Messages from birds
Top: Dead albatross heads returned by a longlining vessel operating in South African waters. Albatrosses are killed by longlining fishing vessels that do not implement measures to protect the birds. Photograph: Peter Ryan
Above: This video still from a night-time camera shows house mice gathering around a large Tristan albatross (Diomedea dabbenena) chick to begin feeding on wounds they open up on the bird’s body, literally eating it alive. Photograph: Angel/Wanless
Southern giant petrel (Macronectes giganteus) in flight. Photograph: Peter Ryan
Above: A tori or bird-scaring line attached to a trawler helps to keep seabirds away from the trawl cables that can drag them under water. Photograph: Peter Ryan
when the baited hooks are deployed from the vessel. Hundreds of thousands of seabirds are estimated to be killed in this way around the world each year. Samantha Petersen works at designing and implementing measures to protect the birds – such as weighting lines to make sure they sink out of reach of seabirds faster. Efforts such as hers have significantly reduced bycatch in the toothfish and hake fisheries, but vessels
Assessing fishing impacts on seabirds Estimating the numbers of birds killed by fisheries depends largely on independent fishery observers recording bird mortalities. ■ For longline fisheries – calculations are fairly straightforward. Most birds killed are hauled on deck as part of the catch. The number killed can be extrapolated to the entire fishing fleet’s effort from what has been observed, though accuracy depends on the coverage by observers. ■ For collisions with trawl wires – estimates are more difficult, as few of the birds killed are brought on board. Dedicated observers watch or videotape the warps to record the number of collisions and the proportion of birds that fail to surface after being dragged under water. The work is labour-intensive, and only a small fraction of fishing effort can be observed, so estimates of total mortality are crude. In both cases, extrapolations are made more accurate by taking into account other factors affecting the likelihood of birds being caught (such as season, and time of setting or state of the moon for longlines, and whether or not offal is being discharged from trawlers).
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targeting tunas and other large pelagic fish still cause problems. The tuna fisheries’ longlines are designed to drift at a predetermined depth, so they can’t be weighted as heavily as lines targeting fish further down, such as hake and toothfish. So pelagic lines tend to remain close to the surface for longer, making it harder to keep baited hooks away from the seabirds. In the last few years, trawl fisheries have been recognized as causing significant deaths among albatrosses. The birds collide with the trawl cables as the trawl net is being released, then they’re dragged under water and drowned. Extrapolation from the evidence suggests that the hake trawl fishery kills some 400 albatrosses each year in South African waters. Skippers, fishery observers, and compliance officers are helping with testing and implementing measures to avoid this problem – such as dragging devices close to the trawl cable to scare the birds away. These measures also help the trawl fishery to keep its Marine Stewardship Council certification as a fishery that’s harvested in a sustainable way and does not harm the ocean ecosystem. Further conservation dangers come from the predators that people have introduced to islands where seabirds breed. At Gough Island in the central South Atlantic, researchers Ross Wanless and others have found that introduced house mice are killing large numbers of seabird chicks, including those of the endangered Tristan albatross. The mice nibble at wounds they’ve opened up on the chicks and literally eat the birds alive. Even though the albatross chicks are about 200 times bigger than the mice, they don’t defend themselves because they’ve evolved in an environment that had no mammalian predators for millions of years before humans arrived. In normal conditions, at least 70% of albatross pairs would manage to raise a chick each breeding season, but in the areas where the mice now abound, fewer than 10% of Tristan albatross pairs manage to raise one. Biodiversity’s economic value Biodiversity and healthy ecosystems are linked with valuable goods and services to society, but politicians and decision-makers often ignore biodiversity conservation. Perhaps conservationists could communicate better the values of biodiversity in the currency of greatest relevance to politicians – its direct economic value. Jane Turpie’s research, for instance, integrates ecological, social, and economic knowledge to reveal the monetary value of various components of biodiversity and ecosystem function. Her projects evaluate individual ecosystems such as estuaries, national parks, and other protected areas, with a view to developing integrated conservation plans for local and national economies. One case study examined the Mngazana estuary in the Eastern Cape, which has the third largest mangrove forest in South Africa – a particularly endangered habitat type. Marketprice methods used information collected in