Distribution And Sources

The amounts of seaborne plastic and other persistent synthetic litter being cast up on the larger Subantarctic islands are greatest on windward (western) shores such as North West Bay, Campbell Island, and Derry Castle Reef, Enderby Island, and least on leeward (eastern) shores (cf. Gregory, 1987). This same pattern is also evident around the semi-enclosed waters of Port Ross, Auckland Islands. Few littering items appear on the protected south facing sandy beach of Enderby Island. Across the harbour some 5 km to the southeast, litter concentrates on the narrow west-facing bouldery beach of Ewing Island, but it is not evident on its open-ocean eastern side. At the southern end of the Auckland Islands, plastic, wood and rubber items and other flotsam and jetsam are swept through Victoria Passage or blasted over Fairchilds Garden, Adams Island. It spreads eastwards in diminishing quantities along the shores of Carnley Harbour (Gregory, 1987).

The cliff-girt coasts of the smaller island groups (The Snares, Antipodes and Bounty Islands) provide little chance for litter accumulation and fewer for inspection. Where examined, only minor quantities, mostly chunks of foamed plastic and plastic strapping together with pieces of wood, cord and the rare fishing float, were identified (Gregory, 1987). Hoating debris of all kinds tends to be entrapped in surge pools and guts around all these islands. On the barren Bounty Islands, some items have been driven by wind, far above the wave-swept zone.

Today, apart from the permanent occupants of the meteorological station at the head of Perseverance Harbour, Campbell Island, the only human presence on these islands, which are otherwise nature reserves with restricted entry by permit, are occasional scientific parties who stay from several days to a month or more and sporadic day trippers from passing tourist vessels.

It follows that the plastics and other persistent litter on these shores are unlikely to have a local land-based origin or reflect casual visitors. Indeed, until quite recently, the meterorological station's residents dumped their domestic garbage directly into the waters of Perseverance Harbour and yet, apart from a couple of confectionary wrappers, no modern litter is to be seen on nearby shores — presumably the strong westerly winds carried this material out to sea (Gregory, 1987).

The character, composition and country of origin for the plastic and other persistent synthetic litter (Table 11.1), on these remote shores, suggest that it is introduced from commercial fishing activity around the region, with particular emphasis to be placed on the lucrative squid fishery centred close offshore around these islands. Several reports have drawn attention to the noticeable increase in materials of these kinds over the past decade or more, and which have accompanied expansion of the fishing industry in coastal and distant waters of New Zealand's Exclusive Economic Zone (e.g., Hayward, 1984; Ridgway and Glasby, 1984; Cawthorn, 1985; Mattlin and Cawthorn, 1986). There is conclusive evidence that some contamination of shores around Port Ross comes from domestic trash and broken fishing gear indiscriminately thrown overboard from vessels seeking haven from the stormy seas outside this harbour (Gregory, 1987; M.W. Cawthorn, pers. comm.).

Summary of numbers of those plastic items on New Zealand's Subantarctic island shores whose country of origin could be determined (for details see Gregory, 1987).

Locality Campbell Carnley Enderby and The

Island Harbour Ewing Islands Snares Total


Asia 12 8 11

United Kingdom 3 2 5

New Zealand 4 4

Australia 3 3

Spain 11 2

Bulgaria 1 1

France 1 1

Norway 1 1

Argentina 1 1

It is now recognized that enormous quantities of plastic and other persistent debris are afloat today across the global ocean (Laist, 1987; Pruter, 1987). It has been suggested by Horsman (1982) that there is a daily contribution of at least 600,000 plastic containers from merchant ships alone to the estimated 6.4 x 106 tonne yr1 that is dumped overboard worldwide (NAS, 1975). As a typical example, Merrell (1980) indicated that 1,635 tonne yr1 of fishing gear was being lost in waters off Alaska and that, on the island of Amchitka, this litter together with discarded garbage increased in quantity rapidly during 1972-82 (from 122 to 345 kg km"1 of beach) but this decreased by 1982 to 255 kg km"1 (Merrell, 1984).

