NOAA Technical Memorandum NMFS-AFSC-231

by

K. R. Smith, R. A. McConnaughey, and C. E. Armistead

Benthic Invertebrates of the 

Eastern Bering Sea: A Synopsis 

of the Life History and Ecology 

of Snails of the Genus Neptunea

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

December 2011
NOAA Technical Memorandum NMFS 

The National Marine Fisheries Service's Alaska Fisheries Science Center 

uses the NOAA Technical Memorandum series to issue informal scientific and 

technical publications when complete formal review and editorial processing 

are not appropriate or feasible. Documents within this series reflect sound 

professional work and may be referenced in the formal scientific and technical 

literature. 

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries 

Science Center continues the NMFS-F/NWC series established in 1970 by the 

Northwest Fisheries Center. The NMFS-NWFSC series is currently used by 

the Northwest Fisheries Science Center. 

This document should be cited as follows: 

Smith, K. R., R. A. McConnaughey, and C. E. Armistead. 2011. Benthic 

invertebrates of the Eastern Bering Sea: A synopsis of the life history 

and ecology of snails of the genus Neptunea. U.S. Dep. Commer., 

NOAA Tech. Memo. NMFS-AFSC-231, 5 p. 

Reference in this document to trade names does not imply endorsement by 

the National Marine Fisheries Service, NOAA. 
December 2011

NOAA Technical Memorandum NMFS-AFSC-231

by

K. R. Smith1, R. A. McConnaughey1, and C. E. Armistead2

Benthic Invertebrates of the 

Eastern Bering Sea: A Synopsis of 

the Life History and Ecology of Snails 

of the Genus Neptunea

1

Alaska Fisheries Science Center

Resource Assessment and Conservation Engineering Division

7600 Sand Point Way N.E.

Seattle, WA 98115

2

Alaska Fisheries Science Center

Resource Assessment and Conservation Engineering Division

Kodiak Laboratory

301 Research Court

Kodiak, AK 99615

www.afsc.noaa.gov

U.S. DEPARTMENT OF COMMERCE

John E. Bryson, Secretary

National Oceanic and Atmospheric Administration

 Jane Lubchenco, Under Secretary and Administrator

National Marine Fisheries Service

Eric C. Schwaab, Assistant Administrator for Fisheries 
This document is available to the public through: 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

www.ntis.gov 
iii 

ABSTRACT 

 Snails of the genus Neptunea have a significant presence among the benthic fauna 

inhabiting the North American continental shelf in the eastern Bering Sea (EBS). This is 

reflected by the catch of annual bottom trawl-net surveys of the continental shelf conducted by 

the Resource Assessment and Conservation Engineering Division of the Alaska Fisheries 

Science Center, National Oceanic and Atmospheric Administration. Together these surveys 

comprise a time-series assessing stocks of groundfish and benthic invertebrates in the EBS, from 

1971 to the present. In the 1975 survey of shelf and upper slope, gastropods constituted 6.6% of 

the biomass of invertebrates caught. In some areas catch per unit effort (CPUE; i.e., catch per 

unit of area swept) exceeded 30 kg/ha. 

Gastropods, mostly of the order Neogastropoda which includes Neptunea, in more recent 

EBS shelf surveys remain one of the top 50 EBS invertebrate taxa in both total abundance and 

frequency of occurrence at trawl stations. Among gastropods, by far the most abundant species in 

these surveys are those of the genus Neptunea, particularly the four species N. pribiloffensis, N. 

heros, N. lyrata, and N. ventricosa. Based on hauls at standard EBS shelf stations in surveys of 

selected years from 1983 to 2010, we include maps for each species showing the year-by-year 

distribution of abundance over the area as extrapolated from haul CPUE. 

Because of its high abundance in the benthic fauna, the genus probably constitutes a 

significant element in the benthic ecology of the region. However, little direct study of local 

populations has occurred to date, leaving a dearth of information available on biology and 

ecological relationships. More extensive observations have been made of species of Neptunea in 

other marine regions of the Northern Hemisphere, and this paper presents information available 

from these studies along with that from local studies. The information forms a synopsis of the 
iv 

probable characteristics of life history, trophic webs, and anthropogenic effects relating to the 

genus in the EBS. 
v 

CONTENTS 

ABSTRACT ................................................................................................................................... iii 

INTRODUCTION ...........................................................................................................................1 

PHYLOGENY AND GEOGRAPHIC ORIGIN OF NEPTUNEA .................................................2 

GEOGRAPHIC DISTRIBUTION OF NEPTUNEA 

 IN THE EASTERN BERING SEA ...............................................................................................3 

 Methods................................................................................................................................3 

 RACE Bottom Trawl Survey Design .......................................................................4 

 Abundance ...............................................................................................................4 

 Distribution Maps ....................................................................................................5 

Regional Species Assemblages ......................................................................................................24 

LIFE HISTORY AND ECOLOGY ...............................................................................................24 

 Extent of Information .........................................................................................................24 

 Growth and Development ..................................................................................................25 

 Morphogenesis .......................................................................................................25 

 Sexes ......................................................................................................................25 

 Average Length ......................................................................................................26 

 Maximum Length...................................................................................................26 

 Weight Versus Length ...........................................................................................27 

 Growth Rate ...........................................................................................................27 

 Maximum Average Length-at-Age ........................................................................29 

 Greatest Age Observed ..........................................................................................29 

 Maturation of Sexes ...........................................................................................................31 

 Length at Maturity .................................................................................................31 

 Age at Maturity ......................................................................................................33 

 Annual Cycles of Reproduction .........................................................................................34 

 Mate Selection .......................................................................................................34 

 Copulation and Spawning Seasons ........................................................................34 

 Incubation ..............................................................................................................35 

 Spawning Physiology.............................................................................................37 

 Brood Size ..............................................................................................................37 

 Spawning Habitat ...................................................................................................38 

 Feeding Methods and Diet .................................................................................................38 

 Prey ........................................................................................................................39 

 Diet Strategies ........................................................................................................40 

 Mortality ............................................................................................................................41 

 Rates .......................................................................................................................41 

 Predators ................................................................................................................42 
vi 

ANTHROPOGENIIC INTERACTIONS ......................................................................................43 

 Incidental Results of Commercial Fishing .........................................................................43 

 Snail Bycatch .........................................................................................................43 

 Changes to the Benthos ..........................................................................................44 

 Pollution-induced Imposex ................................................................................................45 

 Human Consumption .........................................................................................................46 

 Potential Effects on Demographics of Neptunea ...............................................................46 

 Food Poisoning ..................................................................................................................46 

CITATIONS ..................................................................................................................................49 
INTRODUCTION 

Gastropods have a significant presence in the benthos of the eastern Bering Sea (EBS) 

continental shelf and upper slope, as shown in the results of annual bottom trawl surveys 

conducted by NOAA’s National Marine Fisheries Service (NMFS) through the Alaska Fisheries 

Science Center, Resource Assessment and Conservation Engineering Division (RACE). 

Together these surveys comprise an annual time-series, from 1971 to the present (Acuna and 

Lauth 2008), used to assess stocks of groundfish and benthic invertebrates in the EBS. 

In the 1975 NMFS survey of the shelf and upper slope, gastropods constituted 6.6% of 

the biomass of invertebrates caught. In some areas trawl catch per area swept exceeded 30 kg/ha

(MacIntosh 1980). Yeung and McConnaughey (2006) judged gastropods (mainly those of the 

order Neogastropoda) among the top 50 EBS invertebrate taxa in both abundance (by weight) 

and frequency of occurrence (percent of trawl stations where present), in each year from 1982 to 

2002. Among large (length > 50 mm) species of gastropods occurring on the EBS continental 

shelf and upper slope, the most abundant, in both biomass and numbers, are Neptunea species. 

