IMEP #130 What is a Good Clam Soil?

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IMEP #130 - What Is A Good Clam Soil?
"Understanding Science Through History"
The Great Sets of Hard and Soft Shell Clams
Marine Soil Research Over A Century
Viewpoint of Tim Visel – no other agency or organization
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Tim Visel retired from The Sound School June 30, 2022
August 2023

A Note From Tim Visel
This is not a short read.  It is a viewpoint concerning clam soil research from manuscripts, observations and reports/research by others.  It is by no means a complete investigation but rather a summary of past research over a century.  In many respects, marine soil study lags decades (perhaps centuries) behind terrestrial soils – and overlaps the biological role of bacteria in what makes a marine soil healthy or good.
Tim Visel
August, 2023

Frequency of Event Sets

In the historical shellfish records, accounts of great sets can be found.  Areas that had few clams would suddenly experience an intense set.  This is especially found with soft shell clams but hard clams also exhibit this case history.  The Rhode Island shellfish history shows increasing sets of quahogs as oyster sets declined.  This transition has a climate connection as soils were cultivated as storms increased and the climate cooled.  These great sets produce beds of clams of the same age.  I have seen these beds, which have caused me to think that the set was opportunistic - at one time, one or more factors had come together and resulted in an immense set.  One of these factors is pH – and one reported in the oyster fishery.  Once shell planting and seed oyster transplanting happened, oyster growers noticed hard shell clams set underneath, providing evidence of pH moderation from shell hash.  This pH moderation is well-known in terrestrial soil science.  Another factor is soil pore size and the ability of soils to move water in it.  This is soil porosity and soils are sorted for grain size or poorly sorted, a mixture of different grain sizes.  You see evidence of this in the historical literature as washed sand or new sand.

Reports of barrier spit breaks or strong storms causing "new sand" to be deposited in a layer – washed of lighter soil fragments.  These are reported in the soft-shell clam fishery frequently and often in deep water after a hurricane.  The great Nantucket quahog bed, for example, was introduced to me by John Hammond on Cape Cod as an example of a massive storm cultivation event from the 1898 Portland Gate.  Storm cultivation in shallow water is more frequent and so is the positive impact of working the bottom.  Many reports mention previous bottoms or burial of bottoms from these storm events on the soft clam fishery.  The use of hydraulic equipment in the 1940's and 1950's introduced the concept of controlled, man-made soil cultivation.  Opening up stagnant soils was suggested by David Belding in Massachusetts over a century ago.  Different soil types and characteristics have plagued shellfish researchers – soils high in clay had slow growth.  High organic soils failed in extreme heat and under ice in winter.  Stagnant or dead soils could not obtain a set.  Seed clams planted from fast growing soils often showed slow or no growth with soils with high silt fractions.  Once these soils were "dug over," growth improved.  The term dug over appears many times in the Maine, Massachusetts and Rhode Island soft shell clam records.

Shellfishers, because of the knowledge of fast-growing soils, soon experimented with moving seed clams from stunted beds to areas known to exhibit good growth.  These transplants of seed were seen as the first attempts to conduct modern day aquaculture.
Sudden die-off's or kills of shellfish also appear in the historical reports.  These were often without an explanation – a strong storm or high or low temperatures.  These shellfish kills led to examination of soil changes.  One such study was titled "Concerning the Mortality of Soft Clams at Essex Massachusetts" by Harold Watson Nightingale, Scientific Assistant, US Department of Commerce, Bureau of Fisheries – Economic Circular #16. April 8, 1915.  In this account, the soil is examined and evidence of soil structure and soil chemistry are both explored – the observations are from a December 1914 survey – and the result of sulfide buildups – my view.  The location of the study was the Essex Bay and clams on Great Bank or Hog Island Channel "clams were found to be of poor quality, some sickly and others nearly dead."  Some areas of Essex bay were found to contain healthy clams and attention was then placed at soil conditions.  Page 2 of Nightingale's report contains this section:

"Residents stated that clams were dying in places where the soil was perfectly clean, and one of these supposedly clean places on the spits 300 to 400 yards east of Cross Island, was examined. Superficially, the bottom was perfectly clean, but below the surface there was a mat of decaying eelgrass, which alone would account for retarded growth or a sickly product ... east of Cross Island, there was a soft sand covered with the large number of mussels; the amount of decaying vegetable matter was high and the soil was so choked with silt that small clams would be suffocated.  The clams from these localities were also poor in quality and sickly." 

Soils that contained several sets and not one huge set had sandy soils.  These areas also near spits in the Nightingale report had better quality clams.   The report then concentrates on soil conditions:
"The best soil for rapid growth was found to be clean sand with a mixture of fine silt, which formed a cementing substrate, keeping the sand from shifting.  This kind of soil, which is not too hard, is found on the spits in various parts of Essex Bay."

The mention of spits is also frequent in the soft shell clam literature and identifies areas subject to natural soil cultivation.  Storm breaks occur near old spits or may act to widen them or more sand over previous bottoms.

