Age and growth of longfinned eels (Anguilla dieffenbachii) in pastoral and forested streams in the Waikato River basin, and in two hydroelectric lakes in the North Island, New Zealand

Abstract

Growth rates of New Zealand endemic longfinned eels (Anguilla dieffenbachii) from streams in pasture and indigenous forest, and from two hydroelectric lakes (Lakes Karapiro and Matahina), were estimated by otolith examination. Habitat-specific growth was further investigated with measurement of widths of annual bands in otoliths. Longfinned eels 170-1095 mm in length ranged between 4 and 60 years old (N = 252). Eels in pastoral streams grew faster (mean annual length increment ±95% CL = 24 ± 3 mm to 36 ± 7 mm) than eels in streams in indigenous forest (annual length increment 12 ± 2 mm to 15 ± 3 mm). Eels from the hydro-electric lakes had growth rates (annual length increments 19 ± 4 and 19 + 7 mm) similar to eels from pastoral streams. Otoliths of most eels showed annual band widths that indicated growth in several different habitats, corresponding to growth during upstream migration, and limited movement among adult habitats. Estimated age at marketable size (220 g) ranged between 7 and 26 years. The particularly slow growth of longfinned eels in streams in indigenous forest has considerable implications for management. The fast growth rates of eels in hydro-electric lakes provides

Evidence of different habitat use by New Zealand freshwater eels Anguilla australis and A. dieffenbachii, as revealed by otolith microchemistry

“…4). Previous studies have clearly shown that there is considerable variation in the growth rates of these 2 species of eels in various habitats at a number of locations in New Zealand (Chisnall 1989, Chisnall & Hicks 1993, Jellyman 1997, so based on the relatively small sample of this study, it is unclear if the growth rates of eels are typically higher in saline areas of Lake Ellesmere or not. What is evident, however, provided that these otolith age estimates are completely accurate in older eels (see Graynoth 1999), is that A. dieffenbachii, and to a lesser extent A. australis, appear to often reach ages of 30 to 50 yr in Lake Ellesmere and many freshwater habitats in New Zealand (Jellyman 1997).…”

“…Many individuals of A. dieffenbachii have been found to reach ages of 30 to 50 yr in streams and lakes in various areas of New Zealand, and even reach ages of as old as 90 yr in at least one lake, which may have unusually slow growth rates (Chisnall & Hicks 1993, Jellyman 1997. Most of the specimens of the 2 species we examined had growth rates within the same range (13 to 38 mm yr -1 ), except for a few females that had considerably higher growth rates (42 to 56 mm yr -1 ), and the average Sr:Ca values of these individuals were all within the higher range for each species (Fig.…”

Age validation and movement of freshwater eels (Anguilla dieffenbachiiandA. australis) in a New Zealand pastoral stream

“…Eels recaptured from pastoral Ahirau stream after 3 years, Al-3, longfinned eel (Anguilla dieffenbachii) at length 710 mm; and after 2 years, Bl-3, shortfinned eel (A. australis) at length 380 mm; Cl-3, longfinned eel from a similar pastoral stream kept in a tank for 15 months, length 338 mm. Chisnall & Hicks 1993). This difference highlights the variability in annual growth rates of individuals, but may also reflect the low sample size (N = 15) on which absolute growth measurements were based.…”

“…Growth rates of both New Zealand shortfinned eel, Anguilla australis, and longfinned eel, A. dieffenbachii, have been determined mostly by the reading of broken-and-burnt otoliths (Jellyman 1979;Todd 1980;Chisnall 1989;Chisnall & Hayes 1991;Chisnall & Hicks 1993). It is imperative that age determination techniques are validated to support such growth studies (e.g., Beamish & McFarlane 1983).…”

Does one size fit all? An evaluation of length–weight relationships for New Zealand's freshwater fish species

“…Whilst some New Zealand species have no published lengthÁweight data, more common species may have multiple LWR published (e.g. longfin eel, Jellyman 1974;Todd 1980;Chisnall 1989;Chisnall & Hicks 1993; and more), so knowing which equation to apply to a particular dataset can be problematic. Moreover, LWR could vary with abiotic or sexdependent factors so a secondary objective of the study was to evaluate if LWR differed between location or fish sex.…”