Rubbishing the ocean

Forest and Bird, Volume 18, Issue 4, 1 November 1987, Page 25

Rubbishing the ocean

by Dr

Martin Cawthorn

The problem of plastic debris

he whale, a juvenile minke, died soon after it was found stranded on the coast of Palliser Bay, east of Wellington. Despite repeated efforts by locals and Ministry of Agriculture staff to return it to the safety of deep water, the distressed whale could not be rescued. When I conducted a post-mortem of the thin and emaciated whale I found a polythene bag stuck in its oesophagus. Minke whales are known to be attracted to ships at sea and this curiosity may, in part, be responsible for the reports of them eating plastic debris thrown from fishing boats. Again at Cape Palliser a fur seal was seen with plastic strapping stuck around its neck. It had apparently picked up the loop when young and, as it grew, the ‘collar’ tightened, gradually cutting through the fur, skin and blubber, until it was scraping against the muscle tissue underneath. The young animal was emaciated and in poor condition. Such sad occurrences are a telling testament to the effect that one of the so-called benefits of the modern age — plastic — is having upon the environment, especially the marine environment. It appears in a variety of forms — from virgin plastic granules, polythene films and bags, detergent and other containers, chunks of polystyrene, lost or discarded monofilament and polypropylene fishing nets and floats, to synthetic strappings and ropes. A single species, the North Pacific fur seal, is estimated to be losing as many as 50,000 animals a year through being entangled in such rubbish. Anywhere between 300,000 and 700,000 seabirds a year are being killed. The tide of plastic garbage began to surge just after World War II, and the boom in commercial fishing since the 1960s has seen more and more gear either abandoned or lost. Packaging of all sorts is plastic and popular both because of its durability and low cost. For example, the cost of manilla envelopes is almost twice as high as polythene.

Staggering figures

Worldwide, the figures are staggering. In 1975 alone, the world’s fishing fleet is estimated to have dumped about 23,600 tonnes of synthetic packaging bands and material as well as 135,400 tonnes of plastic fishing gear into the sea (National Academy of Sciences 1975). It is not just the fishing indus-

try which is at fault. As much as 6.5 million tonnes of solid waste comes from the world’s merchant fleets. The above figures do not include the rubbish dumped by the world’s navies or pleasure craft. The best evidence of the plastics pollution problem can be found in the North Pacific. There, each night, Japanese, Taiwanese and Korean fishermen set out their thirteen-km-long, eight-metre-deep nets, with weights at the bottom and floats at the top. In all, the night’s work stretches 32,000 km of invisible curtains of net. Each morning, when the nets are retrieved, an average of 16 km of netting escapes detection. These nets are worth thousands of dollars and represent a major financial setback should they be lost. Such ‘ghost’ nets are a hazard not only to marine mammals but also to ships at sea. Ironically, ten times more northern fur seals are killed each year

in the nets than are killed in the hunts opposed by animal-rights groups. Terns and other small migratory birds have been found with virgin plastic granules in their guts. It is thought they pick these up in mistake for food found at the sea surface. It has been estimated that more than 1000 tonnes of similar granules or pellets are scattered along New Zealand's coasts. While plastic pollution is obviously a greater problem elsewhere, nevertheless it has been responsible for a number of unpleasant incidents here — not to mention the unsightliness of our coastlines littered with such material. The following are just a few examples of incidents I have observed or have had reported to me.

Seals

The first record of an entangled fur seal was made in 1975, and collared animals have been sighted regularly since then. Polypropylene strapping was first introduced into New Zealand in 1969. This tough, buoyant material is generally coloured light blue and is fastened around a package either by heat sealing or with a mechanical metal crimp. It appears to be common practice at sea to slip the loop of strapping off the end of the package rather than cut if free, and the loop is then cast overboard along with other ship's garbage. Unfortunately for their own safety, marine mammals are both irrepressibly playful and curious. Fur seals are attracted to floating debris and will dive and roll about in it as they do when swimming in kelp. When playing with rings of plastic strapping they can readily slip their heads through the loop as the lie of the fur allows the ring to pass unimpeded around the neck. However, the long guard hairs, like barbs, prevent the loop being slipped off. Recently two fur seals at Cape Palliser, three at Open Bay Islands in Jacksons Bay, one at Kaikoura and one at Taiaroa Heads were seen with plastic strapping around their necks. Unless entangled seals can either free themselves or else be freed of similar tight collars, they will most likely die a slow death from strangulation, starvation, drowning or infection. One of the most chilling prospects is that when an entangled seal dies and decomposes, the indestructible strapping band that contributed to its death is free to be picked up by any other seal, with the same

