New Zealand Journal of Marine and Freshwater Research abstracts
Age, growth, and condition of freshwater eels {Anguilla sp.) in backwaters of the lower Waikato River, New Zealand
BENJAMIN L. CfflSNALL
Department of Biological Sciences
University of Waikato
Private Bag, Hamilton, New Zealand
Present address: Freshwater Fisheries Research Centre, Ministry of Agriculture and Fisheries P.O. Box 6016 Rotorua, New Zealand
Abstract Growth rates of both species of New Zealand freshwater eel,
Anguilla australis (shortfinned eel) and
A. dieffenbachii (longfinned eel), in backwaters of the lower Waikato River were determined from otolith examination. Condition factors (CF) were calculated for isometric growth on a restricted length range (350-500 mm). Annual length increments for eels less than 500 mm were 13 mm and 15 mm for shortfinned and longfinned eels, respectively. Shortfinned eels grew at rates of between 2 and6 mm per month in summer (December 1984-March 1985), and older eels (10-15 years) grew faster than younger eels in autumn (March-June) (5.0-6.5 mm per month). There was a decline in the mean length of most age classes of shortfinned eel samples taken in July and October. This was probably a result of shrinkage during winter, compounded by the annual formation of new hyaline rings in otoliths during September-October, which lowered mean length-at-age. Backwater shortfinned eels younger than 20 years were smaller than shortfinned eels from nearby Lake Waikare, and backwater longfinned eels younger than 17 years grew slower than those from the Waikato River mainstem. Mean condition of backwater shortfinned eels (CF = 1.97) was similar to the condition of shortfinned eels from Lake Waikare. The mean condition of backwater longfinned eels (CF=2.28) was similar to that of longfinned eels from the Waikato River mainstem.
Keywords Anguilla australis; Anguilla dieffenbachii; Anguillidae; age; growth; condition; commercial fishing; Waikato River; New Zealand
New Zealand Journal of Marine and Freshwater Research, 1989, Vol. 23: 459-465 0028-8330/2304-0459$2.50/0 © Crown copyright 1989 Received 6 March 1989; accepted 1 June 1989
PDF file of entire paper: medium quality (534K); (scanned from paper original: notes about this process)
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