Article

Age, Growth, and Sexual Maturity of the Channeled Whelk Busycotypus canaliculatus (Linnaeus, 1758) and Knobbed Whelk Busycon carica (Gmelin, 1791) in Narragansett Bay, Rhode Island

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Abstract

A total of 840 channeled (female, n = 388; male, n = 452) and 405 knobbed (female, n = 239; male, n = 166) whelks were measured for shell length (SL) and shell width (SW), with age estimates made from corresponding operculum annual growth striae readings. Gonads (ovary and testis) and reproductive structures [nidamental gland (females) and vas deferens (males)] were assessed macroscopically for maturity stage. All whelks used in this study were collected from Rhode Island state waters within Narragansett Bay, Mount Hope Bay, and Little Narragansett Bay (Pawcatuck River). Data were aggregated by species and sex, with each species treated as a single population within the study area. Age at size (growth rates) and age and size at 50% and 95% maturity were estimated for both species by sex. Female channeled whelk had the highest mean annual growth rates and reached minimum legal size quickest [minimum shell length (MSL) = 136.53 mm, minimum shell width (MSW) = 76.20 mm] and at the youngest age. Male channeled and female knobbed had similar growth rates and were the next quickest to reach MSL and MSW. Male knobbed grew slowest and were the last to enter the fishery and at the oldest age. Estimated age at 50% maturity (A50) for female channeled and female knobbed was nearly the same at 8.46 and 8.35 y, respectively. Male channeled had an estimated A50 of 7.35 y and that of male knobbed was 5.65 y. Estimated size at 50% maturity (SL50 and SW50) for female channeled was 136.8 mm SL and 77.5 mm SW; female knobbed was 124.0 mm SL and 68.4 mm SW; male channeled was 116.0 mm SL and 64.9 mm SW; and male knobbed was 89.4 mm SL and 47.7 mm SW. No instances of protandrous hermaphroditism, pseudohermaphroditism, or imposex were observed. A total of 231 newly hatched (age 0) knobbed whelks were measured for SL and SW, with mean SL and SW at age 0 included in age-at-size (growth rate) analyses. © 2018 National Shellfisheries Association. All rights reserved.

