Since the mid-1950s, catches of sardines and other food species in one of the world's largest and most productive lakes have plummeted, prompting some environmentalists to point the finger at overfishing.

But the newest research, published Thursday in the British weekly Nature, says local fishermen are not to blame.

Instead, it points the finger at the greenhouse effect, a finding that strengthens accusations that reckless burning of fossil fuels is changing the Earth's weather system.

According to the study, warmer atmospheric temperatures have slackened the winds which blow during the cool May-September season, stir up the water layers and play a vital role in the lake's ecological health.

These strong south-to-north breezes haul algae and other nutrients from the lake's colder lower layers towards the warmer surface levels, thus providing food for the sardine population and other species.

University of Arizona researcher Catherine O'Reilly and colleagues looked at years of data about atmospheric and water temperatures and wind speed, and measured carbon isotope levels in cores drilled into the lake sediment.

The local temperature has risen by 0.5-0.7 Celsius (0.9-1.25 Fahrenheit) over the last half century -- a figure in line with a global increase of 0.4-0.8 Celsius (0.7-1.4 Fahrenheit) inflicted by global warming.

Wind velocities, meanwhile, have declined by 30 percent since the late 1970s, which is also considered a threshold when planetary temperatures suddenly shot up.

The core sediments were checked for levels of carbon isotopes, which give a reliable indicator of phytoplankton, the basic nutrient at the bottom of the food chain.

They were stable until the start of the 20th century, then started to decline, with a precipitant plunge from 1950 onwards.

That decline points to a fall of 20 percent in algae availability, a phenomenon that reverberates up the food chain and eventually translates into a fall of some 30 percent in fish yields, according to O'Reilly's estimate.

Scientists have already predicted East Africa's Great Lakes region faces a temperature increase of up to 1.7 Celsius (3.06 Fahrenheit) for over the next 80 years, and this suggests Tanganyika's food mechanism faces even worse damage.

"The human implications of such subtle, but progressive environmental changes are potentially dire in this densely populated region of the world, where large lakes are essential natural resources for regional economies," the authors say.

Tanganyika, a rift valley lake around 650 kilometers (400 miles) long by 50 kilometers (30 miles) wide and up to 1,470 metres (4,777 feet) deep, is bordered by Burundi, Tanzania, Zambia and the Democratic Republic of Congo.

It is the world's second deepest lake, the second largest by volume and a treasure store of biodiversity.

Fishing provides up to 40 percent of the animal protein supply for local people, but catches have fallen by between 30 and 50 percent, to 165,000 to 200,000 tonnes per year, since the late 1970s.

TERRA.WIRE