Of these, N. pribiloffensis is generally the most abundant, with N. lyrata, N. heros, and N. 

ventricosa also prominent1

 (MacIntosh 1980). 

In addition to their ecological significance in the benthos, gastropods, mostly species of 

the genus Neptunea, have been harvested in the region as commercial seafood. Pot fishing was 

conducted by Japan in the 1970s (MacIntosh 1980), and by the United States as recently as 1997 

(Bowers et al. 2008). Most of the catch (70%) retained by the Japanese fishery in 1973 was N. 

pribiloffensis, with an additional 23% composed of Buccinum angulosum and B. scalariforme

(MacIntosh 1980).

 

1

 K.R. Smith, pers. obs. 
Species of the genus Neptunea have shells of medium to shortened length (i.e., length of 

the shell from apex to end of anterior canal) relative to width. Shells are dextrally coiled, often 

with species-distinct patterns of spiral/axial sculpture. Sinistral coiling is rare (Nelson 1978, 

MacIntosh 1976a). 

This synopsis outlines the geographic distribution of abundance of the four major 

Neptunea species in the EBS shelf area from 1983 to 2010 inclusively, as reflected by standard 

RACE bottom trawl surveys for selected years representing the period. It also summarizes from 

the available literature the findings by other investigators regarding the life history and ecology 

of species of Neptunea in the EBS shelf area. The total scope of such studies of local populations 

is as yet limited. Therefore, we summarize as well the somewhat more extensive findings of 

investigations of Neptunea species in other geographic regions within the range of the genus in 

the hope of presenting a more complete picture of general characteristics of life history and 

ecology applicable to the genus as a whole. 

PHYLOGENY AND GEOGRAPHIC ORIGIN OF NEPTUNEA 

Among gastropods, the genus Neptunea Röding, 1798, is of the subclass Prosobranchia, 

which includes the order Neogastropoda that in turn encompasses the Buccinidae (loosely termed 

whelks), the parent family of the genus. Species of the Neogastropoda have about twice as many 

chromosomes as other prosobranchs, suggesting a possible origin by polyploidy, and are 

considered the most derived prosobranchs(Ruppert et al. 2004). 

Although the phylogenetic relationships among neogastropod species are often uncertain 

above the level of genus, a close relationship between the buccinid genera Neptunea and 

2
Buccinum has been indicated by both morphological (Haasl 2000) and mitochondrial 16s rRNA 

gene (Hayashi 2005) comparisons. This is despite the obvious difference between the oval 

operculum of Buccinum with its centered nucleus, and the leaf-shaped one of Neptunea having a 

marginal nucleus, by which Neptunea resembles several other buccinid genera1

. 

The genus is thought to have evolved in the western North Pacific (off northern Japan 

and Sakhalin Island) in the early Oligocene epoch (Nelson 1978). Its many species presently 

occur in continental shelf waters of the North Pacific (west and east), Arctic, and North Atlantic 

Oceans, as well as the North Sea and Mediterranean Sea (Nelson 1978). Although systematics 

within the genus are still being developed, several described species have been identified on the 

EBS shelf. In addition to the four major species mentioned above, these include Neptunea 

borealis, N. amianta, N. neptunea, and N. insularis (Clark 2006).

GEOGRAPHIC DISTRIBUTION OF NEPTUNEA 

 IN THE EASTERN BERING SEA 

Methods 

The RACE EBS bottom trawl surveys index the abundance of each individual taxon in 

the catch by calculating the average number of organisms and/or average aggregate weight 

(biomass) caught per unit of bottom area swept by the net mouth (CPUE), for each haul. Area 

swept equals the average width of the net mouth times the distance trawled. Gastropod catch 

efficiency of the trawl gear is unknown. Certainly, bottom trawls are not efficient samplers for 

benthic infauna; however, they are deemed sufficient for monitoring relative abundance of 

certain epifaunal species. The derived abundance estimates may be thought of as a minimum for 

3
potentially burrowing species such as gastropods (Yeung and McConnaughey 2006, MacIntosh 

1980). 

RACE Bottom Trawl Survey Design 

Methods and gear used in these surveys are generally consistent from year to year. The 

present configuration of sampling stations and gear dimensions was first adopted in 1982 under 

the North Pacific Fishery Management Council’s Bering Sea-Aleutian Islands Groundfish 

Fishery Management Plan (Acuna and Lauth 2008, Yeung and McConnaughey 2006). The 

annual surveys conducted since then have covered an area divided into a standard grid of 330 

squares each 20 × 20 nautical miles (nmi) (37.04 × 37.04 km), thus encompassing approximately 

341,880 km2

 overall. The standard trawl stations of the survey include 330 located at the 

respective centers of these squares, plus at the corners of select grid squares an additional 16 

stations northeast of the Pribilof Islands and 10 stations southwest of St. Matthew Island as well. 

These extra stations are included to increase sampling density in areas historically having 

significant concentrations of Paralithodes species (king crab). An additional 20 squares with 

centered trawl stations were added at the northwest margin of the grid in 1988 to extend the 

standard survey area northwest and provide further information on the distribution of 

Chionoecetes opilio (snow crab) and Theragra chalcogramma (walleye pollock; Acuna and 

Lauth 2008). This established the current standard survey design of 376 stations in a grid of 350 

squares covering approximately 362,600 km2

. This survey grid spans the EBS shelf from the 

Alaska Peninsula in the southeast to approximately 62o N near St. Matthew Island in the 

northwest, and cross-shelf from the 20 m isobath to the 200 m isobath.

4
Results: Distribution of Abundance 

Like many benthic invertebrates, species of Neptunea are not uniformly abundant over 

the EBS. Along with other benthic species, these species generally occur as components of 

regional assemblages of taxa, likely the result of differing preferences for environmental 

elements such as temperature, depth, and prey. 

Distribution Maps

Figures 1-4 depict the standard station layout and results from annual RACE EBS bottom 

trawl surveys, along with broad-scale bathymetry of the region. The maps show annual survey 

results for each of the four predominant Neptunea species N. heros, N. ventricosa, N. 

pribiloffensis, and N. lyrata in the EBS, displaying the year-by-year abundance distribution 

expressed as CPUE (kilograms per hectare). For a species, each grid square is color coded to 

represent one of five contiguous CPUE intervals that together cover the full range of densities 

observed during the surveys included. The color of each square is that of the coded interval 

encompassing the average CPUE of that year’s trawl sample(s) taken within the square. This 

standardization of color codes allows comparison of densities between years. 

The maps cover two periods: 1983 through 1988 and 2003 through 2010. These years 

were selected to represent any long-term changes in abundance or distribution, while adhering to 

the most consistent standards of taxonomic identification of any catch of the four individual 

species. Due to variations in emphasis by RACE personnel on taxonomic resolution in 

identification of various species as well as varying conditions and workloads in the field, 

historically such resolution has varied among and within years of the survey. In addition, there 

have been gradual improvements in taxonomic knowledge and training which have led to more 

informed classification of many fish and invertebrate taxa recently than on earlier surveys. Thus 

5
there are prudent limits to confidence when considering the historic catch data for some taxa 

(Stevenson and Hoff 2009). However, a systematic search of the data revealed the years 

described above during which the amount by weight of catch classified as higher taxa 

conceivably including any species of Neptunea (i.e., “gastropod unidentified” or “Neptunea 

species”) was subjectively judged insignificant. These years of relatively unambiguous data 

regarding the four species of interest were chosen using software programmed by the author to 

query the extensive RACE EBS bottom-trawl survey database for years wherein the data meet 

these criteria2. In each of these years, generally the entire catch amount reported for the two 

higher taxa was exceeded by each of the amounts for the four individual species by one or more 

degrees of magnitude. 

