12 Dec 2017

The ultimate irony: Cape Gannets, famed for their greed, are now starving

The word “gannet” is synonymous with gluttony - but lack of food is becoming a serious problem for the Cape Gannet. This year it has been uplisted from Vulnerable to Endangered due to population declines driven by depleted fish stocks.

Cape Gannet populations have fallen by more than half in the past 50 years © Mark Anderson
Cape Gannet populations have fallen by more than half in the past 50 years © Mark Anderson
By Christina Hagen, Marine Conservationist - BirdLife South Africa

The Afrikaans name for the Cape Gannet Morus capensis is “Malgas”, meaning “mad goose”. This makes sense when you see this large seabird on the ground. Their ungainly waddle, coupled with the difficulty they have in taking off when there isn’t any wind, does appear quite comical. But at sea and they are different birds entirely. When feeding, they plunge into the water like arrows, to depths of up to 20 metres.

But these seabirds, endemic to South Africa and Namibia, have recently been uplisted by BirdLife from Vulnerable to Endangered on the IUCN Red List.

Their population has dropped by more than half between 1956 and 2015, with the largest decreases occurring in Namibia.

The main cause is lack of food. In Namibia, overfishing of the gannets’ preferred prey, sardine and anchovy, caused the almost complete collapse of fish stocks in the 1960s, and they have yet to recover. In South Africa, the fish stocks have shifted from the West coast to the South and East.

 

The Cape Gannet's characteristic vertical dive © Philip Augustyn

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To make up for this lack, Cape Gannets congregate behind fishing vessels in search of Cape Hake and other sea floor-dwelling fish. The boats process their catch as they go, dumping the heads, tails and guts of the filleted fish overboard. But while there is evidence that eating hake discards has helped adult Cape Gannets maintain body weight and condition when they cannot find their natural food, it has also proved to be a double-edged sword.

Until very recently, thousands of seabirds, including gannets, were being accidentally tangled and drowned in the fishing gear of these vessels. Thanks to the work of the Albatross Task Force, these deaths have been dramatically reduced – by up to 80% in some fisheries.

However, because of their unique feeding style, some gannets still die from plunging vertically into the net, unable to avoid the allure of the fish so tantalisingly close by.

Another disadvantage of the hake discards is their energy content. Sardine and anchovy are full of omega-3 fatty acids that we humans are always being urged to eat. Hake discards are not. While a diet of “junk food” can sustain the adults, research has shown that chicks fed on hake discards grow more slowly and have a lower chance of survival than those fed on a more natural diet.

 

A Cape Gannet colony © Mark Anderson

 

And it’s not just sub-standard food the juveniles have to worry about. On Malgas Island in South Africa, food scarcity means that both parents are often forced to forage simultaneously, leaving the young unguarded and exposed to attacks from the Great White Pelican Pelecanus onocrotalus. To add to their struggle, Cape Gannets also face threats from oil spills in an increasingly active shipping region at the southern tip of Africa. In 1993 one such incident killed 5,000 Cape Gannet in one go. And in the northernmost part of their range in Angola, there are reports of people hunting gannets for food – the eaters are becoming the eaten.

In 1993 one oil spill killed 5,000 Cape Gannet

In characteristically undignified style, Cape Gannets make their nests using their own guano - so excessive guano harvesting for fertiliser may also be decreasing their breeding succes, as it inhibits some birds from laying.

BirdLife South Africa is currently working with the government and fishing industry to ensure the changed fish distribution is taken into account. Other researchers are working towards identifying and protecting important foraging areas for gannets.  But one thing is for sure: conservation action needs to be ramped up if we are to prevent the world’s most notorious glutton from starving.

 

 

This story is part of the Red List 2017 bird update - click for more