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... Maturity state was determined by macroscopic observation of gonad size, color, and condition (Gendron, 1992;Power et al., 2009;Fisher and Rudders, 2017;Angell, 2018). In males, as gonad size increased there was a corresponding change in the appearance of the testes from a thin, light orange translucent structure (Fig. 3A) to a bright orange raised structure when mature (Fig. 3B). ...
... The operculum of the channeled whelk has visible striae ( Fig. 4) that have been successfully used to establish age for channeled whelk and other whelk species (Pardo and Johnson, 2005;Miranda et al., 2008;Power et al., 2009;Peemoeller and Stevens, 2013;Angell, 2018). Following removal from the foot of the whelk, all remaining soft tissue was scraped off the backside of the operculum using a scalpel blade. ...
... Following removal from the foot of the whelk, all remaining soft tissue was scraped off the backside of the operculum using a scalpel blade. The backside of the operculum has been preferentially used for aging purposes with channeled whelk and Busycon carica (Power et al., 2009;Angell, 2018). Each operculum was placed underneath a light to illuminate striae; a dissecting microscope was used as necessary for further magnification. ...
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... Channeled, Busycotypus canaliculatus (Linnaeus 1758), and knobbed whelks, Busycon carica (Gmelin 1791) also may be important predators of Peconic bay scallops, as suggested by tethering experiments (Carroll et al. 2010;Mladinich 2017) and our direct field observations. These two commercially harvested gastropods (Udelson 2012;Peemoeller and Stevens 2013;Fisher and Rudders 2017;Angell 2018) are regarded as important predators of clams and oysters (Magalhaes 1948;Peterson 1982;Walker 1988;Kraeuter 2001), but much of the basic ecology of these species is not well understood. ...
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Channeled whelks, Busycotypus canaliculatus, support commercial fisheries throughout their range along the US Atlantic seaboard. Given the modest amounts of published information available on channeled whelk, this study focuses on understanding the temporal and spatial variations in growth and reproductive biology in the Mid-Atlantic region. Channeled whelks were sampled from three inshore commercially harvested resource areas in the US Mid-Atlantic: Ocean City, MD (OC); Eastern Shore of Virginia (ES); and Virginia Beach, VA (VB). The largest whelk measured 230-mm shell length (SL) and was recorded from OC. Mean SL was largest in OC site (158.1 mm), followed by ES (137.6 mm) and then VB (132.4 mm). Both VB and ES populations showed a unimodal length-frequency distribution with the single peak at SL less than minimum landing size (MLS) for those regions, whereas OC population showed a bimodal (two peaks) distribution with the smaller peak at SL less than the MLS for that region and larger peak at SL greater than the MLS. Brody growth rate coefficient (k) was higher in males than females from all areas and highest for both sexes in VB (Male 0.245, Female 0.155), followed by ES (Male 0.220, Female 0.151) and then OC (Male 0.112, Female 0.100). The median size (SL) at 50% mature varied between resource area and sex. Males from ES and VB reached maturity at a smaller mean size (123 and 121 mm, respectively) than OC (134 mm). Females from VB reached maturity at a smaller size (148.9 mm) than ES (157.6 mm) and OC (158.6 mm). Recruitment to the fishery was estimated to occur at ∼6 y for VB and ∼7-8 y for ES and OC and was calculated from length at age estimates from von Bertalanffy growth model. Under current MLS for each area, whelk harvested from VB were recruited into the fishery at a much younger age compared with those from OC. The probability of females reaching MLS before sexual maturity in all three commercially targeted resource areas is quite low given current MLS.
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Channel whelks (Busycotypus canaliculatus) were cultured from hatch through 171 days to describe the early life history and growth rates of juveniles. Whelks began to hatch at water temperatures of 15-18 degrees C. Channel whelks grew quickly from average shell lengths (SL) at hatch of 3.8 mm (SE = 0.1) to an average of 48.4 mm SL (SE = 1.3, n = 42 individuals) at 171 days post-hatch. The largest individual reached 53.2 mm SL, a gain of similar to 49.4 mm SL in 171 days, with a growth rate of 0.29 mm/day. Juvenile whelks readily consumed oyster (Crassostrea virginica) and mussel (Geukensia demissa) prey. A linear growth model (SL = 0.21 x [Age (days post-hatch)] + 1.6068) was used to describe the channel whelk age-at-length relationship. This is the first published growth curve for juvenile channel whelks. The observed juvenile growth rates for B. canaliculatus (0.21 mm/day) are higher than those previously described for Busycon carica. Whelk mortality was very low (<2%) after whelks reached SLs of similar to 10-12 mm.
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The age and growth of the whelk, Neptunea arthritica, was estimated based on growth striae on the operculum. Individual whelks were sexed and divided into normal and abnormal groups, based on the presence of imposex and parasite infection. The monthly marginal growth was used to determine the annual growth mark formation on the operculum. The whelk's sex (male and female), condition (normal and abnormal) and size (mature and immature) were evaluated as factors that can affect the marginal growth. Only in normal females did size affect the marginal growth, suggesting that parasite infection and imposex were not a biasing factor in the age estimation. Significant differences between low and high monthly marginal growth in normal males were found. Between operculum length and shell length and total body weight a positive relationship was found, while the same trend was observed in all female groups as well as abnormal males, but differences were not significant. The same relationship was observed between the number of stria with shell length and total body weight in all groups. The results suggest that opercula striae could be used to age N. arthritica. The Gompertz equation was the best curve that fitted the data for growth in normal groups, based on Akaike's information criteria, and it was used for all groups. The age at first sexual maturity was estimated for normal males and females to be 4.6 and 6.1 years, respectively.
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Growth rings present in whole and sectioned statoliths were used to determine the age of red whelks Neptunea antiqua, from the North Sea. Validation of the periodicity of the rings was established in four whelks by comparing the number of statolith rings with the number of seasonal Mg:Ca ratio cycles present in shell calcium carbonate samples drilled sequentially from along the growth axis. There was exact correspondence between the number of growth rings and the number of element ratio cycles in two of the shells and a 1-year difference in the estimated age between the two methods in the other two shells, evidence which is strongly indicative of an annual periodicity of deposition to the statolith rings. The estimated age of the whelks using the statolith rings varied between 4 years (shell length 102 mm) and 17 years (shell length 148 mm). The age of the whelks ascertained from the statoliths was compared with age estimates from the number of adventitious layers in sectioned opercula. The number of adventitious layers in whelks from 51 to 148 mm shell length ranged between 1 and 12 years. No significant difference was observed between the number of strongly defined statolith rings and number of opercula adventitious layers.
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Field studies, a rearing and maintenance program, and a transfer experiment have shown that anomalous male traits found in some female Ilyanassa obsoleta are an expression of environmentally controlled psuedohermaphroditism. The particular pattern of pseudohermaphroditism discovered in this species has not been reported previously from any other group, but may be characteristic of the Neogastropoda.
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We report perhaps the first genic-level molecular documentation of a mammalian-like 'X-linked' mode of sex determination in molluscs. From family inheritance data and observed associations between sex-phenotyped adults and genotypes in Busycon carica, we deduce that a polymorphic microsatellite locus (bc2.2) is diploid and usually heterozygous in females, hemizygous in males, and that its alleles are transmitted from mothers to sons and daughters but from fathers to daughters only. We also employ bc2.2 to estimate near-conception sex ratio in whelk embryos, where gender is indeterminable by visual inspection. Statistical corrections are suggested at both family and population levels to accommodate the presence of homozygous bc2.2 females that could otherwise be genetically mistaken for hemizygous males. Knobbed whelks were thought to be sequential hermaphrodites, but our evidence for genetic dioecy supports an earlier hypothesis that whelks are pseudohermaphroditic (falsely appear to switch functional sex when environmental conditions induce changes in sexual phenotype). These findings highlight the distinction between gender in a genetic versus phenotypic sense.
American seashells, 2 nd edition
  • R T Abbott
Abbott, R. T. 1974. American seashells, 2 nd edition. Princeton, NJ: D. Van Nostrand Co., Inc. 633 pp.
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