None of the species show distinctive density trends of increase or decrease over the range 

of years 1983 through 2010. Rather, each generally shows a pattern of relatively consistent 

presence in a particular geographic portion of the shelf (Figs. 1-4). Thus although separated by 

14 of the 28 years spanned by the data, the selected blocks of years 1983 through 1988 and 2003 

through 2010 were deemed sufficient in representing abundance over the full range of years 

included. 

Neptunea heros showed little change in abundance over the range of years examined. 

However, a vessel bias indicating some sort of misidentification is probable in 1987, 1988, and 

2010. In these years in Bristol Bay parallel north-south lines of stations, each line having been 

trawled by only one of the two survey vessels alternately, repeatedly show N. heros reported in 

one line but not an adjacent one trawled by the other vessel (Fig. 1). This has been called the 

 

2

Addressing ambiguity due to variation in the resolution of taxonomic identification of a species among quantified 

fauna samples within large time-series-based databases, using query-based reclassification to lowest accountable 

inclusive taxon (LAIT). Unpublished data. K. R. Smith, Alaska Fish. Sci. Cent., NOAA, Natl. Mar. Fish. Serv., 

7600 Sand Point Way NE, Seattle, WA 98115. 

6
column effect3

. Nevertheless, even given the likely misidentification in these years, there is 

considerable consistency in the overall geographic range and density distribution of the species 

historically. 

Neptunea ventricosa also showed little change over the range of years examined, except 

for stations in the extreme northwest of the survey area where presence of the species has seemed 

either patchy or fluctuating since the inclusion of these stations in 1988 (Fig. 2). 

Neptunea pribiloffensis displayed the highest abundance overall. The species showed 

considerable shifts in distribution but no overall major trends. Lower than average numbers were 

found in 1986 and 2009. There was a noticeable pattern of occurrence along the shelf break from 

61° N south to the Alaska Peninsula, but with a regular localized gap in presence just east of the 

Pribilof Islands. This gap seems unrelated to historical snail harvesting as the last recorded 

commercial catch in the area was in 1997 (Bowers et al. 2008). The species was reported at a 

block of stations southwest of Nunivak Island in 2010, but as this was an isolated report by a 

single vessel and did not occur in other years it likely represents taxonomic misidentification 

rather than a population shift of N. pribiloffensis (Fig. 3). 

Neptunea lyrata is generally co-located with N. pribiloffensis (i.e., along the shelf break) 

but without the noticeable gap near the Pribilof Islands shown by the latter species. Some vesselrelated misidentification as mentioned above for N. heros and N. pribiloffensis appears to occur. 

On the maps for the year 1983 and 2010, parallel station-columns alternately sampled by the two 

survey vessels show alternating consistent presence and consistent absence reported for the 

species, depending on the respective vessel sampling the column. This pattern occurs in areas on 

the mid-shelf and in Bristol Bay, north and northeast of the otherwise consistent distribution 

 

3

 Chilton, E. A. 2011. NOAA, Alaska Fisheries Science Center, Kodiak Laboratory, Kodiak, Alaska. Pers. comm. 

7
shown for other years along the outer shelf from west of St. Matthew Island thence southeast to 

the Alaska Peninsula (Fig. 4). 

8
Figure 1. -- Abundance of Neptunea heros in the Eastern Bering Sea (EBS) shelf region as catch per unit effort (CPU

RACE annual bottom trawl sample surveys of groundfish and invertebrates for the select years 1983 throthrough 2010. The grid of 20 nmi × 20 nmi contiguous squares represents the standard EBS shelf area co

with each square colored to represent the average CPUE of the species within that square. 

9
Figure 1. – Continued. 

10
Figure 1. – Continued. 

11
Figure 1. – Continued. 

12
Figure 2. -- Abundance of Neptunea ventricosa in the Eastern Bering Sea (EBS) shelf region as catch per unit effort 

standard RACE annual bottom trawl sample surveys of groundfish and invertebrates for the select years 

2003 through 2010. The grid of 20 nmi × 20 nmi contiguous squares represents the standard EBS shelf asurveys, with each square colored to represent the average CPUE of the species within that square. 

13
Figure 2. -- Continued. 

14
Figure 2. – Continued. 

15
Figure 2. – Continued. 

16
Figure 3. -- Abundance of Neptunea pribiloffensis in the Eastern Bering Sea (EBS) shelf region as catch per unit effo

standard RACE annual bottom trawl sample surveys of groundfish and invertebrates for the select years 2003 through 2010. The grid of 20 nmi × 20 nmi contiguous squares represents the standard EBS shelf asurveys, with each square colored to represent the average CPUE of the species within that square. 

17
Figure 3. – Continued. 

18
Figure 3. – Continued. 

19
Figure 3. – Continued. 

20
Figure 4. -- Abundance of Neptunea lyrata in the Eastern Bering Sea (EBS) shelf region as catch per unit effort (CPU

RACE annual bottom trawl sample surveys of groundfish and invertebrates for the select years 1983 throthrough 2010. The grid of 20 nmi × 20 nmi contiguous squares represents the standard EBS shelf area co

with each square colored to represent the average CPUE of the species within that square. 

21
Figure 4. – Continued. 

22
Figure 4. – Continued. 

23
Figure 4. – Continued. 

24
Regional Species Assemblages 

Of the four species of Neptunea predominant in the EBS, N. heros and N. ventricosa both 

occur at depths generally exceeding 50 m, as part of the low-arctic-boreal species assemblage 

occupying the northern portion of the EBS shelf as well as northern and coastal waters of Bristol 

Bay (Shimek 1984). This is relatively cold water that nevertheless warms rapidly in summer. 

Neptunea pribiloffensis and N. lyrata are in the subarctic-boreal assemblage in the southern EBS, 

typically near the outer shelf edge in relatively deep water that is warmed by advection from the 

Pacific and fairly consistently at a temperature of 2-4°C (Shimek 1984). The latter two species 

also occur south of the Aleutian Islands and in shallow coastal areas south of the Alaska 

Peninsula. Their range extends south to at least the Washington coast. 

In the EBS, the distributions of the four Neptunea species meet in a transition zone 

centered near the offshore western extremity of Bristol Bay (roughly 56° N, 165° W; Shimek 

1984). 

LIFE HISTORY AND ECOLOGY 

Extent of Information 

There have been relatively few biological studies of Neptunea species in the EBS, but a 

few specific aspects of the ecology and life history of N. pribiloffensis, N. lyrata, N. heros, 

and/or N. ventricosa in the region have been investigated (Kaimmer et al. 1976, MacIntosh and 

Paul 1977, Nagai 1974, Shimek 1981). In addition, many life history characteristics have been 

examined in species of Neptunea outside the region, including characteristics of some species 

also occurring in the EBS. Because life history characteristics are likely similar among the 

25
various species of the genus as well as among regional populations within a species, available 

findings from all pertinent studies are included in this summary. 

