Growth
  These studies on growth are arranged alphabetically by genus.
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  Clinocardium nuttallii
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Research study 1
 

graph comparing age and growth of cockles Clinocardium nuttallii in Washington and AlaskaResearchers from Stanford University and the U.S. government provide information on age and growth of cockles Clinocardium nuttallii in Washington and Alaska.  Age is determined by counting growth rings, formed during attenuated growth in winter.  The authors’ data suggests that maximum size and age are reached after about 10yr on Washington beaches and much later at sites in Alaska (see graph).  Weymouth & photograph of cockle Clinocardium nuttallii in an aquarium tankThompson 1931 Bull Bur Fish 46: 633. Photograph courtesy Ron Long, Simon Fraser University, British Columbia.

NOTE  known in those days as Cardium corbis

 

Photograph of a 3-4yr old Clinocardium nuttallii (the earliest growth line at 1yr of age is likely hidden) 1.5X

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Research study 2
 

schematic showing relationship between daily tides and growth lines in the shell of cockles Clinocardium nuttalliiIn addition to fairly obvious yearly growth lines in cockles Clinocardium nuttalli (see Research Study 2 below), there exist daily growth lines corresponding to individual tides.  This unusual finding is made after grinding and polishing the shell edge to a smooth finish and making an acetate peel, from which can be distinguished even the finest growth lines. The schematic on Left shows one month of summer tides on the coast at Empire, Oregon with the approximate level inhabited by C. nuttalli indicated. Note that during spring tides a cockle experiences a single low-tide emersion each day. This produces a simple growth increment as shown on Days 16-22 in the shell section below. During the switchover to neap tides on Days 22-26 the cockle experiences 2 low-tide emersions per day, producing a double set of growth lines. Each growth line represents a layer of prismatic calcium material separated by thin layers of proteinaceous conchiolin material.  Although not possible to see for individual days at the scale provided here, the author determines that each “low-tide increment” line has an average duration of 24h and 50min, corresponding exactly with the duration of a daily tide cycle. The author notes that a cockle may be an especially sensitive recorder of tidal exposure because it lies just below the sand surface.  In deeper-dwelling species of bivalves the pattern tends to be obscured or absent.  In a broader context, the author cautions researchers, especially those predicting day lengths at the time certain bivalve shells are fossilised, to be sure that they are actually counting daily growth increments rather than tidal ones.  Evans 1972 Science 176: 416.

NOTE  the 50min delay in the tides each day is explained by the fact that while the earth rotates once on its axis, the moon travels 1/28th of its orbital circumference around the earth each day.  Thus, the earth has to “catch up” this distance every day in its own revolution in order to position once again any given point directly opposite the moon.  This requires an extra 50min or so, equivalent to 1/28 x 24 x 60min

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Research study 3
 

graph plotting shell size against age in 3 populations of cockles Clinocardium nuttallii in OregonA comparison of age and growth in intertidal and subtidal cockles Clinocardium nuttallii in Netarts Bay, Oregon shows that most growth occurs in springtime, growth correlates with degree of submergence, and oldest individuals live subtidally. Maximum life span in these populations is about 10yr.  Ratti 1978 MSc thesis, Oregon State University, 105pp.

NOTE  age is determined by counting yearly growth checks on the shell

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Research study 4
 

photograph of cockle Clinocardium nuttallii with annual growth lines indicatedGrowth lines on the shells of molluscs often indicate age, just like the growth rings on trees.  In both organisms the rings are formed from alternating periods of summer growth and winter quiescence.  However, in the case of cockles Clinocardium nuttallii, because they live so close to the sediment surface they experience more varied and severe environmental fluctuations, and regular laying down of lines is often disrupted.  Contributing effects are extremes in temperature, UV light, excessive freshwater, and other factors.  Gallucci & Gallucci 1982 Mar Ecol Progr Ser 7: 137.

