Their stories will never be fully known.

Driven by conflict, poverty, famine or just a better life, over 4,000 migrants have died so far this year while making their journeys, a new tally from the Geneva-based International Organization for Migration finds.

The grim numbers are outlined the organization's new study, titled Fatal Journeys: Tracking Lives Lost During Migration (pdf), and compiled under IOM's Missing Migrants Project.

Going back to 2000, IOM states that the number of migrants that have perished is over 40,000.

Despite the high figures—which the organization says could be vast underestimates—the report details how this group of people remains quite invisible, as they often need to make clandestine journeys for their own safety. But contributing to the invisibility of this epidemic is the fact that there is a dearth of data on these deaths, with no global-level organization tallying the statistic in border areas, and many national governments offer little data on the deaths.

That stands in contrast to the vast money and efforts spent on border controls, the group adds.

"Although vast sums of money are spent collecting migration and border control data, very few agencies collect and publish data on migrant deaths," stated IOM Head of Research Frank Laczko.

The Mediterranean Sea has been the site of the vast majority of migrant deaths so far this year, accounting for 75 percent of the fatalities. Most of those migrants came from Syria, Palestine, Egypt and the Horn of Africa, many of whom were fleeing conflict.

The report includes the many migrants making the journey between Mexico and the United States as well, making up roughly six percent of the migrants deaths so far this year. Looking back to 2000, the study finds that nearly 6,000 migrant deaths have occurred along this border region.

Better data on these deaths is needed, IOM states, to highlight the immensity of the problem.

"Our message is blunt: migrants are dying who need not," IOM Director General William Lacy Swing said in a press statement. "It is time to do more than count the number of victims. It is time to engage the world to stop this violence against desperate migrants."