The ancestors of modern man were all hunter gatherers. They roamed the land and shorelines killing what they could with primitive weapons and they also collected fruit, nuts, insects and shellfish to fill their stomachs.

Being clever creatures, people developed cunning skills that made them better at killing, trapping and gathering and their population numbers grew quickly wherever food was fairly plentiful. But human success was limited by supply and when most of the slow prey had been caught and the easily gathered foods had been over harvested, population growth slowed.

Eventually people learnt to cultivate crops, like wheat, rice, beans and cabbage, and to domesticate wild animals like sheep, cattle, pigs and chickens. This allowed the human population to expand rapidly and people began to dominate life on the planet.

As farmers and crop growers we no longer needed to hunt or gather wild foods but to survive but it has been difficult to repress our natural instinct to exploit nature. If we go to the beach to gather shellfish today it is not to save ourselves from starving but to find a special treat.

We all enjoy treats and want our children and grandchildren to enjoy them too but all over the world the special shoreline foods we used to gather are becoming harder to find. They have been over harvested or else their habitats have been damaged by silt and other pollutants washed down from the overdeveloped land.

New settlers in New Zealand may think the beaches here are rich with clams, crabs and various snails compared with overseas shores. However, even in New Zealand with its low population and extensive coastline, many seashore animals that were common just 50 years ago are now rare or extinct on many shores.

Crayfish could once be caught in the shallows without diving and paua were found along most rocky shores but are now very hard to find on the shores of Auckland and Northland. Along Northland's west coast the population of large and delicious clam, the toheroa, collapsed and it has now been illegal to gather them for more than 20 years. Many of our broad estuary flats that once held thousand of tonnes of cockles and hundreds of tonnes of pipis now have very few that are big enough to eat.

If we want to preserve the fun and privilege of collecting shellfish for our children and grandchildren it is vital that we begin to exercise control over our hunter gatherer instincts and adopt attitudes of restraint. There are clear legal limits for species like cockles and mussels - just 50 per person per day - but if one person, quite legally, takes the last 50, it would remove the last of the breeding stock.

It would help if we all began to set our own limits. This might be: for every 20 crabs, sea eggs (urchins) or carnivorous snails (whelks) you find on a shore you should only take one. If you cannot find 20 there, don't take any. If the crab, urchin and whelk numbers get too low they will never have a chance to mate and breed and in three or four years there will be none at all. None of us want that.