Seasonal arrival patterns of juvenile freshwater eels (Anguilla spp.) in New Zealand

The arrival season of glass eels of both New Zealand species of freshwater eel, the shortfinned eel (Anguilla australis (Richardson)) and the longfinn ed eel (A. dieffenbachii (Gray)), was studied by electric fishing of 13 str eams/rivers throughout east and west coasts of both North and South Islands at 14-day intervals. Sites were usually located at the most downstream rif fle exposed at low tide, and sampled by single-pass electrofishing. The spe cies composition was dominated by shortfins, with exceptions being west coa st sites, one in the North Island and two in the South Island. From a compa rison of species proportions in adjacent catchments, it was concluded that glass eels make choices about entry in particular water-types. As the stage of pigmentation advanced during the arrival season, "early stage" glass ee ls were defined and densities of these compared to show seasonal arrival pa tterns-densities were generally low in August, highest in September-October , and declined during November-December. Patterns of arrival varied fr-om a lmost continuous in some streams to "intermittent" in others. Longfinned gl ass eels preceded shortfinned glass eels, and probably arrived in the North Island before the South Island; shortfinned glass eels showed the opposite trend. Possible migration routes to New Zealand are discussed.