New Zealand Journal of Marine and Freshwater Research abstracts

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Factors influencing juvenile eel (Anguilla spp.) survival in lowland New Zealand streams

E. Graynoth

National Institute of Water and Atmospheric and Research Limited
P. O. Box 8602
Christchurch, New Zealand
email: e.graynoth@niwa.co.nz

R. I. C. C. Francis

National Institute of Water and Atmospheric and Research Limited
Private Bag 14901
Wellington, New Zealand

D. J. Jellyman

National Institute of Water and Atmospheric and Research Limited
P. O. Box 8602
Christchurch, New Zealand

Abstract Factors influencing the survival rates of juvenile longfin (Anguilla dieffenbachii) and shortfin eels (A. australis) (<400 mm total length) were investigated in three lowland New Zealand streams to manage and conserve eel stocks and fisheries. A survival model which included terms for recruitment, growth, up-stream movement, and vulnerability to sampling was fitted to 3 years of field data using a maximum likelihood approach. The proportion of 0+ glass eels of either species that survived to 400 mm in length was highly variable and ranged from 0.02% to 20% in different streams. Juvenile longfins generally had higher annual survival rates (0.78–0.96) than shortfins (0.43–0.90). Small eels (<150 mm) experienced low and variable survival rates (0.41–0.99) and although survival rates increased (0.80–1.00) for intermediate sized fish (150–299 mm) they then declined (0.23–0.85) for large juveniles (300–399 mm). The decline in survival rates for large juvenile eels supported a habitat bottleneck hypothesis and was possibly caused by competition from adult eels for limited areas of suitable cover (bank cover and debris clusters), although competition for food may also have been important.

Keywords habitat bottleneck hypothesis; maximum likelihood survival model; population dynamics; growth; recruitment; migration

New Zealand Journal of Marine and Freshwater Research, 2008, Vol. 42: 153–172
0028–8330/08/4202–0153     © The Royal Society of New Zealand 2008

M07120; Online publication date 29 April 2008
; Received 11 December 2007; accepted 10 March 2008

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