ghastly consequences. Seals and sea lions have been observed from Campbell Island and the Auckland Islands to as far north as Banks Peninsula with lengths of netting about their necks. At the Auckland Islands, a young sea lion was spotted with about three metres of monofilament line and swivels, thought to be from a squid jigger, wrapped so tightly around its neck that the skin and subcutaneous tissues were severed. Anecdotal evidence from the United States is gruesome. ‘‘I observed a sea lion with a net fragment so deep in its tissues that the net had cut through skin, blubber, and muscle and had actually cut open the trachea," Rich Tinney of the Centre for Environmental Education told a congressional committee. ‘‘The animal was incapable of diving for food because water would enter its throat through the opening cut by the net."

Whales and Dolphins

Whales and dolphins have frequently become entangled in large set nets, but not in New Zealand because of the absence of this type of fishing here. However, the extensive use of floating synthetic buoylines on rock lobster pots and deep sea nets has resulted in the fouling of at least two whales in recent times. In 1979 an orca was discovered by fishermen in a distressed state entangled in ropes and floats in the eastern Bay of Plenty.

In February 1984 a 10-metre juvenile male southern right whale became stranded just north of Banks Peninsula. It died soon after stranding and was found to have a long length of prolypropylene rope, with a small polystyrene buoy attached, wrapped around its tail. The rope had cut 20 cm into the leading edges of both flukes. Around Banks Peninsula, gill netting is known to kill approximately 10-15 percent of the local Hector’s dolphin population a year (see ‘‘The Down Under Dolphin’’ article page 30 this issue).

Turtles

Although turtles are uncommon visitors to New Zealand, they are not rare. In the summer of 1979-80 six leatherback turtles reached the country, one of which beached itself near Whakatane. Soon after coming ashore the turtle died and a post mortem revealed the oesophagus packed with polythene bread bags. It is thought that turtles regularly mistake the bags for their favourite food, jellyfish.

No simple solutions

There are no simple solutions to the problem. However, a start has been made. In November 1984 a workshop on the fate and impact of marine debris was held in Honolulu and attracted participants from New Zealand, the United States, Japan, China, Canada and West Germany. One approach is to work through the International Convention for the Prevention of Pollution from Ships (MARPOL). It contains a provision that prohibits ‘‘the disposal into the sea of all plastics, including but not limited to synthetic fishing nets and plastic garbage bags"’. This has not yet come into force as only 27 nations have ratified it. However, it is not

expected to take long before it becomes enforceable. In the United States a host of environmental groups have formed an association called the Entanglement Network, which sends out a newsletter and coordinates pressure groups to deal with the problem. Of course, laws can only accomplish so much. In the final analysis, responsible housekeeping by everyone is the only way to avoid unnecessary death to wildlife, not only in New Zealand but throughout the world. Martin Cawthorn is a biologist who has had extensive experience in New Zealand’s outlying islands and has represented New Zealand on the Scientific Committee of the International Whaling Commission. Formerly with Fisheries Research Division, he now works for the Department of Conservation, which has undertaken responsibility for marine mammals.

More garbage than fish?

Mize researchers estimate that the amount of garbage placed in the oceans each year now outweighs the fish harvest by three to one. Much of the trash consists of plastic which will not rot. The accumulation of plastic is already a hazard to marine life and the problem is getting worse. The state of California may soon take steps to ensure plastic containers are biodegradable. One bill now before the state legislature calls for a survey by public bodies to determine the extent of damage. They will also be asked to make recommendations on the clean up of coastal waters. Legislation has been introduced in the US Congress seeking better control over the disposal of plastics at sea. The measure would cut future dumping but not reduce existing plastic waste. From Fishing News International, June 1987.