   One of the best documented cases of new sand is from a statement regarding the 1898 Portland Gale – a severe storm (likely with hurricane force winds), which hit the New England coast November 16 to 19, 1898.  This storm caused a tremendous loss of human life, destroyed docks and wharfs and sunk ships.  It also broke open "cuts" and changed spits.  One of these areas was in the towns of Scituate and Marshfield, Massachusetts.  Shorelines from Connecticut to Maine saw a tremendous increase of sets following this storm.  Following is a segment in a March 8, 1906 The Shoreline Times newspaper article, quoting Commissioner Nickerson of the state of Maine about the soft shell clam industry – and one of the first attempts at clam aquaculture:
"The company owns and controls 450 acres of clam flats situated on the North River Mass peculiarly adapted to the culture of clams.  Previous to 1898, no clams were ever dug in the North River, but in the great storm of that year (1898) when the City of Portland was lost, the river cut a new deep mouth through the beach, giving free access to the tide, which soon destroyed the edible grasses of the marshes and made them in large quantities and thousands of bushels have been dug and carried away each year.

Professor A. D. Meade, PhD distinguished biologist, a member of the Rhode Island Fish Commission and probably the best authority in the world on shellfish culture having conducted experiments therein, for seven years, has twice inspected these flats.  Speaking of one place that he looked at said "the set there is thick enough to produce 3,000 bushels to the acre.  The main thing is a suitable bottom."

The Massachusetts Historical Commission Reconnaissance Survey for Marshfield 1981, US National Park Commission, US Department of Interior, contains this segment:
"The Portland storm of 1898, which closed the old inlet of the North River, which as a result tied the development of the Humarock section of Scituate to that of Marshfield."


It was the energy from this storm that created a change in the soil that enabled these clam sets. (These soft shell clam beds still exist and the North and South Rivers Watershed Association was successful after water quality testing reopened some beds in January, 2023).
   Rhode Island also experienced heavy sets after summer gales of 1900, 1902 and 1903.  This information is from The Annual Report of the Commissioners of Inland Fisheries 1905, printed January 1906, pgs. 105-109.

Sets, 1901 abundant, 1902 and 1903 abundant, 1904 good, 1905 poor.  The issue of digging over beds was mentioned:
"It is the common opinion of the clammers that digging over the clams stimulates growth.  The idea, which they seem to have, is that the loosening of the earth about the clams is as good for them as it is for a hill of corn or potatoes."

But concluded that thinning out thick sets (the 1901 set measured 7,910 in a single shovelful) was helpful, that constant digging with no rotation diminished sets.  This is a feature of shallow sets, soils may be prepared, obtain a spat fall, only to see a following storm cast small clams out destroying the set.  This gives the appearance that areas can go from very productive to nothing in just a few years.  This change is from the soil's ability to gain a set and then the ability of it to hold it.  This has a direct soil condition similar to habitat succession following a forest fire.  Once the fire is over, vegetation starts to reappear but imagine another fire that would start the "habitat clock" all over again.  The same thing happens to marine soils and gives the confusing observations or boom to bust reports.  Many times, the wind direction will cultivate the east side of spit – while the other side, soils grow often "stagnant."  This situation was described in a 1887 US Fish Commission Report – The Soft Clam Fishery of Long Island, pg. 591 of The Fisheries and Fishery Industries of The United States has this segment:

"The great irregularity observable between localities in close proximity is perhaps not wholly explainable.  You will hear that in this place or that (as, for example, Cow Bay) they were abundant formerly, but here now died out, while elsewhere (as at Riverhead) they were reported reappearing."

Too Many Variables

   I think the condition of the soil just had so many variables biologists concentrated on larval surveys and reproductive capacity rather than soil science – my view.  The concept of soil "aging" the collapse of pore water space, the formation of toxic sulfides or the ability of clay to bind calcium ions (we call this the soil CEC) were not reported or considered. 

   One person who I met and shared several workshops was Ron Ribb, who fabricated shellfish rakes and spears for small boat fishers.  In conversations with Ron Ribb in the early 1980's and presentations at workshops, he was convinced that bottom soils were becoming softer.  He had modified some of his clam rake designs for soft mud and was experimenting with an eel comb and rake for eels.  This perception was detailed in a survey conducted by Sandra MacFarlane in a report for the Cape Cod Cooperative Service about bay scallops (1999), who conducted a survey of shellfishers on bottom firmness and found that over 40% of the respondents felt bottoms (soils, T. Visel) were softer, only 4% felt they became firmer.

   With the use of hydraulic rakes on Cape Cod, the differences of soil and buried sets became evident.  On the more energy prone spits, these double bottoms could be seen, especially at Jack Knife Beach in Chatham as storm-driven sand over previous sets.  Many soft shell clammers have seen this impact.  The hydraulic clam gear could go over places where the surface held few clams only to expose the remains of previous beds that did not match surface observations.  The deeper you went, the grain size increased signifying a storm, new sand being buried by softer jelly-like organics.
   I was able to observe a storm-driven double bottom on November 14, 2021 in an area I used to dig soft shells growing up.  Below the surface, which had a large blue mussel set, was a previous set of soft shell clams that had all perished.

   This was evident in the Monomoy area as some soils had little large sand but were jelly-like, certainly not the pebble sand beds often with small stones of Connecticut.  These soils were more organic and soft.

   The problem was no one was looking at soils over a period of time.  This was made more difficult as many inshore areas were now closed to shellfishing because of bacterial closures.  When that happened, we lost critical soil – observations in shallow water.  Areas that could obtain a set or some areas showing declines were lost to fishery managers as well as the fishery.