Growth and Development 

Morphogenesis 

Neptunea hatchlings emerge from the eggs at the juvenile stage, with the primary shell 

already developed (Fujinaga 2003), and unlike most prosobranchs which usually produce a freeswimming larva (veliger) they undergo no subsequent metamorphosis. MacIntosh (1976b) 

observed the following shell lengths for newly emerged hatchlings of the four major EBS 

species: N. heros, 6-8 mm; N. ventricosa, 8-11 mm; N. pribiloffensis, 7-11 mm; and N. lyrata, 8-

12 mm. Power and Keegan (2001a) observed 50 newly-hatched juvenile N. antiqua from the 

Irish Sea to have an average shell length of 8.32 mm. Contrary to the limited dispersal expected 

of snails with direct development, the wide geographic distribution of the genus mirrors that of 

some genera of gastropods and bivalves having pelagic larvae (Nelson 1978). 

Sexes 

Neptunea are dioecious (individuals are either male or female throughout life). Nagai 

(1974) observed a sex ratio of 1:1 in N. pribiloffensis near the Pribilof Islands, and male-tofemale ratios observed by Kaimmer et al. (1976) for the four major species of Neptunea in the 

EBS were N. heros (1.12), N. ventricosa (0.93), N. pribiloffensis (0.91), and N. lyrata (1.46). Sex 

ratios were approximately 1:1 in populations of non-EBS species N. arthritica in Japanese waters 

(Fujinaga 2003) and N. antiqua in the Irish Sea (Power and Keegan 2001a) and North Sea 

(Pearce and Thorson 1967). 

26
Fujinaga (1987) found no secondary sexual dimorphism, such as overt differences in 

shell length (apex to end of anterior canal; L) versus shell width, in N. arthritica near Hokkaido, 

Japan. However, Power and Keegan (2001a) reported subtle but significant sex-related 

differences in N. antiqua in L versus such dimensions as aperture length and body whorl width. 

Average Length 

Average individual length (shell apex to end of anterior canal; L) for each of the four 

predominant Neptunea species was reported by MacIntosh (1976a) from the 1975 NMFS EBS 

bottom trawl survey as follows: N. pribiloffensis = 100 mm; N. lyrata = 115 mm; N. heros = 

121 mm; N. ventricosa = 121 mm. As the 1 1⁄4-inch mesh of the codends retained few snails 

< 50 mm long, these averages generally apply to adults. 

Maximum Length 

Maximum L for each of the four predominant Neptunea species was reported from the 

1975 EBS survey as follows: N. pribiloffensis, 150 mm; N. lyrata, 170 mm; N. heros, 170 mm; 

N. ventricosa, 150 mm (MacIntosh 1976a). These lengths fall within the range of reported 

maximums for non-EBS species as well. Borulya and Bregman (2002) observed specimens of N. 

constricta and N. polycostata from the Sea of Japan up to 220 mm and 184 mm long, 

respectively. Neptunea antiqua have been reported from waters near Great Britain exceeding 

200 mm (Fretter and Graham 1962), and from the North Sea near Denmark up to 165 mm 

(Pearce and Thorson 1967). Neptunea lyrata, a species found in the western North Pacific as 

well as in the EBS, attained L = 161 mm in samples from the Sea of Japan (Borulya and 

Bregman 2002). Neptunea arthritica, a species possibly smaller than usual among Neptunea, was 

observed by Miranda et al. (2008) near Hokkaido, Japan, to attain L = 94.2 mm. At least one 

27
other species of Neptunea, N. borealis, occurs in the EBS, but it is not common and reaches a 

maximum L of only about 60 mm (MacIntosh 1976a). 

Weight Versus Length 

Total weight (W) is a power function of L (W = aLb

) for individuals of the four major 

EBS Neptunea species. MacIntosh and Paul (1977) found the following best-fitting formulae for 

W (grams) relative to L (mm) of the respective species, based on least sum-of-squares: N. 

pribiloffensis (W = 0.0381 L3.41344); N. lyrata (W = 0.0411 L3.09406); N. heros 

 (W = 0.0347 L3.63557) ; N. ventricosa (W = 0.439 L3.22321). Other investigators have fitted power 

functions for W versus L to data obtained for other species of Neptunea in other areas. In these 

studies values for parameter b ranged from 2.48 (+ 0.11; Borulya and Bregman 2002)to 2.8 

(Miranda et al. 2008). Although Neptunea juveniles have shells with the same basic width-tolength ratio as do conspecific adults (Fujinaga 1987), Miranda et al. (2008) noted that the growth 

they observed of N. arthritica in W versus L was non-isometric (b ≠ 3, P < 0.001). This may be 

the result of seasonal and/or permanent changes in anatomical proportions over the lifespan of 

individuals. 

Growth Rate 

Several studies have been made of individual growth rate within Neptunea species in 

various regions inhabited by the genus. All have shown growth to be self-limiting (i.e., 

approaching an asymptotic limit of average length-at-age, L∞), but following different models or 

parameters within a model (Miranda et al. 2008, Fujinaga 2003, Borulya and Bregman 2002, 

Power and Keegan 2001a, Suzuki et al. 1996, Fujinaga 1987). Although no such investigations 

have been made in the EBS, together these studies provide a general picture of likely growth 

patterns of the four principal species in the EBS (Table 1). 

28
In the life history of snails, various physical features appear to exhibit cyclical periodic 

change (e.g., straie deposition in opercula, change of Mg:Ca ratio in the chemistry of newly 

formed shell) and therefore to produce patterns that are potential age indicators (Richardson et al. 

2005). However, little research has been done to verify and calibrate these methods for ageing 

Neptunea species. Nevertheless, investigations of populations of Neptunea species in various 

regions tentatively using these methods as well as one analyzing periodic changes in length 

frequency distributions (Fujinaga 1987) have shown some features of the growth rate over the 

individual lifespan (Table 1). The following is a brief summary of the methods used by these 

studies and some of the findings: 

Fujinaga (2003, 1987) and Suzuki et al. (1996) used length frequency distributions 

observed during regular monthly sampling of N. arthritica populations near Hokkaido, Japan, to 

estimate age without relying on any morphological features. Using the method of Harding (1949)

to examine each of these monthly distributions for the presence of multiple latent modal subsets, 

they estimated the composition of each sample by multiple year-class cohorts, “tracking” and 

identifying each cohort over a 4-year sampling period by comparison of the monthly frequency 

distributions. They then plotted average L against age (years), and used the criteria of least 

squares to find best-fitting growth formulae. Both found adult growth to slow with age after 

achieving a maximum rate, although Fujinaga’s (1987) study indicated a Gompertz model while 

Suzuki et al. (1996) found a logistic model best. 

Alternatively, Miranda et al. (2008) aged N. arthritica from the Hokkaido area by 

counting age-related opercula striae, estimating growth to follow a Gompertz model best. All 

three models developed for N. arthritica (Miranda et al. 2008, Suzuki et al. 1996, Fujinaga 1987) 

indicate a pattern of slower growth in the early juvenile stage, faster in late juvenile and early 

29
adult stages, and slowing again in late adulthood while approaching an asymptotic limit. Borulya 

and Bregman (2002) used essentially the same ageing technique as Miranda et al. (2008),

studying N. constricta, N. polycostata and N. lyrata in Ussuriisky Bay, Sea of Japan. Their 

observations in plotting L against operculum-derived age estimates and seeking the best-fit 

model indicated a von Bertalanffy growth pattern for those populations. Power and Keegan 

(2001a) endorsed a von Bertalanffy formula previously fitted to L versus operculum-striae-based 

ages of N. antiqua, using the formula to back-calculate age after measuring L in samples from 

the Irish Sea. In their separate studies referred to above, Fujinaga (2003, 1987) and Miranda et al. 