NOTE although west-coast geoducs Panope abrupta are known as "Methuselah" clams because they live so long (est. maximum 160yr), these are but toddlers in comparison with Arctic quahogs Arctica islandica. One individual collected from 82m water depth off the coast of Iceland in 2006 was found to have 405 annual growth lines, making it the oldest living animal on earth (now dead, of course)

A specimen of cockle Clinocardium nuttallii with the most
obvious growth lines indicated, suggesting 3yr of age 1X

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  Mya arenaria
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Research study 1
 

photograph of soft-shell clam in aquarium tankSoft-shell clams Mya arenaria feed on phytoplankton pumped in with seawater and so, one would think, their growth would be independent of the substratum that they are buried in.  Preliminary tests at Friday Harbor Laboratories, Washington using clams contained in boxes of sand vs. ones  in boxes of mud/gravel/shell mixture (N = 2 for each treatment) and outplanted on a beach for 1yr, however, show almost twice the growth rate in sand than in mud/gravel/shell (increases of approximately 70% and 45%, respectively).  Shell masses, however, are slightly less in the sand treatment as compared with the mud/gravel/shell treatment.  The author discusses various factors that may have been responsible for the differences in growth rates, and several of these are deserving of further investigation.  One in particular, that the clams in sand bury noticeably deeper than ones in  mud/gravel/shell, seems especially interesting from an energetics standpoint.  Swan 1952 Ecology 33 (4): 530.

NOTE  the experiment follows up on an earlier observation by the author that shell masses of M. arenaria differ significantly on beaches with sand vs. mud/gravel/shell substrata (see Research Study 1 above)

NOTE  50 individuals of 5 approximate size-classes are placed in each box

 

 

 

Soft-shell clam Mya arenaria
in an aquarium tank 1X

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  Panopea abrupta
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Research study 1
 

graph showing age versus shell length in geoducs Panope generosaIn Puget Sound, Washington, geoducks Panopea abrupta develop gonads during autumn/winter and spawn in spring.  The author uses mark-recovery techniques to monitor photograph of geoduck clam Panopea abruptaearly growth.  Note in the graph that individuals grow about 30mm in shell length in their first 3yr of life.  Adulthood is reached by 10yr of age at about 16cm shell length. Goodwin 1976 Proc Nat Shellfish Assoc 65: 49.  Photo courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

NOTE all past references to Panope generosa and Panope abrupta in the literature are changed in the ODYSSEY to Panopea abrupta

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Research study 2
 

acetate peel of the hinge plate of a geoduc clam Panopea abrupta showing growth lines and bandsAge and growth in geoducks Panopea abrupta can be determined by counting internal growth lines in the hinge plates of the shells.  Use of hinge plates is more reliable than use of the shell because erosion is less.  Growth-line deposition occurs during winter and is a reliable indicator of age in geoducs.  For example, the particular specimen illustrated here is one known to be 8+yr of age. Note that 8 growth bands (numbered) are separated by 8 growth lines.

A collection of geoducs from Port Gamble, Washington shows ages exceeding 100yr.  histogram showing age distribution of a population of geoducs Panopea abrupta from Port Gamble, WashingtonAverage age in the population is 28yr. Shaul & Goodwin 1982 Can J Fish Aquat Sci 39: 632.

NOTE  the technique involves cutting, polishing, and etching the cut face of the hinge in dilute HCl.  A coating of cellulose acetate is then applied, peeled off when dry, and mounted between microscope slides for examination

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Research study 3
 

histogram showing age-frequencies in a population of geoducs Panopea abrupta in Barkely Sound, British ColumbiaUse of acetate-peel methodology by researchers at the Pacific Biological Station, DFO, Nanaimo provides age/growth data for 5 populations of geoducks Panopea abrupta in British Columbia.  Mean age of clams at the 5 sites ranges from 35-46yr.  Note in the sample data from Brady’s Beach, Vancouver Island the 2 strong modes in the age-frequency distributions, one at about 25yr and the other at about 50yr.  This suggests that recruitment may not be regular in the population; rather, possibly dominated by periodic peaks at long intervals.  Breen & Shields 1983 Can Tech Rep Fish Aquatic Sci No. 1169, 62pp.

