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

Abstract

The arrival season of glass eels of both New Zealand species of freshwater eel, the shortfinned 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- M98073

Dispersal pattern of glass eel stage of Anguilla australis revealed by otolith growth increments

“…To validate this possible route, an intensive and successive collection of leptocephali would be required. Likewise, data on ages of glass eels from the north of New Zealand would help confirm whether recruitment to New Zealand is from the north, as suggested by Jellyman (1987) and Jellyman et al (1999).…”

Spatial and temporal variability in length of glass eels (Anguillaspp.) in New Zealand

“…Glass eels are the life-history stage that arrives in fresh water; arrival times of the two main New Zealand species (Anguilla australis (Richardson) and A. dieffenbachii (Gray)) are generally well documented (Jellyman 1977(Jellyman , 1979(Jellyman , 1987Jellyman et al 1999), and peak between September and October. Upstream migration has a predictable relationship with lunar phase (Jellyman 1979), and size of migration is proportional to the New Zealand Journal of Marine and Freshwater Research, 2002, Vol.…”

“…Jellyman et al (1999) examined the seasonal arrival times of glass eels at 13 locations within both islands of New Zealand between 1995 and 1997. The present paper analyses annual trends in the length and pigmentation stage of glass eels between 1995 and 1998, and tests the hypotheses that significant differences in the length of each species occurs between seasons, regions, and years.…”

Confirmation of morphological differences betweenAnguilla australis australisandA. australis schmidtii

“…Subsequently, Dijkstra & Jellyman (1999) sequenced the control region (611 base pairs) of the mitochondrial DNA (mtDNA) of specimens identified as A. australis australis and A. australis schmidtii, and concluded the two subspecies share a common gene pool. Based on the genetic studies, several recent ecological papers (Aoyama et al 1999;Arai et al 1999;Jellyman et al 1999;Marui et al 2001 ;Shiao et al 2001) eels from Australia and New Zealand as A. australis without commenting on morphological differences between the populations. Jellyman (1987) recognised seasonally consistent differences in number of vertebrae of the glass eels that recruited to New Zealand, and speculated that variations in water temperature during the hatching of eggs could account for the differences.…”