(2008) found no significant difference in growth rate between sexes of N. arthritica in waters 

near Hokkaido. However, in size distributions separated by sex, female Neptunea have tended to 

be larger than males in some populations in the EBS (Kaimmer et al. 1976, Nagai 1974), North 

Sea (Pearce and Thorson 1967), and Irish Sea (Power and Keegan 2001a). Aside from a possible 

difference in growth rates of sexes this could result from differing mortality rates at age. 

Maximum Average Length-at-Age 

For each of the growth studies of (non-EBS) populations of Neptunea mentioned above, 

the respective theoretical asymptotic upper limit of average L (L∞) from the best-fit L-versus-age 

function is presented in Table 1. These values generally mirror the relative differences among 

greatest lengths reported above for the same species, for example showing the lowest values for 

N. arthritica.

Greatest Age Observed 

In addition to the other morphological aging methods outlined above, Richardson et al. 

(2005), although not attempting an analysis of growth rate, used statoliths to age sampled N. 

antiqua of up to 148 mm L from the North Sea. The small (< 0.2 mm dia.) structures in the 

30
gastropod anatomy, integral to an individual’s orientation to gravity, present rings in which 

annually created patterns can be microscopically observed.

Although Golikov (1978) postulated a general age limit for Neptunea of 8 years, most of 

the above-mentioned ageing studies have indicated greater maximums. Maximum ages observed 

in these investigations are presented in Table 1 along with estimates of L∞. 

Table 1. -- Estimated asymptotic upper limit of average L-at-age (L∞), greatest observed age, 

best-fit model type describing growth rate, and ageing method for some studied 

regional populations of Neptunea species. Information not obtained by the studies is 

designated by “NA”. 

Species Area L∞ (mm) Oldest Model Ageing method 

N. arthritica 

Usu Bay, 

Hokkaido 107.5 NA Gompertz L freq. dist. (Fujinaga 1987) 

Shiriuchi, 

Hokkaido 90.5 NA Logistic 

L freq. dist. 

(Suzuki et al. 

1996) 

Saroma Lagoon, 

Hokkaido 

96.5 (males) 

91.6 (females) 

13 yrs 

10 yrs Gompertz 

Opercula striae 

(Miranda et al. 

2008) 

N. lyrata 

Ussuriisky Bay, 

Sea of Japan 

140.5 18 yrs 

Von 

Bertalanffy 

Opercula striae 

(Borulya and 

Bregman 2002) 

N. 

polycostata 204.6 17 yrs 

N. constricta 213.1 16 yrs 

N. antiqua Irish Sea 140 NA Von 

Bertalanffy 

Opercula striae 

(Power and 

Keegan 2001a) 

N. antiqua North Sea NA 17 yrs NA 

Statolith striae 

(Richardson et al. 

2005) 

31
Maturation of Sexes 

Length at Maturity 

MacIntosh and Paul (1977) have examined data indicating L at onset of maturity (Lmat) 

for each sex of the four major Neptunea species in the EBS. Parameter estimates were based on 

the graphical nature of each of the eight best-fit regressions of sampled gonad weight as a power 

function of L for females, penis weight as a power function of L for males. Their study shows a 

general trend of greater Lmat for female Neptunea than for conspecific males, by roughly 

10-15 mm (Table 2). 

Other investigators have used different methods to determine Lmat for other populations of 

Neptunea species. Their results are consistent with those of MacIntosh and Paul (1977) in the 

EBS, after taking into consideration differences in asymptotic average length-at-age (L∞) and 

maximum length observed among the species and populations involved (Table 2). Fujinaga 

(1987, 1985) determined Lmat for N. arthritica from Usu Bay, Hokkaido, Japan, based on 

histological observations of seminal vesicles and female gonads from measured individuals. For 

other Hokkaido waters, Fujinaga et al. (2006) and Fujinaga and Oyama (2007) variously 

estimated Lmat of N. arthritica and N. polycostata with a method similar to that of MacIntosh and 

Paul (1977), albeit without use of a regression formula. This consisted of inspecting scattergrams 

of penis index (PI)4

 and seminal vesicle index (SVI)5 versus L for males, gonadosomatic index 

(GSI)6 and pallial oviduct index (POI)7 versus L for females. An abrupt general rate of increase in 

these indexes with increase in L, as observed in the scattergrams, indicated respective Lmat

 

4

 PI = ([penis weight]/[soft body weight]) × 100 

5

 SVI = ([seminal vesicle weight]/[soft body weight]) × 100 

6

 GSI = ([gonad weight]/[soft body weight]) × 100 

7

 POI = ([pallial oviduct weight]/[soft body weight]) × 100 

32
values. In a similar way, Power and Keegan (2001a) estimated Lmat for N. antiqua from the Irish 

Sea by plotting gonad weight and penis length separately against L for males and gonad weight 

against L for females. Lastly, Pearce and Thorson (1967), observing mating behavior of N. 

antiqua males and females from the Danish North Sea in an aquarium, estimated Lmat for each 

sex. The methods and results of these investigations are summarized in Table 2. 

Table 2. -- Length (L) at maturity of males and females (with method of determination) observed 

in some regional populations of Neptunea species. 

Species Area 

L at maturity (mm) Method of determination 

Males Females 

N. pribiloffensis 

EBS 

90 105 

Regression plots: weight 

of reproductive organ vs. 

L (MacIntosh and Paul 

1977)

N. lyrata 100 110 

N. heros 95 110 

N. ventricosa 87 102 

N. arthritica 

Usu Bay, 

Hokkaido ~50 ~60 

Histology: seminal 

vesicles, female gonads 

(Fujinaga 1985)

Saroma Lagoon, 

Hokkaido 60 75 

Histology: reproductive 

organs (Miranda et al. 

2008) 

Sarufutsu, 

Hokkaido 70 80-90 

Scattergrams: PI4

 & SVI5

vs. L for males, GSI6

 & 

POI7

 vs. L for females 

(Fujinaga et al. 2006) 

Notoro Lake, 

Hokkaido 50 70-80 

Notsuke, 

Hokkaido 60 75 

Erimo, Hokkaido 55-60 70 

Mashike, 

Hokkaido 70 75 

33
N. polycostata Erimo, Hokkaido 120-130 150-160 

Scattergrams: PI & SVI 

vs. L for males, GSI & 

POI vs. L for females 

(Fujinaga and Oyama 

2007)

N. antiqua 

Irish Sea 75-90 95-110 

Scattergrams: gonad wt. 

vs. L for both sexes, penis 

length vs. L for males 

(Power and Keegan 

2001a) 

North Sea 

(Denmark) 50-60 79 

Aquarium observation 

(Pearce and Thorson 

1967) 

Age at Maturity 

Little work has been done to determine the age at which individuals become mature 

among Neptunea. Some estimates have been included as part of the above-mentioned studies 

investigating Lmat for non-EBS Neptunea species. Fujinaga (1987) estimated onset of maturity to 

occur at 2+ years (~ 29 months) for males, 3+ years (~ 42 months) for females of N. arthritica

from Usu Bay, Hokkaido. Level of maturity estimated from the histology of gonads of 

individuals of different lengths (L) was combined with L-at-age inferences from multi-year 

trends in a monthly series of length frequency distributions displaying different year classes. 