NOTE  the sites are located at Brady’s Beach, Bamfield; Sibell Bay, near Ladysmith; Comox Bar, near Comox; Elbow Bar, between Vargus and Meares Islands; and James Island, near Sydney

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Research study 4
 

photograph showing geoducs Panopea abrupta collected and being measured on shipboardgraph showing average annual growth for a geoduc Panopea abrupta in Ladysmith Harbour, British ColumbiaA study at the Pacific Biological Station, DFO, Nanaimo uses growth rings on geoduck clams Panopea sp. to monitor past environmental influences on growth.  Ages of 403 geoducks collected in Ladysmith Harbour, Vancouver Island are estimated from acetate peels of sections of their shells. From these peels the researchers obtain growth data as shown in the graph for a typical individual. The data indicate that annual growth of individuals in the population is about 80% of that in the preceding year, at least for about the first 10yr of life. 

Scrutiny of average annual growth of the population during 1907-1980 reveals abrupt changes in growth rate around 1920 and 1980 (data not shown here).  The first, an 8% increase in growth, coincides with recorded higher than normal water temperatures beginning around 1920, and the second, a 27% decrease in growth, commencing soon after the start of log-booming and log-storage in Ladysmith Harbour around 1960.  The authors discuss the potentially deleterious effects that log-booming can have on the vitality of the benthic community.  The authors remark on the few young clams being present in their sample, suggestive of low potential recruitment.  Noakes & Campbell 1992 Environmetrics 3: 81.

NOTE  summation of annual growth data for the "typical geoduck" shown here suggests a final size at 70yr of age of about 7mm shell length. Based on the more realistic data shown in Research Study 4 below for the same species, the expected size of a 70yr-old individual of the same species would be about 130mm

NOTE  ages of the geoducs range from 7-102yr, with a mean age of about 55yr

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Research study 5
 

graph showing growth of geoducks Panope abrupta in Washington StateResearchers from the Washington Department of Fish & Wildlife use acetate-peel methodology to model growth for populations of geoducks Panopea abrupta in Puget Sound and neighbouring environs, Washington.  Of 11 populations sampled, best growth is exhibited by clams at Fishermen’s Point in the Hood Canal, and worst by clams at Dallas Bank in the Strait of Juan de Fuca (see graph). Hoffman et al. 2000 J Shellf Res 19: 57.

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Research study 5.1
 

graph showing shell length in relation to age in a population of geoduck clams Panope abrupta at Hippa Island on the northwest coast of Haida GwaiA later summary paper, also by researchers at the Pacific Biological Station, British Columbia, provides much information on age and growth of geoducks Panope abrupta at 34 locations in British Columbia between 1993-2000.  One graph out of many is shown here, representing a collection made at Hippa Island on the northwest coast of Haida Gwai.  This site is notable in that the clams surveyed appear to be the oldest in the province.  The data raise the maximum age of B.C. geoducks to 168yr (a single individual in another location also on Haida Gwai).  Note in the graph, which is typical of those presented, that most shell growth is accomplished within the first 20yr; any subsequent production is presumably reproduction.  Bureau et al. 2002 Can Tech Rept Fisheries Aquat Sci No. 2413.

NOTE  age is estimated from growth rings on vertical shell cuts through the umbo.  The cut edges are polished with sandpaper, etched with a few drops of 1% HCl applied for 1min, and rinsed with distilled water.  A few drops of acetone are then applied to the shell edge and a peel made by applying and pressing on an acetyl-cellulose film.  Annual growth rings are then counted through a microscope 

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Research study 6
 

histogram showing age frequencies for a population of Panopea abrupta geoducs in southern British ColumbiaGrowth of geoduck clams Panopea abrupta at a site in southern British Columbia is shown in the accompanying graph.  Note that maximum age is about 80yr in this population.  Male: female sex ratios of P. abrupta are 52:48, similar to that found in other studies.  Campbell & Ming 2003 J Shellf Res 22: 85.