Tidal Exchange and Shellfish Soils

Coastal systems that experienced good flushing (tidal water exchange) could, over time, become "poorly flushed."  One of the case histories I use often is the construction of railroad causeways (Connecticut) with much reduced tidal exchange.  This, in the historical literature, was described as "tidal choking."  Another example is the construction of three massive granite breakwaters at the mouth of New Haven Harbor, CT.  The oyster industry noticed that once these breakwaters were completed, coastal storms no longer cultivated a large natural oyster bed.  While the destruction of its primary shipping wharf "long wharf" declined, organic matter collected and slowed or nearly eliminated sets on the inner harbor natural bed.  The case history was described to me by George McNeil in the early 1980's as private growers sought control (and then subject to "stirring," the industry practice of flipping shell) for oyster sets.   Removing organics (silt) carried downstream by the Mill and Quinnipiac Rivers would prepare this bed for an oyster set (See Oysterman and Fisherman, March 1915 Letter to Editor, J.P. McNeil – Keister Appeal, Connecticut Shellfish Commission).  Energy and temperature have a direct impact to shellfish soils – either one can change soil chemistry.  Energy or storm influence can cultivate or flush organics or "fines" from heavier fractions commonly termed coarse fractions or constituents. 

In the Rhode Island shellfish history, the sets of quahog the hard shell clam (Mercenaria mercenaria) greatly improved after the Hurricane of 1938.  Bay scallop crops in Massachusetts increased immediately after the blizzard of 1978.  In heat and poor flushing, the shellfish industry often reports a decline in in shellfish meat quality.  I observed black soft shell clams in Green Pond Falmouth, Massachusetts that when opened contained a large pocket (often called a water blister) of dark fluid next to an emaciated meat.  These clams had a strong sulfide smell (personal observations, T. Visel).  Clams had died in areas of heavy black mud – a concern brought to me by Green Pond Tackle owner in the spring of 1982.  A large die off of soft shell clams was observed and shells were stained black.  The remaining clams, still alive, had a similar water blister.  William Bauknecht, then the owner of Green Pond Tackle, had noticed small dead flounder in the area of his business and requested a survey.  Green Pond, a tidal salt pond in Falmouth, MA, had a road causeway and stabilized tidal inlet.  Mr. Bauknecht reported the buildup of a sulfur odor black muck near his property and noticed the dead flounder as the ice left.  This buildup of organic matter had been noticed in several coves and salt ponds.  This organic buildup was also noticed in deeper areas as well.  Frank Dolan, a hard clam fisher from Guilford, Connecticut clammed in the Thames River near Long Island Sound, it was the Green Harbor area near the city of New London.  Before bacterial closures, the area had been a significant source for cherry stones, a small quahog.  At the end of his catches (before closures), clams had an off-flavor taste. Mr. Dolan thought the off-flavor was from this muck.  He would relay smalls clams to a mud sand mixture for about a month (large clams would not transplant well – they did not dig in and rolled) and the taste greatly improved.  He felt the poor taste was the result of the muck as hard sand in full salinity clams had no such customer complaints.

   Oyster growers in Connecticut and Massachusetts also noticed heavy mortalities in early spring.  Larry Malloy, was one such oyster grower, whose family owned deeded oyster grounds from the 1880's and operated a shellfish business in 1928.  In a January 1990 edition of New England Coastal News an interview with my brother Raymond Visel mentions a bottom kill of oysters:

"There is something wrong with the oysters out here [in the Thames River] now if I put 500 bushels down, I would get only 250 back.  The rest would be empty shell.  Something's terribly wrong out here.  I just know it, but I can't get anyone to listen to me," Malloy says.
I did a survey with Mr. Malloy and these oysters were stained black and had a sulfide smell.  A few years earlier, John "Clint" Hammond, an oyster grower on Cape Cod, grew bedding stock to market size in Oyster Pond River, Chatham.   At the end of his oystering career, he noticed the same mortality but linked it to decreased tidal flow.  A sulfide rich deposit grew along the edges of his grant and supported eelgrass amongst oysters.  The eelgrass had grown so dense that it was choking the river.  Following is a segment from the Town of Chatham 1965 report of the Select Committee on Dredging (Official Town of Chatham Minutes):

"The Committee found that at low tide it is virtually impossible for a boat drawing over two feet of water to make an entrance from Stage Harbor into the Oyster Pond inlet.  Adding to the difficulty is the huge quantity of eelgrass that has grown up within the last several years.  The entrance to Oyster Pond itself is worse at low tide for not even an outboard can penetrate its way through the thick weeds.  We were fortunate to be able to meet with Dr. Turner of the Woods Hole Oceanographic Laboratories, and from him we learned several interesting facts, one was that as much as eight years ago were there not a complete change of water in the Oyster Pond oftener than once every two weeks.  Since then, the flats have been covered with such a thick marine growth including the newly acquired Japanese seaweed that he doubts if these uses complete water change oftener than every three weeks or even once a month, the health hazard is obvious.  He also said, and I quote, if it needs to be dredged, dredge it."

Respectfully submitted,
Everett R. Eldredge, Chairman
Committee on Dredging Oyster River

A complete description of this dredging project is found in IMEP #107: Eelgrass and John Hammond's Concern About the Right to Fish, posted March 1, 2022, The Blue Crab ForumTM, Fishing, Eeling and Oystering thread.