However, Miranda et al. (2008) estimated maturation to occur at 4.6 years for males and 

6.1 years for females of N. arthritica from Saroma Lagoon, Hokkaido. These values were 

estimated by finding Lmat (from the histology of gonads) for each sex, then projecting those 

lengths onto von Bertalanffy regressions of L on age (as indicated by the number of operculum 

striae). Power and Keegan (2001a) used the same method of back-calculating age-at-maturity for 

N. antiqua from the Irish Sea, estimating ages at 4-5 years for males and 6-9 years for females. 

34
Wherever the studies included age estimations the data have indicated a greater age at 

onset of maturity for females than for males (Miranda et al. 2008, Power and Keegan 2001a, 

Fujinaga 1987). Thus the obvious similarity among the findings in the ubiquitously greater 

length at which this occurs for females, compared with males of the same species (Table 2; 

Miranda et al. 2008, Fujinaga and Oyama 2007, Fujinaga et al. 2006, Power and Keegan 2001a, 

Fujinaga 1985, MacIntosh and Paul 1977, Pearce and Thorson 1967) may be a result of this 

difference in age at maturity rather than a difference in growth rates. 

Annual Cycles of Reproduction 

Insemination of females is internal, via the male penis. Females store sperm in a seminal 

receptacle connected to the oviduct, for later fertilization of eggs released by the ovary (Ruppert 

et al. 2004). Spawning cycle schedules, fecundity, and other aspects of reproductive behavior of 

EBS Neptunea are poorly known, but pertinent observations of the same and congeneric species 

in other regions are available as indicators of general characteristics expected to occur among the 

EBS populations (below and Table 3): 

Mate Selection 

Neptunea antiqua (Pearce and Thorson 1967) from the Danish North Sea and N. 

arthritica (Miranda et al. 2008)from Hokkaido waters observed during mating were 

polygamous; that is, females sometimes copulated with multiple males. 

Copulation and Spawning Seasons 

Copulation timing among species of Neptunea in Alaskan waters has not been observed 

directly, but Shimek (1981) stated that intertidal female N. pribiloffensis and N. lyrata near 

Homer, Alaska, spawn from late April through early June. Based on the ~ 1-3 month copulation35
to-spawning interval observed for other Neptunea (Fujinaga and Oyama 2007, Fujinaga 2003, 

Power and Keegan 2001a), copulation could occur in these nearshore populations of the 

northwest Gulf of Alaska between late January and early May. 

Copulation among N. arthritica near Hokkaido starts in April, peaking/ending in June 

(Fujinaga 2003). It starts in April as well for N. antiqua from the Irish Sea (Power and Keegan 

2001a), with subsequent spawning from May to early summer in both populations. Spawning in 

N. arthritica from the Korean west coast is reported to be from May to August (Chung et al. 

2006). Copulation appears to be somewhat earlier (late winter to early spring) for N. antiqua

from the North Sea (Pearce and Thorson 1967), as in this case spawning itself occurs during 

February through April. For N. polycostata near Hokkaido, Fujinaga and Oyama (2007) report 

copulation from February to May, with spawning from March through August. Latitude varies 

considerably among the areas occupied by these regional populations, but the copulation and 

spawning dates mentioned above and in Table 3 do not present any obvious pattern relating to 

latitude as an influence on timing. However, egg incubation schedules do show a possible 

relationship with latitude. 

Incubation 

Shimek (1981) reported the time required for spawning by individual female N. 

pribiloffensis near Homer, Alaska, to be 2-3 days per cluster, and a spawning-to-hatching period 

of ~1 year. The average duration of spawning by each female N. antiqua from the North Sea was 

21 days, and the incubation period was ~ 6 months (Pearce and Thorson 1967). This incubation 

period is similar to the 6-7 months observed for N. antiqua from the Irish Sea by Power and 

Keegan (2001a). Fujinaga (2003) estimated the process to take 3-4 months for N. arthritica from 

near Hokkaido. Thus the incubation period appears longest for the most northerly population, 

36
Table 3. -- Spawning schedules and characteristics observed in studies of Neptunea species. 

Information not obtained by the studies is designated by “NA”. 

Species Area Spawning 

season 

Incubation 

period 

Egg 

capsules 

per 

cluster 

Embryos 

per 

capsule 

Source 

N. 

pribiloffensis

EBS 

NA NA 103 3.2 

MacIntosh 

and 

Somerton 

(1981)

N. heros NA NA 34 3.4 

MacIntosh 

and 

Somerton 

(1981)

N. 

ventricosa NA NA 81 2.9 

MacIntosh 

and 

Somerton 

(1981)

N. 

pribiloffensis Homer 

AK 

Late April 

– early 

June 

~ 1 year 46 2.46 Shimek 

(1981) 

N. lyrata 

Late April 

– early 

June 

NA NA NA Shimek 

(1981) 

N. antiqua Denmark February - 

April ~ 6 months ~21 NA 

Pearce and 

Thorson 

(1967) 

N. antiqua Irish Sea 

May – 

early 

summer 

6-7 months 40.37 1.58 

Power and 

Keegan 

(2001a)

N. arthritica Hokkaido May - 

June 3-4 months 41.9 1.01 Fujinaga (2003) 

N. 

polycostata Hokkaido March - August NA NA NA 

Fujinaga and 

Oyama 

(2007)

N. arthritica Korea, 

east coast 

May – 

August NA NA NA Chung et al. (2006)

N. lamellosa NA NA NA NA 2.6 Ovsyannikov 

(2007) 

37
and to decrease as the latitude occupied by the population decreases. Further observations would 

be necessary to determine whether or not such an influence actually exists. 

Spawning Physiology 

Females possess a series of organs for applying nutritive and protective materials (e.g., 

albumin, protein) to the outsides of the fertilized ova passing through the oviduct, encasing the 

eggs in capsules prior to spawning (Ruppert et al. 2004). This system includes albumin and 

capsule forming glands, as well as a pedal gland where the capsules are shaped after exiting the 

gonopore. Females lay capsules in clusters, the size and shape of which are distinctive for a 

species and which have been described for N. lyrata, N. pribiloffensis, N. heros, and N. 

ventricosa by Golikov (1961) and Shimek (1981). 

Brood Size 

Egg capsules each contain 1-4 (usually ~3) developing embryos and 1,000-5,000 

immature oocytes as nurse eggs, which do not develop into embryos but rather provide food for 

the latter. Females laid clusters averaging 103 capsules with 3.2 embryos each for N. 

pribiloffensis, 34 capsules with 3.4 embryos each for N. heros, and 81 capsules with 2.9 embryos 

each for N. ventricosa as observed in small samples of each of the three species from the EBS 

(MacIntosh and Somerton 1981). Power and Keegan (2001a) observed female Neptunea antiqua

from the Irish Sea to lay egg clusters averaging 40.37 egg capsules per cluster. These capsules 

contained an average of 1.58 developing juveniles for an average of 63.78 juveniles per cluster. 

Estimations of actual fecundity, however, are hampered by lack of information on the number of 

clusters laid per season per female (MacIntosh and Somerton 1981). Pearce and Thorson (1967) 

observed 11 female N. antiqua from the North Sea to lay, on average, 1.6 clusters each, 

38
containing an average of 37 total capsules per female. Several capsules taken from multiple 

clusters each contained one or two embryos. 

Spawning Habitat 

Egg-capsule clusters are deposited on relatively solid substrate, as opposed to 

unconsolidated material. Such surfaces include dead and living snail shells (conspecific or 

otherwise), upper and upper-lateral surfaces of high-relief bottom structure greater than 50 cm 

height, and upper surfaces of boulders at less than 50 cm height (Fujinaga 2003). This anchoring 

probably mitigates egg mortality caused by displacement by waves or currents. Clusters are often 

located so as to minimize predation, such as on vertical or underside surfaces, in cracks, or in 

some cases near commensal organisms, such as the anemone Tealia crassicornis, which have 

been shown to provide protection by preying on would-be egg predators such as 

Strongylocentrotus droebachiensis (Shimek 1981). 