NOTE  the authors provide data for two locations, but only one of these, Gabriola Island, is considered here

NOTE  age is determined from growth rings imprinted on acetate peels obtained from sections of the shells

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Research study 7
 

illustration showing growth-ring counting methodology for geoduck clams Panope abruptaAn improved method for aging bivalves is described for geoducks Panope abrupta by a group of Oregon and British Columbia fisheries scientists.  The technique, known as “crossdating”, is borrowed from the field of dendrochronology (tree-ring aging) and provides for higher levels of accuracy in aging, particularly for long-lived species.  It relies on the tendency for growth of all members of a local population to be synchronised, such that wide and narrow bands appear in the same relative positions for the same calendar years.  Thus, if a certain growth increment is obscured or missed in an individual, it will be one line offset when compared with all other individuals and can be “reset” to its correct chronology.  An experimentor starts with the clearest record, then builds on that.  Each ring is counted, then its width is compared with the widths of rings on either side to give a “ring-width index”.  An index value of 1 means that a particular ring is the same size as its neighbours; less than 1 that it is smaller; and greater than 1 that it is larger (see illustration). The graph in the illustration represents the mean values for several hundred individuals in the population.  When these average graphed values are visually compared with the photomicrographical record for an individual that started life in the 1940s and died in 2004 (green coloured photograph above the graph), several “signature” years or years of particularly good or particularly poor growth (see dashed lines) match perfectly.  If they had not matched, the record of this individual could be nudged ahead (or back) to correct it.  The method increases overall accuracy by correcting discrepancies arising from counting errors by different readers and ensuring that early errors are not compounded “down the line”.  The method is especially useful for older individuals, where rings are compacted and hard to read.  Black et al. 2008 Can J Fish Aquat Sci 65: 2572.

NOTE  the method is not new.  I has been used in past studies of fishes and other bivalves, including geoducks.  It requires that acetate-peels be made by first cutting the shell along its height axis through the umbo, polishing the cut edge with fine sandpaper, etching with 2% HCl, then pressing a piece of acetate film softened with a drop of acetone onto the edge.  When peeled off the acetate strip is sandwiched between glass slides and microscopically examined

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  Penitella penita
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Research study 1
 

photograph of rock-boring piddock Penitella penita showing thickened, grinding portion of posterior part of shell valvesgraph showing growth of piddocks Penitella penita in soft sandstoneRock-boring piddocks Penitella penita inhabit conical burrows in sedementary rocks that they excavate by back-and-forth grinding action of their shells. At Coos Bay, Oregon Penitella has 2 different life-cycle stages in the rock, "active" and adult.  The active stage is the younger, boring one, and it is at this time that the burrow is enlarged and most growth occurs, processes requiring expenditure of much energy.  This is followed by the adult stage, during which little burrowing or somatic growth takes place, and energy is devoted to maintenance and reproduction.  A comparison of growth and growth form of 3 populations of P. penita in substrata of different hardnesses shows that rates of growth decrease with increasing hardness, and that shell valves are delicate and elongate in soft rock, and heavy and tumid in hard rock.  Growth is cyclical, with burrow enlargement occurring during active burrowing, and growth of shell and body occurring later to fill the space created.  An adult stage is reached after about 3yr (see graph). Bands can be identified in the shell indicating the cyclical nature of these activities. Results show that growth rates in medium-hard and the hardest rock are about 60 and 20%, respectively, of that in the softest rock.  After 1yr of age, a single band is deposited every 16d. Evans 1968 Ecology 49: 619.  

NOTE  the substrata are all sandstones.  Relative rock hardness is measured as the depth of penetration of a weighted masonary bit after a standardised drilling time.  Growth data are mostly obtained from individuals removed from natural burrows and maintained for 11.5mo in artificial burrows drilled into rocks of different hardness

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Research study 2
 

photographs comparing scraping ridges in shells of rock-boring piddocks Penitella penita in soft, medium-hard, and hard sandstone substrataphotograph of shell valve of a rock piddock Penitella penita showing regions used in growth-line studyIn a later study the same research group uses specimens of Penitella penita obtained from sandstone rocks at Coos Bay, Oregon, to identify fine-scale growth lines using thin-section, acetate-peel, and e-microscopy methodology.  The authors are able to identify growth increments of approximately daily duration in the umbonal ventral sulcus and anterior slope regions, and resolve these into increments deposited during active boring (5-8d duration) and increments deposited during resting and growth (7-10d).  Acetate peels from sections through the anterior slope part of the shell, the part bearing the ridges or teeth used in burrowing (see photograph on Left), differ markedly in individuals from soft, medium-hard, and hard sandstone rocks (see photographs on Right).  Fine-scale growth lines are visible in these sections, numbering about 7 per growth band (see top peel on Right), but are not so clear as in sections of the ventral sulcus.  Evans & LeMessurier 1972 Can J Zool 50: 1251.

