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

Abstract

The arrival season of glass eels of both New Zealand species of freshwater eel, the short‐finned eel (Anguilla australis (Richardson)) and the longfmned eel (A. dieffenbachii (Gray)), was studied by electric fishing of 13 streams/rivers throughout east and west coasts of both North and South Islands at 14‐day intervals. Sites were usually located at the most downstream riffle exposed at low tide, and sampled by single‐pass electro fishing. The species composition was dominated by shortfins, with exceptions being west coast sites, one in the North Island and two in the South Island. From a comparison 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 eels were defined and densities of these compared to show seasonal arrival patterns—densities were generally low in August, highest in September‐October, and declined during November‐December. Patterns of arrival varied from almost continuous in some streams to “intermittent” in others. Longfmned glass 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.

Keywords:

• glass eels
• arrival times
• pigmentation
• riffles
• species proportions