Whilst it is clear that quantities of discarded fishing gear and other litter stranded on New Zealand's Subantarctic islands are not yet of the magnitude apparent on Northern Hemisphere shores adjacent to heavily fished areas, that is no reason for complacency. With expanding distant water fisheries all around the Southern Ocean, quantities of discarded fishing gear and other litter can only increase. Already significant amounts of this litter are being reported from amongst the wood and pumice strewn wrack of the South Shetland Island (Torres and Gajardo, 1985), the Falklands and South Georgia (Croxall et al., 1984), as well as Heard and Macquarie Islands (H.R. Burton, pers. comm.). Plastic objects, and other artefacts of local and distant origin, are also not uncommon on the shores of Prince Edward and Marion Islands as well as those of Gough, Tristan da Cunha and Inaccessible Islands in the African Sector of the Southern Ocean (Ryan, 1987a). Further evidence of this wide dispersal in the circumpolar current is the discovery of an Argentinian fishing float at The Snares Islands (C.M. Miskelly, pers. comm.), a large French plastic chemical container, possibly from Kerguelen, stranding on the sandy beach of North West Harbour, Campbell Island, and South African drift cards reaching Macquarie Island and New Zealand (Gregory, 1987).

From the numerous reports of Southern Ocean seabirds ingesting the small virgin plastic granules, as well as other plastics (Table 11.2), it is evident that these pollutants have wide circumpolar distribution, although not with the density found in the Northern Hemisphere (cf. Day et al., 1985). Seasonal migrants may bring some plastic granules with them from the North before feeding commences (e.g., Skira, 1986) but this is not likely to be a source of great importance (cf. Harper and Fowler, 1987).

From the data in Gregory et al. (1984b) and Gregory (1987), it is estimated that virgin plastic granules are dispersed with densities of 15-20 km2 across the remote higher latitude (45°-60°S) waters south of New Zealand. This figure is substantially less than that of 1,500-3,600 km2 recorded by Morris (1980) for the Cape Basin of the South Atlantic lying west of southern Africa, and a region also under the influence of the strong circum-Antarctic west wind drift, although at a lower latitude (c. 35°S). At > 10,000 km2 (Hauraki Gulf) and > 40,000 km 2 (Cook Strait), pellet densities for inshore New Zealand waters are considerably greater, whilst across the South Pacific Ocean north of New Zealand a figure of c. 1,000 km"2 is appropriate (unpubl. data).

Although the data base is inadequate, available evidence suggests there is a strong latitudinal gradient in the areal density distribution of virgin plastic granules in passing southwards from the southern Pacific and Atlantic (and ? Indian) Oceans (> 1,000 km 2) to the Southern Ocean (< 20 km 2). It is inferred (Gregory et al., 1984b) that the southward spread of plastic and other persistent synthetic pelagic debris is effectively arrested at the Polar Front, along which it tends to accumulate with other flotsam (Fig. 11.5). Drifting garbage is known to accumulate at the Humbolt Front off Valparaiso, Chile (Bourne and Clarke, 1984) and has been noted along windrows in the Hauraki Gulf, New Zealand (pers. observ.).

Ross Sea Beaches

Very minor amounts of seaborne man-made debris reach these shores and it is all demonstrably of local origin (Gregory et al., 1984b). The only material to be at all persistent is dressed lumber (Fig. 11.6), much of which appears to come from disintegrating cargo pallets. Exotic logs like those reaching Macquarie, South Sandwich and Campbell Islands (Barber et al., 1969; Smith, 1985; Gregory, 1987) are never seen. Netting, floats and other evidence of distant pelagic fishing activity have not been encountered (Gregory et al., 1984b). Apart from relics of the "Heroic" era spread about at Cape Evans, the most unsightly localities are dump sites at McMurdo Sound and Hallett Stations. Debris-laden, ice-bonded rafts calve from the former and join islands of inorganic waste dumped for disposal on annual sea ice. Sunken debris locally litters the seafloor and has had some detrimental impact on the benthic biota of McMurdo Sound (Dayton and Robil-liard, 1971). The rubbish dump of abandoned Hallett Station lies exposed at the foreshore and is today being eroded by ice push and wave action. Released debris

0 0

Post a comment