Tuna fishing, a major resource for the Ecuadorian economy, has been hit by the vagaries of weather in the Pacific waters believed to have been caused by the La Nina phenomenon, officials said.

Tuna yields in the first 10 months of 2010 dropped 16 percent because of disruptions to marine life caused by La Nina, data released by the Association of Tuna Companies from Ecuador indicated.

Exports of tuna and other salt water fish are a major source of foreign exchange revenue for Ecuador, an oil producer but still largely impoverished. More than 35 percent of Ecuador citizens eke out their livelihoods on fisheries or farms.

Atunec statistics showed the equatorial country's state-regulated Pacific fishing fleets caught 402,868 tons of tuna from January-October 2010, which was 16 percent less than the 478,633 tons landed in the same period in 2009.

Officials said the lower yield resulted from adverse weather conditions caused by La Nina, which creates the opposite of weather conditions usually associated with El Nino.

Ecuador, Chile and other Pacific Latin American countries experienced both La Nina and El Nino episodes in the past, sometimes with devastating results.

Scientists warned a new La Nina episode now in progress could last through the first several months of 2011. Business sources said the weather could greatly diminish Ecuador's earnings from tuna exports, estimated to be 70 percent of the country's foreign exchange earnings.

During the first 10 months of 2010, Ecuador's tuna exports fell both in volume and value compared to the previous year, the Central Bank of Ecuador said.

During last year, Ecuador exported nearly 125,000 tons of fresh, frozen and preserved tuna with a value of $472.9 million. This compared unfavorably with the 2009 statistics, when Ecuador exported 134,000 tons and earned $525.7 million.

The outlook for Ecuador's tuna output in the coming year remains uncertain, mainly because of La Nina, analysts said.

Strong La Nina episodes occurred during 1988-89. La Nina also caused damage in 1995 and again in 1999-2000. A minor La Nina episode affected the region in 2000 and 2001. A stronger La Nina phase developed in mid-2007 and went on through early 2009.

The U.S. National Oceanic and Atmospheric Administration said that moderate La Nina conditions that developed last year would likely continue at least into spring 2010.

The U.S. Climate Prediction Center is among regional environmental forecast services keenly watching developments in the Pacific, including the Ecuador coastline. La Nina effects cannot always be predictable. The flood in Pakistan last year was seen by scientists as a direct result of La Nina.