Fishermen for eons have used seabirds to identify fish hotspots. Although trawlermen are these days armed with hi-tech equipment to identify shoals below the ocean’s surface, out on the high seas they still look to the horizon to see how gannets and short-tailed shearwaters are performing.
In shallower, more sheltered waters the recreational fishermen do the same. They usually watch for crested terns which are adept at spotting fish, before gathering to plunge into the water for a catch. Any day, of any week the recreational fishing columns across the nation’s press will read “sea bird activity pointed to rich fishing grounds”.
Seabirds, however, are assuming another role in how mankind interacts with the oceans. They have become poster children for the health of our oceans.
It only takes a stroll along a beach in Tasmania – any beach, however remote – to discover that our seas have become seriously polluted, and this pollution is taking its toll on seabirds.
What we mainly see washed up on the sand, or floating in deep ocean, is plastic which since its development, manufacture and use from the middle of the last century has built up on both land and sea in unimaginable quantities. On land it gets buried, at sea it is just left to float, resisting natural forces to break it down.
Seabirds confuse the plastic with fish, as do predator fish themselves and mammals higher up the food chain like dolphins and seals, and are poisoned or fatally injured.
It is birds, however, that are allowing scientists to quantify just what this level of pollution is having on the oceans.
The effects of plastics on albatrosses nesting and feeding in the waters off the islands of Hawaii – surrounded by the what is termed the Pacific Gyre of floating debris – has been well documented and now a scientist who has done much work in Tasmania has drawn attention to its menace across Australasian waters.
Jennifer Lavers, a research fellow in marine biology at Monash University, has been studying the effects of plastic on the flesh-footed shearwater (Puffinus carneipes). The species migrates across wide expanses of the Pacific and Indian Oceans but its main breeding grounds are on our doorstep – the largest population is on Lord Howe Island – with the remaining populations spread across south and western Australia and New Zealand. They are seen in Tasmanian waters but are not known to breed here.
Dr Lavers has been studying the shearwaters of Lord Howe Island and has established the levels of plastic pollution there are the worst in the world, and the shearwater is the most contaminated bird. The species is suffering a population collapse and Dr Lavers is now campaigning to have the flesh-footed shearwater – so called because of the colour of its webbed feet – declared a vulnerable species.
In a talk at the latest Birdlife Tasmania meeting, Dr Lavers said multiple factors – encroaching urbanisation, bycatch mortality in fisheries, and introduced predators – accounted for declines of seabirds across the world but emerging as the most serious threat to populations was the confronting issue of plastic pollution in the marine environment.
In an article published earlier this year on The Conversation academic website Dr Lavers said each day our oceans are fed by more than 20 million new plastic items – or more than 6 million tonnes per year. Wind and waves send this plastic around the globe, so that one country’s garbage washes up in another’s backyard.
Dr Lavers said she had found that 100 cent of shearwater chicks on Lord Howe Island contain large quantities of plastic, fed to them by their parents who mistake it for food. One dead chick she examined had more than 275 pieces of plastic in its stomach, equivalent to a human eating around 8kg of the stuff.
Closer to home in Tasmania, previous research has revealed that out of 200 short-tailed shearwaters examined in one study, 100 percent contained plastic.