I think that is actually a huge factor, and one of the key obvious things that the OP overlooked. Latvia (and I suspect the whole Baltic region) was at an artificially inflated population peak when the Soviet Union collapsed. It was one of the most economically prosperous areas of the Soviet Union, and had huge Soviet military bases. Retirement on the Baltic coast was the dream for military brass as well as many other Soviets in the 80s. Additionally, the freedom movements and greater autonomy in the second half of the 80s may have attracted others from other Soviet Republics.

Since independence, and particularly recently, Russians (who once made up over half of Latvia's population) have left, and in many cases not been welcome to stay. One of the major tensions in Latvian politics today is the status of Russian Latvians.

With that backdrop (and given the other factors, such as migration to the rest of the EU) it isn't really that surprising that population levels are returning to that of the 60's.

They are the main component of the population loss. In 1989, the last census while in the USSR, the Baltics held a population of 1.7M ethnic Russians. After regaining independence, Estonia and Latvia denied citizenship to all post-1940 Russian immigrants (and their families). Today, only a million ethnic Russians remain. Some have been naturalized, but a lot have simply bailed, because the national populations are quite hostile to them.

It didn't happen and it does not contribute to the picture at all. People emigrated to the west (mostly Great Britain, Ireland and Spain), including the Russian speaking part.

The jump in the graph happened when the most recent economic crisis hit Baltic countries and drove their GDP roughly 20% down in a year.

Interestingly, according to http://im.kommersant.ru/ISSUES.PHOTO/CORP/2013/02/21/dsryu4...., the Baltics combined have the largest russian diaspora in the world, followed by USA, Germany and Israel. Probably due to the proximity and relative ease of emigration from Russia to the Baltic states.

If you read russian, here is a series of articles with advice on various emigration destinations. It's an interesting view into the current mindset there. http://www.kommersant.ru/doc/2132694