In the shellfish literature, stagnation and tidal flushing are often mentioned as harming shellfish.  These accounts have a temperature and energy connection – they worsened in heat and climate absent strong storms.  At times, salt ponds and lagoons (tidal rivers) can become larval traps and represent intense setting with tidal choking if waters are cold and high in dissolved oxygen.  This can be seen in the scallop fishery of the Niantic River, Connecticut.  In the early 1900's, scallops were scarce in the Niantic River until the mid-1930's when eelgrass disappeared.  Niantic was once the site of a local eelgrass industry – to be used in "Cabot's Quilt," a paper-backed roll home insulation.  Storm intensity increased and it is thought that seed scallops were swept into the Niantic River, clung to seaweed and matured into a fishery.

One case history is detailed for the Poquonnock River in Groton.  This long narrow salt pond is a drowned river mouth.  In times of heat, oyster larva was trapped in the river and flourished above an organic compost.  Records exist of intense sets and fast off bottom growth 1878 to 1881.  Unfortunately, sulfide smells from this organic compost was linked to human disease and state and local officials ordered the oysters to be destroyed (See Appendix #1). 

Marine Soils

   One of the complicating factors about the study of marine soils is the fact that they are submerged.  The areas of tides we know more about because we can observe them.  Another factor is "parent material" terrestrial soils have measurable layers (horizons) from weathering and glacial grinding.  Many times, soils formed only after ice melted so they are relatively "new" compared to others with no ice interaction.  Some soil parent material is bedrock.
Marine soils, however, are the product of land – erosion if terrestrial rock, sand and clay over time.  The term sediment is used to describe them but that leaves out biological processes and the byproducts of natural chemical compounds.  The shallow waters contain soils that reflect the land and vegetation washed from it.  These can be the amount of organic matter, clay, sand and silt and very fine rock flour.  All these can vary and adds to the complexity of soil study, as water can redistribute these soils over time and by doing so change chemical responses.  Temperature can also influence soils and this directly impacts the oxygen levels and bacteria (types) that live in them.

Some of the factors used to describe terrestrial soils are the same, pH, soil pore size, sorting (particle sizes), cation exchange capacity (CEC) (electrical charges), percent organic matter and clay.

Some factors are very different, the sulfide levels, organic composting, bacterial strains tolerant of salt, high iron levels are just a few.  The most important difference is that the primary oxygen system is subject to temperature and the high amount of dissolved sulfate in seawater.  The productivity of soil for clams is limited by soil pore size.  This is well known and reported for terrestrial soils (soil compaction) as the ability to move water, plant nutrients and kept root tissue in oxygen – as "well drained" or "poorly drained."  You could say that marine soils are poorly drained and even more dependent on soil pore size.  This makes clam soils more dependent on cultivation from storm energy.  For example, the 1938 Hurricane was destructive to property and caused tremendous loss of human life, later.  Quahogs set heavily in the "deep water" along Connecticut's coast.  The sets of soft shell clams often happen in storm-driven "new sand" (See IMEP #122: Cultivation Energy Key to Healthy Clam Soils, posted June 22, 2023, The Blue Crab ForumTM, Fishing, Eeling and Oystering thread). 
Several factors go into what makes a good clam soil, a moderate pH, good soil pore exchange and a low CEC.  The CEC is a measure of soil charge in relation to holding positive cations such as calcium carbonate dissolved in seawater that helps build the clam shells.  Soils high in clay and organic matter are negative charges and, therefore, hold calcium cations tightly and influence clam growth.  Soils high in organic matter can support bacterial strains that waste hydrogen sulfide, a foundation for sulfuric acid.  Soils high in silt and rock flour have particles so small that they fill or block soil pores.  This increases the chance of soil stagnation and the buildup of sulfide.  Sulfide is a toxin and clams will stop feeding when levels are high.  Some clams host "friendly" bacteria that oxidize sulfide into less toxic compounds.  If sulfide levels increase, soft shell clams have been observed to leave the soil itself.  High sulfide levels are responsible for many fish and shellfish kills – often with the sulfur smell of "rotten eggs."  These can happen in high heat or very cold winters.
As soils "age," they undergo changes and this explains why some soils obtain a good set and then over time "die out."  At other times, clearing soils of fines increases soil pore water capacity and improves the capacity of a soil to produce clams.  This has been noticed by clammers as "working the bottom."  The mention of loose or dug over soils is common in the literature.  It is also mentioned by clam farmers – notice this reference in a 1984 Aquaculture Magazine article titled "Producing Clams for the US Market" by Jim Conrad on pg. 38 has this segment:

"The reason we keep digging up the beds with hand diggers is that if you let the substrate sit, silt drifts over the beach, plugging up the pores so that water won't circulate through it.  Then the clams, three or four inches down, or even a foot down, no longer can survive because they can't get enough water filtering down to feed on ... we try to make the beach substrate "fluffy" like the soil of a well tilled agricultural field."

