Environmental Implications

There can be little question that the presence of plastic debris and other persistent synthetic litter on remote and wilderness beaches, let alone shores close to metropolitan centres, is aesthetically offensive. While larger items are a particular eyesore to most observers, the environmental hazards and problems they and less conspicuous smaller fragments present are not so clearly manifest.

Entanglements

There are numerous reports of marine mammals, reptiles, birds and fish becoming entangled in marine litter, particularly abandoned netting, strapping loops and recently the plastic carrying yokes for six-packs. Marine mammals appear particularly susceptible because of their well known curiosity in, and attraction to, floating rubbish of all kinds. The problem has been widely publicized for the lucrative fishing grounds of the North Pacific and Alaska where the annual mortality of northern fur seals has been estimated to exceed 50,000 (Coleman and Wehl, 1984; Wallace, 1985). Ultimate death comes from starvation, mutilation, laceration and infection, drowning or increased vulnerability to predation (e.g., Fowler, 1987; Laist, 1987). There are also reports of rope and plastic neck collars on Cape fur seals (Arctocephalus pusillus) from Southern Africa (Shaughnessy, 1980) and Antarctic fur seals (Arctocephalus gazella) from South Georgia (Bonner and McCann, 1982).

There is increasing evidence that the same problems are developing in the waters around New Zealand and its Subantarctic islands. Since an initial observation in 1975, there have been increasingly frequent reports of New Zealand fur seals (Arctocephalus forsteri) and the Hooker's sea lion (Phocarctos hookeri) which is endemic from Cook Strait to Campbell Island and the Auckland Islands, being snared in netting (Fig. 11.8) or collared by plastic loops (see Cawthorn, 1985,1987). Both species are acknowledged to be endangered. Some indication of the magnitude of the threat is evident in Dawson and Slooten's (1987) claim that accidental gillnet entanglement annually kills 10-15% of Hector's dolphins (Cephalorhynchus hectori) in the Banks Peninsula area; they have estimated that the entire population of this endemic species is only 3-4,000 individuals. There are few records of cetacean entanglement around New Zealand waters, probably because large set nets and traps are not a feature of the local inshore fishery. Cawthron (1985) has reported on two recent instances which at the time received reasonably wide publicity. In 1979, a distressed killer whale (Orcinus orca) fouled by ropes and floats was observed in the eastern Bay of Plenty. In February 1984, a juvenile male southern right whale (Eubalaena australis), which died shortly after stranding north of Banks Peninsula, was found to have a lengthy piece of polypropylene rope and attached small polystyrene buoy, wrapped around its tail stock. Caw-thorn (1985) noted that the rope had cut 200 mm into the leading edges of both flukes.

Fig. 11.8. Hooker's sea lion (Phocarctos hookeri) entangled in netting on deck of trawler near the Auckland Islands (Photo : M. Donoghue, World Wildlife Fund).

For the Subantarctic islands, as well as mainland New Zealand, Cawthron (1985) identified hard, embossed polypropylene strapping loops and crimped bands as constituting a particular hazard to seals and sea lions. He made a general appeal for them to be cut or severed before being discarded rather than being simply slipped off any package. Subsequent observations suggest that this plea is being heeded for very few uncut straps were seen in a 1985 survey of the southern regions (Gregory, 1987).

Seabirds of the New Zealand region are also at risk as recent illustrations in Cawthorn (1987) would attest. He recorded the death of a black-backed gull

(Larus dominicanus) following capture in a plastic six-pack carrying yoke, and also the drowning of 14 spotted shags in an Otago Harbour set net. Incidental snaring of both birds and fish by ghost-fishing abandoned or derelict drift nets is a further issue that needs to be addressed (cf. Mattlin and Cawthorn, 1986).

The magnitude of the entanglement mortality problem for the Subantarctic islands is impossible to assess. It has been estimated that up to 130 sea lions die through drowning in trawl nets each year (Donoghue, 1987). However, no animals which had been mutilated through entrapment, snared or collared were sighted during an extensive survey in 1985 (Gregory, 1987), although several bird carcasses entrapped in monofilament fishing line were noted on the Bounty Islands.

Encrustations

Plastics and other synthetic litter afloat on the global ocean afford an important and expanding ecologic niche for a pseudoplanktonic biota (Winston, 1982). Many taxa, including foraminiferids, hydroids, bryozoans, calcareous annelid tubes, barnacles and coralline algae, as well as diatoms and bacteria are known to encrust or attach to floating plastic (see Gregory, 1983). In surveys of Southern Ocean waters and shores between New Zealand and the Ross Sea, the only encrusters so far identified have been goose barnacles and "Spirorbis" on larger plastic objects (Gregory, 1987). No biota have been identified on any of those few virgin plastic granules collected south of New Zealand.

Patches of lichen, identified as Canderlariella sp. and Lecanora dispersa Agg. by C. Meurk (pers. comm.) encrust several large pieces of abraded dense plastic from broken fishing floats, which had been cast-up high and dry beyond the reach of waves on the northeast shore of Enderby Island (Auckland Islands). These are taxa characteristic of rocky, Subantarctic island, coastal environments.

Ingestion

Ingestion of plastic pollutants has been recorded in at least 50 species of marine birds worldwide (Day et al., 1985). Although there are several records from Australasian waters and elsewhere around the Southern Ocean (Table 11.2), where there is evidence for prions ingesting plastics from the early 1960s (Harper and Fowler, 1987), quantity and frequency for the region do not yet seem to have reached the Northern Hemisphere levels reported in the comprehensive review of Day et al. (1985). Plastic objects have been identified in the gizzards and proven-triculi of birds examined but never in the intestinal tract or faeces (Day et al., 1985) which is surprising because some prions can void intact fish vertebrae with no apparent difficulty (Harper and Fowler, 1987). In a review of seabird conservation in the New Zealand region, Robertson and Bell (1984) concluded that the ingestion of rubbish, plastics and plastic pellets was not a significant problem.

The small mostly colourless, virgin or raw polyethylene granules which are so abundant on New Zealand beaches (Gregory, 1978) and widely dispersed across the Southern Ocean (Gregory et al., 1984b; Gregory, 1987) are the most commonly

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