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Last updated: 08 May 2006

Seashore Foraging & Fishing Study

Early Human Diet

Shell Middens & Fish Bones

The absence of shell middens is often cited as evidence that Early Humans did not exploit aquatic foods. 

As the oyster-despising Mr Meighan put it, as quoted by Jon Erlandson:

"In any event, shell middens of real antiquity are rare or absent in world archaeology"

There are some very good reasons why shell middens of 'real antiquity' are not found very often. 

None of them has very much to do with Early Humans not eating shellfish or other marine foods.

• Acid rain

• Selective shellfish harvesting

• Locations of colonial, sessile shellfish

• Changing shorelines

1 - Acid Rain

Natural rain absorbs carbon dioxide from the atmosphere, and is therefore always slightly acid (pH about 5).  Seawater is slightly alkaline (pH about 8).

This dilute acid can dissolve the calcium carbonate shells, and leave nothing but a black smear - presumably the other mineral residues of the shells.

Postdepositional Leaching of Shell in Two Northwest Coast Shell Middens 

If you don't feel this is a realistic excuse for the absence of very early shell middens, try soaking that bright new shiny shell you found on the beach in a glass of Coca-Cola. But, since they'll probably try to sue me for even suggesting  their product is in any way harmful, use a glass of tap water instead.

If you find, overnight, a slight difference, then do the arithmetic:  if just one hundred thousandth of a sea shell is eaten away by acid rain each year, there's not going to be a lot left after 100,000 years. 

You can also see the effects of natural acid rain in the stalagmites and stalactites of any cave system, dissolved as the rain percolates through limestone and then re-deposited wherever the calcium-laden water has to drip from a cavity ceiling.

Contrary to what you may be told, stalagmites and stalactites do not always take thousands of years to build up. There is a famous 'drip cave' at Knaresborough in Yorkshire, where Victorian tourists used to hang up pieces of clothing to catch the calcium-laden drips. I used, once, to have my grandfather's 'petrified' bowler hat.

2 - Selective shellfish harvesting

Many shellfish are 'selectively carried'. Shellfish foraging is mainly done by women and children. With very large shells, such as giant clams (Tridacna) or helmet shells (Cassis sp) carrying them home is simply not worthwhile, and cutting out the meat, then and there on the reef, leaves no archaeological trace at all. 

Both of these shellfish, (or their very close relatives), are found from Madagascar to the Western Pacific. 

In the past, Tridacna were as plentiful throughout that wide area, as they still are, for instance, in the Red Sea, where shellfish are not eaten for very 'modern' religious reasons.

Cassis shells have no operculum, and can easily be harvested on the reef.

The relative importance of various types of shellfish in contemporary Meriam diets is not reflected in either the contemporary accumulations of shell or in the proportional representation of shells in the prehistoric assemblage. In fact, the most important shellfish prey types are virtually absent from the prehistoric archaeology, and conversely, prey that are relatively unimportant are quite common in the shell assemblages.

This situation is predictable when we consider the tradeoffs that foragers face in attempts to collect shellfish from the intertidal and deliver shellfish flesh to a central locale.

Explaining Shellfish Variability in Middens on the Meriam Islands, Torres Strait, Australia Douglas W. Bird
Journal of Archaeological Science (2002) 29, 457–469 doi:10.1006/jasc.2001.0734, available online at http://www.idealibrary.com

On the tiny (27km) Red Sea coastline of Jordan, I have eaten a large, raw, fresh-caught Tridacna, fished up by my friend Bishara, by hand, from about 10m down, and shared with six friends. We also, by night, and a little drunk, paced the fringing reef flat, and caught half a dozen large spiny lobsters by hand. (It's a knack, believe me). Later, Bishara travelled up the almost entirely un-fished Saudi coast to the end of the Gulf of Aqaba.

When I asked if he had caught any lobsters, he held out his hands, 40cm apart. 

'That's tiny!' I scoffed. 

'No', he said, 'That's not the length ... that's the width'. 

I measured the carapace he brought back, and it was. 

Before that tiny coast had a road, and a few factories, I swam among a 'mob' of about 30 mating turtles, and with a pod of pilot whales, close into shore.

At one time, only a few years ago, most of the Indo-Pacific shoreline ecotone was a Garden of Plenty like that.

Indo-Pacific Shoreline Ecotone

Another very common Indo-Pacific food shell is:

Ganga - Common Spider Conch, (Lambis lambis) occurs from East Africa to Tonga, in vast numbers. Ten pieces (excluding shell) give about 150gm of meat (no waste). They cost me just 40¢, about 2½ times the cost of the same weight of skipjack tuna, but are 5 times as delicious. They are normally processed (de-shelled) by breaking the shell back to allow the flesh to be hooked out easily. The snail sucks itself into its front door, so when its back door is opened, and breaks the seal, it can be pulled out easily. This is normally done out on the reef flat, shore, or in a boat; it's a nuisance to carry all those heavy, spiky shells home.

But, if you were to find a few conch shells damaged in this very particular way, you could justifiably conclude they were 'modified by humans'.

Those 35 half-shells of 'small' Tridacna weigh 11kg. Each whole shell would produce about 50 - 150gm of meat. It's not hard to work out that lugging home 22kg of shell for 2 - 5kg of meat is not worth the trouble.

Tridacna gigas is not a common menu item in New York, Paris or Brussels, but, in the 'Shoot-To-Kill*' seaside restaurants of Mactan Island, Cebu, in the Philippines, you can buy just one, and have it prepared any way you want, to feed about six people. 

*'Shoot-To-Kill' doesn't refer to the well-known propensity of Filipinos to kill each other, but to the Visayan  'Sugba-Tinola-Kilawin' food combination - grilled fish, fish soup, raw fish.