You see mention of horse and oxen teams plowing clam flats in areas of finer high clay soils while hand digging in the softer high organic soils.  Heavy sets do happen and Rhode Island mentions clam sets so thick they lacked space in which to grow.  Other reports mention slow clam growth, which caused an investigation of Maine's clam flats in 1957.  Here, two researchers, Spear and Glude, concluded that growth differences between Bedroom Cove and Sagadahoc Bay were environmental and not genetic (See Effects of Environment and Heredity on Growth of the Soft Shell Clam, US Fish and Wildlife Bulletin #57).  Only one research project (that I have located) looked at soil differences when cultivated was conducted on Cape Cod by a colleague who took my marine resource extension position when I left Cape Cod, H. Karl Rask.  His study with hydraulic cultivation equipment examined CEC, grain size and pH See Appendix #5).  After every trial, the CEC was lowered, thus allowing clams to attain calcium ions for shell building.  Areas that had been worked by hydraulics showed improved growth (personal observations, T. Visel).  Oxygen was a signal to good clam growth – these were the surface "brown" soils while anoxic soils were grey to black stains – and frequently the smell of sulfur.  This change was evident in the color of the soils, brown in oxygen and black lacking oxygen. 
Sometimes, you could see this change on the clam shells themselves.  The distance from the soil surface to where iron sulfide dominates in the "deadline" is often mentioned as winter kill (clams subjected to sulfide exhibit poor meat quality as black belly or water belly – thin meats and often off-flavor taste).  In the Maine soft shell clam fishery, this is often referred to as dead flats or a clam graveyard (See IMEP #119: Marine Soils and Soft Shell Clams of the 1950's to 1980's, posted on March 28, 2023, The Blue Crab ForumTM Fishing, Eeling and Oystering thread). 

The Composition of a Clam Soil

First, there is no ideal soil for clams.  They can change from pore water and temperature quickly.  A soil high in clay can be productive on colder more energy-filled habitats.  The same soil could fail over time as fines (rock flour and silt) caused pore water exchange to lessen or even stop.  A high organic soil could, in high heat, become a source of toxic sulfides but the same soil in colder water (with more access to oxygen) be productive.  These changes help explain the rise of good sets only to see setting decline over time.  Researchers in Rhode Island, Pratt and Campbell (1956), found a consistent relationship to poor growth to be the higher percentage of clay.  Belding on Cape Cod, a century ago, detailed those soils high in organic matter tended to be acidic.   Belding also noticed that dredged material, when deposited close to shore, could obtain tremendous sets even after pumping and depositing in a higher energy area.  This is mentioned as "new sand" or double bottoms.  Soft shell clammers experience these storm sands as layers, which show a dense soft clam population below – all dead, suffocated as to a storm event.  That is why there is so little research about clam soils – it may take years to fully assess chemical changes, and storms could change controls complicating before and after trials.  That is why I struggle to present the "best" soils, but just a snapshot in time of successional change.

A good clam soil – New England (no water present as content)
Less than 15% clay, CEC, growth
Low organic matter, 5% or less, pH and sulfide
High sand or coarse fractions 50%, pore water oxygen
Silt or rock flour, fine grain 20% or less, pore water
Shell fragments, 5%, pH moderation, spat falls
Gravel or pebbles – 5%, spat falls, holds soil in place

Belding on Cape Cod 1910's experimented with "resurfacing" flats with gravel with high sets.  Castagna and Kraeuter, 1981 – Manual for Growing the Hard Clam (VIMS) – mentions the use of crushed stone or crushed shell to prevent storm damage on page 42.  Belding, in his 1930 report on the Massachusetts Soft Shell Clam Fishery, mentions experiments with the addition of new soil – in this case, gravel.  Under the section on Spat Collecting is found the following segment:

   "Flats which are being "dug over" by the clammers tend to seed better than untouched flats."

This could be explained that by digging the flat is uneven and contains baffles of relief and low areas with washed sand.  On a much larger scale, a storm could wash or deposit new sand – Belding mentions this as well:

"An uneven surface favors catching the small clams than the level surfaces.  The hollows of clam flats contain more seed clams than the level surfaces."

This was noticed by soft shell clammers, who even at times planted sedge and thatch plants upon smooth flat and "proved successful in Barnstable Harbor," and "clams are found in abundance near or in sedge islands."   Belding, however, warns that this practice may increase sets but it does not ensure a clam harvest.  He alludes to soil conditions that no longer support growth (the dead soils) and need renewal.  Belding notes the following:

"By placing wind rows of sedge on a flat, small eddies were set up by interference with the current and a set of clams was obtained."

(In Maine, this practice was called "brushing" and involved the placing of pine branches into the flat.)  To be a success, however, the soil must be "new" and most likely contained greater pore water and perhaps a higher pH.  Also from Belding – my comments (    ) T. Visel:

"However, not only must the small clams be deposited but conditions for their continued existence must be favorable.  It was found on certain flats that, while the spat was collected (soft shell clams, T. Visel), the conditions on the flat would not permit its growth.  This was remedied by covering the flat with upland soil from the marsh.  After resurfacing, the clams caught grew very well (most likely a higher pH and lower CEC, T. Visel) and gave a good yield."

Soils that obtain high levels of clay or silt are known to have pore circulation (pore water) in the soil.  In the historical fisheries literature, these are known as stagnant or dead bottoms.  Over time, these soils "age" or capacity to sustain clams declines as the pores fill with "fines."  In this area, Belding also alludes to soil death in respect to the clams (See IMEP #77-A: The Cultivation and Chemistry of The Dead Soils, posted May 20, 2020, The Blue Crab ForumTM Fishing, Eeling and Oystering thread).  He mentions the need to "resoil" them at intervals.  Belding continues:

"It was found necessary to resoil in this particular locality at least every five years, owing to the development of deleterious substances in the soil."

