Geoff Thomas: Home comforts

Dolphins can easily become tangled in plastic or nets. Photo / Alan Gibson.

Many years ago trout fishing was often combined with providing housing. This may seem strange but it related to a custom to which young blokes adhered firmly and to some extent may be practised in certain circles today.

It involved establishing homes where koura, freshwater crayfish, could live.

The connection was with Pat Burstall, a former boss of the trout fishery in Rotorua. Pat was the conservator of wildlife for the district and, in those days, management of the trout fisheries came under the auspices of the Department of Internal Affairs.

Responsibility for freshwater gamefish has since been transferred to Fish and Game. But this was about 40 years ago, and Pat was a good mate as well as being the expert on the trout which we spent a lot of time and effort trying to extract from the water - pretty successfully, it should be said.

One day the discussion arose over the question of tin cans, which originally contained beer, and the disposal thereof. In those days it was common practice to punch a couple of holes in the empty cans and sink them in the lake. The theory was that, being made of tin, they would rust away without doing any harm to the underwater environment.

Pat said the cans actually provided excellent shelter for the koura, which from the point of view of the koura was a godsend as the trout loved to gorge on them.

So everybody was a winner. The young blokes had a good time, the boat was not cluttered with empty cans, and some koura were safe from the trout.

"But of course I shouldn't be promoting it publicly," Pat would say. He is long gone, and so is the practice of providing koura with housing in Lakes Tarawera and Taupo.

Attitudes towards dropping anything other than lures into the water have changed radically, and aluminium has replaced tin for making cans. Now the koura have to go back to hiding among the rocks and weed. That's a problem for them because there is insufficient light for weed below about 20m so the koura must resort to hiding in the mud.

It is not always successful as trout are often caught with their stomachs bulging with koura, and such fish are most welcome as their flesh will be firm and salmon-red from the calcium in the crayfish shells.

The cans will still be there, as overseas studies indicate tin cans take 50 years to break down even in seawater, which is more corrosive than lakewater. But aluminium cans last twice as long. Cardboard can last five months and fruit peel can drift around for as long as two years. Waxed cardboard milk cartons bob around for five years and cotton rags will last from one to five years.

But of all the material which is deposited in the sea, plastic is the real villain. Plastic bags can last 20 years and plastic cartons 80 years. The plastic ring which holds a six-pack of cans together takes 450 years to break down in the sea and fish and diving birds can easily become tangled, causing a slow death.

Turtles mistake plastic bags for their favourite food, jellyfish, and try to eat them.

Squid occur in vast numbers and provide a large part of the diet of many fish and animals such as dolphins and some whales. It is easy to imagine how a plastic bag drifting on the ocean currents can resemble a squid.

Huge quantities of such detritus gets washed up on beaches throughout the country, and when people get together for organised clean-ups they collect tonnes of material, much of it plastic.

Bags which contained bait are often blown off the back of a boat and are difficult to recover, but it's easy to prevent. So think twice before consigning anything to the water, whether it be fresh or salt. If fish shouldn't eat it, don't drop it.