Complex sentence: In 2006 US officials say they detected three; in 2008 they were spotting an average of ten per month, but only one out of ten was seized, as their crews scuttle them upon interception and they sink within a minute or so.
Split into simpler sentences: In 2006 US officials say they detected three; in 2008 they were spotting an average of ten per month, but only one out of ten was intercepted. Few were seized as their crews scuttle them upon interception and they sink within a minute or so.