Unfortunately, he did not describe what those "deleterious substances" were.  He does, however, mention the washing and resurfacing of soils as helpful to clams.  Some of the most noticeable was the placement of dredged material.  This was, in effect, a massive resurfacing trial.  Belding:

"Several instances of a large clam set occurring on barren flats, which had been covered with material from dredging operations, are on record.  In 1905 in the Annisquam River at Gloucester, a heavy set of clams on the flats were resurfaced from the soil taken from the channel.  In 1920, the dredgings from the Yarmouth Cold Storage Company, were placed on certain flats in Yarmouth.  These operations were followed by a heavy set over some fifty acres, which yield about 40,000 bushels of clams."

The first new sand experiments were likely conducted in Clinton, CT.  A January 23, 1903 Clinton Recorder (weekly newspaper) article titled "To Propagate Shellfish" contained this segment:

"M. I. Blaisdell said he had experimented with a spot of mud flat about 30 feet square.  He had sprinkled such a spot with sand to the depth of about two and one-half inches and in a short time, clam holes were found so numerous that he could hardly put his fingers between them.  One man he knew of had dug twenty bushels from this tract and another as many more."

And Belding reports similar findings:

"Experiments of this department have obtained similar results by resurfacing and building up flats, particularly with gravel.  The clam culturist, by covering irregularly with gravel the smooth surface of his flat, particularly in a soft mud, can hope to obtain a set of clams provided current conditions are favorable."

Belding's comments, although published in 1930, were his observations and experiments of some two decades before (1905-1916).  They resemble the clam growth experiments reported by Turner in 1948, the clam spat box collector developed by A. D. Mead in 1902.  Dr. Mead had devised a spat collector box "which consisted of a box partially filled with sand and covered with a coarse wire screen" and further – This device was reported as being very successful even in localities where sets did not occur around outside of the box."

The concept of soil health was a century away and only a few researchers looked at soil cultivation as a successful component.  H. K. Rask also did so on Cape Cod in the mid-1980's.  He examined soil components of grain size, pH and CEC (See Appendix #5).  After cultivation, all these soil factors were different and positive for clam growth.
The study of marine soil and its impact upon benthic species remain underreported in the research literature – my view, Tim Visel.


Appendix #1

An Experimental Study in Production and Collection of Seed Oysters
Galtsoff et al.
US Bureau of Fisheries 1930
Production and Collection of Seed Oysters, Pg. 251
Experiments in 1925

Marine Soil Composts and Bacterial Sulfide in High Heat
"In the United States, brush spat collectors have been employed but very little chiefly because of the cheaper and better results generally obtained with oyster shells.  Brush, however, is superior to shells in many respects and in certain regions has proved to be a very suitable collector for use on soft mud tidal flats, which cannot be utilized for any other purpose.  In Connecticut, the profitable utilization of soft muddy tracks by brush methods is described in the reports of the Connecticut Shellfish Commission for 1882-1883.  At that time, 50 acres of muddy bottoms in the Poquonnock River near Groton were planted with white Birch brush and yielded as high as 1,000 bushels of oysters per acre.  The brush or really young trees, which were used, measured around 4 inches at the butt and are said to have yielded as much as 25 bushels on one branch.  The average yield, however, is said to have been approximately 5 bushels per branch."

This report mentions that this use of brush as a spat collector was accidental.  Galtsoff states on page 203:   
"The first use of brush in America was made in 1868 (Collins, 1891, pg. 477) in the Poquonnock River, Connecticut when a farmer, after trimming his orchard and throwing the branches of the trees into the river, found them in the succeeding autumn covered with oyster.  This suggested the employment of the method by others, and for several years it was known as the "brush" or Poquonnock method.  It was, however, only moderately successful and later was discontinued."

But that is not the complete account of the Poquonnock River method.  The use of brush and the increase of heat would lead to a health emergency.  The following note on The Oyster Fishery of Connecticut by J.W. Collins, US Fish Commission 1891, Groton, CT, pg. 177 provides further details – my comments (T. Visel):

"The Poquonnock method (placing of birch branches for off bottom culture T. Visel) has been moderately successful, and perhaps is the best for the locality where it is employed.  The are several reasons why it has not proved entirely successful on which may be mentioned the collection of large quantities of eelgrass about the flats at the mouth of the stream, causes stagnation of water producing such conditions (Putrid smells – T. Visel) that the board of health of the town has caused the brushes to be pulled up and destroyed." 

(What is not mentioned in this section is that the Poquonnock River is known to have a restricted tidal opening – a barrier spit that closes in high heat and very deep accumulations of sapropel.  That is why the oyster sets occurred on the brush). 

The accumulation of the deposit of this organic compost soon went anoxic and sulfide smells drifted into people's homes.  This was still the time at which the spread or cause of disease was thought the result of a "Miasma" – a stench.  Carol W. Kimball provides how this sulfate metabolism by bacteria caused this off bottom culture to end.  In the book titled "The Poquonnock Bridge Story" 1984,294 pages, Groton Public Library, Library of Congress #84-82324.  The village of Poquonnock Bridge suffered an outbreak of Scarlet Fever (caused by a bacterial strain of streptococcus A strep), killing nine people.  Kimball then describes the sulfide smells and thought to be the source of the Scarlet Fever epidemic.  Page 121 has this segment – my comments, T. Visel (   ):
"Poquonnock was in panic with the nineteenth century ignorance of bacteriology, frantic residents were at a loss to explain the cause of the epidemic (May 1881 during hot weather, T. Visel).  The village lived in fear until the sickness abated at the end of August.  During the warm weather, birch brush in the oyster beds sent up a dreadful stench and villagers settled on this nuisance as the cause of the epidemic.  Residents petitioned the Groton Board of Health for an investigation."

