spatially correlated in most of the habitats that were examined. In field and laboratory observations, urchins pick up and cover their tests with as many as 40 live snails continuously for up to two days. I examined whether urchins cover to avoid predation, and whether growth and survival of snails is negatively affected by this behavior. The presence of predators prompted urchins to collect ten times as many snails, which gained 47% less tissue weight and 75% less shell lip thickness than snails unassociated with urchins. However, the survival rate of snails positioned on urchins was three times greater than that of free snails on sandy backreef substratum. Results of this study imply a biomass gain versus survival trade-off, and provide insights into complex interactions.

New species and records of Pyrgulopsis (Gastropoda: Hydrobiidae) from the Snake River basin, southeastern Oregon: further delineation of a highly imperiled fauna

Here we describe two new species from southeastern Oregon based on morphologic and molecular (mtCOI) evidence. Pyrgulopsis fresti n. sp., commonly known as the “Owyhee hot springsnail” and long considered to be distinct and critically imperiled, lives in thermal springs along a short reach of the Owyhee River above Three Forks. This snail differs from other regional species in its squat shell; penial ornament consisting of a large, disc-shaped ventral gland; absence of a seminal receptacle; and mtCOI sequences. Pyrgulopsis owyheensis n. sp. ranges among five disjunct groups of springs in the Owyhee and Malheur river drainages and is occasionally sympatric with P. fresti. This snail is closely similar to another regional congener, P. intermedia (Tryon, 1865), but is smaller and further differentiated by its typically disjunct inner shell lip, longer and narrower penial filament, more distally positioned ventral gland of penis, and mtCOI sequences. The type locality (Owyhee Spring) population of P. owyheensis is genetically differentiated from the other geographical subunits of this species (1.5–1.8% sequence divergence) and should perhaps be managed as a separate conservation unit. New records are provided for P. intermedia which extends the range of this conservation priority species into the lower Owyhee River basin. We also show that the “Malheur springsnail,” which has been listed in various conservation-related publications and documents, is the same as P. intermedia. This study provides critical information for the conservation of springsnails in southeastern Oregon and underscores the need for additional field surveys in the region.

The operculum of Otostoma Retzii (Nilsson, 1827) (Gastropoda, Neritidae; Late Cretaceous) and its phylogenetic significance

The Neritimorph gastropod genus Otostoma d'Archiac, 1859 (p. 871), with its hemispherical shell and typical axial ribs and lamellae, is a characteristic fossil in (sub)tropical, nearshore deposits of the late Early and Late Cretaceous ages (Saul and Squires, 1997; Kiel, 2002; Kiel et al., 2002; Bandel and Kiel, 2003). The genus survived Cretaceous/Paleogene boundary perturbations and appears to have become extinct during the Middle Eocene (Glibert, 1973; Saul and Squires, 1997). Its placement in the Neritimorpha Golikov and Starobogatov, 1975 is clear from its typical hemispherical shell and D-shaped inner lip with a row of denticles. Long considered linked to Recent Nerita Linnaeus, 1758 (see Wenz, 1938-1944; Kase, 1984; Squires and Saul, 1993; Bandel and Kiel, 2003), assignment of Otostoma to the Neritoidea Rafinesque, 1815 has recently been corroborated by documentation of dissolved internal walls in Otostoma divaricatum (d'Orbigny, 1842) from the Campanian (Upper Cretaceous) of northeast Spain (Bandel and Kiel, 2003). However, axial (collabral) ornament as seen in Otostoma is unknown in modern neritids, which usually are either smooth or spirally sculptured. Here we describe the operculum of Otostoma retzii (Nilsson, 1827) for the first time; it closely resembles that of Nerita and many species of Neritina Lamarck, 1816, yet differs significantly from those of other neritimorph clades, including Neritopsidae Gray, 1847 and Neritiliidae Schepman, 1908.

Variation in shell morphology of Calliostoma zizyphinum (Gastropoda: Trochidae)

Differences in shell morphology in the intertidal prosobranch mollusc Calliostoma zizyphinum were studied from a number of sites within four geographical regions of the British Isles with varying exposures to wave action and crab predation. Mean values of damage scarring were highest in shells sampled from Strangford Lough, Northern Ireland, and lowest in individuals from the Atlantic Coast. Shells collected from the Isle of Man were smaller than those from either the Atlantic coast of Ireland or Strangford Lough. Shells from Strangford Lough had taller shells (higher aspect ratio) than shells from the County Down and Atlantic Coast and shells from the County Down coast were more squat (lower aspect ratio) than those from all other areas. Shells from Strangford Lough were significantly thinner than shells from all other geographical areas. The relationships between shell damage scarring and shell size and tallness were not consistent among areas. Shells from Strangford Lough are notable in showing a steep, positive relationship between shell size and scarring and a steep, negative relationship between scarring and tallness. The unusual shell phenotypes observed in shells from Strangford Lough may be explained by rapid shell growth, which would not only allow Calliostoma to attain a size refuge from crab predators but also to recover successfully from repeated crab attacks on the shell lip. Such a strategy would result in larger, thinner shells with a high number of damage scars.

Age and growth of Nassarius reticulatus in the Ria de Aveiro, north-west Portugal

Shell growth of the whelk Nassarius (=Hinia) reticulatus was studied in the Ria de Aveiro (north-west Portugal) between 1995 and 1998. Temporal analysis of shell height frequency distributions demonstrated that growth occurs during the first five years of life, whelks attaining a size of 6·7–7·8 mm in the 1st year, 12·1–14·5 mm in the 2nd year, 18–19·5 mm in the 3rd year, 22·7–23·6 mm in the 4th year and by the 5th year males have achieved an average size of ∼25 mm whilst females have reached ∼27 mm. Age estimates from internal microscopic annual growth lines present in the shell lip suggest that large whelks may achieve a longevity of at least 11 years. External annual rings become less discernible as the whelks increase in size and estimates of their age based solely on ring counts can underestimate their age. In males sexual maturation is reached between the 3rd and 4th years whilst in females it is attained between the 4th and 5th years. Imposex was visible in ∼2 year old females and attained maximum development by the 5th year.