Feeding Methods and Diet 

In general, species of Neptunea are carnivorous, as are other buccinids and most other 

gastropods in the order Neogastropoda. Buccinidae feed via an eversible proboscis that extends 

the mouth. The mouth carries a relatively unspecialized radula having three teeth per row, which 

can be protruded from the mouth (Ruppert et al. 2004). Species of Neptunea are able to evert the 

proboscis ~ two times the length of the shell, into tubes as narrow as 4.5 mm in diameter, to 

access bait (Pearce and Thorson 1967, Avery 1961). The radula is used to cut or rasp food, and 

to pull it into the mouth. 

The Neptunea are primarily predators. Although individuals have been observed naturally 

or in experiments to be feeding on or attracted to carrion, the few systematic studies to date of 

39
feeding behavior among the species mostly suggest that they scavenge only opportunistically, 

and that their metabolic needs are modest. Direct observations of Neptunea in the field indicate 

most feeding is on live prey (Fujinaga 2003, Shimek 1984). 

Surveys of stomach and gut contents of populations of the four major species from the 

EBS, as well as N. pribiloffensis and N. lyrata from near Homer, Alaska, and N. antiqua from the 

Clyde Sea, have indicated feeding to be infrequent, with most guts containing no food remains 

(Shimek 1984, Taylor 1978). The responses and feeding by individuals of non-EBS populations 

of N. lyrata, N. tabulata, N. antiqua, and N. amianta, experimentally exposed to live bait, 

carrion, or the scents thereof, have been relatively sluggish and limited when compared with 

behaviors of other co-occurring invertebrate scavengers and predators (Bergmann et al. 2002, 

Power et al. 2002, Tamburri and Barry 1999, Pearce and Thorson 1967, Avery 1961). Specimens 

of the bathyal N. amianta from Monterey Canyon, CA, survived 12 months without food until 

observation ceased in a deprivation experiment (Tamburri and Barry 1999). 

Neptunea produce relatively high concentrations of the neurotoxin tetramine 

(tetramethyl-ammonium chloride) in the salivary gland, a possible adaptation for subduing live 

prey. Neptunea antiqua specimens have been observed in feeding experiments probing the 

hinge-side juncture of the closed valves of a live mussel with the proboscis, ultimately feeding 

on the opened bivalve. Possibly, the snails use salivary toxin to paralyze bivalves and access the 

inside of the shell, or use it to arrest flight response in other prey (Kawashima et al. 2002, Power 

et al. 2002, Shiomi et al. 1994). 

Prey 

Shimek (1984) observed the diet of populations of N. pribiloffensis, N. lyrata, N. heros, 

and N. ventricosa in the EBS, as well as a mixed aggregation of the first two species occurring 

40
intertidally near Homer, Alaska. Identifiable food items consisted of: 1) primarily live 

polychaetes; 2) somewhat less frequently bivalves and barnacles (Cirripedia); and 3) trace 

occurrences of gastropods, decapods, fish (probably carrion), and ophiuroids. Comparison of the 

distributions of N. pribiloffensis and N. lyrata with those of prey species in intertidal water near 

Homer showed little or no effect on the total prey population, suggesting the two Neptunea

species are not food-limited at this location (Shimek 1984). Neptunea arthritica observed in Usu 

Bay, Hokkaido, ate mostly live Mytilus spp., followed less frequently by carrion and other live 

bivalves (Fujinaga 2003). Feeding on infauna such as tubiculous polychaetes may be less 

apparent to divers, as snails may be able to use proboscides to locate and ingest prey hidden in 

the substrate. Among gut contents of N. antiqua from the Clyde Sea, identifiable food items were 

usually indeterminate bivalve remnants or the bivalve Abra alba, followed less frequently by 

Priapulus caudatus, Polychaeta, and Decapoda (Taylor 1978). 

Diet Strategies 

Classifying prey items generally by class, Shimek (1984) compared diet compositions 

among allopatric and sympatric EBS populations of the four major Neptunea species in a 

southern and a northern assemblage region, respectively, and in a transitional zone between the 

regions near the mouth of Bristol Bay. He found considerable diet-composition overlap within 

each of the two intra-assemblage species pairs (N. heros/N. ventricosa and N. pribiloffensis/N. 

lyrata) within each of the assemblage regions, and also overlap between the two species pairs 

when allopatric (i.e., in separate assemblage regions). However, he found less diet overlap 

between the same two pairs in the inter-assemblage transition zone, or when comparing each pair 

in the transition-zone with either pair in its customary assemblage area. Thus he observed 

possible niche partitioning between sympatric species, which might result from selective 

41
pressures on respective non-interbreeding populations. Such partitioning according to species 

does not by itself seem consistent with Shimek’s observations of diet overlap within sympatricspecies pairs in the respective assemblage areas, unless the partitioning is only triggered by a 

larger number of species present within the relatively small transition zone compared with either 

assemblage area. Alternatively, there could be more hybridization occurring within each of the 

species pairs than between pairs. 

Mortality 

Mortality rates among Neptunea populations are likely to vary with the season, with life 

stage, and with biotic and abiotic elements of the local environment. Pre-recruit mortality can 

occur through displacement of egg clusters by turbulence, encumbrance by epifauna (e.g., 

sponges), or by consumption of egg clusters or individual embryos by such predators as 

echinoids, asteroids, or other gastropods (Fujinaga 2003, Shimek 1984). 

Rates 

In some populations of N. antiqua and N. arthritica, mortality rate decreases after age 1 

and before maturity but increases for mature adults during and immediately after the spawning 

season. Feeding activity decreases during the copulation-through-spawning period, when both 

sexes, particularly females, have recently expended considerable energy in reproduction. In fact, 

one or both sexes may often die after spawning (Fujinaga 2003, Pearce and Thorson 1967). 

In addition to providing the species with solid substrate on which to attach egg capsules, 

the post-mortem durability and persistence of snail shells in the environment may be of use as an 

indicator of relative population viability. Sampling Neptunea antiqua with a beam trawl, Ten 

Hallers-Tjabbes et al. (2003) calculated the percentage that live shells constituted of all shells 

42
taken (alive or empty) at each of 11 stations in the North Sea. The results, averaging 56 + 8% 

and ranging from 4% in the Skagerrak to 93% in the open sea, were used as one parameter 

relating to population health. 

Predators 

Little is known of the extent and influence of predation-induced mortality in the life cycle 

of large prosobranchs such as Neptunea in the EBS. Consequently, there are gaps in the 

knowledge of their exact role in the benthic food webs. Taxonomic identification of gastropods, 

more specifically than at the level of class, among stomach contents from potential predators is 

difficult in the absence of shell remains. Even opercula are often morphologically indistinct 

among related taxa, with some exceptions (e.g., the distinctive oblong operculum with centered 

nucleus exhibited by Buccinum species uniquely among Buccinidae). However, observations 

have shown several types of predators are capable of feeding upon large gastropods like 

Neptunea, such predators including Asteroidea, larger species of Decapoda, and Octopus 

(Ruppert et al. 2004, Shimek and Gardner 1979, MacIntosh 1976b). Neptunea remains have been 

identified in stomach contents of a few fish, invertebrate, and marine mammal species occurring 

in the EBS, from samples taken in the region or in other Alaskan waters. These include Gadus 

macrocephalus (Pacific cod; Jewett 1978), Paralithodes camtschaticus (red king crab; Feder and 

Paul 1979, Feder et al. 1978, Feder et al. 1977), Pycnopodia helianthoides (sunflower starfish; 

Feder et al. 1980), Hippoglossus stenolepis (Pacific halibut; Rosenthal 1979), Hemilepidotus 

jordani (yellow Irish lord; Feder et al. 1979), Cancer magister (Dungeness crab; Feder and Paul 

1979), Odobenus rosmarus (Pacific walrus; Fay and Burns 1988, Lowry and Frost 1981), and 

Erignathus barbatus (bearded seal; Dehn et al. 2007). None of the data in these investigations 

43
indicated large gastropods such as Neptunea were a major component of the predator’s diet. 