Kimball describes how productive the off bottom oyster culture had been up to this time and Gideon F. Raymond of New London had purchased deeded beds between 1879 and 1881.  The number of brush planted spat collectors was in the thousands.  The industry failed not because of few oyster sets – in fact, the set was intense.  The investigation, however, centered on beliefs that the sulfide smell from sapropel was the cause of the Scarlet Fever outbreak and the Board of Health ordered the removal of all brush during the winter – as it was believed to be, (pg. 122) a danger to remove them (the oysters) in hot weather:

"Dr. Chamberlin (State Board of Health) warning that it would be dangerous to remove the brush except in very cold weather.  He said it must be done with thorough disinfection to avoid dangerous gases liberated from mud, water and brush.
Although no causes of Scarlet fever had occurred since August, the brush was loaded on scows and taken away during December and January, sometimes with the temperature nine degrees below zero."   

Mr. Raymond brought suit against the local health board but lost the case.  In the 1980's, a floating raft organized by the Marine Advisory Program and Project Oceanology obtain immense sets on scallop shells suspended in the water column in bags in areas once held by Gideon F. Raymond one century later.  Shells planted on the bottom sunk into an organic ooze.

Appendix #2
Northeastern Regional Aquaculture Center

University of Maryland
2113 Animal Science Bldg.
College Park, MD 20742-2317
Phone 301-405-60XX; FAX 301-314-94XX

November 3, 2006

Mr. Timothy C. Visel, Coordinator
The Sound School Regional
Vocational Aquaculture Center
17 Sea Street
New Haven, Connecticut 06519

Dear Mr. Visel:
I am sorry to be so slow in getting back to you concerning clam dredging.  I have enclosed some references on the effect of clam dredging on the bottom.  Some of these references are not all enclosed (e.g. the study from the National Academy of Science) as they are quite long.  Others I have provided only an abstract.

I hope the enclosed will be helpful to you.
Sincerely,
Fred Wheaton
Director
Northeastern Regional Aquaculture Center


The Sound School Regional                  Timothy C. Visel
Vocational Aquaculture Center                  Coordinator
17 Sea Street
New Haven, CT 06519

MEMORANDUM

TO:      Dr. Fred Wheaton, Executive Director
      University of Maryland – Northeast Regional Aquaculture Center

FROM:   Timothy C. Visel
      The Sound School Regional
       Vocational Aquaculture Center

DATE:      September 25, 2006

RE:      Shellfish Habitat Indexing – Impacts of Hydraulic Clam Dredging

I was recently contacted by a colleague who stated that the Northeast Regional Aquaculture Center was involved in research about the practice of bottom cultivation (soil manipulation) by clam harvesting industry (hydraulic harvesting).  My research in the field was during a 10-year period during which I was employed full or part time by three cooperative extension services, URI, UMASS and finally the University of Connecticut.

In all three states, I conducted adult and outreach education for inshore fishermen.  They represented part time and full time commercial fishermen and about half were involved in the shellfisheries, hard clam, soft shell, clam oyster and bay scallop fisheries.  It soon became apparent that bottom manipulation was an accepted practice and associated with increased shellfish production.  The experiences of these commercial fishermen (it didn't matter what fishery) all related personal observations of bay, cove and river bottoms.  Some retired fishermen attended just for interest so occasionally we had viewpoints from the 1920's to late 1970's early 1980's.  Within a ten-year period about 2,000 fishermen participated.  Although it's far from a peer review study the generalized comments below are representative.

1.    Almost all reported increasing concerns about accumulations of organic debris – leaves, sticks, vegetation, algal blooms that has changed fisheries habitat from hard bottoms to soft.

2.    A negative correlation between the growth of bottom vegetation to a loss of shellfish productivity – much of the concern involved tidal movement, restriction, stagnation and low oxygen levels.  In some cases, the growth of vegetation got so thick it suffocated shellfish and eliminated benthic fishes (Mostly flounder and blue crabs).

3.    Almost all of the fishermen recounted experiences in tidal coves and bays about advantages of working the bottom, removing organics and silts from the sediments and breaking up hard bottom.  This was quite evident with hydraulic shellfishing here in Connecticut after 1958.

I would like to exchange information on hydraulic shellfish harvesting here in Connecticut if that would be of interest.  I'm especially interested in any research that talks about habitat indexing or suitability for shellfish or the benefit of bottom manipulation.  It would be very helpful.  Several fishermen asked if the marine soils were ever classified or indexed for shellfish suitability.  Information on such habitat indexes would especially be helpful if they also included references to our winter or black back flounder.

Thank you for your assistance and interest.

TCV/ad   


Appendix #3

MASSACHUSETTS AQUACULTURE ASSOCIATION
P.O. Box 154   West Yarmouth, Mass.  02673

                              1987
Tim -
   Reports enclosed with corrected graph on page 5.  If you make additional copies, use this one (on the first copy computer print out reversed the X and square on graph legend.  I told Jeff Kassner to get in touch with you at Hofstra conference to talk about 1900-1910 reports.  Stormwater conference scheduled for October 2.
   See you in Maine?
HKR

Appendix #4

Aquaculture Today, Fall 1988
Getting More From Your Bottoms – The Effects of Hydraulic Harvesting
By H.K. Rask
Regional Marine Resource Specialist
Co-operative Extension
University of Massachusetts

When the beds are not worked, many areas suffer from increased sedimentation, followed by poor setting and recruitment.  A closer look at the sediment often reveals larger populations of worms and other invertebrates, instead of clams or quahogs, many of which are predators of the newly-set seed.  In addition, sediments can become anaerobic, sulfurous or otherwise chemically altered.

