TLDR, no one wants to fund a GPS tagging operating for European and American eels (that are a crop to be harvested), it was attempted in the 2010's but the tags

TLDR, no one wants to fund a GPS tagging operating for European and American eels (that are a crop to be harvested), it was attempted in the 2010's but the tags fell off before they got close to the spawning grounds in the Sargasso Sea. The Japanese have already done this for their native eels and know the full life cycle for their population of eels. This is important because then one knows more clearly if the species is in danger of being overfished.