Fishing: Can the cans and store all rubbish

It is easy to imagine how a plastic bag drifting on the ocean currents can resemble a squid when located by the sonar of hunting mammals. Photo / 123RF

Many years ago, trout fishing was often combined with "housing construction". This may seem a little strange to modern aficionados but it related to a custom which young blokes adhered firmly to, and to some extent may be practised in certain circles today. It involved establishing estates in which koura could live.

Now, koura are freshwater crayfish and while the connection may appear tenuous, it was real, and it came from a former boss of the trout fishery in Rotorua.

Pat Burstall was the conservator of wildlife for the district, and in those days management of the trout fisheries came under the auspices of a government department — the Department of Internal Affairs. Responsibility for freshwater game fish has since been transferred to the Fish and Game structure.

But this was about 40 years ago, and Pat was a good mate as well as being the expert on the trout in the lakes which we spent a lot of time and effort trying to extract from the water; 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 from tin, they would break down and rust away without doing any harm to the underwater environment.

Pat pointed out that 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 the koura. So everybody was a winner. The young blokes had a good time, the boat was not cluttered with empty containers at the end of the day, and the koura were safe from the attentions of the trout.

"But of course I shouldn't be promoting it publicly," Pat would add with a grin.

He is long gone, and so is the practice of providing koura housing facilities in Lakes Tarawera and Taupo, particularly when the fishing was good.

Attitudes towards dropping anything other than lures into the water have changed radically, and aluminium has replaced tin for making cans.

Now the poor koura have to fare on their own and go back to hiding among the rocks and weed. It is obviously a problem for them, as divers report weed does not grow below about 20m as the light does not penetrate beyond that depth, so the koura must resort to hiding in the mud.

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

The cans will still be there, as overseas studies indicate tin cans take 50 years to break down in sea water, which is more corrosive than lake water.

But aluminium cans last twice as long underwater, up to 100 years, while paper will disappear in two to four weeks. Cardboard lasts up to five months while 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 up to 20 years in the water and plastic cartons up to 80 years. The plastic ring which holds a six-pack of cans together takes 450 years to break down in the sea, and they can easily become entangled around the bodies of diving birds or fish, causing a slow death. Some creatures such as turtles mistake plastic bags for their favourite food, jellyfish, and eat them.

Squid occur in vast numbers and provide a large part of the diet of many fish and animals like dolphins and whales.

It is easy to imagine how a plastic bag drifting on the ocean currents can resemble a squid when located by the sonar of hunting mammals.

Huge quantities of such detritus is washed up on ocean-facing beaches all around the country, and when people get together for organised clean-up operations they collect tonnes of material, mainly containers and other forms of plastic products.

Bags which contained bait are often blown off the back of a boat and are difficult to recover, but can be easily secured with a little foresight.

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.

Freshwater
The record high level of the Rotorua lakes after record rainfall during winter and spring could have an unexpected benefit for anglers later this season. The lakes are so high that the some jetties and launching ramps are under water.

Much of the trout food is generated in the margins, and the water has submerged grassy areas and penetrated into the surrounding bush lining many of the lakes' shorelines.

This can create a bonus for the trout in terms of the food which is inundated, like insects and worms. But smelt and koura can also take advantage of the rich pickings, and the result of this bounty may be trout growing to good sizes and excellent condition. This is particularly relevant in fisheries which contain brown trout, as they are accustomed to foraging in the shallows, mainly at night.

Tip of the week

When setting nets, always ensure the net is well secured at both ends. Nets which have broken free and drift around the oceans are called "ghost nets" and when this happens on a commercial scale, the nets will continue killing fish for many years. Dead fish will also attract predators such as sharks, which in turn become entangled and die.

Bite times

Bite times are 5.55am and 6.20pm tomorrow and 6.40am and 7.05pm on Sunday. More fishing action can be found at GTTackle.co.nz.