Eels face a number of dangers during their lives- like all animals. Quantifying these dangers, be they natural or anthropogenic, is not always easy or straightforward. Recently, we have been looking into eel mortality in the early phase of their oceanic migration. This is arguably the most dangerous time for silver eels: they are vulnerable to fisheries, to predators, to barriers across rivers or estuaries.
If you are interested to know more about this, click here: http://www.alphagalileo.org/ViewItem.aspx?ItemId=94661&CultureCode=en, where you will find a summary of some recently published research into the cause of mortality in the early migration phase. This is important work, because it helps to define our expectations for those eels that are allowed to escape from rivers and enter the sea- the eels that have a chance to reach the Sargasso and start the next generation.