Enhanced growth of longfin eels, Anguilla dieffenbachii, transplanted into Lake Hawea, a high country lake in South Island, New Zealand

Lake Hawea was stocked with c. 9500 juvenile longfinned eels (Anguilla dieffenbachii Gray) (mean weight 173 g) from the lower Clutha River of which a subsample of 2010 was tagged with coded wire tags. Three years later, the eel population in Lake Hawea was sampled resulting in 216 recaptures of transferred eels of which 42 were tagged. Eels had grown an average of 14 cm and 325 g (all recaptures). Growth rate of tag-recaptures averaged 4.1 cm year(-1), was linear and faster than pre-transfer when it was 2.4 cm year(-1) (P < 0.01). Eels transferred into Lake Hawea experienced accelerated growth and increased condition ascribed to low density (density dependent) and abundant food. Eels dispersed throughout the lake, but density was highest adjacent to the Neck, the point of release. Eels caught outside the Neck were larger and in better condition than those inside the Neck-further evidence of density-dependent growth. Recaptured eels examined for sex were all females, indicating that either eels differentiated into females because density was low, or that males moved out of the lake to more preferred habitat downstream. Tag retention was high and tagging had no adverse effect on growth. Enhancement or stocking with longfins is viable for low density recruitment-limited, high country lakes, but growth is likely to be density dependent.