New Zealand longfin eels (Anguilla dieffenbachii) are remarkable animals facing an increasingly difficult future. They hatch in the tropical Southwest Pacific as tiny “glass eels,” drifting on ocean currents to Aotearoa before migrating upstream into rivers and lakes, where they spend decades growing and maturing. At the end of their lives, they undertake a final journey back to their ocean birthplace to breed, dying shortly afterward.
These migratory specialists depend on free passage through New Zealand’s wetlands to complete their life cycle. However, human activity has filled these waterways with barriers. Dams, hydroelectric turbines, weirs, culverts, and pumps can block, injure, or kill eels as they move upstream as juveniles or downstream as adults returning to the sea. Although longfin eels have evolved extraordinary abilities—climbing near-vertical rock faces and even travelling briefly over land to bypass natural obstacles—the sheer density of artificial barriers has cut off vast areas of their habitat.
Longfin eels breed only once, at the very end of their long lives, after travelling thousands of kilometres back to the tropical Pacific where they were born. The loss of even a single individual permanently reduces the breeding population, earning them the title as “endangered” in today’s modern world.