Growth patterns and age validation from otolith ring deposition in New Zealand longfin eels Anguilla dieffenbachii recaptured after 10 years at large

Published source details Beentjes M.P. & Jellyman D.J. (2015) Growth patterns and age validation from otolith ring deposition in New Zealand longfin eels Anguilla dieffenbachii recaptured after 10 years at large. Journal of Fish Biology, 86, 924-939.
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This study is summarised as evidence for the following.

	Action	Category
	Translocate wild eels to re-establish or boost native populations (‘stocking’ or ‘restocking’) Action Link

Translocate wild eels to re-establish or boost native populations (‘stocking’ or ‘restocking’)

A before-and-after study in 1998 and 2008 in a lake in Otago region, New Zealand (Beentjes & Jellyman 2015) found that translocated wild longfin eels Anguilla dieffenbachii were recaptured in low numbers, and they grew faster and were in better condition than before translocation. Of 2,010 translocated, tagged eels, 79 (4%) were recaptured 10 years later. During 10 years after release, translocated eels grew at faster rates (average 3.7 cm/year) and were in significantly better condition (data reported as condition factor) than before translocation (average 2.4 cm/year). Growth rates increased after translocation and remained high for 4–5 years before declining (see paper for details). On average, eels were larger after 10 years (total length: 77 cm, body mass: 1,462 g) than before translocation (42 cm, 173 g), although the difference was not statistically tested. In February 1998, approximately 9,500 juvenile longfin eels were caught by commercial fishers in the tidal reaches of a river. Captured eels were transported 200 km upstream to a lake, of which 2,010 were tagged, weighed and measured before release. During one night in 2008, 399 eels were recaptured in fyke nets by a commercial eel fisher, 79 of which (all females) had tags. Condition, length and body mass were measured for all 79 recaptured tagged eels. Otoliths were examined for 76 recaptured tagged eels to determine changes in growth rate.

(Summarised by: Vanessa Cutts)