Upstream and Downstream Passage of Eels in New Zealand, 20 Years on – Lessons Learned

Since about 1993 there has been increasing efforts made in New Zealand to provide upstream passage for shortfin (Anguilla australis) and longfin eels (A. dieffenbachii) at hydro-electric dams scattered around the country. Most sites now operate some form of upstream passage mitigation activity with fourteen sites currently providing annual records. The numbers of elvers using these upstream transfer facilities peaked at over 10 million nationwide during the 2012-13 migration season, with numbers varying markedly between seasons and sites. Species composition has also varied markedly between seasons and sites. Because of the variation observed in the age of elvers arriving at each sites, nationwide trends in recruitment and the underlying causes for the variation observed have been difficult to discern. What is clear however is that the mitigation activities have re-established eel populations upstream of these barriers, and in some cases have created new fisheries. There is now a concentrated effort at some locations to provide downstream passage for the adults. The success of the solutions installed to date has been variable, and more research is required to determine their effectiveness.