Cultivation a solution
Recent work with hydraulic seed harvesters and other hydraulic gear also shows that cultivating the bottom enhances setting; good sets can also be found when storms, currents or dredging activities wash the sediments free of organic material and detritus.
   There is a link here to the excellent sets of shellfish found in new sand deposited by storms or currents.  Clams (Mya), for example, are a colonizer species and can quickly populate an empty area.  New sand is not only free or decaying organic detritus, but is also free from predators.  Hydraulic action can easily be seen to imitate some of these natural phenomena.

Practical results

   As part of the study, two sample areas (Barnstable and Warcham) were hydraulically harvested.  Sediment samples were taken in triplicate, both before and after, and analyzed for grain size distribution, cation exchange capacity (CEC), nutrient and metals content, and pH.  The sediments were also compared to those from areas that had excellent and recent clam sets.

   In all cases, hydraulic harvest had distinct effects on sediment quality.  The major physical effect was the reduction in percentage of fine particles such as clays, fine silt and small organics.  This was reflected in an increase in grain size (Tables 1 and 2) and a reduction in CEC1 (Table 3).
Positive results

   From all observations, it would seem that any activity which removes the silt/clay and decomposing organic fractions from sediments, increasing the percentage of sands and coarser particles would benefit shellfish setting, growth and survival. 

1Cation exchange capacity (CEC) measures the sediment's ability to hold onto positively-charged ions such as calcium, potassium, magnesium, aluminum, etc.  Sediments high in organic material or clays will tend to have higher CEC's than those compared primarily of sand.  A reduction in the CEC therefore corresponds to some reduction in these fractions; the end result is a coarser grain sediment, having fewer clays, silts and fine organic particles.


Appendix #5

Toxic Sulfide Concentrations in the Sediments and Water Column of the Suwannee River Estuary and Its Influence on Hard Clam Survival



Investigators
Derk C. Bergquist
Department of Fisheries and Aquatic Sciences
University of Florida

Shirley M. Baker
Department of Fisheries and Aquatic Sciences
University of Florida

David Julian
Department of Zoology
University of Florida


Summary:

The survivorship of hard clam nursery seed (4-6mm) and grow-out seed (12-15mm) was reduced when exposed to sulfide in laboratory experiments.  Addition of the antibiotic chloramphimicol tended to increase hard clam survivorship, suggesting the sulfide indirectly affects hard clam survivorship by facilitating bacterial proliferation.  It was concluded that sulfide is present in the sediments of Florida's hard clam aquaculture areas at concentrations capable of reducing hard clam survivorship.  However, with our current understanding, predicting which HDLA's and which lease areas within an HDLA are most at risk and when they are most at risk for potential toxic sulfide levels will require sampling of sediment porewater at specific planting locations and planting times.

Introduction:

   In eutrophic environments, high nutrient inputs lead to increased rates of primary production followed by increased organic material availability (Borum and Sand-Jensen, 1996).   As this organic material is oxidized, the increased bacterial respiration rates can translate to reduced oxygen availability, particularly in benthic waters and sediments (Rosenberg and Loo, 1988; Turner and Rabalais, 1994).  Sediments are especially prone to oxygen limitation because of reduced diffusion rates, and, as a result, deeper sediments are often completely anoxic.  In environments lacking sufficient oxygen to support aerobic respiration, microbes utilize alternate electron acceptors (such as NO3- and SO42-) and produce reduced compounds (such as N2 and H2S, respectively) as a by-product of organic matter decomposition (Diaz and Rosenberg, 1995).  Of these byproducts, hydrogen sulfide (H2S) is particularly important from a biological perspective because it is a component of marine sediments worldwide (often reaching concentrations of several millimolar) and it is toxic to animal tissues in only micromolar concentraions (Fenchel and Riedl, 1970; Bagarinao, 1992).  The primary toxic effect of sulfide is that it inhibits aerobic respiration in the mitochondria by binding to cytochrome c oxidase (National Research Council, 1979).  Recent evidence also suggests that sulfide produces conditions favorable for bacterial proliferation, thus increasing rates of bacterial infection in sediment-dwelling animals (de Zwaan and Babarro, 2001).

   There is some anecdotal evidence to suggest anoxia and/or hydrogen sulfide may play a key role in clam survival at aquaculture sites on Florida's Gulf coast.  High clam and oyster mortalities were observed to be associated with a layer of "black water" lying on the bottom at several sites currently being used as part of a field experiment of bivalve growth in the Suwannee estuary (Debra Murie, personal communication).  The chemical characteristics of this water layer were not determined, but the investigators suspect it was at least anoxic.  Several of the field personnel also reported a sulfur smell.  Additionally, the shells of hard clams harvested from field nurseries often carry a dark gray or black stain characteristic of exposure to iron sulfides (personal observation).  This suggests that hard clams in aquaculture areas are prone to sulfide exposure, but this has never been confirmed quantitatively.  Because of the linkages between eutrophication and sulfide generation and the location of clam aquaculture areas in regions of potentially high organic matter input, understanding the potential role of toxic sulfide in decreasing harvests of the hard clam M. mercenaria is important to improving bottom culture practices.