Rather, they seemed to be taken opportunistically. 

ANTHROPOGENIIC INTERACTIONS 

Incidental Results of Commercial Fishing 

Snail Bycatch 

Commercial bottom-trawling for demersal fish species in the EBS captures numerous 

snails among the bycatch. From 23 June 1986 to 30 July 2011 domestic fishing vessels in the 

EBS caught an estimated 2,601,898 kg of unidentified snails in 61,190 hauls 8, according to 

fishery observers reporting the catch for NOAA’s Alaska Fisheries Science Center, division of 

Fisheries Monitoring and Analysis (FMA). Although fishery observers generally do not identify 

snail taxa more specifically than “snail unidentified”, the preponderance of Neptunea among 

snails in RACE bottom trawl surveys in the same area indicates that a considerable portion of 

this catch was likely Neptunea. 

Even with subsequent discard at sea, mortality or lessened viability as a direct result of 

capture and discard has potential significance. Although these effects are not easily quantified, at 

least one study has directly evaluated some of them in a non-EBS fishery. Bergmann et al. 

(2001) studied severity and frequency of injury to individuals of invertebrate species among the 

bycatch in commercial otter trawls targeting Norway lobster (Nephrops norvegicus) in the 

Scottish Clyde Sea. Although faring better than some species, approximately 40% of Neptunea 

antiqua thus taken sustained at least mild shell damage. It should be noted that hypoxia, 

 

8

 Narita, R. 2011. Personal communication, data from the NORPAC database of the Fisheries Monitoring and 

Analysis Division (FMA), Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration. 

44
temperature change, or pressure change may also contribute to or compound mortality associated 

with capture/discard.

Changes to the Benthos 

In addition to collateral mortality, fishing could have several other less direct (negative or 

positive) affects on Neptunea, altering demographics, selecting for physical traits among 

survivors, or physically altering substrates and the availability of infauna prey. For example, 

invertebrate catch of experimental bottom-trawl samples from a heavily fished (HF) area of the 

EBS was compared with that of samples from an adjacent area where bottom trawling had never 

occurred (unfished, UF; McConnaughey et al. 2005, McConnaughey et al. 2000). The study 

found individuals of the genus Neptunea as a whole to be significantly more abundant as 

measured by CPUE, as well as significantly larger by average individual weight, in the UF area. 

Food windfalls from fishing discards may also be important. Substantial amounts of 

carrion or moribund organisms discarded as fishing bycatch in the EBS may constitute a 

significant supplement to the nutrition of Neptunea species through opportunistic scavenging. 

The extent to which this incidental nutrition mitigates negative effects of the industry on 

Neptunea populations due to injury, mortality, or environmental damage by the gear is unknown. 

Although N. antiqua, N. lyrata, and N. tabulata in laboratory experiments have shown more 

limited response to olfactory signals than other prosobranch species in finding live bait or carrion 

(Pearce and Thorson 1967, Avery 1961), Bergmann et al. (2002) found N. antiqua among 

scavengers in traps baited and placed to approximate typical discarded bycatch from the 

Nephrops norvegicus trawl fishery in the Scottish Clyde Sea. The species showed a clear 

preference for crustacean bait (Munida rugosa, Liocarcinus depurator) over echinoderm bait 

(Asterias rubens and Ophiura ophiura). In a separate study of the Nephrops norvegicus trawl 

45
fishery in the English North Sea, Catchpole et al. (2006) estimated that Neptunea antiqua, among 

other identified scavenger species, could receive as much as 21% of their annual energy 

requirement from fishery discards. 

Pollution-induced Imposex 

Exposure to organotins, especially tributyltin (TBT), has been shown to cause abnormal 

development in female Neptunea. The affected individuals develop homologues of the male 

penis and/or vas deferens (imposex), in addition to the regular female characteristics. This 

compound has been used in paint on vessel hulls to minimize fouling by periphyton or epifauna. 

In certain gastropod species the deformation results in female sterility and/or the higher TBT 

concentrations are associated with lower female/male ratios. In one study in the offshore Irish 

Sea, Power and Keegan (2001b) found incidences of TBT-induced imposex in monthly samples 

of female N. antiqua to be 90-100% of individuals but detected no related sterility or higher 

female mortality. Conversely, Bright and Ellis (1990) found female N. phoenicia from Howe 

Sound, British Columbia, exhibiting signs of TBT-induced imposex, seemingly rendered sterile 

by the development of an aberrant vas deferens, which in this species tended to occlude the 

gonopore and would thus preclude egress of egg capsules at spawning. In general, organotin 

concentrations in snail soft tissue and also in bottom sediments decrease with increasing distance 

and isolation from marine shipping traffic. Large-scale restrictions on marine use of TBT in 

paint, instituted internationally since 1989 (Champ 2000), have effectively reduced both TBT 

concentrations and related incidence of imposex. Nevertheless, some fairly recent monitoring has 

still detected the disease (e.g., Fujinaga et al. 2006). No information is available concerning past 

or present TBT concentrations, nor any related imposex, in the benthos of the EBS. 

46
Human Consumption 

Among gastropods popular in the human diet, several Neptunea species have been 

harvested commercially or by subsistence fishing in various parts of the range of the genus. In 

the EBS this has included commercial harvesting, principally of N. pribiloffensis (Bowers et al. 

2008, MacIntosh 1980, Nagai and Suda 1976, Nagai 1974). No commercial targeting is known to 

have occurred in Alaskan waters since 1997, the last year in which any such catch was reported 

(Bowers et al. 2008). Neptunea species previously or presently harvested in areas outside of 

Alaska include: 1) N. arthritica, N. polycostata, N. constricta, and N. lyrata in the western North 

Pacific (Borulya and Bregman 2002, Suzuki et al. 2002, Kato 1979, Fujiwara and Ashino 1972); 

and 2) N. antiqua in the North Sea (Anthoni et al. 1989). 

Potential Effects on Demographics of Neptunea

Using multiple tagging, Suzuki et al. (2002) in 1994 estimated a total annual mortality of 

86% for a population of N. arthritica near Hokkaido exposed to commercial pot fishing. Their 

calculations attributed 53% of that mortality to the fishery, which retained individuals ≥ 60 mm 

long. As Fujinaga (1985) had previously estimated Lmat of female N. arthritica at 60 mm, Suzuki 

et al. (2002) postulated that such a low minimum-size-retained would cause the population to 

decline. 

Food Poisoning 

Incidents of human poisoning by ingestion of tetramine have been reported for certain 

Neptunea species that were otherwise thought to be edible (including some fished 

commercially). Among species involved are N. arthritica and N. intersculpta from the western 

North Pacific (Saitoh et al. 1983) and N. antiqua from the eastern North Atlantic (Reid et al. 

47
1988, Ayres and Wood 1973, Fleming 1971). Unlike the report of Saitoh et al. (1983) concerning 

N. arthritica, Anthoni et al. (1989) found tetramine in tissue of N. antiqua was not confined to 

the salivary gland. Based on their findings of the characteristics and in vivo concentration of the 

compound, they classified N. antiqua as unfit for human consumption. As such, use of any 

Neptunea species as human food must be subject to controlled testing and other practices 

intended to minimize the risk 

48
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