The large Cassis cornuta shell held by the girl in the photo above would yield about 400gm of prime shell meat, none of which is waste. The shell weighs about 3kg. Although the shell itself is banned from international trade by CITES, the flesh is tasty, and often for sale in Surigao City market.

The main point of the Birds' research, in this case, was to study the different strategies of adults and children when foraging. Adults do it for food, and kids do it for fun. Children were more likely to forage nearer home, and to bring smaller, and often uneconomical shells home, where they would end up on the midden, if there was one. 

The end result of selective collecting is that you don't find many clues of the really big  juicy shellfish back at the village dump.

That has obvious implications for the archaeologists studying that midden in detail at some time. A majority of uneconomical, small shells could lead to a quite mistaken impression that seashells were 'famine food'.

Which is precisely what the majority of archaeologists, reared on the notion that big game meat was the be-all and end-all, have concluded.

Clearly, while the majority of Early Humans had shellfish resources around the Indian Ocean like these, there was no need for shell middens at all.

3 - Location of colonial sessile shellfish

This map shows the distribution of zooplankton in the world's oceans.

Yellow and red show the richest areas.

That's where the colonial shellfish are.

Steep coastlines bordering those areas may have 'recent' shell middens.

Others, on less steep coasts, were probably drowned millennia, or millions of years, ago.

Jomon

Japanese archaeology began with the first excavation of a shell midden by an American conchologist in 1877, looking, not for human bits & pieces, but clues to shell evolution. Later excavations of vast shell middens around Tokyo revealed the Jomon people, who made the first pottery vessels on Earth, and were probably the ancestors of the 'Hairy Ainu' now restricted to tribal areas in Hokkaido. 

"The dietary importance of the molluscs has been discussed in considerable detail in many papers. Some authors speculate that the large amount of shells prolonged the occupation of the same site. For example, the Horinouchi shellmound, which is a typical horseshoe-shaped midden, was estimated to have 10,000m³ of shell deposits; the period of settlement was thought to span about 1,000 years, from Late Jomon to Latest Jomon. These figures suggest only 10 m³ of shell deposit per year. On the other hand, shells are not preserved in the acidic humus soil of Japan except when large numbers of shells are accumulated at once. This would be possible if the Jomon people used many molluscs in one season. They might dry the meat of the shellfish in order to trade it for inland products: the distributions of pottery, stone implements, and ear-ornaments suggest each Jomon settlement had a particular product for trade".

Bulletin 18 Tokyo University

So it's no surprise that Emperor Hirohito of Japan was one of the world's leading conchologists, or scholars of shells, and it's no accident that one of the most advanced and complex hunter-gatherer groups in world history lived mainly on shellfish. 

That big red triangle covering Indonesia and the Philippines is quite different to the other zooplankton-rich areas. They are mostly due to deepwater upwelling, bringing sunken nutrients to the surface. The Indo-Philippine area produces its own zooplankton, and enough competition to exclude dense sessile molluscs.

Another ecotone that produces dense sessile mollusc populations (and associated shell middens) is the freshwater river, producing freshwater clams (Unionaceae). They are common along the Mississippi and Ohio rivers in America. But after only a couple of centuries of greedy European colonists in that country, many of the North America Unionaceae are gone forever.

Like the feathers of snowy egrets, the pearls of freshwater mussels went to decorate the dames of New York. Some sentimental animal lovers saved a few snowy egrets, but no one much cared about a few muddy mussels.

The most extensive shell middens known in the Philippines stretch for 40km along the Cagayan river in northern Luzon, but are only 3-4000  years old.

Perhaps a good place to look for very similar, but much earlier, Unionaceae shell middens would be by the shorelines of the Great Rift Valley lakes and the great African rivers. But they will only be preserved by exceptional accident, where, say, a landslide, lava, or a flood covered the midden, and preserved it with an impermeable layer.

African freshwater shellfish

4 - Retreating Shorelines 

More detail, including a map showing the shoreline of the Indian and West Pacific oceans for about 80% of the Pleistocene, is given in

Indo-Pacific Shoreline Ecotone.

Many current shorelines, except a very few on steep coasts, are now many miles away from ancient shorelines.

And this is not the only problem. Sea levels are constantly changing, up as well as down.

Only 6000ya, sea levels on the Indian coast were 6m higher than now.

Many of the ancient Iraqi cities, such as Ur and Eridu, the first civilisations in the Western world, now desert ruins well inland, were on the shoreline of an extended Gulf.  Ur, the very epitome of the beginnings of civilisation, is now a mere adjunct to the permanent military base now established by the descendants of the very same greedy European colonists who wiped out their own country's natural resources (and most of its native people).

Much of the coastline of East Africa consists of raised coral terraces, often barren, because rainfall sinks straight into the ancient fossil limestone reefs, and the fresh water doesn't come out again until it is under sea level. Some of those coral reefs were probably alive at the same time that Early Humans were running around the old Olduvai lake (and a lot more of them along those coral reefs), and have been rising and falling ever since. 

To build up a waste dump that is worth mining for building materials (as on the coast of Senegal, where the government sells midden-mining licenses) you need a great mass of waste shells. Only a reasonably great mass of people, sitting around, could put them there.

The food remains of a nomadic, wandering group of shellfish foragers would be almost archaeologically invisible, as would those from very large shells or non-colonial shells.

I live in a coastal Philippines town with about 4000 inhabitants, all of whom eat shellfish regularly.

There is absolutely no sign of a 'shell midden' anywhere, but fragments of shell are scattered everywhere. Many of the most prominent are sigay - small money cowries. Due to their structure and size, they are virtually inedible, but children love them, and collect them by the thousand.