Growth of juvenile eels ( Anguilla spp.) in lowland streams in New Zealand

Abstract

Growth rates of 2500 juvenile (<400 mm) shortfinned ( Anguilla australis) and longfinned eels ( A. dieffenbachii) in three lowland streams were estimated using burnt and stained otoliths. Growth rates averaged 17–27 mm per year in the first year of life but were then constant (9.4–19.8 mm per year) for the next 10 years. Rates were slow but comparable to those in similar forested and lowland streams elsewhere in New Zealand. Growth varied between individuals, waters and reaches. It was fastest (16.0 mm per year) in warm reaches (mean annual water temperatures >12.4 °C) with low eel densities (<14 g m 2). Growth was also positively correlated to the biomass of benthic macroinvertebrates. There were minor differences in growth between species and survey years. In the stream with the slowest growth rates, mature shortfinned males grew faster than immature eels. Parasite loads were low and considered unlikely to influence growth. It was concluded that, unless there is strong evidence of biphasic or asymptotic growth, simple linear growth equations, with a biologically realistic fixed intercept at age 0 or 1, should be used to describe the growth of juvenile and adult eels in New Zealand.