NOTE the groove between the ridged (toothed) anterior part and the smooth posterior part of the shell

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  Protothaca staminea
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Research study 1
 

Growth of clams Protothaca staminea is highly variable depending upon locality.  For example, time to reach harvestable size of 30mm shell length is more than twice as fast in Victoria, British Columbia as in locations in Alaska (see map and graph).  The shells are aged by counting the number of annuli or winter lines on the shell (see photograph).  These prominent lines are usually interspersed with other lines known as “disturbance checks” or “false checks”.  Maximum life span at Galena Bay, Alaska is 15yr or about 5cm shell length.  Paul & Feder 1973 Fish Bull 71: 665; Paul et al. 1976 The Veliger 1976 Veliger 19: 163.

NOTE  these are induced from temperature, rainfall, and other stresses

 
map showing collecting sites for study of growth in littleneck clams Protothaca staminea
photograph of littleneck clam Protothaca staminea with possible annual growth lines indicated
graph comparing growth rates of littleneck clams Protothaca staminea in British Columbia and Alaska
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  Siliqua patula
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Research study 1
 

graph relating age and shell length in razor clams Siliqua patula in Washington and AlaskaGrowth rates of razor clams Siliqua patula differ significantly between Washington and Alaska.  The graph shows age and size at reproductive maturity at a site in Washington and 2 sites in Alaska (data analysed at Stanford University, California).  Reproductive maturity occurs in all specimens at about 10cm shell length, with Washington specimens being about 1yr younger than Alaska specimens. Weymouth et al. 1925 Bull US Bureau Fisheries 41: 201.

NOTE  defined by the author as when 50% of the population is capable of spawning

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Research study 2
 

graph showing growth of razor clams Siliqua patula in Copalis, Washington

The same research group later investigates growth in west-coast razor clams Siliqua patula at several locations from California to Alaska.  The authors use growth rings to provide an estimate of age, with the assumption that each ring or annulus is an annual marker.  A typical set of growth curves for specimens taken from Copalis, Washington and 2 other locations shows that Siliqua reaches a maximum of about 9yr of age in this area.  However, other data presented by the authors indicate that age increases latitudinally from about 9yr in California to 19yr in Alaska.  Weymouth et al. 1931 J Exp Biol 8: 228.

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Research study 3
 

photograph of a razor clam Siliqua patulaAn early study on growth razor clams Siliqua patula attempts to correlate growth parameters with average air temperatures for populations ranging from Juneau, Alaska to San Diego, California.  The author’s data suggest that an Alaskan clam of mean length 17cm is about 14yr old, while a southern California clam of 12cm is about 4yr of age.  Taylor 1959 J du Conseil 25 (1): 93.

NOTE  the paper is really a test of application of the Bertalanffy growth equation to razor clams (and codfish) and offers little practical data on growth rates.  Correlations with air temperatures are particularly uninformative and one wonders why the author chooses not to include seawater temperatures as well, or instead of

Pacific razor clam 0.8X

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  Tresus spp.
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Research study 1
 

photo composite showing shell shape of fossilised clam Tresus nuttallii inhabiting rock-piddock burrowsPaleontological investigation of sandstone rocks around Santa Cruz, California reveals the presence of fossilised clams Tresus nuttallii within the burrows of fossilised rock piddocks Penitella penita.  The author notes that the clams have distorted shell shapes in comparison with those of live specimens.  Addicott 1963 Veliger 5: 143.

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Research study 2
 

comparison of depths inhabited by juvenile versus adult gaper clams Tresus nuttalliigraph showing allometry in shell proportions of gaper clams Tresus nuttallii as they grow olderA study on Pacific gaper clams Tresus nuttallii collected in Tomales Bay, California shows that there is an ontogenetic change in shell form and mode of life.  First, juveniles live close to the sediment-water interface, while adults live up to 1m deep in the sediments (see drawings on Left). In this location the juveniles are more likely to be displaced by moving surface sediments and they, not surprisingly, have a greater relative ability to burrow than the adults. Reburial for the youngsters requires 4-5min, as compared with 18-120min for the adults (at 13oC).  The more pointed anterior end and more streamlined shape of the shell of juveniles facilitates burial. 

Second, there is a positive allometry of posterior shell proportions in relation to anterior proportions, as shown in the graph.  Note that at a size of about 70mm the posterior part of the shell begins to increase in length out of proportion to the anterior part. The author suggests that this allometry is associated with increased space requirements of the siphons in older animals.  Finally, in older animals the shell is orientated more obliquely in the burrow than in younger animals (see drawing on Left). The significance of this is unclear, but the author remarks that since an upward pull is exerted on the shell when the siphons are being retracted, an obliquely oriented shell will offer greater resistance. Pohlo 1964 Malacologia 1: 321.

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Research study 3
 

graph relating shell length and age in gaper clams Tresus nuttalliiResults of growth studies on gaper clams Tresus capax at 2 locations in British Columbia are shown here.  Bourne & Smith 1972? Proc Nat Shellfish Assoc 62: 38.

NOTE  Seal Island is in the Strait of Georgia, while Doyle Island is in the Queen Charlotte Strait

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Research study 4
 

graph showing growth rate of gaper clams Tresus nuttallii in Elkhorn Slough, CaliforniaA 2-yr study of life-history characteristics of Pacific gapers Tresus nuttallii in Elkhorn Slough, California shows that spawning is in Feb-Apr, with settlement about 1mo later.  Growth to 2mm shell length takes 10d, and it takes 25d to reach 5mm shell length.  The graph shows growth over the first 1.5yr of life.  Thus, a 6cm animal is about 550d of age.  Clark et al. 1975 Calif Fish Game 61: 215.

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Research study 5
 

graph showing growth of gaper clams Tresus capax over a 2-year period in Humboldt Bay, CAGrowth of gaper clams Tresus capax in Humboldt Bay, California is primarily in late spring to early summer.  Note in the graph the slackening of growth during autumn/winter and the recruitment of juveniles in springtime for each of 2 cohorts.  Wendell et al. 1976 Cal Fish Game 62: 41.

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Research study 6
 

graph comparing growth of clams Tresus capax in intertidal and subtidal locationsIn Yaquina Bay, Oregon, gaper clams Tresus capax  spawn in late winter, coincidental with yearly low temperatures.  Counts of annual growth checks, or rings, on the shell valves provide estimates of age.  Growth appears to be slightly more rapid in subtidal populations in comparison with intertidal ones (see graph).  Note in the graph that relative growth decreases with age, as expected.  Maximum age is about 9yr intertidally and 9-12yr subtidally.  Breed-Willeke & Hancock 1980 Proc Nat Shellfish Assoc 70: 1.

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Research study 7
 

graph comparing growth of fat gaper clams Tresus capax in British ColumbiaCounts of winter annuli indicate that gaper clams Tresus nuttallii at 2 sites in British Columbia reach about 17cm shell length at 17yr of age.  The fat gaper Tresus capax attains a similar size, but this species may live to about 20yr.  Campbell et al. 1990 J Shellf Res 9: 273; Campbell et al. 2000 J Shellf Res 19: 933.

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  Venerupis philippinarum
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Research study 1
 

graph showing growth of Manila clams Venerupis philippinarum at several locations in British Columbiaphotograph of shell valves of Manila clams Venerupis philippinarumManila clams Venerupis philippinarum were introduced into British Columbia in Ladysmith Harbour in 1936, likely with seed of Japanese oysters.  Over the next few decades they spread throughout the southern part of the province and now inhabit muddy bays along much of the west coast.  Growth of manila clams at several locations in B.C. is shown in the accompanying graph. Bourne 1982 J Shellf Res 2: 47.

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